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Plant cycling interaction with soil minerals. For explanations of the processes illustrated in parts A , B , and C , see text.
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Key Words plant cycling, organometallic complexes, biological weathering, soil genesis, stability of soil minerals s Abstract The recycling of elements by plants and plant-induced biological ac-tivity cause the rates and products of weathering to be markedly different from what would result in abiotic processes. Plants directly control water dynami...
Contexts in source publication
Context 1
... The main source for most elements is the soil solution. For some elements, such as N, S, and P or Cl, Na, and Ca in coastal areas, a significant amount may come from rainfall and dry deposition of aerosols. Direct leaf absorption may also occur and was postulated by Alfani et al (1996) for Cu and Pb. Because of their economic importance, the uptake and cycling of macronutrients and many trace elements are well documented—in natural ecosystems as well as in cultivated areas, in both tropical and temperate areas (Likens et al 1977, Mengel & Kirkby 1987, Attiwill & Adams 1993, Marschner 1995). The uptake of toxic, harmful, or environmentally hazardous elements such as heavy metals has been the focus of numerous studies. Comparatively few studies have been done of the cycling of those elements that constitute most of the secondary minerals and thus are most involved in the results of weathering: Si, Al, and, to a lesser extent, Fe, Mn, and Ti. Si uptake is metabolically regulated and can be independent of the plant’s transpiration rate (Barber & Shone 1966, Leo & Barghoorn 1976). Si is precipitated in phytoliths, although many plants do not have readily observable phytoliths yet contain relatively large amounts of amorphous silica. Precipitation occurs near transpiration termini, but it can also occur in the xylem vessels and in the endo- dermis of roots (Raven 1983). Terrestrial plants contain Si in appreciable concentrations, ranging from a fraction of 1% of the dry matter to several percent and in some plants > − 10%. Si concentrations in leaf litterfall in tropical forests range from 0.05 to 25 mg g − 1 dry weight. The lower value (0.05 mg g − 1 ) is from a forest in Malaysia growing on limestone, a Si-depleted rock. Most values range between 4 and 8 mg g (Klinge & Rodrigues 1968, Gautam-Basak & Proctor 1983, Lucas et al 1993, Cornu et al 1995). Plants contain Al in lower concentrations than Si. Al is toxic for plants when absorbed in excess, but Al tolerance varies greatly between species and even between varieties of the same species. Al uptake is metabolically regulated by exclusion mechanisms from root uptake and by active excretion (Andersson 1988). Al can be precipitated with Si in phytoliths (Bartoli & Wilding 1980). Al concentrations in leaf litterfall in tropical forests range from 0.12 to 6.2 mg g − 1 dry weight, and most values range between 0.2 and 0.8 mg g − 1 (Webb et al 1969, Fölster & de Las Salas 1976, Gautam-Basak & Proctor 1983, Lucas et al 1993, Cornu 1995). The elements that have accumulated in plant tissues constitute a reservoir of those elements in and above the soil profile. Assuming that the amount and composition of the vegetation cover are in steady state, all of the elements taken up annually from the soil return annually to the top of the soil profile. This return occurs mainly by means of litterfall or decaying plants; however, foliar leaching by rainfall (especially during leaf senescence in autumn) and stem flow (the leaching of elements along the branches and trunks by the downward flowing water) can also be significant. If the mass vegetation increases with time or if vegetation is cropped, there is a net loss of elements from the soil volume influenced by the roots. Litterfall is decomposed within the organic horizons in the upper part of the soil, so that most of the mineral elements contained in plant tissues are released into the soil solution that percolates downward. At a few centimeters in depth, the soil solution may be potentially enriched with Si, Al, Fe, and other elements that control the stability of secondary minerals. Direct interaction of an element with a soil mineral is significant if the considered element is a constituent of the mineral and if its concentration in the soil solution is sufficient with regard to thermodynamic equilibrium. Grimaldi (1987, 1988) described, for example, the control of Al in catchment waters in French Guyana by precipitation with a low rate of a secondary mineral, likely gibbsite. Three main types of plant cycling are possible (Figure 3). If the element is not a constituent of any mineral of the considered soil, the biogeochemical cycling of this element involves only atmosphere, soil solution, and plants (Figure 3 A ). This happens to N and S in most soils and to Ca, Mg, or K in highly leached soils where all primary minerals have been weathered and no secondary minerals contain these elements. If the element is a constituent of minerals of the considered soil, but its concentration in the soil solution remains below saturation with any secondary minerals, plant cycling only increases the dissolution of the element-bearing minerals (Figure 3 B ). This happens, for example, to Ca, Mg, or K in many soils. If the element is a constituent of minerals of the considered soil and its concentration in the soil solution reaches saturation with secondary minerals, plant cycling directly interacts with the result of pedogenesis (Figure 3 C ). This may happen for Si, Al, or Fe, because of the low solubility of oxides or clay minerals. Table 2 gives values, in kilograms per hectares per year, of measured annual turnover resulting from litterfall in some tropical and temperate forest ecosystems. The values for Si are high, comparable with the values for Ca, which is the main macronutrient. The values for Al and Fe are lower but significant with respect to the solubility of these elements in water. Assuming that all of the elements contained in the annual litterfall are dissolved in the water that annually percolates through the litter, we can obtain average concentrations in the soil solution beneath the litter. The water that annually percolates through the litter was considered equal to the trough flow, which is annual rainfall minus rain intercep- tion by the canopy. The results of these calculations are given in Table 3. Assuming that the elements contained in the litter are released in the soil solution as free ions, these waters are plotted in the solubility diagrams of Figure 1. With such an assumption, the waters are supersaturated with Al and Si with respect to gibbsite and kaolinite for a pH > − 4.5 at 25 ◦ C (Figure 1). These waters are ...
