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Cross section of a rhizome of S. argentinensis. Sclerenchyma and parenchyma tissues are visible. A bud is emerging protected by lignified tissue.
Source publication
Monk's tonsure-like gaps develop inside gramineans and other plants. The tonsures of Spartina argentinensis originate as a result of tussock development and disturbance. As the tonsure develops the ring of tillers around it breakes down and new tussocks develop from the fragments, regenerating the grassland matrix vegetatively. The microenvironment...
Context in source publication
Context 1
... h izomes had l ign if ied tissues of several cell lay- ers, cells thick sclerenchy- m a st r ip, a l l w it h t h ick- e n e d a n d l ig n i f ie d wa l l s ( Fig u r e 5) . T h e va s cu la r bundles are arranged in the cha racter istic atactostelae of grasses, sur rounded by lignified tissue. ...
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Citations
... Wiregrass, however, could still generate plant-soil feedbacks affecting other species. For instance, the bunchgrass-like structure and high flammability of wiregrass could generate plantsoil feedbacks by altering microclimate conditions (Iacona et al. 2012) or by promoting interannual variation in nutrient accumulation from tiller decomposition and post-fire ash deposition (Vinton and Burke 1995; Lewis et al. 2001). ...
Purpose
Previous research alludes to two wiregrass (Aristida beyrichiana) ecotypes from mesic and xeric environments. It is unknown whether these ecotypes are restricted by conspecific plant-soil feedbacks or specific components of mesic and xeric soils. We investigated whether biomass production of wiregrass ecotypes grown in mesic and xeric soil was affected by conspecific plant-soil feedbacks, and whether wiregrass ecotypes responded differently to the soil biota and nutrients that characterize each of the two soil types.
Methods
We established a greenhouse experiment to compare the biomass production of mesic and xeric wiregrass ecotypes in mesic and xeric soil. To establish the effects of conspecific soil conditioning, each soil type was either conditioned or unconditioned by wiregrass. To to isolate the effects of soil biota and nutrients, each combination of soil type and conditioning was replicated in three soil manipulations (i.e., whole, inoculated, and sterile soil) where each wiregrass ecotype was grown.
Results
Biomass of the xeric ecotype was marginally greater in xeric soil than in mesic soil. The mesic ecotype tended to grow more in mesic than xeric soil, but it was not significant. Soil conditioning did not affect biomass production of either ecotype. Soil biota coupled with nutrients affected biomass production of both ecotypes when not growing in their own soil.
Conclusions
We found some evidence for wiregrass ecotypes that have increased growth in their own soil type, but not for conspecific plant-soil feedbacks. Ecotypes were affected by negative interactions with soil biota when growing in a different type. Thus, the soil environment should be considered when sourcing seeds for restoration.
... Early in development of the tussock the rhizomes branch and become physically independent of each other, similar to other clonal species (Wilhalm 1995;Briske & Derner 1998), and eventually the tussock fragments into new circular tussocks or clones (Clewell 1989;authors' observations). This growth form has been observed for several other bunchgrass and shrub species growing in environments that are xeric with respect to either climate or soil drainage (Muller 1953;Barbour 1969;Danin & Orshan 1995;Lewis et al. 2001;Ravi et al. 2008). Wiregrass tussocks typically survive fire, but seedlings are fire sensitive (Outcalt et al. 1999;, and large tussocks can be partially or completely killed by unusually severe fire-associated combustion of woody fuels or duff (van Eerden 1997). ...
