3.3 Structural equation modeling analysis on CO2 efflux
To quantify the effects of stoichiometry of root exudates on CO2 efflux as a proxy of SOM mineralization, a SEM was constructed based on biotic parameters (microbial biomass and enzyme activity) and products of biological activity (DOC and NH4+). The SEM showed a reasonable fit to our hypothesized causal relationships (GEI = 0.98, Chi/DF= 1.00, RESEA < 0.01. Fig. 5) and explained 58% of the variance in CO2 emissions using all available biotic parameters and the products of biological predictors. The increase in C/N ratios had a negative effect on CO2 emissions (−0.29, P< 0.05, Fig. 6). Extracellular enzyme stoichiometry (BG/NAG and XYL/NAG ratios) exerted a positive direct effect (+0.39, P< 0.001), whereas the DOC/NH4+ ratio showed a negative direct effect (−0.30, P < 0.001).
DISCUSSION