Context 2
... The incorporation of H, C, and O mainly occurs during photosynthesis, and these are generally not considered to be mineral nutrients. The other elements are mostly taken up from the soil solution by roots. N, P, S, K, Mg, and Ca are found in relatively high concentrations in plant tissues. They are considered major elements or macronutrients. Fe, Mn, Zn, Cu, B, Mo, Cl, and Ni are found in low concentrations in plant tissues and are considered minor elements or micronutrients. Na, Si, Co, I, and V are needed by only some plant species. Si has a special status because it is strictly essential only for some plant species, but it is beneficial for many others (Epstein 1994). All of the other elements are found in plant tissue in small quantities. Some of them, such as Al, although potentially toxic to plants, may be found in significant concentrations because of their abundance in acid soil solutions. The main source for most elements is the soil solution. For some elements, such as N, S, and P or Cl, Na, and Ca in coastal areas, a significant amount may come from rainfall and dry deposition of aerosols. Direct leaf absorption may also occur and was postulated by Alfani et al (1996) for Cu and Pb. Because of their economic importance, the uptake and cycling of macronutrients and many trace elements are well documented—in natural ecosystems as well as in cultivated areas, in both tropical and temperate areas (Likens et al 1977, Mengel & Kirkby 1987, Attiwill & Adams 1993, Marschner 1995). The uptake of toxic, harmful, or environmentally hazardous elements such as heavy metals has been the focus of numerous studies. Comparatively few studies have been done of the cycling of those elements that constitute most of the secondary minerals and thus are most involved in the results of weathering: Si, Al, and, to a lesser extent, Fe, Mn, and Ti. Si uptake is metabolically regulated and can be independent of the plant’s transpiration rate (Barber & Shone 1966, Leo & Barghoorn 1976). Si is precipitated in phytoliths, although many plants do not have readily observable phytoliths yet contain relatively large amounts of amorphous silica. Precipitation occurs near transpiration termini, but it can also occur in the xylem vessels and in the endo- dermis of roots (Raven 1983). Terrestrial plants contain Si in appreciable concentrations, ranging from a fraction of 1% of the dry matter to several percent and in some plants > − 10%. Si concentrations in leaf litterfall in tropical forests range from 0.05 to 25 mg g − 1 dry weight. The lower value (0.05 mg g − 1 ) is from a forest in Malaysia growing on limestone, a Si-depleted rock. Most values range between 4 and 8 mg g (Klinge & Rodrigues 1968, Gautam-Basak & Proctor 1983, Lucas et al 1993, Cornu et al 1995). Plants contain Al in lower concentrations than Si. Al is toxic for plants when absorbed in excess, but Al tolerance varies greatly between species and even between varieties of the same species. Al uptake is metabolically regulated by exclusion mechanisms from root uptake and by active excretion (Andersson 1988). Al can be precipitated with Si in phytoliths (Bartoli & Wilding 1980). Al concentrations in leaf litterfall in tropical forests range from 0.12 to 6.2 mg g − 1 dry weight, and most values range between 0.2 and 0.8 mg g − 1 (Webb et al 1969, Fölster & de Las Salas 1976, Gautam-Basak & Proctor 1983, Lucas et al 1993, Cornu 1995). The elements that have accumulated in plant tissues constitute a reservoir of those elements in and above the soil profile. Assuming that the amount and composition of the vegetation cover are in steady state, all of the elements taken up annually from the soil return annually to the top of the soil profile. This return occurs mainly by means of litterfall or decaying plants; however, foliar leaching by rainfall (especially during leaf senescence in autumn) and stem flow (the leaching of elements along the branches and trunks by the downward flowing water) can also be significant. If the mass vegetation increases with time or if vegetation is cropped, there is a net loss of elements from the soil volume influenced by the roots. Litterfall is decomposed within the organic horizons in the upper part of the soil, so that most of the mineral elements contained in plant tissues are released into the soil solution that percolates downward. At a few centimeters in depth, the soil solution may be potentially enriched with Si, Al, Fe, and other elements that control the stability of secondary minerals. Direct interaction of an element with a soil mineral is significant if the considered element is a constituent of the mineral and if its concentration in the soil solution is sufficient with regard to thermodynamic equilibrium. Grimaldi (1987, 1988) described, for example, the control of Al in catchment waters in French Guyana by precipitation with a low rate of a secondary mineral, likely gibbsite. Three main types of plant cycling are possible (Figure 3). If the element is not a constituent of any mineral of the considered soil, the biogeochemical cycling of this element involves only atmosphere, soil solution, and plants (Figure 3 A ). This happens to N and S in most soils and to Ca, Mg, or K in highly leached soils where all primary minerals have been weathered and no secondary minerals contain these elements. If the element is a constituent of minerals of the considered soil, but its concentration in the soil solution remains below saturation with any secondary minerals, plant cycling only increases the dissolution of the element-bearing minerals (Figure 3 B ). This happens, for example, to Ca, Mg, or K in many soils. If the element is a constituent of minerals of the considered soil and its concentration in the soil solution reaches saturation with secondary minerals, plant cycling directly interacts with the result of pedogenesis (Figure 3 C ). This may happen for Si, Al, or Fe, because of the low solubility of oxides or clay minerals. Table 2 gives values, in kilograms per hectares per year, of measured annual turnover resulting from litterfall in some tropical and temperate forest ecosystems. The values for Si are high, comparable with the values for Ca, which is the main macronutrient. The values for Al and Fe are lower but significant with respect to the solubility of these elements in water. Assuming that all of the elements contained in the annual litterfall are dissolved in the water that annually percolates through the litter, we can obtain average concentrations in the soil solution beneath the litter. The water that annually percolates through the litter was considered equal to the trough flow, which is annual rainfall minus rain intercep- tion by the canopy. The results of these calculations are given in Table 3. Assuming that the elements contained in the litter are released in the soil solution as free ions, these waters are plotted in the solubility diagrams of Figure 1. With such an assumption, the waters are supersaturated with Al and Si with respect to gibbsite and kaolinite for a pH > − 4.5 at 25 ◦ C (Figure 1). These waters are ...