Aristida beyrichiana (wiregrass) is a foundation bunchgrass species in many southeastern U.S. native pine communities, but it has been dramatically reduced in extent. The potential for reintroduced wiregrass to reproduce and spread is not well studied because of its slow growth and limited conditions for successful reproduction. We present a case study where tussocks of wiregrass were transplanted and recensused 18 and 37 years later to study their population dynamics. We remeasured a subset of tussocks to estimate diameter growth over two years. With frequent prescribed fires (1–3 year intervals, about half in April–July when flowering is induced), the initial population of 160 tussocks increased to 1,199 through seed dispersal and clonal fragmentation, and the total basal area approximately tripled. Relationships among tussock density, diameter, and basal area per m² and their changes over time suggest density‐dependent regulation of population structure, possibly from intraspecific competition and competitive exclusion. Tussock diameter growth averaged 0.9 cm per year over a two year period and was independent of initial diameter. This study, the longest of a wiregrass population to date, suggests that a low‐density population established in native soil types has a slow but robust tendency to reproduce by seed and expand if provided frequent fire, including April–July burns, in a high light environment without soil disturbance. Wiregrass can be characterized as a competitive, late‐successional, dominant species in stable, climax‐like native savannas, promising long‐term success under appropriate conditions as part of restoration efforts.
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... In addition, the probability of a tussock having a central die-back increased with tussock circumference. This suggests that the fire, especially the mid-season treatment, affected the largest tussocks causing the death of their centres (Lewis et al. 2001). Even though the tussocks with a central die-back are observed worldwide (Ravi et al. 2008, Sheffer et al. 2007, Wikberg & Mucina 2002, a comprehensive understanding of the processes that lead to the formation of this pattern is still not clear. ...
This study assesses the impact of four fire treatments applied yearly over 3 y, i.e. early fire, mid-season fire, late fire and no fire treatments, on the grass communities of Lamto savanna, Ivory Coast. We describe communities of perennial tussock grasses on three replicated 5 × 5-m or 10 × 5-m plots of each fire treatment. Tussock density did not vary with fire treatment. The relative abundance of grass species, the circumference of grass tussocks and the probability of having a tussock with a central die-back, varied with fire treatment. Mid-season fire had the highest proportion of tussocks with a central die-back while the late fire had the smallest tussocks. Tussock density, circumference, relative abundance and probability of having a central die-back varied with species. Andropogon canaliculatus and Hyparrhenia diplandra were the most abundant of the nine grass species. They had the largest tussocks and the highest proportion of tussock with a central die-back. Loudetia simplex was the third most abundant species but was very rare in no fire plots. The distribution of tussock circumferences was right skewed and dominated by small tussocks. The proportion of the tussocks with a central die-back strongly increased with circumference, which could lead to tussock fragmentation. Taken together, this study suggests that fire regimes impact grass demography and that this impact depends on grass species and tussock size.
... The spatial expansion of plant stands could have irregular shape as well as symmetrical shape in form of circles and rings. The circular patch corresponds to the normal radial expansion of plant species, especially vegetative propagation by rhizomes with tussock for- mation, on a homogeneous substrate in the absence of a strong competitive species (Feist and Simenstad, 2000;Lewis et al., 2001; Perillo and Iribarne, 2003;Dennis et al., 2011;Marangoni and Costa, 2012). Widely separated circular patches at the leading edge of the mud flat invasions grow until coming in contact with another patch, however very frequently after years and even decades of growth, the central part of the patches show signs of die-back, leaving a depleted plant cover or empty central gap and finally a ring-shape patch ( Lewis et al., 1990Lewis et al., , 2001Castillo et al., 2003;Perillo and Iribarne, 2003;Minkoff et al., 2006;Escapa et al., 2015). ...
... The circular patch corresponds to the normal radial expansion of plant species, especially vegetative propagation by rhizomes with tussock for- mation, on a homogeneous substrate in the absence of a strong competitive species (Feist and Simenstad, 2000;Lewis et al., 2001; Perillo and Iribarne, 2003;Dennis et al., 2011;Marangoni and Costa, 2012). Widely separated circular patches at the leading edge of the mud flat invasions grow until coming in contact with another patch, however very frequently after years and even decades of growth, the central part of the patches show signs of die-back, leaving a depleted plant cover or empty central gap and finally a ring-shape patch ( Lewis et al., 1990Lewis et al., , 2001Castillo et al., 2003;Perillo and Iribarne, 2003;Minkoff et al., 2006;Escapa et al., 2015). Meanwhile these central gaps may be colonized by other successional plant species ( Lewis et al., 1990;Castellanos et al., 1994;Alberti et al., 2008). ...
