A model selection analysis (see Materials and Methods) confirmed that responses of soil C storage were best predicted by N-induced changes in LME activity over a broad range of climate factors, vegetation and soil types, and N application methods ( Fig. In contrast, the effects of N addition on soil C storage were unrelated to the responses of cellulase activity ( Fig. The response of LME activity explained 40.4% of the variation in soil C storage to N addition. S2 and S3), although it was not significant for studies with high soil C/N ratios (>21.4 fig. This negative relationship held over a range of ecosystems and N addition methods (figs. Changes in soil C storage with N addition were negatively correlated with N suppression of LME activity, such that N-induced suppression of LME activity was associated with increases in soil C content ( Fig. N addition significantly increased cellulase activity by 15.2% and repressed LME activity by 12.8% ( Fig. RESULTSĪveraged across all studies, N addition significantly increased soil C storage by 11.0%. Through meta-analysis, we then investigated the role of enzyme activity and a wide range of environmental and experimental factors in determining changes in soil C storage with N addition.
We assembled a database of C-degrading enzyme activity and soil C storage from 40 N addition studies across four continents (fig. Here, we tested the hypothesis that N-induced shifts in C-degrading extracellular enzyme activities control changes in soil C storage. These responses are apparent in short-term assays of enzyme activity and consistent across ecosystems ( 19, 21, 22), but how they translate to long-term changes in soil C in response to N input is unknown. N addition can alter extracellular enzyme activity, suppressing the activity of lignin-modifying enzymes (LMEs enzymes that catalyze the breakdown of chemically recalcitrant substrates) and enhancing cellulase activity (table S1) ( 9, 17– 20). Incorporating this microbial influence on ecosystem biogeochemistry into Earth system models could improve predictions of ecosystem C dynamics.ĭecomposition is catalyzed by microbially produced extracellular enzymes, which break down dead plant and microbial biomass, and depolymerize macromolecules ( 14– 16). Our results suggest that, through responses of a single enzyme system to added N, soil microorganisms drive long-term changes in soil C accumulation. Moreover, the effects of added soil N on LME activity accounted for more of the variation in responses of soil C than a wide range of other environmental and experimental factors. In contrast, N-induced changes in cellulase activity were unrelated to changes in soil C. We show, using meta-analysis, that added N reduced the activity of lignin-modifying enzymes (LMEs), and that this N-induced enzyme suppression was associated with increases in soil C. Changes in microbial decomposition could also influence soil C storage, yet this influence has been difficult to discern, partly because of the variable effects of added N on the microbial enzymes involved. N deposition can stimulate plant growth and soil carbon (C) input, enhancing soil C storage. Agricultural and industrial activities have increased atmospheric nitrogen (N) deposition to ecosystems worldwide.
0 kommentar(er)