Context 3
... soil solution by roots. N, P, S, K, Mg, and Ca are found in relatively high concentrations in plant tissues. They are considered major elements or macronutrients. Fe, Mn, Zn, Cu, B, Mo, Cl, and Ni are found in low concentrations in plant tissues and are considered minor elements or micronutrients. Na, Si, Co, I, and V are needed by only some plant species. Si has a special status because it is strictly essential only for some plant species, but it is beneficial for many others (Epstein 1994). All of the other elements are found in plant tissue in small quantities. Some of them, such as Al, although potentially toxic to plants, may be found in significant concentrations because of their abundance in acid soil solutions. The main source for most elements is the soil solution. For some elements, such as N, S, and P or Cl, Na, and Ca in coastal areas, a significant amount may come from rainfall and dry deposition of aerosols. Direct leaf absorption may also occur and was postulated by Alfani et al (1996) for Cu and Pb. Because of their economic importance, the uptake and cycling of macronutrients and many trace elements are well documented—in natural ecosystems as well as in cultivated areas, in both tropical and temperate areas (Likens et al 1977, Mengel & Kirkby 1987, Attiwill & Adams 1993, Marschner 1995). The uptake of toxic, harmful, or environmentally hazardous elements such as heavy metals has been the focus of numerous studies. Comparatively few studies have been done of the cycling of those elements that constitute most of the secondary minerals and thus are most involved in the results of weathering: Si, Al, and, to a lesser extent, Fe, Mn, and Ti. Si uptake is metabolically regulated and can be independent of the plant’s transpiration rate (Barber & Shone 1966, Leo & Barghoorn 1976). Si is precipitated in phytoliths, although many plants do not have readily observable phytoliths yet contain relatively large amounts of amorphous silica. Precipitation occurs near transpiration termini, but it can also occur in the xylem vessels and in the endo- dermis of roots (Raven 1983). Terrestrial plants contain Si in appreciable concentrations, ranging from a fraction of 1% of the dry matter to several percent and in some plants > − 10%. Si concentrations in leaf litterfall in tropical forests range from 0.05 to 25 mg g − 1 dry weight. The lower value (0.05 mg g − 1 ) is from a forest in Malaysia growing on limestone, a Si-depleted rock. Most values range between 4 and 8 mg g (Klinge & Rodrigues 1968, Gautam-Basak & Proctor 1983, Lucas et al 1993, Cornu et al 1995). Plants contain Al in lower concentrations than Si. Al is toxic for plants when absorbed in excess, but Al tolerance varies greatly between species and even between varieties of the same species. Al uptake is metabolically regulated by exclusion mechanisms from root uptake and by active excretion (Andersson 1988). Al can be precipitated with Si in phytoliths (Bartoli & Wilding 1980). Al concentrations in leaf litterfall in tropical forests range from 0.12 to 6.2 mg g − 1 dry weight, and most values range between 0.2 and 0.8 mg g − 1 (Webb et al 1969, Fölster & de Las Salas 1976, Gautam-Basak & Proctor 1983, Lucas et al 1993, Cornu 1995). The elements that have accumulated in plant tissues constitute a reservoir of those elements in and above the soil profile. Assuming that the amount and composition of the vegetation cover are in steady state, all of the elements taken up annually from the soil return annually to the top of the soil profile. This return occurs mainly by means of litterfall or decaying plants; however, foliar leaching by rainfall (especially during leaf senescence in autumn) and stem flow (the leaching of elements along the branches and trunks by the downward flowing water) can also be significant. If the mass vegetation increases with time or if vegetation is cropped, there is a net loss of elements from the soil volume influenced by the roots. Litterfall is decomposed within the organic horizons in the upper part of the soil, so that most of the mineral elements contained in plant tissues are released into the soil solution that percolates downward. At a few centimeters in depth, the soil solution may be potentially enriched with Si, Al, Fe, and other elements that control the stability of secondary minerals. Direct interaction of an element with a soil mineral is significant if the considered element is a constituent of the mineral and if its concentration in the soil solution is sufficient with regard to thermodynamic equilibrium. Grimaldi (1987, 1988) described, for example, the control of Al in catchment waters in French Guyana by precipitation with a low rate of a secondary mineral, likely gibbsite. Three main types of plant cycling are possible (Figure 3). If the element is not a constituent of any mineral of the considered soil, the biogeochemical cycling of this element involves only atmosphere, soil solution, and plants (Figure 3 A ). This happens to N and S in most soils and to Ca, Mg, or K in highly leached soils where all primary minerals have been weathered and no secondary minerals contain these elements. If the element is a constituent of minerals of the considered soil, but its concentration in the soil solution remains below saturation with any secondary minerals, plant cycling only increases the dissolution of the element-bearing minerals (Figure 3 B ). This happens, for example, to Ca, Mg, or K in many soils. If the element is a constituent of minerals of the considered soil and its concentration in the soil solution reaches saturation with secondary minerals, plant cycling directly interacts with the result of pedogenesis (Figure 3 C ). This may happen for Si, Al, or Fe, because of the low solubility of oxides or clay minerals. Table 2 gives values, in kilograms per hectares per year, of measured annual