Abstract Changes in the abundance of speciesespecially those that influence water and nutrient d... more Abstract Changes in the abundance of speciesespecially those that influence water and nutrient dynamics, trophic interactions, or disturbance regimeaffect the structure and functioning of ecosystems. Diversity is also functionally important, both because it ...
... identity and community composition Amy J. Symstad, David Tilman, John Willson and Johannes MH... more ... identity and community composition Amy J. Symstad, David Tilman, John Willson and Johannes MH Knops Symstad, AJ, Tilman, D., Willson, J. and Knops, JMH 1998. ... (1996). t-tests were performed on Ix to test for significant impacts of functional groups and individual species. ...
We tested the hypothesis that biological trait-based plant functional groups provide sufficient d... more We tested the hypothesis that biological trait-based plant functional groups provide sufficient differentiation of species to enable generalization about a variety of plant ecophysiological traits or responses to nitrogen (N). • Seedlings of 34 North American grassland and savanna species, representing 5 functional groups, were grown in a glasshouse in an infertile soil with or without N fertilization.
Despite increasing evidence that plant diversity in experimental systems may enhance ecosystem pr... more Despite increasing evidence that plant diversity in experimental systems may enhance ecosystem productivity, the mechanisms causing this overyielding remain debated. Here, we review studies of overyielding observed in agricultural intercropping systems, and show that a potentially important mechanism underlying such facilitation is the ability of some crop species to chemically mobilize otherwise-unavailable forms of one or more limiting soil nutrients such as phosphorus (P) and micronutrients (iron (Fe), zinc (Zn) and manganese (Mn)). Phosphorus-mobilizing crop species improve P nutrition for themselves and neighboring non-P-mobilizing species by releasing acid phosphatases, protons and/or carboxylates into the rhizosphere which increases the concentration of soluble inorganic P in soil. Similarly, on calcareous soils with a very low availability of Fe and Zn, Fe- and Zn-mobilizing species, such as graminaceous monocotyledonous and cluster-rooted species, benefit themselves, and al...
Habitat destruction is driving biodiversity loss in remaining ecosystems, and ecosystem functioni... more Habitat destruction is driving biodiversity loss in remaining ecosystems, and ecosystem functioning and services often directly depend on biodiversity. Thus, biodiversity loss is likely creating an ecosystem service debt: a gradual loss of biodiversity-dependent benefits that people obtain from remaining fragments of natural ecosystems. Here, we develop an approach for quantifying ecosystem service debts, and illustrate its use to estimate how one anthropogenic driver, habitat destruction, could indirectly diminish one ecosystem service, carbon storage, by creating an extinction debt. We estimate that c. 2-21 Pg C could be gradually emitted globally in remaining ecosystem fragments because of plant species loss caused by nearby habitat destruction. The wide range for this estimate reflects substantial uncertainties in how many plant species will be lost, how much species loss will impact ecosystem functioning and whether plant species loss will decrease soil carbon. Our exploratory ...
Anthropogenic changes in biodiversity and atmospheric temperature significantly influence ecosyst... more Anthropogenic changes in biodiversity and atmospheric temperature significantly influence ecosystem processes. However, little is known about potential interactive effects of plant diversity and warming on essential ecosystem properties, such as soil microbial functions and element cycling. We studied the effects of orthogonal manipulations of plant diversity (one, four, and 16 species) and warming (ambient, +1.5 degrees C, and +3 degrees C) on soil microbial biomass, respiration, growth after nutrient additions, and activities of extracellular enzymes in 2011 and 2012 in the BAC (biodiversity and climate) perennial grassland experiment site at Cedar Creek, Minnesota, USA. Focal enzymes are involved in essential biogeochemical processes of the carbon, nitrogen, and phosphorus cycles. Soil microbial biomass and some enzyme activities involved in the C and N cycle increased significantly with increasing plant diversity in both years. In addition, 16-species mixtures buffered warming induced reductions in topsoil water content. We found no interactive effects of plant diversity and warming on soil microbial biomass and growth rates. However, the activity of several enzymes (1,4-beta-glucosidase, 1,4-beta-N-acetylglucosaminidase, phosphatase, peroxidase) depended on interactions between plant diversity and warming with elevated activities of enzymes involved in the C, N, and P cycles at both high plant diversity and high warming levels. Increasing plant diversity consistently decreased microbial biomass-specific enzyme activities and altered soil microbial growth responses to nutrient additions, indicating that plant diversity changed nutrient limitations and/or microbial community composition. In contrast to our expectations, higher plant diversity only buffered temperature effects on soil water content, but not on microbial functions. Temperature effects on some soil enzymes were greatest at high plant diversity. In total, our results suggest that the fundamental temperature ranges of soil microbial communities may be sufficiently broad to buffer their functioning against changes in temperature and that plant diversity may be a dominant control of soil microbial processes in a changing world.
