毛竹扩张对阔叶林土壤微生物碳氮利用效率的影响OACHSSCD

Microbial carbon(C)and nitrogen(N)use efficiency are key factors regulating soil Cand N cycling.The expansion of Phyllostachys edulis(moso bamboo)alters C inputs and soil resource availability,significantly influencing below-ground ecological processes and enzymatic stoichiometry.However,the mechanisms by which moso bamboo expansion affects microbial C and N use efficiency(CUE and NUE)remain unclear.Using a space-for-time substitution approach,sampled two expansion transects comprising broadleaf forest,mixed bamboo-broadleaf forest,and pure bamboo forest to examine the effects of Phyllostachys edulis.bamboo expansion on soil physicochemical properties,C:N stoichiometric imbalance,microbial biomass carbon and nitrogen(MBC,MBN),extracellular enzyme activities,microbial resource limitation,and microbial CUE and NUE.The results showed that,compared to broadleaf forest,moso bamboo expansion significantly decreased soil organic carbon(SOC),total nitrogen(TN),dissolved organic carbon(DOC,62％—72％),dissolved organic nitrogen(DON,32％—61％),electrical conductivity(EC),and the soluble C:N ratio(RDOC:DON,31％—44％),but increased soil pH and NH4+content(by 23％—81％).These changes collectively reduced the soil C:N stoichiometric imbalance ratio(by 16％—69％),indicating a significant shift in C and N resource supply favoring higher relative N availability compared to C.Bamboo expansion decreased soil MBC(by 38％—46％),MBN(by 56％—73％),and the activities of β-glucosidase(BG,14％—32％),leucine aminopeptidase(LAP,23％—57％),β-N-acetylglucosaminidase(NAG,16％—53％),and the threshold elemental ratio difference(RC:N-TERC:N,57％—64％)significantly decreased with bamboo expansion.In contrast,the soil MBC/MBN ratio(by 22％—125％)and the BG/(LAP+NAG)ratio(by 0％—67％)rose,It is indicated that microorganisms respond to the imbalance of nutrient resources by adjusting their own biomass activity and stoichiometric ratio.Bamboo expansion significantly increased microbial CUE(by 4％—15％)but decreased microbial NUE(by 1％—53％).Partial least squares path revealed that bamboo expansion enhanced CUE and reduced NUE primarily by raising soil pH and alleviating C:N stoichiometric imbalance,which promoted an increase in MBC/MBN.In contrast,the direct path involving C and N acquiring enzyme activities was not significant.This indicates that under reduced N limitation,microbial strategies shifted from a resource-acquisitive mode,dependent on extracellular enzyme investment,toward an efficiency-oriented strategy relying on intracellular biomass reallocation.Mantel tests and random forest analysis further supported these results,identifying MBC/MBN ratio,soil C:N stoichiometric imbalance,pH,BG activity,and RC.N-TERC:N as key drivers of CUE,while the MBC/MBN ratio,soil C:N stoichiometric imbalance,pH,MBC,and RC:N-TERC.N were major predictors of NUE.The above study demonstrates that moso bamboo expansion alters soil resource stoichiometric,leading to adaptation strategies that prioritize C metabolism under limited resources availability.These findings provide a scientific basis for a deeper understanding of microbially mediated C and N cycling in subtropical forest ecosystems.