turnover resulting from litterfall in some tropical and temperate forest ecosystems. The values for Si are high, comparable with the values for Ca, which is the main macronutrient. The values for Al and Fe are lower but significant with respect to the solubility of these elements in water. Assuming that all of the elements contained in the annual litterfall are dissolved in the water that annually percolates through the litter, we can obtain average concentrations in the soil solution beneath the litter. The water that annually percolates through the litter was considered equal to the trough flow, which is annual rainfall minus rain intercep- tion by the canopy. The results of these calculations are given in Table 3. Assuming that the elements contained in the litter are released in the soil solution as free ions, these waters are plotted in the solubility diagrams of Figure 1. With such an assumption, the waters are supersaturated with Al and Si with respect to gibbsite and kaolinite for a pH > − 4.5 at 25 ◦ C (Figure 1). These waters are ...
Context 4
... species, but it is beneficial for many others (Epstein 1994). All of the other elements are found in plant tissue in small quantities. Some of them, such as Al, although potentially toxic to plants, may be found in significant concentrations because of their abundance in acid soil solutions. The main source for most elements is the soil solution. For some elements, such as N, S, and P or Cl, Na, and Ca in coastal areas, a significant amount may come from rainfall and dry deposition of aerosols. Direct leaf absorption may also occur and was postulated by Alfani et al (1996) for Cu and Pb. Because of their economic importance, the uptake and cycling of macronutrients and many trace elements are well documented—in natural ecosystems as well as in cultivated areas, in both tropical and temperate areas (Likens et al 1977, Mengel & Kirkby 1987, Attiwill & Adams 1993, Marschner 1995). The uptake of toxic, harmful, or environmentally hazardous elements such as heavy metals has been the focus of numerous studies. Comparatively few studies have been done of the cycling of those elements that constitute most of the secondary minerals and thus are most involved in the results of weathering: Si, Al, and, to a lesser extent, Fe, Mn, and Ti. Si uptake is metabolically regulated and can be independent of the plant’s transpiration rate (Barber & Shone 1966, Leo & Barghoorn 1976). Si is precipitated in phytoliths, although many plants do not have readily observable phytoliths yet contain relatively large amounts of amorphous silica. Precipitation occurs near transpiration termini, but it can also occur in the xylem vessels and in the endo- dermis of roots (Raven 1983). Terrestrial plants contain Si in appreciable concentrations, ranging from a fraction of 1% of the dry matter to several percent and in some plants > − 10%. Si concentrations in leaf litterfall in tropical forests range from 0.05 to 25 mg g − 1 dry weight. The lower value (0.05 mg g − 1 ) is from a forest in Malaysia growing on limestone, a Si-depleted rock. Most values range between 4 and 8 mg g (Klinge & Rodrigues 1968, Gautam-Basak & Proctor 1983, Lucas et al 1993, Cornu et al 1995). Plants contain Al in lower concentrations than Si. Al is toxic for plants when absorbed in excess, but Al tolerance varies greatly between species and even between varieties of the same species. Al uptake is metabolically regulated by exclusion mechanisms from root uptake and by active excretion (Andersson 1988). Al can be precipitated with Si in phytoliths (Bartoli & Wilding 1980). Al concentrations in leaf litterfall in tropical forests range from 0.12 to 6.2 mg g − 1 dry weight, and most values range between 0.2 and 0.8 mg g − 1 (Webb et al 1969, Fölster & de Las Salas 1976, Gautam-Basak & Proctor 1983, Lucas et al 1993, Cornu 1995). The elements that have accumulated in plant tissues constitute a reservoir of those elements in and above the soil profile. Assuming that the amount and composition of the vegetation cover are in steady state, all of the elements taken up annually from the soil return annually to the top of the soil profile. This return occurs mainly by means of litterfall or decaying plants; however, foliar leaching by rainfall (especially during leaf senescence in autumn) and stem flow (the leaching of elements along the branches and trunks by the downward flowing water) can also be significant. If the mass vegetation increases with time or if vegetation is cropped, there is a net loss of elements from the soil volume influenced by the roots. Litterfall is decomposed within the organic horizons in the upper part of the soil, so that most of the mineral elements contained in plant tissues are released into the soil solution that percolates downward. At a few centimeters in depth, the soil solution may be potentially enriched with Si, Al, Fe, and other elements that control the stability of secondary minerals. Direct interaction of an element with a soil mineral is significant if the considered element is a constituent of the mineral and if its concentration in the soil solution is sufficient with regard to thermodynamic equilibrium. Grimaldi (1987, 1988) described, for example, the control of Al in catchment waters in French Guyana by precipitation with a low rate of a secondary mineral, likely gibbsite. Three main types of plant cycling are possible (Figure 3). If the element is not a constituent of any mineral of the considered soil, the biogeochemical cycling of this element involves only atmosphere, soil solution, and plants (Figure 3 A ). This happens to N and S in most soils and to Ca, Mg, or K in highly leached soils where all primary minerals have been weathered and no secondary minerals contain these elements. If the element is a constituent of minerals of the considered soil, but its concentration in the