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Carbon economy of sour orange in response to different Glomus spp
Abstract
Vesicular-arbuscular mycorrhizal (M) fungal colonization, growth, and nonstructural carbohydrate status of sour orange (Citrus aurantium L.) seedlings were compared at low- and high-phosphorus (P) supply following inoculation with four Glomus isolates: G. intraradices (Gi, FL208), G. etunicatum (Ge, UT316), G. claroideum (Gc, SC186), and Glomus sp. (G329, FL906). Nonmycorrhizal (NM) seedlings served as controls. At low-P supply, increases in incidence of M colonization, vesicles and accumulation of fungal fatty acid 16:1omega(5)C in roots were most rapid for G329-inoculated seedlings, followed closely by Gi- and Gc-inoculated seedlings. Glomus etunicatum was a less aggressive colonizer and produced lower rates of fungal fatty acid accumulation in seedling roots than the other Glomus species. Nonmycorrhizal and Ge-inoculated seedlings had lower P status and growth rates than seedlings inoculated with Gi or G329. Glomus claroideum increased seedling P status, but growth rate was lower than for seedlings colonized by Gi or G329, suggesting higher belowground costs for Gc colonization. In P-sufficient roots colonized by Gi, Gc, or G329, starch and ketone sugar concentrations were lower than in P-deficient NM and Ge-inoculated plants. Under conditions of high-P supply where mycorrhizae provided no P benefit to the seedlings, colonization by Gc, Gi, and G329 was delayed and reduced compared to that at low-P supply; however, the relative colonization rates among Glomus spp. were similar. Colonization by Ge was not detected in roots until 64 days after inoculation. Compared to NM seedlings, growth rates of mycorrhizal seedlings were reduced by the three aggressive fungi but not by the less aggressive Ge. After 64 days, starch and ketone sugar concentrations were lower in fibrous roots colonized by Gc, Gi, and G329 than in NM roots, indicating greater utilization of nonstructural carbohydrates in roots colonized by the aggressive fungi. After 49 days, colonization by the aggressive fungi increased root biomass allocation which may have contributed to the lower growth rate of mycorrhizal seedlings compared to NM seedlings. Thus, Glomus spp. that were aggressive colonizers of roots at low-P supply were also aggressive colonizers at high-P supply, resulting in greater belowground C costs and growth depression compared with the less aggressive colonizer, Ge.
... The accumulation of lipids in AMF-colonized roots has been found to be directly proportional to the number of intraradical AMF vesicles (Pacovsky and Fuller 1987;Johansen et al. 1996). As a consequence, colonized roots contain generally more lipids than non-colonized ones (Graham et al. 1996;Gaspar et al. 1997). Depending upon P availability, such content can be either increased (Bethlenfalvay et al. 1994), decreased (Bethlenfalvay et al. 1997), or in some cases remain unchanged (Campagnac et al. 2010) and be dependent on the fungal symbiont and related to its aggressiveness (Nordby et al. 1981;Graham et al. 1996). ...
... As a consequence, colonized roots contain generally more lipids than non-colonized ones (Graham et al. 1996;Gaspar et al. 1997). Depending upon P availability, such content can be either increased (Bethlenfalvay et al. 1994), decreased (Bethlenfalvay et al. 1997), or in some cases remain unchanged (Campagnac et al. 2010) and be dependent on the fungal symbiont and related to its aggressiveness (Nordby et al. 1981;Graham et al. 1996). The increase in lipid content was reported to be much smaller with Gigasporaceae-than Glomeraceae-colonized plants. ...
... Nemec (1981) previously detected dehydrogenase activity in young arbuscles as well as in intraradical hyphae, and he detected peroxidase and catalase activities in senescing arbuscles which were tentatively attributed to FA oxidation. As a whole, total lipid contents of AM roots were found to be proportional to root colonization levels (Graham et al. 1996;Johansen et al. 1996;Pacovsky and Fuller 1987) and the number of spores in soil correlated well with AMF NL content (Olsson et al. 1997). ...
This chapter deals with the distribution, biochemistry and physiology of lipids in mycorrhizas including plant-fungi interactions aspects. Considering the heterogeneity of existing symbiosis and the diversity of associated fungi and plant partners, the main mycorrhizal types, ecto, arbuscular, ericoid and orchid symbiosis, are treated separately inside each section of the text. Subdivided into six sections, the text begins with a survey of mycorrhizal fungal lipids profiles with qualitative and quantitative treatments of lipid constituents included. The second section deals with the impact mycorrhizas, mineral nutrition and carbon cycling have on plant lipid metabolism. The third section focuses on lipid changes during the different stages of mycorrhizal fungi development as of the storage lipids. The fourth section describes up to date research investigations on the impact of fungicides, pollutants and exogenous lipids on fungal lipid metabolism. The final section covers evaluation tools currently available to characterize and quantify mycorrhizas and mycorrhizal soil communities. This chapter is directed towards both fundamental and applied research workers and aims to provide an extensive and up to date review of present knowledge relevant to a diversity of aspect related to mycorrhizas.
... Olsson et al. 2010). Further, C allocation could be affected greatly by plant size, nutritional status and phenology, which may invalidate some of the comparisons between mycorrhizal and nonmycorrhizal plants differing in size and/or nutrition Graham et al. 1996;Grimoldi et al. 2006;Peng et al. 1993;Püschel et al. 2016). ...
... Using several nonmycorrhizal control treatments with increasing levels of nutrient supplementation as described here is an alternative, although requiring additional effort to establish and maintain. What must be noted is that, for some combinations of symbiotic partners and environmental conditions, it may not be possible to produce nonmycorrhizal and mycorrhizal plants of the same size and mineral nutrition because of mycorrhizal C costs outweighing the growth benefits conferred to plants (Graham et al. 1996;Lendenmann et al. 2011;Peng et al. 1993). This tended to be the case in our experiment, especially when comparing the inoculation and all P supplementation treatments together (Fig. 2), where the mycorrhizal plants with the same P content showed significantly lower biomass (at least for the roots) than their Fig. 5 Partitioning of excess 13 C (i.e. the 13 C originating from the 13 CO 2 pulse) between shoots (white bars), roots (dark grey bars), the CO 2 respired from the belowground compartments during 6 days following the 13 CO 2 labelling (light grey bars) and the substrate (dotted bars), as affected by the mycorrhizal status of the plants (M mycorrhizal plants, NM nonmycorrhizal plants). ...
... Nevertheless, these calculations are missing the aboveground respiration component, so they might be even smaller in absolute terms. These figures for mycorrhizal C costs are at the low end compared to other published studies (Graham et al. 1996;Grimoldi et al. 2006;Jakobsen and Rosendahl 1990;Lendenmann et al. 2011;Wright et al. 1998a), where the measured mycorrhizal C costs are usually between 4 and 15 % of the plant C budget, and the maximum reported value of 20 % plant C allocated to the AM fungus was reached only under atypical conditions with young plants and low light intensities (Jakobsen and Rosendahl 1990). ...
Quantification of carbon (C) fluxes in mycorrhizal plants is one of the important yet little explored tasks of mycorrhizal physiology and ecology. 13CO2 pulse-chase labelling experiments are increasingly being used to track the fate of C in these plant–microbial symbioses. Nevertheless, continuous monitoring of both the below- and aboveground CO2 emissions remains a challenge, although it is necessary to establish the full C budget of mycorrhizal plants. Here, a novel CO2 collection system is presented which allows assessment of gaseous CO2 emissions (including isotopic composition of their C) from both belowground and shoot compartments. This system then is used to quantify the allocation of recently fixed C in mycorrhizal versus nonmycorrhizal Medicago truncatula plants with comparable biomass and mineral nutrition. Using this system, we confirmed substantially greater belowground C drain in mycorrhizal versus nonmycorrhizal plants, with the belowground CO2 emissions showing large variation because of fluctuating environmental conditions in the glasshouse. Based on the assembled 13C budget, the C allocation to the mycorrhizal fungus was between 2.3% (increased 13C allocation to mycorrhizal substrate) and 2.9% (reduction of 13C allocation to mycorrhizal shoots) of the plant gross photosynthetic production. Although the C allocation to shoot respiration (measured during one night only) did not differ between the mycorrhizal and nonmycorrhizal plants under our experimental conditions, it presented a substantial part (∼10%) of the plant C budget, comparable to the amount of CO2 released belowground. These results advocate quantification of both above- and belowground CO2 emissions in future studies.
... As a consequence, roots of colonized plants which contain such lipid-rich mycelium must contain more lipids than uncolonized ones. Such an increase has been reported by several authors (Cooper and Lose11978; Nagy et al. 1980;Nordby et al. 1981;Pacovsky 1989;Bago et al. 1995;Graham et al. 1996;Gaspar et al. 1997). The mycorrhizal and nonmycorrhizal roots contained, respectively, 3.4 and 2.7mgg-1 fresh weight (onion), 4.1 and 3.3 (clover) or 6.6 and 3.7 (ryegrass) of lipid (Cooper and LoseI1978). ...
... The importance of the changes can depend on the mycorrhizal fungus and be related to its aggressivity. The lipid content of Citrus roots was found lower with the less aggressive Glomus etunicatum than with Glomus claroideum and Glomus intra radices (Graham et al. 1996) or Glomus mosseae (Nordby et al. 1981). The increase in lipid content was reported as being much smaller with plants colonized by Gigasporaceae fungi than with plants colonized by Glomus species. ...
... With arbuscular mycorrhizae, it has been pointed out by several workers that the total lipid content of mycorrhizal roots is usually found to be proportional to the root colonization levels (Cooper and Losel 1978;Graham et al. 1996). Moreover, a direct correlation between lipid content and the number of vesicles inside roots has been made by Gnekow and Marschner (1989), Johansen et al. (1996), and Pacovsky and Fuller (1988). ...
Research dealing with the composition, diversity and role of lipids in mycorrhizal associations has, during the past decades, attracted the interest of an increasing number of investigators from diverse disciplines. First considered as a biochemical tool for the quantitative evaluation of mycorrhizae in a given system (Seitz et al. 1979; Salmanowicz and Nylund 1988; Salmanowicz et al. 1990; Schmitz et al. 1991; Davis and Lamar 1992; Nylund and Wallender 1992; Bermingham et al. 1995; Olsson et al. 1995), the composition and the transformation of plant and fungal lipids during the establishment of the symbiosis has been gradually pursued (Olsson et al. 1998) and is now, to a certain extent, considered as a potential biochemical approach for the comprehension of evolutionary (Bentivenga and Morton 1994a; Weete and Gandhi 1997) and chemotaxonomic studies (Sancholle and Dalpe 1993; Bentivenga and Morton 1994b; Graham et al. 1995, GrandmouginFerjani et al. 1996, 1999).
... Glasshouse studies predict AMF that aggressively colonize roots and stimulate plant growth at low P supply (Abbott and Robson, 1981), will also aggressively colonize at high P supply, but may provide no additional P benefit and reduce growth ( Graham et al., 1996). Wilson and Trinick (1983) first used the term 'aggressiveness' to refer to the ability of AMF to compete with other fungi for colonization space in the root. ...
... Fungi that aggressively colonize roots commonly occur in the field ( Abbott and Robson, 1991;Brundrett, 1991), but their relevance to mycorrhizal effectiveness remains to be determined (Abbott and Gazey, 1994). Carbon cost analysis of citrus ( Graham et al., 1996;Peng et al., 1993) and observations of several crops in the field reveal that effectiveness of AMF from managed crop soils ranges from mutualistic to parasitic depending mostly on the soil P supply ( Johnson et al., 1997). In moderate to high P soils, growth of field-grown citrus supports the hypothesis that within communities of AMF there exist aggressive fungi capable of colonization sufficient to produce carbon cost without off-setting benefit (Graham and Eissenstat, 1998). ...
... Leaf nutrient concentration of P, K, Ca, Mg, Fe, Zn, Mn, Cu was analyzed by inductively coupled plasma atomic emission spectroscopy after acid digestion of dried and ground tissue. Root starch and sucrose were analyzed in ground root tissue as previously described (Graham et al., 1996) and expressed on a percent dry weight basis. Plant growth and carbohydrate responses to AMF were expressed relative to the NM response by calculating the mycorrhizal response as [AM dry weight/NM dry weight]-1. ...
In southwestern Australia fields, colonization of wheat roots by arbuscular mycorrhizal fungi (AMF) is reduced due to repeated
use of phosphate (P) fertilizers. We predicted AMF that aggressively colonize wheat roots at low P supply would also aggressively
colonize at high P supply, but provide no additional P uptake benefit and reduce growth. Wheat (cv. Kulin) seedlings were
non-mycorrhizal (NM) or inoculated separately with 10 isolates of AMF from wheat-belt soils in a glasshouse experiment. Kojonup
loamy sand was supplied with P to provide suboptimal and supraoptimal P for growth of NM wheat in this soil. At low P supply,
wheat growth was limited by P availability. All AMF isolates colonized wheat roots at 14 days after emergence of seedlings.