... According to these authors, as the tussocks age, gaps like a "monk's tonsure" develop at their center and they are later colonized by Solidago chilensis and Neptunia pubescens. Lewis et al. (2001) found that the soil of S. argentinensis gap is richer in organic matter and phosphate and it has lower pH than that of the soil outside the gap. Alberti et al. (2008) pointed out that the colonization of central part of Sarcocornia perennis colonizing patches in NE Argentina saltmarshes by Spartina densiflora resulted in out-competition of this forb and probably not due to differences in desiccation or salt stress between evaluated health circular patches and depleted ring patches of S. perennis. ...
Circular (RP) and ring-shape (RP) patches of vegetation in intertidal flats have been associated with the radial expansion of tussock growth forms and die-back gap in older central stands, respectively. RP formation has not yet been sufficiently explained. We accomplished a comparative geochemical study of CP and RP structures of Spartina densiflora within a single saltmarsh in a microtidal estuary (<0.5 m). The pore water under these structures demonstrated distinctive physical-chemical properties by marked seasonal changing in water level and salinity. During high-water period dissolved H2S was frequently low in pore waters of S. densiflora structures due to reactive-Fe, which scavenge the sulfide from solution and form solid sulfides. During less flooded-brackish water period, pore water pH goes down below 4 inside the vegetated bordering areas of RP. In these locations the concentration of soluble sulfides dramatically increases up to 140 μM L⁻¹. The high concentration of protons in pore water is the result of solid sulfides atmospheric oxidation to sulfuric acid. High dissolution of H2S, along with the low pH, creates a toxic environment for S. densiflora and die-back central gap formation in RP. CP structure was 5 cm higher in the intertidal than RP but shows frequent presence of a water layer, less severe oxidation of sulfides and limited building-up of toxic condition to plants. Development of S. densiflora RP probably indicates the uplift of sediment by this bioengineer grass and/or periodic lowering of the water surface below a certain critical level.
... In a recent review, Bonanomi et al. (2014) reported that herbs, shrubs and even trees with clonal propagation, during their ontogenetic cycles, produce clones in a "ring" shape that progressively degenerate in the older inner area, thus producing a dieback central zone. This vegetation pattern has been called fairy rings (Hitchcock 1935), rings (Watt 1947), hollow crowns (Strickland 1983), central dieback (Adachi et al. 1996), and monk's tonsure-like gaps (Lewis et al. 2001). Noteworthy is that the majority of the "ring" shaped plants has been found during colonization of bare substrates or in environments with discontinuous plant cover such as deserts (Danin 1996, Sheffer et al. 2007, primary succession over bare substrates such as lava flow (Adachi et al. 1996), harvested peat lands (Lanta et al. 2008), salt marshes (Castellanos et al. 1994), and sand dunes (Pemadasa 1981). ...
Spatial patterns and self-organization of plants has been a subject of fascination because the underlying mechanisms have been hard to determine, raising different explanatory hypotheses. Plant–soil negative feedback (PSNF) – defined as the induction of negative conditions for conspecific establishment – has been widely studied in both field and laboratory conditions, and conceptually demonstrated by some modelling works. We present a mechanistic model, integrating individual plants inside an agent-based framework, to explore the effects of PSNF on the spatial and temporal dynamics of virtual populations and communities of plants of diverse growth forms. This endeavour led to the reproduction of well-known vegetation patterns observed at various scales, demonstrating for the first time a unified mechanism behind the spatial patterns of Janzen–Connell seedlings’ distribution, ring formation, and the high species mobility in species-rich grasslands. These results support the ecological relevance of PSNF in the regulation of spatial organization and biodiversity dynamics in plant communities. More specifically, PSNF due to autoxicity seems most coherent with the spatio-temporal scale of dynamics displayed here. This article is protected by copyright. All rights reserved.