soil solution remains below saturation with any secondary minerals, plant cycling only increases the dissolution of the element-bearing minerals (Figure 3 B ). This happens, for example, to Ca, Mg, or K in many soils. If the element is a constituent of minerals of the considered soil and its concentration in the soil solution reaches saturation with secondary minerals, plant cycling directly interacts with the result of pedogenesis (Figure 3 C ). This may happen for Si, Al, or Fe, because of the low solubility of oxides or clay minerals. Table 2 gives values, in kilograms per hectares per year, of measured annual turnover resulting from litterfall in some tropical and temperate forest ecosystems. The values for Si are high, comparable with the values for Ca, which is the main macronutrient. The values for Al and Fe are lower but significant with respect to the solubility of these elements in water. Assuming that all of the elements contained in the annual litterfall are dissolved in the water that annually percolates through the litter, we can obtain average concentrations in the soil solution beneath the litter. The water that annually percolates through the litter was considered equal to the trough flow, which is annual rainfall minus rain intercep- tion by the canopy. The results of these calculations are given in Table 3. Assuming that the elements contained in the litter are released in the soil solution as free ions, these waters are plotted in the solubility diagrams of Figure 1. With such an assumption, the waters are supersaturated with Al and Si with respect to gibbsite and kaolinite for a pH > − 4.5 at 25 ◦ C (Figure 1). These waters are ...
Citations
... For example, dissolved silicon can improve SOC stability by inhibiting the hydrolysis and polymerisation of Fe 3+ and reducing the transformation of low-crystalline minerals into the crystalline Fe 3+ phase (Hiemstra et al., 2007;Jones et al., 2009;Pokrovski et al., 2003), moreover. Silicon and aluminium in soil solution can stabilise SOC by combining with Si-Al secondary clay minerals and their nano-, micro-, and macroaggregates (Lucas, 2001;Song et al., 2018). Additionally, investigations conducted on farmland soil have demonstrated that the utilisation of silicon fertiliser can enhance the activity of the soil bacterial community and the concentrations of microbial organic carbon by regulating soil pH . ...
... By these and other activities, roots and associated soil biota also strongly affect soil aggregate formation and turnover (Six et al., 2004), producing legacy effects on soil biota and plant communities. Roots also affect mineral weathering, mobilize and redistribute plant, nutrients in the soil profile (Jobbágy and Jackson, 2001;Lucas, 2001). These phenomena likely affect not only the plants that cause them but also generations of plants that follow. ...
... This in interaction with climate and topography affects the intensity of soil erosion (Yair, 1995;Le Bayon and Binet, 2001;Jouquet et al., 2006;Román-Sánchez et al., 2019) and deposition, which again alter soil properties. On an even longer temporal and large spatial scale, soil-forming processes, affected by vegetation and soil biota (Jobbágy and Jackson, 2001;Lucas, 2001), affect the balance between the acquisition of new nutrients by weathering and their loss from the system. This affects nutrient availability, which leads to changes in vegetation, plant species traits, nutrient turnover, and how organic matter is stored in soil (Vitousek, 2004;Kuneš et al., 2011;Vindušková et al., 2019). ...
... Notably, soil inorganic and organic environments of forests are not independent . Plants typically accumulate large quantities of potassium (K) in their tissues and K is primarily cycled via mineral weathering, but also by biological pumps during leaf litter decomposition (Lucas 2001;Castro and Fernandez-Nu ñez 2014). However, K is easily leached from leaves and plant tissues (Aber and Melillo 2001;Castro and Fernandez-Nu ñez 2014). ...
Context. Studies of afforestation have traditionally neglected the influences of plant microhabitats on the growth and carbon sink capacities of planted forests. Aims. We investigated the potential mechanisms related to the relationship of afforestation elevation to soil organic carbon density (SOCD). Methods. The carbon density of three plantation ecosystems and barren land soils were evaluated at two elevations in the Donglingshan Mountains of Beijing, with structural equation modelling and variation partitioning analyses used to identify the environmental factors that influenced the carbon densities of plantation ecosystems. Key results. Afforestation elevation was related to the vegetation phenology of plantation forests. Specifically, growth periods at higher elevations were delayed relative to those at lower elevations, while different growth periods affected growth rate of diameter at breast height (R DBH), in addition to the carbon and nitrogen contents of ground surface litters. Consequently, lower elevation afforestation reduced the carbon sink capacity of coniferous plantation ecosystems in the study area. Lower plantation elevations were associated with significantly reduced R DBH values of Pinus tabuliformis. Further, biomass carbon density (BCD) and SOCD of Larix principis-rupprechtii plantations were significantly lower due to decreased elevations. Soil nitrogen concentrations, litter nitrogen density (LND), soil phosphorus concentrations, and BCD were the primary drivers of plantation SOCD. Conclusions. Overall, different plantation elevations were associated with different vegetation phenologies and R DBH values, which further affected LND and BCD, thereby ultimately affecting variation of SOCD. Implications. This study provides important insights into the selection of afforestation plots to maximise plantation carbon sequestration capacities.