At 42 days, percentage root length colonized (%RLC) was highest for two isolates of Scutellospora calospora, WUM 12(2) and WUM 12(3), followed by Glomus sp. WUM 51, G. invermaium WUM 10(1), Acaulospora laevis WUM 11(4) and Gigaspora decipiens WUM 6(1). These isolates, designated as `aggressive colonizers', ranged from 50 to 89%RLC. A second group of AMF ranged from
1 to 19%RLC at 42 days. This group, termed `non-aggressive colonizers', included Acaulospora spp. WUM 11(1), WUM 46, and WUM 49 and Glomus sp. WUM 44. High soil P supply increased seedling growth 2–3 fold, but reduced%RLC. Grouping of aggressive and non-aggressive
AMF based on colonization rate at high P supply was similar to that at low P. At low P supply, only the two isolates of S. calospora increased wheat growth compared to the NM plant. The remaining aggressive and non-aggressive AMF reduced growth of wheat
at low P, while aggressive colonizers reduced growth at high P. At low P supply, the aggressive colonizers increased shoot
P concentration, while at high P, shoot P was not affected by AMF. Growth depression by aggressive colonizers was associated
with reduced sucrose concentration in roots. Based on the negative growth response under low and high P fertility in the glasshouse,
AMF could be expected to produce non-beneficial effects on wheat in the field depending on the P status of the soil and the
aggressiveness of AMF in the community.
... 1. Quantitative Changes, Colonized Versus Non-Colonized Roots a) Lipids and Fatty Acids The accumulation of lipids in AMF-colonized roots has been found to be directly proportional to the number of intraradical AMF vesicles (Pacovsky and Fuller 1987; Johansen et al. 1996 ). As a consequence, colonized roots contain generally more lipids than non-colonized ones (Graham et al. 1996; Gaspar et al. 1997). Depending upon P availability, such content can be either increased (Bethlenfalvay et al. 1994), decreased (Bethlenfalvay et al. 1997), or in some cases remain unchanged (Campagnac et al. 2010) and be dependent on the fungal symbiont and related to its aggressiveness (Nordby et al. 1981; Graham et al. 1996). ...
... As a consequence, colonized roots contain generally more lipids than non-colonized ones (Graham et al. 1996; Gaspar et al. 1997). Depending upon P availability, such content can be either increased (Bethlenfalvay et al. 1994), decreased (Bethlenfalvay et al. 1997), or in some cases remain unchanged (Campagnac et al. 2010) and be dependent on the fungal symbiont and related to its aggressiveness (Nordby et al. 1981; Graham et al. 1996). The increase in lipid content was reported to be much smaller with Gigasporaceae-than Glomeraceae-colonized plants. ...
... Nemec (1981) previously detected dehydrogenase activity in young arbuscles as well as in intraradical hyphae, and he detected peroxidase and catalase activities in senescing arbuscles which were tentatively attributed to FA oxidation. As a whole, total lipid contents of AM roots were found to be proportional to root colonization levels (Graham et al. 1996; Johansen et al. 1996; Pacovsky and Fuller 1987) and the number of spores in soil correlated well with AMF NL content (Olsson et al. 1997). ...
... The arbuscular mycorrhizal (AM) symbiosis is functionally characterized by the reciprocal exchange of nutrients between the symbionts: Carbon (C) in form of nonstructural carbohydrates (CHO) from plants to the AM fungus and phosphorus (P) from AM fungi to plants. The outcome of the symbiosis measured as plant growth or reproduction depends on the balance in the nutrient flow between the symbionts, which can be influenced by plant species/variety (Ravnskov & Jakobsen, 1995;Syvertsen & Graham, 1999), AM fungus species/isolate (Pearson & Jakobsen, 1993;Graham et al ., 1996;Boucher et al ., 1999) and external factors such as soil P supply . Thus, the functioning of AM symbioses may occur along a continuum from mutualism to parasitism ( Johnson et al ., 1997). ...
... Plants were placed in a completely randomized design in a glasshouse in central Florida with temperatures varying from 20 to 32 ° C and relative humidity from 60 to 100% for 25 d from 16 March to 11 April 2001. Pots were watered as previously described (Graham et al ., 1996) with a modified Hoagland's nutrient solution (Hoagland & Arnon, 1939) with or without P, depending on the treatment. The position of the plants on the bench was changed every second day to minimize effects of variation in glasshouse conditions. ...
... These differences in C source-sink relationships between host and AM fungus could be due to the varying functional compatibility between the symbionts. Earlier experiments have shown that the flow of nutrients between the organisms in the mycorrhizal symbiosis depends on the species of plant (Ravnskov & Jakobsen, 1995;Jifon et al., 2002), and the isolate of the AM fungus (Pearson & Jakobsen, 1993;Graham et al., 1996). The present experiment confirms that C utilization as measured here by gene expression in maize roots probably depends on species/isolate of the AM fungus involved in the symbiosis. ...
Summary • The effects of three arbuscular mycorrhizal (AM) fungal isolates on the expression of genes coding for sucrose synthase and on the nonstructural carbohydrate (CHO) status of maize roots were evaluated. Gene expression and CHOs were compared with their status in nonmycorrhizal plants grown at three soil phosphorus (P) concentrations. • The AM fungi and soil P supply influenced expression of genes coding for sucrose synthase in maize roots. In general, up to 18 d after plant emergence, AM colonization increased the expression of genes coding for sucrose synthase in maize roots, whereas increasing soil P decreased this gene expression. The responses in gene expression were detected earlier than other effects of AM fungal colonization, such as increased leaf P status and plant growth response under limiting P supply. • Higher sucrose-synthase gene expression was not related to the concentration of sucrose, reducing sugars or starch in the root tissue. • Higher gene expression in AM roots confirms that there is greater allocation of sucrose from nonstructural CHO pools in roots for the AM fungus during the earliest phase of colonization than in nonmycorrhizal roots.
... Michelini et al. (1993) compared site effect on indigenous mycorrhiza and they found that the significant correlations between measures of AM fungal infection and site characteristics varied between Caribbean islands. Different species in different geographic isolates of the same species of AM fungi might vary with respect to their ability to colonize roots and improve plant growth (Camprubi and Calvet, 1996;Graham et al., 1996;Graham et al., 1982). de Souza et al. (2002) in order to quantify AMF spores present in citrus nurseries and orchards in Rio Grande do Sul, Brazil, soil and root samples were collected at ten nurseries and twelve citrus orchards and found that AMF species, in decreasing order of occurrence were: Glomus macrocarpum > Scutellospora heterogama > Acaulospora scrobiculata = Acaulospora birreticulata > Glomus invermaium = Glomus occultum = Entrophospora colombiana > Glomus claroideum = Glomus constrictum > Scutellospora persica. ...
... Ortas et al (unpublished data) shown that indigenous mycorrhizae inoculation has high response to citrus plant than single spore inoculation ( Fig. 23.2). Graham et al. (1996) indicated that the relevance of species diversity to the function of AM fungi in the field is poorly understood, because data comparing different communities of AM fungi on plant growth and physiology are lacking (Graham, 1986). Sharma et al. (2009) isolated and identified twelve AMF species in citrus orchards grown in nine different plantation areas of north-western Himalayan region (NWHR) of India and re-inoculated and thy fund that significant in-crease in growth parameters such as height, diameter, root length and leaf area was more evident for the seedlings inoculated with G. fasciculatum and G. mosseae. ...
In this review, effect of mycorrhizal inoculation on citrus growth, nutrient and water uptake, and mycorrhizal dependency was searched. Arbuscular mycorrhiza (AM) is symbiotic associations between 90% of higher plants and fungi. Since citrus plants have very few and short root hair, in order to get sufficient nutrient and water, they need mycorrhizal colonization. It has been shown that the host plant was a factor affecting the interaction between mycorrhizal fungi. It has been shown that greater fungal activities in AM hyphae have a significant effect on citrus growth and nutrient uptake.
... The failure of colonisation of winter wheat in winter has also partly been attributed to the low infectivity of fungal propagules (Daniels- Hetrick et al., 1984). The differences in fungal aggressiveness towards wheat plants also resulted in different extents of colonisation (Graham et al., 1996). Increasing plant density or decreasing the soil volume per plant decrease percent AM colonisation (Baath & Hayman, 1984;Koide, 1991a). ...
... When P is not growth limiting, e.g. when P fertiliser is applied, plants may not benefit from extra P taken up by AM fungi. The cost of the symbiosis may then exceed benefits, resulting in a parasitic relationship between fungus and plant (Graham et al., 1996;Graham & Eissenstat, 1998). Positive mycorrhizal responses at intermediate soil P levels have, however, been reported in wheat (Al-Karaki & Clark, 1999;Yao et al., 2001;Al-Karaki & Al-Omoush, 2002). ...
... Johnson et al. (1992) found that G. occultum proliferated in corn fields, and that spore abundance of G. occultum was negatively correlated with corn plant dry mass and yield. Likewise, growth depression of tobacco plants in high phosphorus soil has been linked to AM fungi (Modjo and Hendrix, 1986), and aggressive strains of AM fungi which enhance plant P uptake and growth at low soil phosphorus cause growth depression of citrus at high soil phosphorus (Graham et al., 1996). ...
... Single species from the Yuma inoculum could be isolated, and inoculation of citrus with isolates individually and in combination would confirm which fungus was responsible for poor plant growth. Management of AM fungi that cause growth suppression might involve reducing phosphorus fertilization to enhance the carbon efficiency of the fungi (Graham et al., 1996). M *** *** *** W*M ** ** NS z Values are treatment means, n=5. ...
Volkamer' lemon (Citrus volkameriana Tan. and Pasq.) seedlings were inoculated with either of five communities of arbuscular mycorrhizal (AM) fungi collected from either citrus orchards in Mesa and Yuma, Arizona or from undisturbed Sonoran or Chihuahuan desert soils. Plants were then grown for four months under low or high irrigation frequency treatments such that soil water tension reached about -0.01 MPa (moist) or -0.06 MPa (periodically dry), respectively. Plants grown in moist substrate had greater shoot mass than plants grown in periodically dry substrate. Plants inoculated with AM fungi from the Yuma orchard soil had significantly less shoot and root mass, higher specific soil respiration rates, and lower photosynthesis rates than plants treated with inoculum from other soils. Plant phosphorus nutrition did not limit growth. These data show that growth of 'Volkamer' lemon seedlings can be substantially affected by arbuscular mycorrhizal fungal communities in moist or periodically dry soils.
... Duponnois et al. (2001) reported that inoculation of the tropical legume, Sesbania species with G. aggregatum did not increase shoot biomass despite good mycorrhizal colonization of the root system. This introduces the concept of aggressive AMF species that may not necessarily be effective on plant growth (Graham et al. 1996). This indicates a greater utilization of carbohydrates in roots colonized by the aggressive AMF, resulting in a greater belowground C cost and growth depression (Graham et al. 1996). ...
... This introduces the concept of aggressive AMF species that may not necessarily be effective on plant growth (Graham et al. 1996). This indicates a greater utilization of carbohydrates in roots colonized by the aggressive AMF, resulting in a greater belowground C cost and growth depression (Graham et al. 1996). Thus, the optimum mycorrhizal root colonization rate that would be effective on growth depends on AMF isolates, plant species and soil and environmental factors. ...
The benefits of inoculation with six arbuscular mycorrhizal fungi (AMF) isolates (Glomus aggregatum, G. fasciculatum, G. intraradices, G. manihotis, G. mosseae, and G. verriculosum) were investigated on seedlings of Acacia senegal (L.) Willd., a multipurpose tree legume highly valued for arabic gum production. Mycorrhizal root colonization, plant growth and relative mycorrhizal dependency (RMD) were measured in A. senegal seedlings growing in soils from three geographical sites in Senegal (Dahra, Bambey and Goudiry) and two soil conditions (sterilized vs unsterilized) in the glasshouse. The impact of inoculation on mycorrhizal root colonization and plant growth depended on AMF isolates, soil origins and soil conditions. Mycorrhizal root colonization and plant growth were increased in sterilized soils regardless of soil origin and AMF isolates. The degree of RMD of A. senegal seedlings varied with soil origin, soil condition and AMF isolates. A. senegal showed the highest RMD values, reaching a maximum of 45 %, when inoculated with G. manihotis. However, in unsterilized soils, no significant effect of AMF inoculation on plant growth was observed despite significant root colonization with certain AMF isolates in Dahra and Goudiry soils. This indicates that the most infective AMF isolates were not the most effective and unsterilized soils may contain effective mycorrhizal propagules. In conclusion, it is important to consider the native mycorrhizal component of the soils before harnessing mycorrhizal inoculation programs for sustainable agroforestry systems.
... Although AM can infect a wide range of hosts from various geographical localities, the responses of host plants to mycorrhizae vary greatly depending on the combination of plant and fungus genotypes Smith 1996, Johnson et al. 1997). Different fungal genotypes can have positive, negative, or little effect on the growth of the same host species (Boerner 1990, Monzon and Azcon 1996, van der Heijden and Kuyper 2001), because AM may differ in their ability to infect a given host, efficiency of P transferred to the host, carbon demand, soil adaptation, and host compatibility (Johnson 1993, Graham et al. 1996, Monzon andAzcon 1996, Johnson et al. 1997). Thus, assessment of the effects of AM on plant invasion must consider the genotype and source of fungal isolates. ...