ABSTRACT Background/Question/Methods Anthropogenic changes in biodiversity and atmospheric temper... more ABSTRACT Background/Question/Methods Anthropogenic changes in biodiversity and atmospheric temperature rise significantly influence ecosystem processes. However, little is known about the interactive effects of biodiversity and warming on soil microbial biomass and functions in grassland. Here, we report results from the BAC experiment (Biodiversity And Climate) in Cedar Creek, MN, USA, where we studied effects of varying plant diversity (1, 4, and 16 species) and temperature rise (ambient, +1.5°C, and +3°C) on soil microbial biomass, respiration, nutrient limitations, and activities of extracellular enzymes in 2011 and 2012. The focal enzymes are involved in essential biogeochemical processes of the carbon cycle (cellobiohydrolase, ß-1,4-glucosidase, ß-1,4-N-acetylglucosaminidase, Phenol oxidase and Peroxidase), nitrogen cycle (urease), and phosphorus cycle (acid phosphatase). Results/Conclusions We found fairly consistent results in both years. Soil microbial biomass as well as most enzyme activities increased significantly with increasing plant diversity. However, we found no significant warming effects on soil microbial properties suggesting temperature optima for soil organisms are sufficiently broad to buffer them against small changes in temperature. In contrast to our expectations, we also found no interactive effects of plant diversity and warming indicating that plant diversity significantly influences soil microbial properties irrespective of warming scenarios. Overall, we found plant diversity to strongly affect soil microorganisms across years and temperature treatments whereas temperature had non-significant effects on soil microorganisms and microbial functions, pointing to the significance of plant diversity in driving belowground processes.
If you do not have access to the article you require, you can purchase the article (see below) or... more If you do not have access to the article you require, you can purchase the article (see below) or access it through a site license. A site license includes a minimum of four years of archived content; institutions can add additional archived content to their license at any time. ...
ABSTRACT Background/Question/Methods Recent theoretical and empirical work suggests the presence ... more ABSTRACT Background/Question/Methods Recent theoretical and empirical work suggests the presence of ectomycorrhizal (ECM) fungi allows plants to compete directly with decomposers for soil nitrogen (N) via exo-enzyme synthesis. Experimental ECM exclusion often results in a release from competition of saprotrophic decomposers, allowing for increased C-degrading enzyme production, microbial biomass and eventually declines in soil C stocks. Our knowledge of this phenomenon is limited, however, to the presence or absence of ECM fungi. It remains unknown if competitive repression of saprotrophic microbes and soil C-cycling by ECM fungi varies with ECM abundance. This is particularly relevant to global change experiments when manipulations are thought to alter plant C-allocation to ECM symbionts. To test if variation in ECM abundance alters the competitive inhibition of saprotrophic soil microbes (quantitative inhibition) we established experimental ECM exclusion treatments along an age gradient of ECM trees. To test for competitive release, we dug trenches in these stands to exclude roots and ECM fungi. To control for disturbance we placed root in-growth bags both inside and outside of trenches. ECM abundance was quantified by measuring ergosterol concentrations in a separate set of in-growth bags filled with sand (organic matter-free), which have been shown to exclude saprotrophic, but not ECM fungi. Results/Conclusions Ergosterol concentrations in sand in-growth bags increased from younger to older stands, suggesting the gradient does reflect variation in ECM abundance. Consistent with the quantitative inhibition hypothesis, older sites have significantly less microbial biomass per unit soil C and lower rates of N mineralization. Consistent with a release from competition, we found C-degrading enzyme activities to be higher and gross proteolytic rates to be lower per unit microbial biomass inside compared to outside trenches. We interpret this to reflect increased microbial investment in C-acquisition and decreased investment in N-acquisition in the absence of ECM fungi. Furthermore, the increase in C-degrading enzymes per unit microbial biomass is significantly greater in sites with the most ECM fungi. Based on these results, ECM-saprotroph competition does appear to slow soil C-cycling and the effect is quantitative. More ECM fungi leads to more ECM-saprotroph competition for N and in turn slower cycling of C in soil. Environmental change that alters ECM abundance may thus alter soil C stocks by ameliorating or exacerbating plant-decomposer competition.