... In a recent review, Bonanomi et al. (2014) reported that herbs, shrubs and trees capable of clonal propagation, during their ontogenetic cycles, produce clones with a "ring" shape that progressively degenerate in the older inner area, thus producing a "dieback" central zone (Fig. 4c). This vegetation pattern has been also called fairy rings, rings, hollow crowns, central dieback, and monk's tonsure-like gaps (Adachi et al., 1996;Lewis et al., 2001;Watt, 1947). Interestingly, in many cases the inner area is colonized by multiple species, different from the dominant plant that generated the ring, thus resulting in an increased local biodiversity (Castellanos et al., 1994;Bonanomi et al., 2005b). ...
... A further evidence against the nutrient depletion hypothesis came from clonal perennial plants forming "ring" (Fig. 4c). For this type of plants, several studies reported a higher nutrient concentration in the inner "dieback" area compared with the soil outside the ring (Adachi et al., 1996;Castellanos et al., 1994;Incerti et al., 2013;Lewis et al., 2001;Otfinowski, 2008;Ravi et al., 2008;Wikberg et al., 2002). In an early study, Curtis and Cottam (1950) found that the prairie sunflower Helianthus rigidus in the field is able to form clones with central "dieback". ...
Soil sickness (SS) is the rise of negative conditions for plant vegetative and reproductive performances induced into the soil by the plant itself. In natural ecosystems, plant ecologists refer to SS as negative plant-soil feedback (NPSF). Scope of this review is to provide an updated picture of the current SS understanding by an explicit comparison between agro-ecosystems and natural plant communities. By an extensive analysis of literature we found that SS is pervasive in agro-ecosystems, occurring in 111 cultivated plants belonging to 41 taxonomic families. Concerning NPSF in natural plant communities, we found evidence of this phenomenon for a total of 411 vascular plants belonging to 72 plant families. NPSF occurs in most of the terrestrial ecosystems, including tropical and temperate forests, coastal sand dunes, old fields and grassland, deserts, as well as heathland and tundra. Three main hypotheses have been proposed to explain SS: (i) soil nutrient depletion or imbalance; (ii) buildup of soilborne pathogen and parasite populations, coupled with a shift in soil microbial community composition; (iii) release of phytotoxic and autotoxic compounds during decomposition of crop residues. Evidences from both agroecosystems and natural plant communities undoubtedly ruled out the nutrient deficiency as a primary causal factor. Moreover, the massive use of mineral fertilizers, especially under intensive cultivation systems, appears an incorrect strategy that only exacerbates the decline of soil quality by inducing acidification and salinization. Soilborne pathogens are often isolated from symptomatic plants and many autotoxic compounds have been identified and quantified from sick soil. However, both the pathogenic and autotoxicity hypotheses are still unable to fully explain the species-specificity, as well as the long durability of SS observed in field conditions. The recent discovery that extracellular DNA (exDNA) has self-inhibitory effects, support the autotoxicity hypothesis, nevertheless this is a totally new topic, and more solid and systematic field investigations are needed. A better understanding of the causes of SS is a necessary step to develop eco-friendly solutions to overcome this problem.
... During this process, the ramets of an integrated genet progressively become disconnected with each other because of dieback of inner and older organs (Falińska 1995). Such vegetation pattern has been called fairy rings (Hitchcock 1935), rings (Watt 1947), hollow crowns (Strickland 1983), central dieback (Adachi et al. 1996a), and monk's tonsurelike gaps (Lewis et al. 2001). ...
... However, the emergence of the ring was also a question of time, with drought making it appear abruptly due to the massive dieback in the inner area while the external belt survived. Since then, several authors have proposed that further physical disturbances, such as overgrazing (Strickland 1983), fire (Lewis et al. 2001), or airborne depositions (Ravi et al. 2008) may contribute to the formation of rings. As far as fire is concerned, for some perennial grasses (e.g., Ampelodesmos mauritanicus, Spartina argentinensis) the inner gap is not manifest until fire occurs, even in the case of very large tussocks (diameter > 1 m), because dead but standing culms and leaves persist in the inner area. ...