... Possibly the costs of the two Glomus species were greater than their benefits at the light levels used in this experiment. Mycorrhizal fungi can demand up to 20% of the total C budget of a plant in extreme cases (Peng et al. 1993), and carbon costs can vary widely among fungal genotypes (Graham et al. 1996). The differences between inoculum types may also be mediated by fungal diversity. ...
Mycorrhizae improve phosphorus availability to host plants and alter their morphology, physiology, and competitive ability. We examined how different isolates of arbuscular mycorrhizal fungi, soil-P, light, and competition affect the growth, physiology, and biomass allocation of seedlings of an exotic invasive shrub of the southeastern United States, Ardisia crenata, in two greenhouse experiments. When Ardisia seedlings were grown singly in pots without competition, soil phosphorus concentration and light had no effect on seedling growth. Relative growth rates (RGR) and leaf area ratio (LAR), however, were higher for seedlings inoculated with mycorrhizal fungi isolated from Ardisia roots than those inoculated with single-spore isolates and nonmycorrhizal controls. In the second experiment, an Ardisia seedling was grown in each pot in competition with another conspecific seedling or with a seedling of Prunus caroliniana, a native subcanopy tree. The identity of the competitor had little effect on seedling RGR of Ardisia, but LAR was significantly higher for seedlings in conspecific competition. Overall, Prunus seedlings had higher RGR than Ardisia, but RGR and survival of Prunus seedlings were significantly reduced in competition with Ardisia when mycorrhizal fungi were suppressed by benomyl. These results suggest that competitive interactions of exotic invasive plants with native plants are dependent on the isolates of mycorrhizae present.
... In addition, the overall benefit of mycorrhizae to plants may decrease with fertilization if the fungal symbionts allocate more resources to growth and reproduction at the expense of nutrient exchange with the plant host. If plants in high fertility soils allocate less carbon to root exudates, mycorrhizal strains that are more aggressive colonizers may proliferate because they convert more of the plant's resources to internal fungal growth and respiration instead of nutrient gathering and exchange (Peng et al., 1993;Graham et al., 1996;Johnson et al., 1997). For example, high fertility may promote shifts in fungal community composition that promote the proliferation of less generous fungi. ...
... Rapid fungal colonizers that can overcome plant control of mycorrhizal colonization rates and carbon allocation would be at an advantage over slower fungal colonizers sensitive to plant regulation (Johnson et al., 1997). Rapid utilization of non-structural carbohydrates by aggressive fungal colonizers would result in increased belowground costs to plants associated with the construction and maintenance of intra-and extraradical fungal structures (Peng et al., 1993;Graham et al., 1996). We predict that if fertilization reduces plant exudates and favors shifts towards a more aggressive, mycorrhizal community composition, then fertilization will increase the production of structures associated with growth and storage (hyphae and vesicles) relative to those associated with the plant host (arbuscules and coils) (''Investment Hypothesis'' hereafter, developed by Johnson, 1993;Johnson et al., 1997Johnson et al., , 2006. ...
Mycorrhizal fungi are ubiquitous components of terrestrial ecosystems that can influence plant performance, abundance and diversity. Patterns of allocation to specific mycorrhizal fungal structures could provide a useful context for understanding belowground dynamics in response to changing resources. Specifically, increased soil nutrient availability has been predicted to favor plants with lower rates of mycorrhizal association. In addition, fertilization has been predicted to favor mycorrhizae with higher investment in storage structures relative to uptake and exchange structures. A 3 y field experiment was conducted in coastal tallgrass prairie to examine how fertilization affects mycorrhizal abundance and investment patterns. Fertilization significantly increased total mycorrhizal abundance. Specifically, mycorrhizal investment in hyphae, coils and vesicles were significantly increased 53%, 252% and 440% in fertilized plots, respectively. Together these results suggest that mycorrhizae in high fertility soils allocate more to internal fungal storage at a potential cost to plant hosts. Thus, fertilization could have important indirect effects on the aboveground plant community by potentially altering the costs and benefits of mycorrhizae to host plants.
... The soil fatty acid signature 16:1o5 has been used to quantify biomass of AM fungi (Olsson et al., 1995). This fatty acid accumulates in roots during AM fungus colonisation (Graham et al., 1996; Olsson et al., 1995) and the amount accumulated is correlated to microscopically estimated measures of total root colonisation (Olsson et al., 1997). Fatty acid methyl ester (FAME) 16:1o5 analysis of roots not only provided a measure of colonisation development but also served as an index of carbon allocated to intraradical fungal growth and lipid storage (Graham et al., 1995). ...
... Soil FAME 16:1o5 was used to indicate AM fungal biomass (Olsson et al., 1995). Root FAME 16:1o5 analysis was used as index for the development of AM fungus colonisation in the olive tree roots (Graham et al., 1995Graham et al., , 1996 Olsson et al., 1995). ...
Olive mill wastewater (OMW) constitutes a major environmental problem for Mediterranean countries, where most of the world olive oil production takes place. The recycling of the OMW and its use as water for irrigation in agriculture, provided that its impact on soil and plant is established, is an attractive possibility for the Mediterranean countries. Investigations were performed on the influence of agronomic application of OMW (amount applied: 30, 60, 100 and 150 m 3 ha À1) in a field of olive trees on trees characters (photosynthesis, root-soluble carbohydrate and root colonisation), soil properties, and soil microbial community structure. Specific attention was paid to arbuscular mycorrhizal (AM) fungi. The soil fatty acid methyl ester (FAME) 16:1o5 was used to quantify biomass of AM fungi and the root FAME 16:1o5 analysis was used as index for the development of colonisation in the olive trees roots. A significant increase in organic C, C/N ratio, extractable phosphorus and exchangeable potassium was found after one year of agronomic application of OMW. The development of saprophytic fungi was significantly higher in the OMW amended soils, whereas the abundance of the soil FAME 16:1o5, root FAME 16:1o5, photosynthetic rates and the amount of the total root-soluble carbohydrate were decreased significantly after agronomic application of OMW. A principal component analysis (PCA) of the trees characteristics profiles showed discrimination between the nonirrigated and the OMW irrigated olive trees. These findings suggest that the altering functioning of arbuscular mycorrhizas should be considered as potential factors mediating olive trees responses to agronomic application of OMW when the OMW dose applied is higher than 30 m 3 ha À1 . To our knowledge, this is the first report of alterations in the soil FAME 16:1o5 and root FAME 16:1o5 due to land spreading of OMW.
... For instance, P-sufficient, mycorrhizal Citrus plants expended 37% more C on soil / root respiration, which led to a 10 -20% reduction in the specific C gain of AM compared to NM plants (Peng et al. , 1993). The total nonstructural carbohydrate (TNC) content in host tissues, particularly root TNC, is a good indicator of the amount of C allocated to the AMF (Graham et al. , 1996(Graham et al. , , 1997. ...
... Nonmycorrhizal ( NM) soil received an extract of inoculum that had been passed through a 38-µm sieve to establish the same microflora associated with maize roots. G. intraradices is widespread in native and orchard soils and is considered an aggressive colonizer (defined as the rate of root colonization in the absence of competing AMF; Graham et al. , 1996) of citrus roots both at low and high soil-P. G. intraradices is also less sensitive to agricultural management practices such as fertilization and tillage compared to members of other genera such as Gigaspora (Miller & Jastrow, 1992;Graham & Abbott, 2000). ...
Gas exchange and growth responses of pot‐grown sour orange ( Citrus aurantium ) and sweet orange ( C. sinensis ) were studied at high soil‐P where growth depression is predicted.
Seedlings were either inoculated (AM) with the arbuscular mycorrhizal fungus Glomus intraradices or not inoculated (NM), and grown at elevated (eCO 2 ) or ambient CO 2 (aCO 2 ) for 11 wk.
At aCO 2 , growth of AM sour orange was depressed (18%) compared with NM seedlings, but at eCO 2 , AM sour orange plants were 15% larger than NM plants. Growth depression coincided with increased rhizosphere respiration, reduced root starch concentration, and lower relative growth rates. Net photosynthesis (Pn) of both genotypes was enhanced by eCO 2 . For sour orange, the stimulation was greater in AM than in NM seedlings and this may have compensated for the carbon (C) expenditure on mycorrhizas. Gas exchange and growth of sweet orange were unresponsive to colonization by G. intraradices .
Differential responses to treatments suggest that C expenditure on mycorrhizas is more tightly regulated in citrus genotypes of low mycorrhizal dependency (MD) such as sweet orange than in high MD genotypes (e.g. sour orange).
... This fatty acid has been demonstrated to be of use in the detection and biomass quantification of AM mycelium growth in soil (Olsson et al., 1995). This fatty acid accumulates in roots during AM fungus colonization (Graham et al., 1996;Olsson et al., 1995), and the amount accumulated is correlated to microscopically estimated measures of total root colonization (Olsson et al., 1997). We used this approach to understand the abundance of AM fungi in soil and also the olive trees root colonization following land spreading of OMW. ...
... Soil FAME 16:15 was used to indicate AM fungal biomass (Olsson et al., 1995). Root FAME 16:15 analysis was used as index for the development of AM fungus colonization in the olive trees roots (Graham et al., 1996;Olsson et al., 1995). ...
Olive mill wastewater (OMW) management is a serious environmental issue for the Mediterranean area where there is the most production of olive oil. OMW contains a high organic load, substantial amounts of plant nutrients but also several compounds with recognized toxicity towards living organisms. Moreover, OMW may represent a low cost source of water. We studied the influence of irrigation with OMW (amounts applied: 30, 60, 100 and 150 m3 h−1) in a field of olive trees on root colonization, photosynthesis, chlorophyll fluorescence, leaf nutrient concentration and soluble carbohydrate. The soil fatty acid methyl ester (FAME) 16:1ω5 was used to quantify biomass of arbuscular mycorrhizal (AM) fungi and the root FAME 16:1ω5 analysis was used as index for the development of colonization in the roots. Agronomic application of OMW decreased significantly the abundance of the soil FAME 16:1ω5 and the root FAME 16:1ω5 in the soil amended with 60, 100 and 150 m3 ha−1 OMW. Decreased root FAME 16:1ω5 due to OMW amendment was associated with a significant reduction of tissue nutrient concentrations in the olive trees. The highest application of OMW to the soil reduced significantly the olive trees uptake of N, P, K, Ca, Mg, Fe, Cu, Mn and Zn. Land spreading of OMW increased concentration of soluble carbohydrate in the olive leaves, mostly due to decreased sink demand for carbon by the root. In the olive trees amended with 150 m3 ha−1 OMW, net CO2 uptake rate (A), quantum yield of photosystem II electron transport (ΦPSII), maximal photochemical efficiency of photosystem II ( ), photochemical quenching (qp) and the electron transport rate (ETR) were significantly depressed, whereas non-photochemical quenching (NPQ) was found to increase. Taken with data from experiments in field conditions, our results suggest that agronomic application of OMW alters the functioning of arbuscular mycorrhizas and can even disrupt the relationship between AM fungi and olive trees.
... So, the root of the citrus plant may be colonized by more than one AMF at the same point, which indicates that the soil of citrus orchard is rich in diversity of AMF, and this will improve the nutrient's uptake and growth of a citrus plant. The same AMF but isolated with different geographical locations are varied in their ability to colonize the plant and improving growth rate (Graham et al., 1996). The quantification of spores of AMF in the soil of 12 orchards and 10 nurseries of citrus shows the great diversity of AMF species and the descending order of occurrence of these species was Glomus macrocarpum > Scutellospora heterogama > Acaulospora scrobiculata = Acaulospora birreticulata > Glomus invermaium = Glomus occultum = Entrophospora colombiana > Glomus claroideum = Glomus constrictum > Scutellospora persica (de Souza et al., 2002). ...
Plant root and fungus combined, results in a single structure through which exchange of nutrients takes place. There are many other mycorrhizal species found in the rhizosphere of citrus plants, but the major AMF found is Glomus species. The mycorrhizal association is also helpful in maintaining yield of the citrus plant. The soil of citrus orchards has many communities of AMF instead of a single species. So, the root of the citrus plant may be colonized by more than one AMF at the same point, which indicates that the soil of citrus orchard is rich in diversity of AMF, and this will improve the nutrient’s uptake and growth of a citrus plant. Citrus plants inoculated with mycorrhiza have more resistance against soil-borne pathogens and diseases than nonmycorrhizal plants. The mycorrhizal association releases the antibiotics in the soil which can control soil microorganisms such as nematodes and pathogenic fungi so the chances of infection reduced.
... Menge et al. (1978), por su parte afirman que existen evidencias de que la concentración de P es un factor que determina el comportamiento de la colonización y producción de esporas de hongos HMA. Graham et al. (1996), de igual manera coinciden afirmando que existen numerosas evidencias que demuestran que los altos niveles de P disminuyen la colonización. ...