Abstract Changes in the abundance of speciesespecially those that influence water and nutrient d... more Abstract Changes in the abundance of speciesespecially those that influence water and nutrient dynamics, trophic interactions, or disturbance regimeaffect the structure and functioning of ecosystems. Diversity is also functionally important, both because it ...
... identity and community composition Amy J. Symstad, David Tilman, John Willson and Johannes MH... more ... identity and community composition Amy J. Symstad, David Tilman, John Willson and Johannes MH Knops Symstad, AJ, Tilman, D., Willson, J. and Knops, JMH 1998. ... (1996). t-tests were performed on Ix to test for significant impacts of functional groups and individual species. ...
We tested the hypothesis that biological trait-based plant functional groups provide sufficient d... more We tested the hypothesis that biological trait-based plant functional groups provide sufficient differentiation of species to enable generalization about a variety of plant ecophysiological traits or responses to nitrogen (N). • Seedlings of 34 North American grassland and savanna species, representing 5 functional groups, were grown in a glasshouse in an infertile soil with or without N fertilization.
Despite increasing evidence that plant diversity in experimental systems may enhance ecosystem pr... more Despite increasing evidence that plant diversity in experimental systems may enhance ecosystem productivity, the mechanisms causing this overyielding remain debated. Here, we review studies of overyielding observed in agricultural intercropping systems, and show that a potentially important mechanism underlying such facilitation is the ability of some crop species to chemically mobilize otherwise-unavailable forms of one or more limiting soil nutrients such as phosphorus (P) and micronutrients (iron (Fe), zinc (Zn) and manganese (Mn)). Phosphorus-mobilizing crop species improve P nutrition for themselves and neighboring non-P-mobilizing species by releasing acid phosphatases, protons and/or carboxylates into the rhizosphere which increases the concentration of soluble inorganic P in soil. Similarly, on calcareous soils with a very low availability of Fe and Zn, Fe- and Zn-mobilizing species, such as graminaceous monocotyledonous and cluster-rooted species, benefit themselves, and al...
Habitat destruction is driving biodiversity loss in remaining ecosystems, and ecosystem functioni... more Habitat destruction is driving biodiversity loss in remaining ecosystems, and ecosystem functioning and services often directly depend on biodiversity. Thus, biodiversity loss is likely creating an ecosystem service debt: a gradual loss of biodiversity-dependent benefits that people obtain from remaining fragments of natural ecosystems. Here, we develop an approach for quantifying ecosystem service debts, and illustrate its use to estimate how one anthropogenic driver, habitat destruction, could indirectly diminish one ecosystem service, carbon storage, by creating an extinction debt. We estimate that c. 2-21 Pg C could be gradually emitted globally in remaining ecosystem fragments because of plant species loss caused by nearby habitat destruction. The wide range for this estimate reflects substantial uncertainties in how many plant species will be lost, how much species loss will impact ecosystem functioning and whether plant species loss will decrease soil carbon. Our exploratory ...
Anthropogenic changes in biodiversity and atmospheric temperature significantly influence ecosyst... more Anthropogenic changes in biodiversity and atmospheric temperature significantly influence ecosystem processes. However, little is known about potential interactive effects of plant diversity and warming on essential ecosystem properties, such as soil microbial functions and element cycling. We studied the effects of orthogonal manipulations of plant diversity (one, four, and 16 species) and warming (ambient, +1.5 degrees C, and +3 degrees C) on soil microbial biomass, respiration, growth after nutrient additions, and activities of extracellular enzymes in 2011 and 2012 in the BAC (biodiversity and climate) perennial grassland experiment site at Cedar Creek, Minnesota, USA. Focal enzymes are involved in essential biogeochemical processes of the carbon, nitrogen, and phosphorus cycles. Soil microbial biomass and some enzyme activities involved in the C and N cycle increased significantly with increasing plant diversity in both years. In addition, 16-species mixtures buffered warming induced reductions in topsoil water content. We found no interactive effects of plant diversity and warming on soil microbial biomass and growth rates. However, the activity of several enzymes (1,4-beta-glucosidase, 1,4-beta-N-acetylglucosaminidase, phosphatase, peroxidase) depended on interactions between plant diversity and warming with elevated activities of enzymes involved in the C, N, and P cycles at both high plant diversity and high warming levels. Increasing plant diversity consistently decreased microbial biomass-specific enzyme activities and altered soil microbial growth responses to nutrient additions, indicating that plant diversity changed nutrient limitations and/or microbial community composition. In contrast to our expectations, higher plant diversity only buffered temperature effects on soil water content, but not on microbial functions. Temperature effects on some soil enzymes were greatest at high plant diversity. In total, our results suggest that the fundamental temperature ranges of soil microbial communities may be sufficiently broad to buffer their functioning against changes in temperature and that plant diversity may be a dominant control of soil microbial processes in a changing world.