... In such conditions, the ring becomes evident only after fire occurrence and burning of the standing litter, with living tussocks resprouting only at the external belt of the patch (Fig. 1i). The mechanisms underlying such asymmetric pattern of resprouting were not investigated (Lewis et al. 2001, Incerti et al. 2013. Therefore, we suggest to test for differential distribution of belowground reserves between the inner and outer parts of the clones before fire occurrence, in order to assess whether a differential growth could occur in the two areas, according to the spatial distribution of potential causal factors, such as clone internal features (e.g., growth constraints, age), and/or external environmental variables (e.g., resources). ...
Ring shaped patches of clonal plants fascinated plant ecologists since long time. In this work we review the reports on the occurrence of ring pattern in different environmental conditions, the growth forms of ring-forming plants, the mechanisms underlying ring formation, and the consequences for species diversity at community scale. Rings formed by 83 species of clonal vascular plants have been found in grasslands, deserts, bare substrates of lava flow, harvested peat lands, salt marshes, and sand dunes. Four causal hypotheses have been proposed for the emergence of ring patterns: i. occurrence of architectural constraints for ramets development; ii. induction by fire, drought, trampling or overgrazing; iii. nutrient and water depletion by competition inside the ring; and iv. onset of species-specific negative plant-soil feedback in the inner zone of the clone. Since almost all the available studies are observations of ring structure or modelling exercises, none of the putative mechanisms for ring formation emerged from the literature as either generally applicable or suitable for rejection. Therefore, long-term field experiments are needed to investigate the relative prevalence of different mechanisms in different environments. Ring formation bears important consequences at community scale, because ring forming plants often act as “nurses”, enhancing the recruitment and development of different plant species. In fact, ring establishment modifies above- and below-ground environmental conditions, providing specialized safe sites for beneficiaries in the inner zone of the clones. Such interspecific facilitation by ring forming plants, particularly in chronically stressed environments, contributes to increase plant species richness and can locally promote the successional dynamics.
... Recently, Otfinowski (Otfinowski, 2008) also found only a small reduction of living biomass in the centre of B. inermis clones. In contrast, many studies reported completely empty central areas of most investigated rings (Watt, 1947;Curtis and Cottam, 1950;Lewis et al., 2001;Danin, 1996;Caldwell, 1957;Castellanos et al., 1994). These observations are consistent with the large variability of experimentally observed negative plant-soil feedback intensity, ranging from small reductions of plant growth to lack of regeneration of conspecific individuals (Mazzoleni et al., 2007;Packer and Clay, 2000;Klironomos, 2002;Kardol et al., 2007;Kulmatisky et al., 2008). ...
Ring shaped patches of clonal plants have been reported in different environments, but the mechanisms underlying such pattern formation are still poorly explained. Water depletion in the inner tussocks zone has been proposed as a possible cause, although ring patterns have been also observed in ecosystems without limiting water conditions. In this work, a spatially explicit model is presented in order to investigate the role of negative plant-soil feedback as an additional explanation for ring formation. The model describes the dynamics of the plant biomass in the presence of toxicity produced by the decomposition of accumulated litter in the soil. Our model qualitatively reproduces the emergence of ring patterns of a single clonal plant species during colonisation of a bare substrate. The model admits two homogeneous stationary solutions representing bare soil and uniform vegetation cover which depend only on the ratio between the biomass death and growth rates. Moreover, differently from other plant spatial patterns models, but in agreement with real field observations of vegetation dynamics, we demonstrated that the pattern dynamics always lead to spatially homogeneous vegetation covers without creation of stable Turing patterns. Analytical results show that ring formation is a function of two main components, the plant specific susceptibility to toxic compounds released in the soil by the accumulated litter and the decay rate of these same compounds, depending on environmental conditions. These components act at the same time and their respective intensities can give rise to the different ring structures observed in nature, ranging from slight reductions of biomass in patch centres, to the appearance of marked rings with bare inner zones, as well as the occurrence of ephemeral waves of plant cover. Our results highlight the potential role of plant-soil negative feedback depending on decomposition processes for the development of transient vegetation patterns.