Con el objetivo de determinar el efecto de la micorriza arbuscular (MA) y niveles de fósforo
Glomus fasciculatum en el desarrollo y productividad de cinco variedades nativas de papa. El
diseño experimental que se utilizó fue el de Bloques Completos al Azar (BCA), con
tratamientos estructurados de 6x2x3 con 3 repeticiones. Las variedades de papa nativa
tuvieron diferentes respuestas tanto a la inoculación con G. fasciculatum, y a fósforo. La
longitud de raiz incrementó linealmente en las variedades Malkacho 1 (63.7 cm), Polonia
(51.75 cm), Waych’a (50.25 cm) y Yuraj Imilla (52.8 cm). El rendimiento fue mayor con la
inoculación de 100 kg/h de micorriza G. fasciculatum (5.41 tn/h), siendo las variedades con
mayor rendimiento las variedades Malkacho 1 (7.02 tn/h) y Malkacho 2 (7.14 tn/h). Las
variables frecuencia de colonización (%), número de esporas, peso fresco de follaje fue mayor
con la aplicación de 100 kg/h de la micorriza G. fasciculatum, en las variedades Malkacho 1
(29.35%), Malkacho 2 (31.62 %), Yuraj imilla (29.16%) y Yana Runa (28.70%). El fósforo
afectó la frecuencia de colonización (%) y número de esporas disminuyéndolas con dosis
superiores a 60 kg/h y 65 kg/h, respectivamente.
... The AM association can facilitate plant uptake of soil phosphorus and nitrogen as well as increase plant local and systemic disease resistance (Liu et al. 2007;Parniske 2008;Smith and Read. 2008) whereas, in exchange, plants spare up to 20% of photosynthate for AM fungi for their growth and proliferation (Chiu and Paszkowski 2019;Genre et al. 2020;Graham et al. 1996;Jiang et al. 2017;Keymer et al. 2017;Luginbuehl et al. 2017;Wang et al. 2017). This nutrient exchange takes place through tree-shaped, subcellular structures called arbuscules that are formed in cortical cells of the host root (Choi et al. 2018;Genre et al. 2005Genre et al. , 2008Gutjahr and Parniske 2013;Wang et al. 2017). ...
Arbuscular mycorrhizal (AM) fungi form a mutual association with the majority of land plants, including most angiosperms of the dicotyledon and monocotyledon lineages. The symbiosis is based upon bidirectional nutrient exchange between the host and symbiont that occurs between inner cortical cells of the root and branched AM hyphae called arbuscules that develop within these cells. Lipid transport and its regulation during the symbiosis have been intensively investigated in dicotyledon plants, especially legumes. Here, we characterize OsRAM2 and OsRAM2L, homologs of Medicago truncatula RAM2, and found that plants defective in OsRAM2 were unable to be colonized by AM fungi and showed impaired colonization by Magnaporthe oryzae. The induction of OsRAM2 and OsRAM2L is dependent on OsRAM1 and the common symbiosis signaling pathway pathway genes CCaMK and CYCLOPS, while overexpression of OsRAM1 results in increased expression of OsRAM2 and OsRAM2L. Collectively, our data show that the function and regulation of OsRAM2 is conserved in monocot and dicot plants and reveals that, similar to mutualistic fungi, pathogenic fungi have recruited RAM2-mediated fatty acid biosynthesis to facilitate invasion.
[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .
... For example, fungal species within a genus and different isolates have been shown to express different symbiotic lifestyles ranging from mutualism to parasitism. This variation in lifestyle expression within a genus or species may occur due to host physiology (Graham et al. 1996;Graham and Eissenstat 1998); and is known as the Symbiotic Continuum (Schardl and Leuchtmann 2005;Schulz and Boyle 2005). ...
... For example, fungal species within a genus and different isolates have been shown to express different symbiotic lifestyles ranging from mutualism to parasitism. This variation in lifestyle expression within a genus or species may occur due to host physiology (Graham et al. 1996;Graham and Eissenstat 1998); and is known as the Symbiotic Continuum (Schardl and Leuchtmann 2005;Schulz and Boyle 2005). ...
Endophytic Fungi stress adaptation in agriculture crops especially tomato
... Plants often respond less positively to mycorrhizal fungi when nutrients are in excess because the nutrient acquisition services that mycorrhizal fungi provide become reduced or superfluous, though they continue to drain carbon from their plant hosts. For example, numerous studies based on inoculations of plants with pure cultures have shown that mycorrhizal interactions can shift from mutualistic to parasitic with the addition of phosphorous and/or nitrogen (Bethlenfalvay et al. 1983;Bougher et al. 1990;Buwalda and Goh 1982;Graham et al. 1996;Johnson 1993;Kiernan et al. 1983;Koide 1985;Mosse 1973). However, many of the studies demonstrating "mycorrhizal parasitism" have been conducted with arbuscular mycorrhizal (AM) fungi and there is less support for mycorrhizal parasitism in ectomycorrhizal (ECM) fungi (Karst et al. 2008), though there is still a strong potential for the outcome of such interactions to be nutrient-dependent (Jonsson et al. 2001). ...
Background and aimsPlant-soil feedbacks are the result of multiple abiotic and biotic mechanisms. However, few studies have addressed how feedbacks vary based on abiotic context or attempted to identify microbiota responsible for feedbacks. We investigated whether plant-soil feedbacks of an ectomycorrhizal tree (Quercus macrocarpa) varied based on soil nutrient status and whether fungal community composition and diversity could explain feedback patterns.Methods
We inoculated Q. macrocarpa seedlings with field-sampled soils taken from five soil origins – including heterospecific and conspecific trees and an old field – which were profiled using fungal DNA metabarcoding.ResultsThere was a positive home vs. away plant-soil feedback, though feedbacks with individual hosts were not significant regardless of fertilization. Still, hosts harbored distinctive fungal communities that were predictive of plant growth. There was a growth promotive effect of ectomycorrhizal OTU diversity that was weakened with fertilization, suggesting context-dependent relationships between plant growth and a guild of fungal mutualists.Conclusions
Our results demonstrate that the host-specific accumulation of functionally important soil microbes is not always sufficient to drive species level plant-soil feedbacks. Our data provide support for a role of ECM fungal diversity in mediating plant growth responses, though it is unclear whether this effect was direct or indirect.
... Previously, it has been claimed that plant root colonization is related with carbon drainage to rhizosphere area. Graham et al. (1996) reported that under low-P supply conditions Glomus spp. would be aggressive colonizers for sour orange roots, and under high P supply conditions the fungi would not only be aggressive colonizer, but also would result in a greater belowground carbon cost. ...
In 2001, a long term Satsuma Mandarin experiment was set up in Menzilat soil series. Glomus mosseae, Glomus etunicatum, Glomus clarium, Glomus caledonium and a cocktail of mycorrhizal species were applied to one-year-old sour orange seedlings during transplant to the field. Since 2004, the yield per tree was recorded every year and every year in May plant leaves were sampled for nutrient analyses. In 2014, the macro and micro nutrients (C, N, P, Fe, Mn, Cu, Zn) concentration in leaves were determined. Every year the soil properties were also analyzed. Data showed that the yield per plant increased every year. Some years, because of climatic conditions, a decrease in yield was observed. During 11 years, G. clarium inoculated trees produced the highest yield and control trees produced significantly less. Trees inoculated with the mycorrhizal cocktail had 48.6% of C, while non-inoculated plant had 39.9%. Trees inoculated with G. mosseae had the highest N concentration (2.41%), whereas control plants had the lowest (1.54%). The P and Zn concentration of plant leaves also increased with mycorrhizal inoculation. Since soil had a low Zn concentration, mycorrhizal inoculation assisted the plants to sufficiently uptake this nutrient. Results showed that mycorrhizal fungi can successfully be applied to Mandarin under field conditions. © 2018 International Society for Horticultural Science. All rights reserved.
... Il a été fréquemment montré que la mycorhization permet une augmentation de la biomasse des plantes (Janos, 1980, Lovelock et al., 1996, Moyersoen et al., 1998, Sharma et al., 2001. D' autres études rapportent cependant un effet nul (Stribley et al., 1980, Nielsen et al., 1998 ou négatif (Peng et al., 1993, Graham et al., 1996, Khaliq et Sanders, 1997 de la mycorhization. Cela se produit si le phosphore n'est pas le facteur limitant de l'acquisition du carbone (Smith et Read, 1997). ...
... Moreover, depending on the balance between net costs and benefits of the symbiosis, mycorrhizal phenotypes appear to cover a whole continuum of plant responses to AM fungal colonization ranging from positive to neutral to negative (Johnson et al. 1997;Klironomos 2003). For some combinations of symbiotic partners and environmental conditions, mycorrhizal C costs may simply outweight the growth benefits conferred to plants , and it may not be possible to produce nonmycorrhizal and mycorrhizal plants of the same size and mineral nutrition (Peng et al. 1993;Graham et al. 1996;Lendenmann et al. 2011). Here, the solution to compare physiology of mycorrhizal and nonmycorrhizal plants may be in using P fertilization to produce mycorrhizal and nonmycorrhizal plants of the same size (Brown and Bethlenfalvay 1987;Baas and Lambers 1988;Slavíková et al. 2017). ...
Although declared as a research priority more than 40 years ago, the knowledge about the magnitude and mechanisms of carbon (C) fluxes between plants and their mycorrhizal fungal symbionts remains fragmentary. In spite of a number of experiments with isotopically labeled C documented rapid and directed C transfer from the host plant to its mycobionts, the molecular mechanisms and their regulation involved in such a transport remain largely unknown. It seems that in many arbuscular mycorrhizal (AM) symbioses, the C costs remains well below 10% of the C fixed photosynthetically by the host plants. Higher values were detected in the past only under specific situations such as in young plants, under low light intensities, and/or for particular partner combinations, involving very costly (in terms of C demand) and little nutritionally beneficial AM fungi such as Gigaspora sp. Ecological context of the common mycorrhizal networks in terms of redistribution of symbiotic C costs and nutritional benefits on one hand and C movement through soil food webs beyond mycorrhizal hyphae on the other are briefly discussed in this chapter, and further research challenges and open knowledge gaps with respect to C fluxes in mycorrhizal plants are outlined.
... Dentre os fungos testados, esperava-se maior sucesso com a inoculação de G. margarita, G. clarum e do isolado 35, que apresentaram maiores valores de eficiência (Quadro 1). Entretanto, o isolado 35 mostrou estreita faixa de mutualismo, que pode significar efeitos depressivos em condições de elevadas doses de P. Fungos com elevada colonização como este isolado podem-se tornar parasitas em doses elevadas de fósforo, devido à demanda por carboidratos da planta (Graham et al., 1996). Tal comportamento difere dos obtidos por Saggin Júnior & Siqueira (1995) que encontraram correlação positiva entre o potencial de inoculação e o limite superior da faixa de mutualismo (P aplicado) para os diferentes fungos avaliados, para o cafeeiro, em solo não fumigado. ...
Para que os fungos micorrízicos arbusculares (FMA) possam ser utilizados em um programa de inoculação, é necessário que sejam capazes de apresentar eficiência simbiótica em solo que contenha populações indígenas de FMA. Com o objetivo de avaliar a eficiência simbiótica e o potencial de inoculação de fungos MA em solo não fumigado, para o mamoeiro, foi desenvolvido um experimento em condições de casa de vegetação da Embrapa Mandioca e Fruticultura, Cruz das Almas (BA), utilizando a variedade de mamoeiro Tainung nº 1. Utilizou-se amostra de um Latossolo Amarelo álico que continha 3 mg dm-3 de P disponível e que recebeu doses crescentes de P (0, 20, 40, 80 e 140 mg dm-3), combinadas com inoculação de três espécies previamente selecionadas e três isolados nativos de FMA, obtidos de agrossistema de mamoeiro. As plantas foram inoculadas com solo-inóculo no ato da repicagem e cultivadas por 50 dias, quando se determinaram a colonização, matéria seca da parte aérea e teores de nutrientes nas plantas. Todos os fungos inoculados apresentaram eficiência simbiótica em solo não fumigado, destacando-se Glomus clarum, Gigaspora margarita e isolado 29 (Gigaspora sp.), que apresentaram eficiência alta. Os isolados nativos foram mais eficientes em doses mais elevadas de fósforo no solo; a eficiência esteve relacionada com a absorção de fósforo e potássio. Os fungos previamente selecionados em solo fumigado foram também eficientes em solo que continha população indígena de FMA, portanto, validando este procedimento.
... Discussion sections above). This may reflect the high photosynthetic compensation ability of T repens towards mycorrhizal C costs (Wright et al., 1998 (Peng et al., 1993;Graham et al., 1996). Our experimental fungal isolates may have been selected by the original soil conditions, which were rich in available P, and thus should be adapted to such growth conditions. ...
• Altered environmental conditions may change populations of arbuscular mycorrhizal fungi and thereby affect mycorrhizal functioning. We investigated whether 8 yr of free-air CO2 enrichment has selected fungi that differently influence the nutrition and growth of host plants.
• In a controlled pot experiment, two sets of seven randomly picked single spore isolates, originating from field plots of elevated (60 Pa) or ambient CO2 partial pressure (pCO2), were inoculated on nodulated Trifolium repens (white clover) plants. Fungal isolates belonged to the Glomus claroideum or Glomus intraradices species complex, and host plants were clonal micropropagates derived from nine genets.