... Bauxitization is favoured by abundant vegetation because root systems favour effective water percolation, organic matter creates acidic conditions favouring the dissolution and transport of Fe and Al, and plants also remove silica from soils (Bárdossy & Aleva, 1990;Lucas, 2001;Petersen, 1971;Power & Loh, 2010). Organic acids lower environmental pH and accelerate mineral dissolution rates (Drever & Stillings, 1997). ...
Lithology plays a fundamental role in rock weathering and erosion, and in landscape evolution. When weathering‐ and erosion‐prone lithologies are protected from erosion by more resilient rock types (e.g., quartzites and banded iron formations) unusual weathering products result. At the Southern Espinhaço Range, Minas Gerais, Brazil, bauxitic weathering profiles are found in a unique geomorphological–lithological–climatic setting. Resistant quartzites acted as a barrier against erosion of interbedded hematite‐phyllite lenses, channelling solution flows and facilitating the formation of deep weathering profiles. The long‐term exposure of the hematite‐phyllites under alternating wet and dry tropical climates favoured widespread bauxitization. Here we investigate the geochemical, mineralogical, geochronological and micromorphological signatures of scaffolded bauxites in order to reconstruct their evolutionary history. Our data suggest that recurrent aluminium and iron mobilization within the profiles were mainly driven by mineral dissolution‐reprecipitation mediated by bioturbation and the influx of vegetation‐derived organic species. (U–Th)/He geochronology of Al‐goethite reveals that bauxitization started at least since the Lower Miocene, with important intensification of weathering in the Upper Miocene and Lower Pleistocene. The adjacent resilient quartzites acted as scaffolds for bauxitization and supported the preservation of more erodible weathering profiles developed over phyllites. Surface waters that could not infiltrate into the impermeable adjacent quartzites preferentially infiltrated into the more weathereable phyllites, enhancing their porosity and permeability, further enhancing weathering. The evolutionary history of Southern Espinhaço Range bauxites suggests a new model of bauxitization in ancient land surfaces evolution underlain by quartzites, where erosion‐prone lithologies are scaffolded by resilient quartzites and survive long‐term weathering with minimum erosion, producing bauxites.
... For example, strain-induced porosity production due to root-wedging between existing fractures may contribute significantly to subsurface weathering . Abiotic chemical weathering is strongly influenced by plant water uptake and redistribution, which can alter weathering pathways (Lucas, 2001). As deeply rooted oaks utilize water stored within the saprolite for transpiration (Hahm et al., 2020, depletion in water content Figure 9. Two frameworks to explain similar hillslope steepness and/or saprolite thickness between hillslopes with opposing aspects. ...
The structure of the critical zone (CZ) is a product of feedbacks among hydrologic, climatic, biotic, and chemical processes. Past research within snow‐dominated systems has shown that aspect‐dependent solar radiation inputs can produce striking differences in vegetation composition, topography, and soil depth between opposing hillslopes. However, far fewer studies have evaluated the role of microclimates on CZ development within rain‐dominated systems, especially below the soil and into weathered bedrock. To address this need, we characterized the CZ of a north‐facing and south‐facing slope within a first‐order headwater catchment located in central coast California. We combined terrain analysis of vegetation distribution and topography with soil pit characterization, geophysical surveys and hydrologic measurements between slope‐aspects. We documented denser vegetation and higher shallow soil moisture on north facing slopes, which matched previously documented observations in snow‐dominated sites. However, average topographic gradients were 24° and saprolite thickness was approximately 6 m across both hillslopes, which did not match common observations from the literature that showed widespread asymmetry in snow‐dominated systems. These results suggest that dominant processes for CZ evolution are not necessarily transferable across regions. Thus, there is a continued need to expand CZ research, especially in rain‐dominated and water‐limited systems. Here, we present two non‐exclusive mechanistic hypotheses that may explain these unexpected similarities in slope and saprolite thickness between hillslopes with opposing aspects.
... The multiplier by which plants increase CO 2 drawdown as a global average has proven challenging to measure; there are many feedbacks, and plants may inhibit weathering in some settings (Volk, 1987;Pagani et al., 2009;Beerling et al., 2012;Brantley et al., 2012;Doughty et al., 2014;Lawrence et al., 2014;Quirk et al., 2014;D'Antonio et al., 2020). However, results from field, glasshouse, and modeling studies indicate that plants can multiply weathering rates by 2-109 or more, especially in wet and warm climates, on acidic mafic and ultramafic rocks, and in areas with high topographic relief (Schwartzman & Volk, 1989;Drever, 1994;Cochran & Berner, 1996;Moulton et al., 2000;Lucas, 2001;Berner, 2004;Taylor et al., 2012;Johnson et al., 2014;Lenton et al., 2018;Ibarra et al., 2019;Perez-Fodich & Derry, 2019). ...