... Several theories have been proposed to explain the formation and growth of grass ring patterns such as external disturbances like fires, negative soil–plant feedbacks and changes in plant growth architecture (Danin and Orshan, 1995; Lewis et al., 2001; Bonanomi et al., 2005). The role of soil erosion processes in modifying grass growth patterns have been documented in many arid and semi-arid landscapes . ...
... As the ring grows in size, it becomes less efficient at trapping windblown sediments (Ravi et al., 2008). At a certain point the grass ring breaks down into pieces, which become " separate " bunch grasses, thereby contributing to the vegetative regeneration of the community (Lewis et al., 2001). Each of these bunch grasses will then undergo a similar process of lateral growth, ring formation, and ring break-up. ...
Land degradation in drylands is one of the major environmental issues of the 21st century particularly due to its impact on world food security and environmental quality. Climate change, shifts in vegetation composition, accelerated soil erosion processes, and disturbances have rendered these landscapes susceptible to rapid degradation that has important feedbacks on regional climate and desertification. Even though the role of hydrologic–aeolian erosion and vegetation dynamic processes in accelerating land degradation is well recognized, most studies have concentrated only on the role of one or two of these components, and not on the interactions among all three. Drawing on relevant published studies, here we review recent contributions to the study of biotic and abiotic drivers of dryland degradation and we propose a more holistic perspective of the interactions between wind and water erosion processes in dryland systems, how these processes affect vegetation patterns and how vegetation patterns, in turn, affect these processes. Notably, changing climate and land use have resulted in rapid vegetation shifts, which alter the rates and patterns of soil erosion in dryland systems. With the predicted increase in aridity and an increase in the frequency of droughts in drylands around the world, there could be an increasing dominance of abiotic controls of land degradation, in particular hydrologic and aeolian soil erosion processes. Further, changes in climate may alter the relative importance of wind versus water erosion in dryland ecosystems. Therefore acquiring a more holistic perspective of the interactions among hydrologic–aeolian erosion and vegetation dynamic processes is fundamental to quantifying and modeling land degradation processes in drylands in changing climate, disturbance regimes and management scenarios.
... The S. argentinensis tall grasslands have a dense upper layer, more than 1 m height of the dominant species with few or no individuals of other species. The dominant species' tussocks can be more than a meter in diameter and often with a big gap, like a monk's tonsure in its centre ( Lewis et al. 2001). Fire is a common disturbance of these communities that may determine their structure ( Lewis et al. 1990b;Stofella 1995), although this is not supported by experimental evidence. ...
Question: What are the effects of fire on the structure and the diversity of a Spartina ar gentinensis tall grassland in the short and medium run. S. argentinensis is the dominant species of tall grasslands on inland marshes of the Chaco-Pampean region (Argentina), where spontaneous or man-made fires are very frequent.
Location: Federico Wildermuth Reserve (31°57′S; 61°23′W), Province of Santa Fe, Argentina, an area never ploughed that supported cattle until its exclusion in 1988.
Methods: Vegetation was surveyed in randomly placed permanent plots using the Braun-Blanquet cover-abundance scale. The data were analysed by multivariate methods (PCA and MRPP) for synthesizing information and testing hypotheses.
Results: Fire did not have a long-lasting effect on the tall grassland. There was only a temporarily reduction of cover-abundance of S. argentinensis which allowed an increase in the number of accompanying species such as Heliotropium curassavicum, Pluchea sagittalis, and Verbena litoralis and of some naturalised or weed species, such as Melilotus alba and Cirsium vulgare, respectively. Fire increased diversity, which remained relatively high for two to three years. Three years after the fire there were no significant differences on the amount of litter accumulated on burned and unburned plots.
Conclusion: Fire should be considered an intrinsic part of the dynamics of S. argentinensis tall grassland.