• Total nitrogen (N) concentration was increased in leaves of plants inoculated with fungal isolates from elevated-pCO2 plots. These isolates took up nearly twice as much N from the soil as isolates from ambient-pCO2 plots and showed much greater stimulation of biological N2 fixation. The morpho-species identity of isolates had a more pronounced effect on N2 fixation and on root length colonized than isolate identity.
• We conclude that rising atmospheric pCO2 may select for fungal strains that will help their host plants to meet increased N demands.
... In that regard, it has been shown that members of the Gigasporaceae have higher carbon requirements than Glomus species (Thomson et al. 1990). Differences may exist even within the same genus (see e.g., Graham et al. 1996). The different carbon demands are probably related to the intrinsic differences in the formation of the external mycelia and the intraradical development of each species (Chagnon et al. 2013). ...
Arbuscular mycorrhizal (AM) fungi usually improve plant performance yet our knowledge about their effects on seed germination and early plant establishment is very limited. We performed a factorial greenhouse experiment where the seeds from four low Arctic co-occurring mycorrhizal herbs (Antennaria dioica, Campanula rotundifolia, Sibbaldia procumbens, and Solidago virgaurea) were germinated alone or in the vicinity of an adult Sibbaldia plant with or without AM fungi; given either as spores or be- ing present in a common mycorrhizal network (CMN). Three different AM fungal species were examined to assess species-specific differences in symbiont acquisition rate. Of the four plant species investigated, the presence of AM fungi affected seed germination only in Campanula and this effect was dependent on whether the AM fungi were present in the soil as spores or as a CMN. Overall, after germination, developing seedlings showed AM fungal colonization in their roots as soon as 2 days after cotyledon emergence. Our results show that CMN may provide germinating seedlings faster acquisition of the AM fungal partner in comparison to acquisition from spores. Furthermore, there were AM species-specific differences in the symbiont acquisition rate highlighting the importance of species identity in AM interactions. These findings suggest that while AM fungi may not play a fundamental role during seed germination, plant com- munity composition may be affected by the species-specific AM fungal effects on seedling establishment and CMN acquisition.
... Likewise, higher fatty acid was observed in seed-raised rootstocks of Citrus reticulata, C. sinensis, C. aurantium, C. limon, C. paradisi and Poncirus trifoliata x C. sinensis in fibrous roots infected with the arbuscular mycorrhizal fungi Glomus fasciculatus, G. mosseae or G. etunicatus , but not in non-infected roots (Nordby and Nemec 1981). Another study showed that Glomus etunicatum was less aggressive colonizer and produced lower rates of fungal fatty acid accumulation in sour orange seedling roots than the other Glomus species (Graham et al. 1996). Effects of growth regulators as mediators of mycorrhizal sink strength must be considered since the carbohydrate balance is believed to change in the symbiotic association (Lewis 1975). ...
Citrus by its avid nutrient-absorbing capacity, is considered a highly nutrient-responsive perennial fruit crop. Differential efficacy of two conventional methods of fertilization (soil versus foliar application), although helped in improving the quality citrus, but of late, continuous fertilization, has failed to sustain the same yield expectancy on a long-term basis due to depletion of soil carbon stock and consequently emerged multiple nutrient deficiencies, irrespective of soil type. The menace of multiple nutrient deficiencies would be further triggered through increase in air temperature via changes in microbial communities and activities within the rhizosphere in the light of climate change. Such changes will dictate adversely on the orchard’s productive life in the long run.
... Fertilizing a system can potentially eliminate resource limitations so that mycorrhizas become superfluous for facultatively mycotrophic plants (e.g. Mosse, 1973 ;Bethlenfalvay, Bayne & Pacovsky, 1983 ;Kiernan, Hendrix, & Maronek, 1983 ;Koide, 1985 ;Johnson, 1993 ;Graham, Drouillard & Hodge, 1996). If colonization does not decrease with fertilization, then net costs will remain intact ( Fig. 3 b) but where colonization and hence total fungal biomass decreases the net costs to the plant will also decrease. ...
A great diversity of plants and fungi engage in mycorrhizal associations. In natural habitats, and in an ecologically meaningful time span, these associations have evolved to improve the fitness of both plant and fungal symbionts. In systems managed by humans, mycorrhizal associations often improve plant productivity, but this is not always the case. Mycorrhizal fungi might be considered to be parasitic on plants when net cost of the symbiosis exceeds net benefits. Parasitism can be developmentally induced, environmentally induced, or possibly genotypically induced. Morphological, phenological, and physiological characteristics of the symbionts influence the functioning of mycorrhizas at an individual scale. Biotic and abiotic factors at the rhizosphere, community, and ecosystem scales further mediate mycorrhizal functioning. Despite the complexity of mycorrhizal associations, it might be possible to construct predictive models of mycorrhizal functioning. These models will need to incorporate variables and parameters that account for differences in plant responses to, and control of, mycorrhizal fungi, and differences in fungal effects on, and responses to, the plant. Developing and testing quantitative models of mycorrhizal functioning in the real world requires creative experimental manipulations and measurements. This work will be facilitated by recent advances in molecular and biochemical techniques. A greater understanding of how mycorrhizas function in complex natural systems is a prerequisite to managing them in agriculture, forestry, and restoration.
... It is presumed that during the first weeks (before root initiation), the plantlets developed on their own nutrient reserves (starch accumulated in the corm) (Aragón et al. 2006). In addition, competition for carbon may have occurred between the plantlets and the AMF, resulting in a lack of stimulation of the mycorrhized plantlets in the MSR+AMF treatment relative to the controls (Graham et al. 1996;Balla et al. 1998;Smith and Smith 2011). ...
Micropropagated banana plantlets represent a good planting material to establish new growing areas or replace old plantations. The plantlets are devoid of pathogens but also of beneficial root inhabitants (e.g., endophytes and arbuscular mycorrhizal fungi [AMF]) that may help plants withstand stresses. Mycorrhization of banana is usually conducted at the hardening/post-hardening phases. Only a few studies have reported their application in vitro, and none have investigated the subsequent impact on ex vitro acclimatization. Here, we report for the first time the effects of in vitro mycorrhization of banana plantlets on growth following transfer to soil. Banana plantlets were pre-mycorrhized under autotrophic conditions. During in vitro culture, heavy root colonization of the banana plantlets was observed. At 5 and 7 wk after transfer to a peat-sand soil substrate, the root system remained highly colonized. The growth (pseudostem height) and biomass were significantly higher than those of control plants grown on media without AMF. The mean shoot dry weight of the pre-mycorrhized plants at 5 wk after transplanting was 66.7 and 34.6% greater than those of non-mycorrhized plantlets grown on modified Strullu-Romand (MSR) and Murashige and Skoog (MS) media, respectively, and was also greater at week 7 (by 64.7 and 40%, respectively). In vitro mycorrhization under autotrophic culture conditions thus represents a promising tool for the pre-adaptation of micropropagated banana plantlets to ex vitro conditions.
... This observation is contrary to reports on arbuscular mycorrhizal systems. High nutrient levels (usually P) frequently decrease the growth of mycorrhizal plants (e.g., Buwalda and Goh 1982;Graham et al. 1996;Mosse 1973). The negative growth effects of mycorrhizal colonization under high nutrient levels have been attributed to either carbon drain under non-limiting nutrient levels (Buwalda and Goh 1982) or toxic effects of high nutrient levels (Amijee et al. 1989). ...
Dark septate endophytes (DSE) are a miscellaneous group of ascomycetous anamorphic fungi that colonize root tissues intracellularly and intercellularly. The limited selection of studies quoted here exemplifies the range of host responses to symbiotic DSE fungi. Like my-corrhizal associations, DSE associations vary from negative to neutral and positive when measured by host performance or host tissue nutrient concentrations. This range of host responses is partially attributable to variation between different fungus taxa and strains. Similarly, hosts differ in their responses to a single DSE strain. Experimental conditions may also govern the nature of the sym-biotic association. It is concluded that DSE are capable of forming mutualistic associations functionally similar to mycorrhizas. If the variation in host response to mycorrhi-zal fungi is considered to represent a continuum ranging from parasitism to mutualism, DSE symbiosis must be considered mycorrhizal, at least under some conditions.
... As mentioned earlier, Guo et al. (1994) found that continued cropping of tobacco led to the dominance of one species of Glomus in the community of AMF which correlated with reductions in yields in a soil with extremely high levels of P and other nutrients. This apparent mycorrhizal-induced growth depression of plant growth at high levels of P has been noted for certain Citrus/AMF combinations too (Graham et al., 1996). The imbalance caused by employing agricultural practices, such as high levels of fertiliser and pesticide inputs and long-term monocultures, is reflected in their effects on the soil microbiota. ...
... although no positive effect was observed on dry matter production, aMf increased plant P concentrations after the addition of up to 48 mg kg -1 (P100). aMf species with high levels of colonization at high P levels may become parasitic as a result of the great plant demand for carbohydrates (Graham et al., 1996;Moreira & siqueira, 2006). ...
Nos últimos anos, a cultura do pinhão-manso (Jatropha curcas L.) tem despertado grande interesse pelo seu alto potencial na produção de matéria prima para a produção de biocombustíveis. Apesar de sua adaptabilidade às condições de baixa fertilidade do solo, as plantas requerem a correção da acidez do solo e a adição de considerável quantidade de fertilizantes para alta produção de frutos. O objetivo deste trabalho foi avaliar a efetividade de fungos micorrízicos arbusculares em mudas de pinhão-manso em diferentes doses de P no solo. O experimento foi conduzido em casa de vegetação, utilizando solo arenoso (LVd) autoclavado como substrato em vasos com capacidade de 4 kg. Foram avaliados em um delineamento completamente casualizado - em um esquema fatorial, com quatro repetições - os tratamentos de fungos micorrízicos (controle, Gigaspora margarita ou Glomus clarum) e a adição de P (0, 25, 50, 100, 200 e 400 mg kg-1 de solo). O experimento foi conduzido por 180 dias. A inoculação micorrízica proporcionou aumento no crescimento das plantas, nos teores de P e na eficiência de absorção de P pelas raízes nas baixas doses de P. O pinhão-manso apresentou decréscimo no quociente de utilização de P com o aumento da adição de P. O índice de eficiência de utilização de P aumentou nas menores doses e diminuiu nas altas doses de adição deste nutriente. A colonização micorrízica e a esporulação foram influenciadas negativamente pela adição de P. A mais alta eficiência micorrízica ocorreu entre as concentrações de 7,8 e 25 mg kg-1 de P no solo. O pinhão-manso respondeu positivamente à adição de P, indepedentemente da presença micorrízica.
... The diverse behaviour of three Glomus species used in our study could be related to their varying developmental patterns. Normally, G. intraradices is a very aggressive AM fungus in terms of intensity of root colonization and production of fungal structures such as vesicles and chlamydospores (Graham et al., 1996). ...
... Positive relationships between fatty acid concentrations and colonization have been used to assess (1) the impact of soil type on AMF development in roots and (2) differences in carbohydrate allocation patterns plants. Graham et al. (1996) used 16:1w5c (from total lipids) to assess differences in the rate at which four Glomus species colonized roots of sour orange, and found that 16:1w5c accumulated under low phosphorus but not high phosphorus conditions, and at different rates in different AMF species. Concentrations of PLFA 16:1w5c and arbuscule occurrence have been shown to track each other very effectively, while fatty acid concentrations and vesicle numbers are less well correlated (van Aarle and Olsson 2003). ...
... (location on continuum) Because mycorrhizal function is an emergent property, studies of it must incorporate measurements at There are numerous reports linking C costs to mycorrhizal induced plant growth depressions (e.g. Peng et al. 1993;Graham et al. 1996;Graham and Eissenstat 1998;Jifon et al. 2002;Lendenmann et al. 2011). A recent study by Vannette and Hunter (2011) is particularly illuminating because it indicates that some plants face trade-offs between allocating C to AM fungi or to defense compounds. ...
Background
Recent studies have questioned the validity of the mutualism-parasitism continuum of mycorrhizal function. This paper re-evaluates the continuum model and analyzes these concerns.
Scope and Conclusions
Three insights arise from this analysis. First, the continuum model defines mycorrhizal function as an emergent property of complex interactions. The model identifies resource trade and symbiotic control as key determinants of the costs and benefits of the symbiosis for plants and fungi, and the interaction of these factors with the environment ultimately controls mycorrhizal function. Second, analysis of carbon costs and phosphorus benefits is too narrow a focus to accurately predict mycorrhizal function. Analysis of plant and fungal fitness responses in ecologically and evolutionarily relevant systems are required to elucidate the full range of nutritional and non-nutritional factors embodied within mycorrhizal functioning. Finally, the definition of the term ‘parasitism’ has evolved. Some fields of science maintain the original definition of a nutritional relationship between host and parasite while other fields define it as a +/- fitness relationship. This has generated debate about whether the continuum of mycorrhizal functioning should properly be called a positive–negative response continuum or a mutualism-parasitism continuum. This controversy about semantics should be resolved, but it does not overturn the continuum concept.