ABSTRACT Background/Question/Methods Anthropogenic changes in biodiversity and atmospheric temper... more ABSTRACT Background/Question/Methods Anthropogenic changes in biodiversity and atmospheric temperature rise significantly influence ecosystem processes. However, little is known about the interactive effects of biodiversity and warming on soil microbial biomass and functions in grassland. Here, we report results from the BAC experiment (Biodiversity And Climate) in Cedar Creek, MN, USA, where we studied effects of varying plant diversity (1, 4, and 16 species) and temperature rise (ambient, +1.5°C, and +3°C) on soil microbial biomass, respiration, nutrient limitations, and activities of extracellular enzymes in 2011 and 2012. The focal enzymes are involved in essential biogeochemical processes of the carbon cycle (cellobiohydrolase, ß-1,4-glucosidase, ß-1,4-N-acetylglucosaminidase, Phenol oxidase and Peroxidase), nitrogen cycle (urease), and phosphorus cycle (acid phosphatase). Results/Conclusions We found fairly consistent results in both years. Soil microbial biomass as well as most enzyme activities increased significantly with increasing plant diversity. However, we found no significant warming effects on soil microbial properties suggesting temperature optima for soil organisms are sufficiently broad to buffer them against small changes in temperature. In contrast to our expectations, we also found no interactive effects of plant diversity and warming indicating that plant diversity significantly influences soil microbial properties irrespective of warming scenarios. Overall, we found plant diversity to strongly affect soil microorganisms across years and temperature treatments whereas temperature had non-significant effects on soil microorganisms and microbial functions, pointing to the significance of plant diversity in driving belowground processes.
If you do not have access to the article you require, you can purchase the article (see below) or... more If you do not have access to the article you require, you can purchase the article (see below) or access it through a site license. A site license includes a minimum of four years of archived content; institutions can add additional archived content to their license at any time. ...
ABSTRACT Background/Question/Methods Recent theoretical and empirical work suggests the presence ... more ABSTRACT Background/Question/Methods Recent theoretical and empirical work suggests the presence of ectomycorrhizal (ECM) fungi allows plants to compete directly with decomposers for soil nitrogen (N) via exo-enzyme synthesis. Experimental ECM exclusion often results in a release from competition of saprotrophic decomposers, allowing for increased C-degrading enzyme production, microbial biomass and eventually declines in soil C stocks. Our knowledge of this phenomenon is limited, however, to the presence or absence of ECM fungi. It remains unknown if competitive repression of saprotrophic microbes and soil C-cycling by ECM fungi varies with ECM abundance. This is particularly relevant to global change experiments when manipulations are thought to alter plant C-allocation to ECM symbionts. To test if variation in ECM abundance alters the competitive inhibition of saprotrophic soil microbes (quantitative inhibition) we established experimental ECM exclusion treatments along an age gradient of ECM trees. To test for competitive release, we dug trenches in these stands to exclude roots and ECM fungi. To control for disturbance we placed root in-growth bags both inside and outside of trenches. ECM abundance was quantified by measuring ergosterol concentrations in a separate set of in-growth bags filled with sand (organic matter-free), which have been shown to exclude saprotrophic, but not ECM fungi. Results/Conclusions Ergosterol concentrations in sand in-growth bags increased from younger to older stands, suggesting the gradient does reflect variation in ECM abundance. Consistent with the quantitative inhibition hypothesis, older sites have significantly less microbial biomass per unit soil C and lower rates of N mineralization. Consistent with a release from competition, we found C-degrading enzyme activities to be higher and gross proteolytic rates to be lower per unit microbial biomass inside compared to outside trenches. We interpret this to reflect increased microbial investment in C-acquisition and decreased investment in N-acquisition in the absence of ECM fungi. Furthermore, the increase in C-degrading enzymes per unit microbial biomass is significantly greater in sites with the most ECM fungi. Based on these results, ECM-saprotroph competition does appear to slow soil C-cycling and the effect is quantitative. More ECM fungi leads to more ECM-saprotroph competition for N and in turn slower cycling of C in soil. Environmental change that alters ECM abundance may thus alter soil C stocks by ameliorating or exacerbating plant-decomposer competition.
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