Differential responses of soil hydrolytic and oxidative enzyme activities to the natural forest conversion

Effects of natural forest conversion (NFC) on soil nutrient turnover are substantially mediated by soil microbial extracellular hydrolytic enzymatic activities (Hy-EEAs) and oxidative enzymatic activities (Ox-EEAs). Yet it remains largely unknown the indicative links between soil Hy- and Ox-EEAs and soil carbon (C), nitrogen (N) and phosphorus (P) supplies based on economic theories of microbial metabolism under NFC. Here we used a meta-analysis approach to synthesize the responses of the soil C-, N-, P-degrading Hy-EEAs and Ox-EEAs, soil microbial biomass, soil organic C, total N, P and available P parameters to natural forest conversion from 51 peer-reviewed studies. Our results showed that NFC notably decreased soil Hy-EEAs but statistically insignificant reduction of soil Ox-EEAs. The changes of soil Hy- and Ox-EEAs were significantly and positively associated with soil organic C, available P as well as microbial biomass C and N but significantly and negatively correlated with soil pH, whereas the changes of soil C/N impacted on soil Ox-EEAs remarkably but not for soil Hy-EEAs. The depletion of soil organic carbon stimulated soil microbial secretion of Hy- and Ox-EEAs. The soil total N scarcity only provoked soil microbial Hy-EEAs rather than Ox-EEAs. The soil total P dearth quickened the soil Ox-EEAs, however, the plenitude of soil available P suppressed soil Hy- and Ox-EEAs. Moreover, the eco-enzymatic stoichiometry of soil Hy-EEAs indicated that soil N and P nutrient limitation after NFC restricted soil microbial N- and P-acquiring enzymes secretion, which ultimately reduced resources availability for C acquisition. Altogether, the distinct responses of soil Hy- and Ox-EEAs depended on substrate availability peculiarly for soil N and P gains of microorganisms for further enzymatic ability on soil C decomposition and highlighted the abundant or absent supply of soil N and P for positive or negative enzymatic activities on metabolic requirement of soil edaphons.