... However, the C-costs incurred by the host were balanced by P-uptake. It is known that AM fungi may enhance plant P-uptake and growth at low soil P (Graham et al. 1996). In our study, total P-uptake rate was significantly (p £ 0.05) higher in AM than in non-AM plants during the initial stages of growth (days 0 to 77), showing a clear positive AM effect on P accumulation. ...
Relatively little is currently known about the seedling physiology of arbuscular mycorrhizal (AM) Agathosma betulina, a sclerophyllous crop plant cultivated for its high-value essential oils and food additives. In addition, virtually nothing is known about the AM associations of this plant. Consequently, the effect of an indigenous community of AM fungi on P nutrition and C economy in seedlings, grown in nursery conditions, was determined during different stages of host and AM fungal establishment. AM fungal ribosomal gene sequence analyses were used to identify some of the fungi within the roots, responsible for the nutritional changes. During the early stages of host and AM fungal establishment (0 to 77 days after germination), host growth was reduced, whereas the rate of P-uptake and growth respiration was increased. Beyond 77 days of growth, the rate of P-uptake and growth respiration declined. These findings, together with results obtained after molecular analyses of root associated fungal DNA. indicate that AM fungi belonging to the genera Acaulospora and Glomus, improve P-up-take and costs of utilization during the early stages of seedling establishment in a nutrient-poor soil.
... These results may be explained in terms of salt tolerance of the AMF isolates: they can maintain or even increase colonization capacity under saline conditions. On the other hand, Ri collect has been previously described to have a very high rate of colonization (Graham, Drouillard & Hodge 1996;Ruiz-Lozano et al. 2001), thus it seems not surprising that it maintained or even increased the colonization rate. Nevertheless, under saline conditions the native AMF strains isolated from saline areas maintained a higher symbiotic efficiency with maize plants than the collection strain. ...
Soil salinity restricts plant growth and productivity. Na(+) represents the major ion causing toxicity because it competes with K(+) for binding sites at the plasma membrane. Inoculation with arbuscular mycorrhizal fungi (AMF) can alleviate salt stress in the host plant through several mechanisms. These may include ion selection during the fungal uptake of nutrients from the soil or during transfer to the host plant. AM benefits could be enhanced when native AMF isolates are used. Thus, we investigated whether native AMF isolated from an area with problems of salinity and desertification can help maize plants to overcome the negative effects of salinity stress better than non-AM plants or plants inoculated with non-native AMF. Results showed that plants inoculated with two out the three native AMF had the highest shoot dry biomass at all salinity levels. Plants inoculated with the three native AMF showed significant increase of K(+) and reduced Na(+) accumulation as compared to non-mycorrhizal plants, concomitantly with higher K(+) /Na(+) ratios in their tissues. For the first time, these effects have been correlated with regulation of ZmAKT2, ZmSOS1 and ZmSKOR genes expression in the roots of maize, contributing to K(+) and Na(+) homeostasis in plants colonized by native AMF.
... Shreshtha et al. (1995) observed comparatively better growth parameters of VAM-infected Satsuma mandarin trees on account of improved photosynthesis and transpiration rates in P deficient acidic red soil under high temperature stress, suggesting, thereby, the existence of an efficient sink-source relationship in inoculated trees. Glomus etunicatum was found to be a less aggressive colonizer and produced lower rates of fungal fatty acid accumulation in sour orange seedling roots than the other Glomus species (Graham et al. 1996). Effects of growth regulators as mediators of mycorrhizal sink strength must be considered since the carbohydrate balance is believed to change in symbiotic or parasitic association (Lewis 1975). ...
Increasing realization of the ill effects of long sustained, exclusive use of chemical fertilizers, and consistent growing demand from the consumers for fruit quality, coupled with unsustainable productivity of citrus, have fostered experimentation with some alternative cultural practices. Organic culture is claimed to be the most benign alternative. Use of organic materials such as farmyard manure, cakes of plant origin, vermicompost, and microbial bio-fertilizers on one hand, and exploiting the synergism between citrus-vesicular arbuscular mycorrhizal fungus on the other hand, are important components of the bio-organic concept of citrus cultivation. Mycorrhizae were observed to be highly effective in low fertility, coarse textured soils. Mycorrhizal-treated trees had better plant growth and uptake of nutrients like P, Ca, Zn, Cu, and Fe compared to non-mycorrhizal trees. Inoculation of soil with mycorrhizae also helped in regulating the water relations and carbohydrate metabolism of citrus trees. Phosphorus nutrition of mycorrhizal-treated citrus trees was best improved by using rock phosphate as a source of P as opposed to other sources.
... Discrepancies in fungal growth in N-enriched soils have been linked to changes in the allocation of photosynthates between the plant root and shoot (Graham and Eissenstat 1990, Peng et al. 1993, Graham et al. 1996, or differences in C use among fungal taxa (Douds and Schenck 1990). A parsimonious explanation, based on the increase in hyphal abundance and sporulation we observed in C 3 , is that AMF likely allocate C resources (photosynthates) towards both active hyphal exploration for nutrient uptake and transfer (soil, root colonization; Sylvia and Neal 1990), and the sporulation of small-spored AMF species. ...
Arbuscular mycorrhizal fungi (AMF) are considered both ecologically and physiologically important to many plant communities. As a result, any alteration in AMF community structure following soil nitrogen (N) enrichment may impact plant community function and contribute to widespread changes in grassland productivity. We evaluated the responses of AMF communities to N fertilization (!100 kg NÁha À1 Áyr À1) in five perennial grasslands within the Long-Term Ecological Research network to generate a broader understanding of the drivers contributing to AMF species richness and diversity with increasing soil N fertility, and subsequent effects to host-plant communities. AMF spore and hyphal community data at three mesic sites (Cedar Creek, Kellogg Biological Station, Konza Prairie) and two semiarid sites (Sevilleta, Shortgrass Steppe) were collected over two consecutive years and used to test four hypotheses about AMF responses to N fertilization. Under ambient soil N, plant annual net primary productivity and soil phosphorus (P) were strongly related to climatic differences in AMF communities (semiarid vs. mesic). Following N fertilization, the drivers of AMF community structure were soil N availability, N:P supply ratio, and host-plant photosynthetic strategy (C 3 vs. C 4) but not climate. In P-rich soils (low N:P), N fertilization reduced AMF productivity, species richness, and diversity and intensified AMF community convergence due to the loss of rare AMF species and the increased abundance of Glomus species. In P-limited soils (high N:P), AMF productivity, species richness, and diversity increased with N fertilization; the most responsive AMF taxa were Acaulospora, Scutellospora, and Gigaspora. Soil N or N:P 3 host-plant (C 3 , C 4) interactions further modified these responses: AMF hyphae (primarily Gigasporaceae) associated with C 3 plants increased in abundance with N fertilization, whereas C 4 plants hosted nitrophilous Glomus species. Such responses were independent of the duration or quantity of N fertilization, or the time since cessation of N fertilization. This synthesis provides a new understanding of AMF community patterns and processes, and it identifies three key drivers (soil N, N:P, host plant) of AMF community structure that may be tested in other communities.
... Mycorrhizae are helpful to improve the uptake of diffusion limited nutrients such as P, Ca, Zn, Cu, Mn, and Fe by the host plants (Treeby 1992;Onkarayya and Mohandas 1993;Graham et al. 1996), on account of their ability to dissolve and promote absorption of these nutrients. This is accomplished primarily by extension of root geometry through symbiotic association in which fungus utilizes carbohydrates produced by the host plants, and plants in turn benefit by increased nutrient uptake, especially noticeable in soils of low fertility. ...
Introduction Diagnostic Methods Citrus Decline and Nutrient Constraints Nutrient Constraints Remediation Summary and Conclusion Literature Cited
... Root systems of mycorrhizal leek, Allium porrum (Berta et al. , 1990) and mycorrhizal grapevine, Vitis vinifera (Schellenbaum et al. , 1991), formed more, but shorter and more profusely ramified roots than nonmycorrhizal plants. The size of root systems of mycorrhizal vs nonmycorrhizal plants is variable and this is due, at least in part, to differences in the effectiveness of the colonizing arbuscular mycorrhizal fungi and in soil fertilitity (Graham et al. , 1996). ...
Abstract • Root responses to elevated CO2 concentrations, where nutrient demand was expected to be higher than at ambient CO2, and possible interactions with mycorrhizal symbionts are reported for pea (Pisum sativum). These are important below-ground components affecting carbon flow into the soil. • A video-minirhizotron system was used to study root growth in pot-grown mycorrhizal (inoculated with Glomus caledonium) and nonmycorrhizal pea plants at ambient or elevated CO2 concentrations over 9 wk. Analyses were made of root length changes, cohort size and survivorship. • Root length production at ambient, but not at elevated CO2, was higher in nonmycorrhizal than in mycorrhizal plants from week 4–7. Root loss began at week 5, peaking 2 wk later with 40–50% loss of the root length produced by week 8. The decline in root production and increase in root loss coincided with the onset of flowering. • Neither mycorrhizal inoculation nor CO2 concentration has a strong effect on pea root production and root loss, although mycorrhizal infection has a greater effect than CO2.
... It has been shown previously that mycorrhiza is not always beneficial in terms of biomass accumulation. In some cases, this has been explained by high inorganic P supply (Peng et al., 1993;Graham et al., 1996) or low light conditions (Bethlenfalvay & Pacovsky, 1983). The lack of growth benefit by mycorrhizas indicates high carbon cost of mycorrhizal symbiosis and competition for assimilates between the host and the root symbionts (Buwalda & Goh, 1982). ...
• The benefits or costs of mycorrhizal symbiosis for the host plants are most frequently estimated in terms of positive or negative effects on plant growth and biomass. The effect of mycorrhizal symbiosis on evolutionarily important fitness traits, such as reproduction, and effects on the next generation are poorly known.• In a set of glasshouse experiments involving two plant generations we investigated the impact of mycorrhiza on fitness traits in perennial hand-pollinated Campanula rotundifolia.• Mycorrhiza reduced plant growth and flower production, but increased root-shoot ratio, and shoot phosphorus (P) concentration. Mycorrhiza had no effect on seed number per capsule, mean seed weight or germination rate, but increased seed P concentration. Seedlings from mycorrhizal plants had a higher relative growth rate (RGR) than seedlings from nonmycorrhizal plants. Self-pollinations yielded fewer seeds per capsule that had inferior germination than seeds from cross-pollinations.• Mycorrhizal infection was associated with a cost for the reproductive output of the C. rotundifolia host plant, whose progeny, however, were better than those from the nonmycorrhizal plants. Mycorrhiza also showed the potential to affect the plant mating system by increasing self-incompatibility and inbreeding depression expressed during seedling growth.
Colonization of roots by arbuscular mycorrhizal [AM] fungi results in many changes in the carbon partitioning and metabolism of the host plant. The rate of carbon assimilation, the export of photosynthates from leaves, and the sink strength of roots may be increased relative to that in uncolonized plants. Hexose is taken up by the obligately symbiotic fungus for its growth, maintenance, and reproduction. This can represent a significant cost to the host, most notably under conditions in which the fungus offers little nutritive benefit. The components of the carbon partitioning and cost of arbuscular mycorrhizas, as well as current knowledge of the carbon metabolism of germinating spores and infra- and extraradical hyphae of AM fungi are reviewed in this chapter.
Mycorrhizal fungi may play an important role in plant invasions, but few studies have tested this possibility. Chinese Tallow (Sapium sebiferum) is an invasive tree in the southeastern United States. An experiment was conducted to examine the effects of mycorrhizal inoculation, fungicide application, and fertilization on the growth of Sapium and five native tree species (Liquidambar styraciflua, Nyssa sylvatica, Pinus taeda, Quercus alba, and Q. nigra) that co-occur in forests in the Big Thicket National Preserve in east Texas. Seedlings were grown in a greenhouse for twenty weeks under full factorial combinations of mycorrhizal inoculum, fungicide, and fertilizer. Mycorrhizal inoculation increased Sapium growth but caused zero to negative growth changes of the five native species. This suggests that Sapium may gain unusual benefits from mycorrhizal associations. Liquidambar styraciflua benefitted from mycorrhizal inoculation only in fertilized conditions which indicates that the potential advantage Sapium might gain from mycorrhizal associations may vary with native species and soil fertility.
