Search

While it is well established that plants associating with arbuscular mycorrhizal ( AM) and ectomycorrhizal ( ECM) fungi cycle carbon (C) and nutrients in distinct ways, we have a limited understanding of whether varying abundance of ECM and AM plants in a stand can provide integrative proxies for key biogeochemical processes., We explored linkages between the relative abundance of AM and ECM trees and microbial functioning in three hardwood forests in southern Indiana, USA. Across each site's 'mycorrhizal gradient', we measured fungal biomass, fungal : bacterial (F : B) ratios, extracellular enzyme activities, soil carbon : nitrogen ratio, and soil pH over a growing season., We show that the percentage of AM or ECM trees in a plot promotes microbial communities that both reflect and determine the C to nutrient balance in soil. Soils dominated by ECM trees had higher F : B ratios and more standing fungal biomass than AM stands. Enzyme stoichiometry in ECM soils shifted to higher investment in extracellular enzymes needed for nitrogen and phosphorus acquisition than in C-acquisition enzymes, relative to AM soils., Our results suggest that knowledge of mycorrhizal dominance at the stand or landscape scale may provide a unifying framework for linking plant and microbial community dynamics, and predicting their effects on ecological function. [ABSTRACT FROM AUTHOR]

While multiple experiments have demonstrated that trees exposed to elevated CO2 can stimulate microbes to release nutrients from soil organic matter, the importance of root- versus mycorrhizal-induced changes in soil processes are presently unknown., We analyzed the contribution of roots and mycorrhizal activities to carbon (C) and nitrogen (N) turnover in a loblolly pine ( Pinus taeda) forest exposed to elevated CO2 by measuring extracellular enzyme activities at soil microsites accessed via root windows. Specifically, we quantified enzyme activity from soil adjacent to root tips (rhizosphere), soil adjacent to hyphal tips (hyphosphere), and bulk soil., During the peak growing season, CO2 enrichment induced a greater increase of N-releasing enzymes in the rhizosphere (215% increase) than in the hyphosphere (36% increase), but a greater increase of recalcitrant C-degrading enzymes in the hyphosphere (118%) than in the rhizosphere (19%). Nitrogen fertilization influenced the magnitude of CO2 effects on enzyme activities in the rhizosphere only. At the ecosystem scale, the rhizosphere accounted for c. 50% and 40% of the total activity of N- and C-releasing enzymes, respectively., Collectively, our results suggest that root exudates may contribute more to accelerated N cycling under elevated CO2 at this site, while mycorrhizal fungi may contribute more to soil C degradation. [ABSTRACT FROM AUTHOR]

While multiple experiments have demonstrated that trees exposed to elevated CO2 can stimulate microbes to release nutrients from soil organic matter, the importance of root- versus mycorrhizal-induced changes in soil processes are presently unknown., We analyzed the contribution of roots and mycorrhizal activities to carbon (C) and nitrogen (N) turnover in a loblolly pine ( Pinus taeda) forest exposed to elevated CO2 by measuring extracellular enzyme activities at soil microsites accessed via root windows. Specifically, we quantified enzyme activity from soil adjacent to root tips (rhizosphere), soil adjacent to hyphal tips (hyphosphere), and bulk soil., During the peak growing season, CO2 enrichment induced a greater increase of N-releasing enzymes in the rhizosphere (215% increase) than in the hyphosphere (36% increase), but a greater increase of recalcitrant C-degrading enzymes in the hyphosphere (118%) than in the rhizosphere (19%). Nitrogen fertilization influenced the magnitude of CO2 effects on enzyme activities in the rhizosphere only. At the ecosystem scale, the rhizosphere accounted for c. 50% and 40% of the total activity of N- and C-releasing enzymes, respectively., Collectively, our results suggest that root exudates may contribute more to accelerated N cycling under elevated CO2 at this site, while mycorrhizal fungi may contribute more to soil C degradation. [ABSTRACT FROM AUTHOR]

While multiple experiments have demonstrated that trees exposed to elevated CO₂ can stimulate microbes to release nutrients from soil organic matter, the importance of root- versus mycorrhizal-induced changes in soil processes are presently unknown. We analyzed the contribution of roots and mycorrhizal activities to carbon (C) and nitrogen (N) turnover in a loblolly pine (Pinus taeda) forest exposed to elevated CO₂ by measuring extracellular enzyme activities at soil microsites accessed via root windows. Specifically, we quantified enzyme activity from soil adjacent to root tips (rhizosphere), soil adjacent to hyphal tips (hyphosphere), and bulk soil. During the peak growing season, CO₂ enrichment induced a greater increase of N-releasing enzymes in the rhizosphere (215% increase) than in the hyphosphere (36% increase), but a greater increase of recalcitrant C-degrading enzymes in the hyphosphere (118%) than in the rhizosphere (19%). Nitrogen fertilization influenced the magnitude of CO₂ effects on enzyme activities in the rhizosphere only. At the ecosystem scale, the rhizosphere accounted for c. 50% and 40% of the total activity of N- and C-releasing enzymes, respectively. Collectively, our results suggest that root exudates may contribute more to accelerated N cycling under elevated CO₂ at this site, while mycorrhizal fungi may contribute more to soil C degradation., (© 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.)