Many tree genera in the Malesian uplands have Southern Hemisphere origins, often supported by austral fossil records. Weathering the vast bedrock exposures in the everwet Malesian tropics may have consumed sufficient atmospheric CO2 to contribute significantly to global cooling over the past 15 Myr. However, there has been no discussion of how the distinctive regional tree assemblages may have enhanced weathering and contributed to this process. We postulate that Gondwanan‐sourced tree lineages that can dominate higher‐elevation forests played an overlooked role in the Neogene CO2 drawdown that led to the Ice Ages and the current, now‐precarious climate state. Moreover, several historically abundant conifers in Araucariaceae and Podocarpaceae are likely to have made an outsized contribution through soil acidification that increases weathering. If the widespread destruction of Malesian lowland forests continues to spread into the uplands, the losses will threaten unique austral plant assemblages and, if our hypothesis is correct, a carbon sequestration engine that could contribute to cooler planetary conditions far into the future. Immediate effects include the spread of heat islands, significant losses of biomass carbon and forest‐dependent biodiversity, erosion of watershed values, and the destruction of tens of millions of years of evolutionary history.
... The formation of secondary minerals such as clay minerals and aluminum hydroxide is among other factors controlled by biogenic activity since organic acids and an acidity increase by elevated organic-derived CO 2 contents accelerate dissolution rates of primary minerals (see e.g., Lucas, 2001;Lawrence et al., 2014). This effect needs to be considered for the organic-rich and acidic subsurface of NA (see Bernhard et al., 2018). ...
Subsurface fluid pathways and the climate-dependent infiltration of fluids into the subsurface jointly control the intensity and depth of mineral weathering reactions. The products of these weathering reactions (secondary minerals), such as Fe(III) oxyhydroxides and clay minerals, in turn exert a control on the subsurface fluid flow and hence on the development of weathering profiles.
We explored the dependence of mineral transformations on climate during the
weathering of granitic rocks in two 6 m deep weathering profiles in
Mediterranean and humid climate zones along the Chilean Coastal Cordillera.
We used geochemical and mineralogical methods such as (micro-) X-ray
fluorescence (μ-XRF and XRF), oxalate and dithionite extractions, X-ray diffraction (XRD), and electron
microprobe (EMP) mapping to elucidate the transformations involved during
weathering. In the profile of the Mediterranean climate zone, we found a low weathering intensity affecting the profile down to 6 m depth. In the profile of the humid climate zone, we found a high weathering intensity. Based on our results, we propose mechanisms that can intensify the progression of weathering to depth. The most important is weathering-induced fracturing
(WIF) by Fe(II) oxidation in biotite and precipitation of Fe(III)
oxyhydroxides and by the swelling of interstratified smectitic clay minerals that promotes the formation of fluid pathways. We also propose mechanisms that mitigate the development of a deep weathering zone, like the precipitation of secondary minerals (e.g., clay minerals) and amorphous
phases that can impede the subsurface fluid flow. We conclude that the depth and intensity of primary mineral weathering in the profile of the
Mediterranean climate zone is significantly controlled by WIF. It generates
a surface–subsurface connectivity that allows fluid infiltration to great
depth and hence promotes a deep weathering zone. Moreover, the water supply
to the subsurface is limited in the Mediterranean climate, and thus, most of the weathering profile is generally characterized by a low weathering
intensity. The depth and intensity of weathering processes in the profile of the humid climate zone, on the other hand, are controlled by an intense
formation of secondary minerals in the upper section of the weathering
profile. This intense formation arises from pronounced dissolution of
primary minerals due to the high water infiltration (high precipitation
rate) into the subsurface. The secondary minerals, in turn, impede the
infiltration of fluids to great depth and thus mitigate the intensity of
primary mineral weathering at depth.
These two settings illustrate that the depth and intensity of primary
mineral weathering in the upper regolith are controlled by positive and
negative feedbacks between the formation of secondary minerals and the
infiltration of fluids.
... Overall, the pool of fast (0-10 and 10-100 h) water-leachable, mobile Si in forest soil ranges, depending on pH, from 0.04 mg Si g soil − 1 for luvisol to 0.08 mg Si g soil − 1 for hypereutric cambisol and calcaric cambisol ( Cornelis et al., 2011;Cornelis and Delvaux, 2016). In the temperate forest, Si uptake flux by deciduous trees and Douglas fir ranges from 36 to 46 kg ha − 1 y − 1 , and that of the pine forest does not exceed 7 kg ha − 1 y − 1 (Lucas, 2001;Gérard et al., 2008). Therefore, experimentally measured mobile Si pool in forest soils is potentially capable of providing the totality of this demand; however, more measurements on specific soils are needed to further quantify this potential. ...
Despite the importance of silicon (Si) as benefecial nutrient for many plants, including economically-important cereals, the reactivity of various Si pools in soils (silicate minerals, amorphous compounds, phytoliths, organic litter) is not fully quantified which does not allow predicting the capacity of agricultural or forested soil to provide soluble Si to soil porewaters where it can be used by plants. Towards better understanding of factors controlling bioavailable Si in soils, here we quantified the release rate of Si from several pairs of French forest and agricultural topsoils, developed on calcareous or loess parent material. We used mixed-flow and column reactors, in acetate and carbonate buffers and distilled water, at various pH (4–8) and time of reaction (day to month).
The rate of Si release from soil (RSi) exceeded that of crystalline clay minerals by 1–2 orders of magnitude, being 5–10 times lower than that of various allophanes. The rates were weakly dependent on pH (compared to clays or phytoliths) and varied from 5 × 10−7 to 2 × 10−6 mol/gsoil/day at 4 < pH ≤ 8. In terms of Si reactivity, four studied soil groups followed the order: “calcaric cambisols ≈ hypereutric cambisols ≥ luvisols ≥ albeluvisol”. Calcaric and hypereutric cambisols as well as luvisols exhibited a weak decrease of RSi with pH increase. The rate of Si release from albeluvisol increased 2 times with a pH increase from 4 to 8. There was no measurable difference in RSi between agricultural and forest soils.