We hypothesized that greater photosynthate supply at elevated [CO_2] could compensate for increased below-ground C demands of arbuscular mycorrhizas. Therefore, we investigated plant growth, mineral nutrition, starch, and net gas exchange responses of two Citrus spp. to phosphorus (P) nutrition and mycorrhizas at elevated atmospheric [CO_2]. Half of the seedlings of sour orange (C. aurantium L.) and `Ridge Pineapple' sweet orange (C. sinensis L. Osbeck) were inoculated with the arbuscular mycorrhizal (AM) fungus, Glomus intraradices Schenck and Smith and half were non-mycorrhizal (NM). Plants were grown at ambient or 2X ambient [CO_2] in unshaded greenhouses for 11 weeks and fertilized daily with nutrient solution either without added P or with 2 mM P in a low-P soil. High P supply reduced AM colonization whereas elevated [CO_2] counteracted the depressive effect of P on intraradical colonization and vesicle development. Seedlings grown at either elevated [CO_2], high P or with G. intraradices had greater growth, net assimilation of CO_2 (A_{CO2}) in leaves, leaf water-use efficiency, leaf dry wt/area, leaf starch and carbon/nitrogen (C/N) ratio. Root/whole plant dry wt ratio was decreased by elevated [CO_2], P, and AM colonization. Mycorrhizal seedlings had higher leaf-P status but lower leaf N and K concentrations than nonmycorrhizal seedlings which was due to growth dilution effects. Starch in fibrous roots was increased by elevated [CO_2] but reduced by G. intraradices, especially at low-P supply. In fibrous roots, elevated [CO_2] had no effect on C/N, but AM colonization decreased C/N in both Citrus spp. grown at low-P supply. Overall, there were no species differences in growth or A_{CO2}. Mycorrhizas did not increase plant growth at ambient [CO_2]. At elevated [CO_2], however, mycorrhizas stimulated growth at both P levels in sour orange, the more mycorrhiza-dependent species, but only at low-P in sweet orange, the less dependent species. At low-P and elevated [CO_2], colonization by the AM fungus increased A_{CO2} in both species but more so in sour orange than in sweet orange. Leaf P and root N concentrations were increased more and root starch level was decreased less by AM in sour orange than in sweet orange. Thus, the additional [CO_2] availability to mycorrhizal plants increased CO_2 assimilation, growth and nutrient uptake over that of NM plants especially in sour orange under P limitation.
Citrus volkameriana Tan. and Pasq. (‘Volkamer’ lemon) seedlings were inoculated with five different communities of arbuscular mycorrhizal (AM) fungi collected from citrus orchards in Mesa and Yuma, AZ, USA, and undisturbed North American Sonoran Desert and Chihuahuan Desert soils. Plants were then grown in a glasshouse for four months under continually moist or periodically dry conditions achieved by altering watering frequency so that before watering events container soil water tensions were approximately −0.01MPa (continually moist) or −0.06MPa (periodically dry) one half way down the container profile. Plants grown in continually moist soil had greater shoot growth than plants grown in periodically dry soil. Plant P status did not limit growth, and there was no interaction between watering frequency and AM fungal inoculum treatments. Plants inoculated with AM fungi from the Yuma orchard soil had significantly less root dry weight and total root length, and lower photosynthetic fluxes than plants treated with inoculum from the other soils. Specific soil respiration and an estimated carbon cost to benefit ratio were also higher for plants inoculated with AM fungi from the Yuma orchard soil than for plants treated with inoculum from the other soils. The Yuma orchard inoculum was distinctive in that > 80% of the total number of AM fungal spores were from a single species, Glomus occultum. These data showed that root growth suppression of plants treated with the Yuma inoculum, compared with plants treated with inoculum from all other sites, was substantial and greater in magnitude than the effect of periodic soil drying. Suppression of root growth might have resulted from increased AM fungal activity resulting in higher carbon costs to the plant.
A great diversity of plants and fungi engage in mycorrhizal associations. In natural habitats, and in an ecologically meaningful time span, these associations have evolved to improve the fitness of both plant and fungal symbionts. In systems managed by humans, mycorrhizal associations often improve plant productivity, but this is not always the case. Mycorrhizal fungi might be considered to be parasitic on plants when net cost of the symbiosis exceeds net benefits. Parasitism can be developmentally induced, environmentally induced, or possibly genotypically induced. Morphological, phenological, and physiological characteristics of the symbionts influence the functioning of mycorrhizas at an individual scale. Biotic and abiotic factors at the rhizosphere, community, and ecosystem scales further mediate mycorrhizal functioning. Despite the complexity of mycorrhizal associations, it might be possible to construct predictive models of mycorrhizal functioning. These models will need to incorporate variables and parameters that account for differences in plant responses to, and control of, mycorrhizal fungi, and differences in fungal effects on, and responses to, the plant. Developing and testing quantitative models of mycorrhizal functioning in the real world requires creative experimental manipulations and measurements. This work will be facilitated by recent advances in molecular and biochemical techniques. A greater understanding of how mycorrhizas function in complex natural systems is a prerequisite to managing them in agriculture, forestry, and restoration.
There is now ample evidence to support the common assertion that most plants in natural ecosystems have mycorrhizal associations. Information about the worldwide distribution of plants with different types of mycorrhizal associations is used to establish correlations with the major climatic factors (water, temperature) which regulate the distribution of plants, as well as more localized edaphic conditions. Ecological implications of mycorrhizal associations in natural ecosystems and the role of soil or environmental factors, mycorrhizal fungus characteristics or host plant properties alone or in combination are considered. Factors which can influence the occurrence and effectiveness of mycorrhizal associations include (i) root properties (ii) edaphic or climatic factors (iii) soil organisms, (iv) soil disturbance and (v) host-fungus compatibility. More complex ecological topics (involving, the environment. plants and mycorrhizal fungi) that are discussed include (i) mycorrhizal phenology, (ii) factors responsible for varying degrees of mycorrhizal dependency in host plants, (iii) the role of mycorrhizal hyphae in soil, (iv) nutrient competition involving mycorrhizal and non-mycorrhizal plants and (v) mycorrhizal interactions involving pollution and other stresses, the rhizosphere, soil properties and allelopathy. The population ecology of mycorrhizal fungi and the influence of their associations on plant population ecology are also considered.
Mycorrhizal-induced growth depression of plants in high-P soil has been reported in many species. The carbon costs of factors contributing to this growth depression were analyzed in Volkamer lemon (Citrus volkameriana Tan. & Pasq.) colonized by the mycorrhizal (M) fungus Glomus intraradices Schenck and Smith. M and nonmycorrhizal (NM) plants were each grown at two P-supply rates. Carbon budgets of M and NM plants were determined by measuring whole-plant carbon assimilation and respiration rates using gas-exchange techniques. Biomass, M colonization, tissue-P concentration, and total fatty acid concentration in the fibrous roots were determined. Construction costs of the fibrous roots were estimated from heat of combustion, N, and ash content. Root-growth respiration was derived from daily root growth and root-construction cost. M and NM plants grown in high-P soil were similar in P concentration, daily shoot carbon assimilation, and daily shoot dark respiration. At 52 d after transplanting (DAT), however, combined daily root plus soil respiration was 37% higher for M than for NM plants, resulting in a 20% higher daily specific carbon gain (mmol CO2 [mmol carbon]-1 d-1) in NM than M plants. Estimates of specific carbon gain from specific growth rates indicated about a 10% difference between M and NM plants. Absolute values of specific carbon gain estimated by whole-plant gas exchange and by growth analysis were in general agreement. At 52 DAT, M and NM plants at high P had nearly identical whole-plant growth rates, but M plants had 19% higher root dry weight with 10% higher daily rates of root growth. These allocation differences at high P accounted for about 51% of the differences in root/soil respiration between M and NM plants. Significantly higher fatty acid concentrations in M than NM fibrous roots were correlated with differences in construction costs of the fibrous roots. Of the 37% difference in daily total root/soil respiration observed between high-P M and NM plants at 52 DAT, estimated daily growth respiration accounted for only about 16%, two-thirds of which was associated with construction of lipid-rich roots, and the remaining one-third with greater M root growth rates. Thus, of the 37% more root/soil respiration associated with M colonization of high-P plants, 10% was directly attributable to building lipid-rich roots, 51% to greater M root biomass allocation, and the remaining 39% could have been used for maintenance of the fungal tissue in the root and growth and maintenance of the extramatrical hyphae.
In August, eight 4-m tall citrus trees were pruned by removing the top third of their canopy. Eight unpruned trees served
as controls. Root growth, which was examined nondestructively with minirhizotrons over a four-month period, tended to be less
in the pruned than unpruned trees seven days after pruning and this difference was significant (P < 0.05) from 14 to 49 days after pruning. Total reducing and ketone sugars (includes free fructose, sucrose and fructans)
in the fine roots were less in pruned than unpruned trees 20 days after pruning, but not thereafter. By 30 days after pruning,
at least 20% of the roots of the pruned trees at a soil depth of 9 to 35 cm apparently died. By 63 days after pruning, root
length density had recovered to that of the unpruned trees, although starch reserves were 18% less in the fine roots of pruned
than unpruned trees at this time. Nine to eleven months after pruning (May to July), total biomass of leaves and fine roots
to a depth of 1 m were similar in pruned and unpruned trees. However, fruit biomass harvested in April from pruned trees was
only 24% of that in the unpruned trees. In May, nonstructural carbohydrates in the fine and coarse roots of pruned trees were
generally greater than in unpruned trees, possibly reflecting previous differences in fruit production.
This study tests the hypothesis that plant species of low mycorrhizal dependency (MD) tend to limit vesicular-arbuscular mycorrhizal (VAM) colonization more than species of high MD. Mycorrhizal dependency (MD = VAM plant dry weight/non-mycorrhizal plant dry weight) was determined for six citrus rootstocks in three green-house trials in a sterilized, P-deficient soil. In order to isolate the process of VAM colonization from shoot growth responses, colonization of the rootstocks with the same scion was examined in high-P soil in a rootstock field trial. Colonization of roots of known age was evaluated in soil cores extracted from beneath the canopy of mature trees. Initially, the soil was replaced in the resultant holes after dry sieving to remove roots and mix VAM fungal propagules (disturbed soil). Extraradical (ER) colonization of young roots in disturbed soil increased rapidly up to 5 weeks and approached that of mixed-age roots in undisturbed soil by 19 weeks. Intraradical (IR) colonization of young roots increased up to 19 weeks and was less than that of mixed-age roots. Differences in IR colonization of rootstock species that developed with time were correlated with their ER colonization at 10 and 19 weeks. Variation among citrus rootstocks in colonization of new roots was not related to root diameter or root extension rate. Colonization of rootstocks at 19 weeks was positively correlated (r =0.88-0.99, P < 0.05) with rootstock MD in P-deficient soil. Therefore, our data support the hypothesis that species that have evolved root systems that are less dependent on mycorrhizas have also evolved presently unknown mechanisms to regulate mycorrhizal colonization and presumably, carbon expenditure on the fungus.
The exchange of solutes between a plant and invading microorganism involves transport across both plant and microorganism membranes separated by a common apoplast. An empirical analysis of the interrelationship between these two membrane transport steps is undertaken with emphasis on transfer of reduced carbon from host to microorganism. The analysis leads to the conclusion that solute efflux from the plant partner has the potential to exert significant control over net transport of solutes from the plant to microorganism. The nature of solute efflux from the plant partner was evaluated for examples of pathological, mycorrhizal and Rhizobium associations. Estimates of solute efflux across the perceived interfacial membrane of the plant were greater than those of non-infected tissues. The principal factors contributing to the enhanced solute efflux in the presence of a microorganism were considered to be elevation of solute concentrations in the plant cytoplasm and modification of membrane transport. Possible modes of action by the invading microorganism on these factors are examined with particular attention being paid to the modification of membrane transport.
The growth of subterranean clover inoculated with two types of vesicular arbuscular endophytes was compared with that of uninoculated plants at five levels of applied superphosphate in a high phosphatefixing soil. Plants were grown in both untreated soil and soil steamed to eliminate the natural population of mycorrhizal fungi. Marked increases in the growth and phosphorus content of plants inoculated with a fungus isolated in Western Australia were apparent at intermediate levels of superphosphate in both soils. This fungus, which resembles Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, was more efficient at increasing growth and phosphorus content of subterranean clover than Glomus fasciculatus (Thaxter) Gerd. & Trappe. The greater growth response of plants inoculated with the fungus resembling G. mosseae was associated with a greater amount of mycorrhizal roots. Responses in nodulation closely paralleled responses in growth. Non-mycorrhizal plants produced more dry matter at a given phosphorus concentration in tops than did mycorrhizal plants.
Phosphorus transport by hyphae of the three VA mycorrhizal fungi, Acaulospora laevis Gerdemann & Trappe, Glomus sp. and Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders, associated with Trifolium subterraneum L. was investigated by means of radiotracer techniques. Plants with roots heavily colonized by each mycorrhizal fungus were transplanted to two-compartment systems, where a hyphal compartment was separated from the main compartment by a fine mesh preventing root penetration. The hyphal compartment contained layers of 32P-labelled soil, which were placed at 0, 1, 2.5, 4.5 or 7 cm from the root compartment.
A time-course study over 37 d showed that Glomus sp. transported most 32P to shoots over soil-root distances shorter than 1 cm. In contrast, A. laevis transported most 32P to shoots over soil–root distances longer than 1 cm. This ability of A. laevis to transport phosphorus over longer distances than Glomus sp. parallels previous observations that hyphae of A. laevis spread faster and further in soil than hyphae of the Glomus sp.
Scutellospora calospora transported much less 32P to plants, but accumulated more 32P in its hyphae, than the two other fungi. The higher specific radioactivity in the hyphae of S. calospora than of A. laevis and Glomus sp. indicated a retarded translocation of 32P in its hyphae or retarded transfer of 32P across its interface with the host. However, the poor phosphorus transport by S. calospora might also have resulted from its reaction to root trimming at transplanting; percentage root colonization by S. calospora decreased markedly after transplanting to the labelling system.