The pool of labile Si in forest soils was quantified via soil column flow-through experiments. The breakthrough curves of Si demonstrated high concentrations (1.6–5.7 mg/L) over first several hours of reaction in the soil column. The water leachable Si pool ranged from 0.04 to 0.08 mg Si gsoil−1, corresponding to labile Si stock in the 0–20 cm soil of 80–160 kg ha−1. These values can meet the annual requirements of plants in forests and cultivated soils. The pool of labile Si correlated (RPearson > 0.90; p < 0.05) with Si associated with amorphous Fe and Al compounds and soluble bioavailable Si extracted using CaCl2 method, but negatively correlated with total Si content in soils and Si of phytoliths. The main pools of soil labile Si could be allophanes, organo-Fe-Al-Si compounds and adsorbed forms of Si onto Fe and Al hydroxides. We hypothesize that, because of low sensibility of RSi to type of soil and fluid pH, the majority of soils regulate Si release at some ‘universal’ rate which is further reflected in relatively narrow range of riverine Si concentrations and export fluxes across the world. Therefore, the modeling of chemical weathering and element export flux in the watersheds should incorporate the experimentally measured reactivity of the whole soil rather than individual constituting primary or secondary minerals.
... Base cation loss also causes a soil pH decrease, as seen in Figure 9, where the Bazuja River catchment stands out with lower pH values. Plants also have a large effect on pH lowering in soils by producing humic acids [74,75]. The influence of vegetation cover induced a higher production of organic and chelating ligands in the soil solution, which can cause significant changes in weathering rates within short periods of approximately 100 years [76]. ...
... Plant roots and their symbionts can speed up the weathering of rocks by chemically attacking them with a variety of organic acid compounds [80]. This can lower the pH of soil water around roots by up to two units [75]. In addition, organic acids can also form complexes with metals, which can help transfer them from minerals to plants [80]. ...
Physical and chemical weathering, together with biological and biochemical processes, form soil from bedrock and strongly influence the chemical composition of natural waters. Erosive processes, primarily through the agents of running water and wind, remove the products of weathering from catchments. The aim was to determine the chemical weathering of minerals because of changes in land-use and natural forestation in two small neighboring catchments of the rivers Argilla and Bazuja. Agricultural land-use practice is very intense in the Argilla catchment, while the Bazuja catchment’s arable land is mostly abandoned, with progressive forestation. Chemical weathering in soils and sediments was evaluated with the aid of bulk chemistry analysis focused on major elements, trace elements, and zirconium. Weathering indices, mass balance, and strain were calculated. The abandonment of arable land and intense forestation in the Bazuja catchment caused increased chemical weathering with the loss of base cations (Ca and Mg) and enrichment of conservative elements (Zr and Ti) in surface horizons. EIC and MTF values are positive (enrichment) in areas with agricultural activities, while forested areas show negative values (loss). A comparison of the oldest and youngest parts of the overbank sediment profiles in the swallow hole zone and stream sediments shows that chemical and mechanical weathering in the Bazuja catchment was similar to present weathering in the Argilla catchment, while agriculture was active in the Bazuja catchment. The integrated knowledge gained in small catchment studies can be broadly applicable to larger systems.
... The 3-to 5-fold higher fluxes of these nutrients in the A horizon can be attributed to the corresponding 3-to 5-fold higher element concentrations in the soil water solutions ( Fig. 8a-b, e) rather than to the water fluxes (Table 4). The high concentrations and fluxes of Ca, Mg (for tussocks), and K (for cushions) in the near-surface horizons might reflect their uptake and cycling by plants (Amundson et al., 2007;Kelly et al., 1998;Lucas, 2001;White and Buss, 2014;White et al., 2009). Vegetation type has a minimal but not significant effect on Na and DSi fluxes (Fig. 9, Table 5). ...
Vegetation plays a key role in the hydrological and biogeochemical cycles. It can influence soil water fluxes and transport, which are critical for chemical weathering and soil development. In this study, we investigated soil water balance and solute fluxes in two soil profiles with different vegetation types (cushion-forming plants vs. tussock grasses) in the high Ecuadorian Andes by measuring soil water content, flux, and solute concentrations and by modeling soil hydrology. We also analyzed the role of soil water balance in soil chemical weathering. The influence of vegetation on soil water balance and solute fluxes is restricted to the A horizon. Evapotranspiration is 1.7 times higher and deep drainage 3 times lower under cushion-forming plants than under tussock grass. Likewise, cushions transmit about 2-fold less water from the A to lower horizons. This is attributed to the higher soil water retention and saturated hydraulic conductivity associated with a shallower and coarser root system. Under cushion-forming plants, dissolved organic carbon (DOC) and metals (Al, Fe) are mobilized in the A horizon. Solute fluxes that can be related to plant nutrient uptake (Mg, Ca, K) decline with depth, as expected from biocycling of plant nutrients. Dissolved silica and bicarbonate are minimally influenced by vegetation and represent the largest contributions of solute fluxes. Soil chemical weathering is higher and constant with depth below tussock grasses but lower and declining with depth under cushion-forming plants. This difference in soil weathering is attributed mainly to the water fluxes. Our findings reveal that vegetation can modify soil properties in the uppermost horizon, altering the water balance, solute fluxes, and chemical weathering throughout the soil profile.