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The ability of several species of vesicular–arbuscular (VA) mycorrhizal fungi to form hyphae in soil was compared in two glasshouse experiments. We measured the length of hyphae in soil and related this to the length of infected root. Species of VA mycorrhizal fungi differed in the length of external hyphae produced per cm of infected root. Glomus fasciculatum (Thaxter sensu Gerd.) Gerd. and Trappe produced less external hyphae per cm infected root than did Gigaspora calospora (Nicol. and Gerd.) Gerd. at all harvest times and when inoculum was either placed in a band below the seed or mixed throughout the soil. Glomus tenue (Greenall) Hall and Acaulospora laevis Gerd. and Trappe both produced similar lengths of external hyphae per cm infected root to that formed by G. calospora .
Differences among isolates of VA mycorrhizal fungi in the distribution of hyphae in soil may be as important as differences in the length of external hyphae when selecting fungi that are effective at increasing nutrient uptake.
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Six species of vesicular‐arbuscular mycorrhizal fungi originally isolated from orchard soils were evaluated at low phosphorus (approx. 30 mg kg ⁻¹ ) and high phosphorus (approx. 180 mg kg ⁻¹ ) levels for root colonization and effects on growth of apple (Malus domestica Borkh.) seedlings. Fungi tested were Gigaspora calospora (Nicol. & Gerd.) Gerd. & Trappe, Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, Glomus maculosum sp. ined., Glomus manihotis Howeler, Sieverding & Schenck, Glomus bitunicatum sp. ined., and two isolates of Glomus occultum Walker. Trees grew larger and had higher leaf P concentrations at high soil P than at low soil P regardless of mycorrhizas. At low P, fungal species differed in percentage root length colonized, intensity of colonization, types of mycorrhizal structures formed, and number of spores produced. Fungal species also differed in effects on plant growth. At harvest, five treatments were taller than the non‐mycorrhizal control trees, and two were not. Stem diameter and total dry weight were increased by only three treatments. At high P, no treatment resulted in greater than 5 % of root length colonized, and endogonaceous fungi had little influence on plant growth.
Using a ‘split root’ technique, it was found that phosphorus fertilization of half of the root system of sudangrass could significantly reduce the number of chlamydospores of the mycorrhizal fungus Glomus fasciculatus in the unfertilized half of the root system. In a second experiment, vials of soil containing different concentrations of phosphorus were inserted into pots of sudangrass which were fertilized with different amounts of phosphorus and inoculated with G. fasciculatus. The numbers of chlamydospores, vesicles and arbuscles and the amount of hyphae produced by G. fasciculatus on roots within the vials were not influenced by the soil P in the vials but were inversely correlated with the concentration of P in roots outside the vial. All evidence indicates that it is the concentration of P within the plant and not the soil P which leads to a reduction in colonization, infection, and spore production of G. fasciculatus.
Four vesicular-arbuscular endophytes were inoculated into onions cultured in soil in a growth chamber. Dry weight, root length, infected root length, phosphorus content and quantity of external mycelium were measured at intervals. Three endophytes produced similar hyphal inflows, growth increments and external mycelium. One endophyte produced no growth increase in the host, and had little external mycelium and slow increase in percentage infection.
One isolate of Glomus clarus, two of G. etunicatus, and one of G. claroideum, obtained from plants growing on abandoned stripmine sites in Kentucky, and an isolate of G. fascicutatus known to stimulate growth of various woody plants, were evaluated for their influence on growth of sweetgum seedlings in a mixture of sand and stripmine soil. Soils were supplemented with various rates of a complete slow-release fertilizer. Throughout the growth period, G. fasciculatus, and most of the stripmine isolates, stimulated growth at low fertilizer rates. At higher fertilizer rates, including the level optimum for non-mycorrhizal plants, the stripmine isolates inhibited plant growth. After 14 weeks, plants inoculated with one of the four stripmine isolates overcame the early growth depression, and those inoculated with a second isolate appeared to be overcoming the growth depression. G. fasciculatus was not inhibitory at any fertilizer rate. Root colonization by all three isolates evaluated was inhibited by the highest fertilizer rate, but this effect was not related to growth inhibition of plants. The other two isolates colonized roots at an extremely low rate (< 1%). Sporulation of all the stripmine isolates, but not G. fasciculatus, was also inhibited by the highest fertilizer rate. The G. fasciculalus isolate used in this study may be atypical of mycorrhizal fungi occurring randomly in nature in its mutualistic or neutral effect on plants under a wide range of growth conditions.
The hypothesis was tested that the amount of external hyphae of a vesicular-arbuscular mycorrhizal (VAM) fungus extending from roots out into soil is not always proportional to the extent of colonization of the root cortex. Growth enhancement and amount of external hyphae were compared for eight isolates of five Glomus spp. that differed in their geographic origin and capacity to enhance growth of Troyer citrange, but were similar in their capacity to extensively colonize Troyer citrange roots. In general, isolates from California increased growth in a P-deficient (9.8 mg kg−1) California soil more than did non-native isolates from Florida soils. The difference between the capacity of California and Florida isolates to enhance growth was not a function of the degree to which they colonized the roots since all had colonized over 95% of the root length by the time of harvest. Differences in growth enhancement did appear, however, to be a function of the amount of external hyphae that had developed as estimated by the weight of soil they had bound into aggregates. This study suggests that isolates of VA mycorrhizal fungi may differ in their capacity to develop an external hyphal system independent of their capacity to colonize the root cortex, and that we cannot assume that high levels of colonization will necessarily mean the fungus has also developed the mycelium in the soil necessary to transport nutrients responsible for plant growth enhancement.
VA mycorrhizae, the most ancient type of mycorrhizal symbiosis, are present in the most phytogenetically advanced groups.
Few plants have evolved mechanisms to completely prevent infection by VAM fungi. Yet, plant species that are less dependent
on VA mycorrhizae for nutrient acquisition (e.g., grasses) generally have less root colonization in the field than more dependent
species (e.g., Citrus). Among closely related Citrus genotypes, there is a greater tendency for less dependent species to limit the rate but not
the extent of colonization, even in high-P soils. We hypothesize that colonization represents a significant carbon cost that
may be regulated by the host genotype. Carbon expenditure on the fungus at high P may result in mycorrhizal-induced growth
depression. The potential value of breeding plants for greater susceptibility to colonization will depend on the cost/benefit
of VA mycorrhizae for the specific crop, soil and environmental conditions. Although the genetics and physiology of host control
over VAM colonization are barely known, recently discovered mycorrhizal colonization mutants (myc-) of pea offer great promise for the study of host-fungus compatibility.
In spite of the major advances in understanding the functioning of symbioses between plants and arbuscular mycorrhizal fungi,
details of the ecology of mycorrhizal fungi are not well documented. The benefits of the association are related to the timing
and extent of colonization of roots, and fungi differ in their contribution to plant growth and presumably to soil aggregation.
Knowledge of the processes that lead to successful colonization of roots by beneficial fungi at appropriate times for the
host plants will form the basis of guidelines for soil management to maximize the benefits from the symbiosis.
Fungi differ in the manner and extent to which they colonize roots. They also differ in their capacity to form propagules.
The importance of hyphae, spores and propagules within living or dead mycorrhizal roots also differs among species and for
the same species in different habitats. The relationships between colonization of roots and propagule formation, and between
propagule distribution and abundance and subsequent mycorrhiza formation, for different fungi in field environments, are not
well understood.
Methods for quantifying mycorrhizal fungi are not especially suitable for distinguishing among different fungi within roots.
Consequenctly, the dynamics of colonization of roots by different fungi, within and between seasons, have been little studied.
Research is required that focuses on the dynamics of fungi within roots as well as on changes in the abundance of propagules
of different fungi within soil. Interactions between fungi during the colonization of roots, the colonization of soil by hyphae
and sporulation are all poorly understood. Without knowledge of these processes, it will by difficult to predict the likely
success of inoculation with introduced fungi. Such knowledge is also required for selecting soil management procedures to
enhance growth and survival of key species within the population.
The relative tolerance of various fungi to perturbations in their surroundings will provide a basis for identifying those
fungi that are likely to persist in specific environments. The processes that influence mycorrhizal fungi in field soils can
be identified in controlled studies. However, greater emphasis is required on studying these processes with mixed populations
of fungi. The role played by diversity within populations of mycorrhizal fungi is virtually unexplored.
A regional study was made to identify vesicular-arbuscular mycorrhizal (VAM) fungi effective in promoting plant growth in diverse plant and soil systems. Eight cooperators in six states of the eastern United States evaluated six VAM fungal isolates on soybean (Glycine max L. Merr.) and sorghum (Sorghum bicolor L. Moench) in a shared soil and in at least one regional soil from each location. Plants were grown with high VAM inoculum densities (minimum of 20 VAM propagules ml(-1)) for 42-57 days in pasturized soils in greenhouses or growth chambers. Shoot and root dry masses, total and colonized root lengths and shoot-P concentrations were determined at harvest. Under the experimental conditions tested, the VAM fungal isolate was more important than the soil or host plant in determining effectiveness. In the shared soil, inoculation with two isolates of Glomus (GE329 and GENPI) resulted in the greatest shoot masses for soybeans, while the same two isolates and GE312 provided maximum response in sorghum. In the regional soils, GE329 and GENPI had the widest range of growth promotion with both soybean and sorghum; however, for both plant species the mycorrhizal response was greatest in soils with less than 10 mg extractable P kg(-1). For soybeans, colonized root length was not related to VAM growth response. For sorghum, there was a positive correlation between colonized root length and plant growth response. We conclude that VAM isolates exist which are effective in promoting plant growth over a range of edaphic and host conditions.
The effects of plant phosphorus (P) status and the mycorrhizal (M) fungus, Glomus intraradices Schenck & Smith, on the carbon (C) economy of sour orange ( Citrus aurantium L.) were determined during and following active M colonization. There were four treatments: M seedlings grown at standard-strength (1 mM) P (M1) and nonmycorrhizal (NM) plants grown at one, two and five times standard-strength P (NM1, NM2 and NM5). Mycorrhizal colonization, tissue dry mass, P content, root length and leaf area were determined in five harvests from 6 to 15 weeks of age. Rate of C assimilation (A) was determined at 7, 8 and 12 weeks by gas exchange. Partitioning of 14 C was determined from 7 to 15 weeks using a 10-min pulse followed by a 24-h chase period. For a given attribute, M1 plants were compared to the curve defining the NM response as a function of tissue P concentration. In contrast to the large effects of P nutrition on C economy of sour orange, M effects were generally subtle. Mycorrhizae increased the root biomass fraction, the root length/leaf area ratio and the percentage of 14C recovered from below-ground components. A higher percentage of below-ground 14 C was in the respiration and soil fractions in M than NM plants of equivalent P status. Mycorrhizal plants tended to enhance A only for a brief period. Mycorrhizal plants had lower relative growth rates than NM plants of equivalent P status, suggesting that the temporarily enhance A of M plants did not fully compensate for their greater below-ground carbon expenditure. Problems of interpreting the dynamic effects of mycorrhizae on C economy that are independent of P nutrition are discussed. Copyright 1993, 1999 Academic Press
Arbuscule-forming fungi in the order Glomales form obligate endomycorrhizal associations with plants that make them difficult to quantify, and taxonomy of the group is only beginning to be objectively understood. Fatty acid methyl ester (FAME) profiles were analyzed to assess the diversity and quantity of fatty acids in 53 isolates of 24 glomalean species. Spores and endomycorrhizal roots of sudan grass (Sorghum sudanense) and the citrus rootstock Carrizo citrange (Poncirus trifoliata x Citrus sinensis) were examined. Spores yielded reproducible FAME profiles from replicate spore collections extracted from soil pot cultures despite being grown in association with a host plant and with contaminating microorganisms present. Unweighted pair group analysis revealed relatively tight clusters of groups at the intraspecific, specific, and generic levels; however, lipid profiles at the family level were convergent. Thus, FAME profile comparisons provided a robust measure of similarity below the family level. FAME profiles in sudan grass roots containing vesicles and/or spores of Glomus intraradices were more similar to spore profiles than to profiles from nonmycorrhizal roots. The FAME profiles for Gigaspora species, which do not form vesicles or spores in roots, were less distinct from nonmycorrhizal roots. G. intraradices and G. rosea produced fatty acids in roots that were distinguishable from each other as well as from the host root. Production in citrus roots of the fatty acid 16:1(inf(omega)5) cis by two Glomus species was correlated with the development of mycorrhizal colonization as measured by clearing and staining procedures and by estimates of total incidence and vesicle intensity. FAME analysis of roots not only provided a measure of colonization development but also served as an index of carbon allocated to intraradical fungal growth and lipid storage.
Factors influencing the occurrence of vesicular-arbuscular mycorrhizal fungi
- L K Abbott
- A D Robson
Abbott, L.K. and A.D. Robson. 1991. Factors influencing the occurrence of vesicular-arbuscular mycorrhizal fungi. J. Agric. Ecosyst.
Environ. 35:121--150.