东北黑土区不同覆盖作物对土壤酶活性的影响及调控机制探究OA

[Objective]To explore the changes in soil enzyme activities under different cover crops systems and the regulatory mechanisms by which biotic and abiotic factors within the cropping system affect soil enzyme activities.[Methods]Conventional corn monoculture was used as the control treatment(CT),and three cover crops treatments were established:alfalfa monoculture(A),ryegrass monoculture(R),and a mixed sowing of both(AR).Soil samples were collected from 0-10 cm and 10-20 cm depths,and soil physicochemical properties,microbial phospholipid fatty acids(PLFA)contents,and enzymatic activities were measured and analyzed comprehensively.[Results]Compared with CT,alfalfa monoculture significantly reduced the concentrations of dissolved organic carbon(DOC),dissolved organic nitrogen(DON),nitrate nitrogen(NO3--N),total phosphorus(TP),and available phosphorus(AP)at 0-10 cm and 10-20 cm depths.It also decreased the AP content in the 0-10 cm layer,ammonium nitrogen(NH4+-N)in the 10-20 cm soil layer,and the DON∶AP ratio(p<0.05),along with the biomass of various microbial groups,such as fungi and bacteria.In addition,alfalfa monoculture notably increased the DOC∶DON ratio in 0-10 and 10-20 cm layers,and the activity of carbon,nitrogen and phosphorus cycling-related enzymes,including β-Glucosidase(βG)、Cellobiohydrolase(CB)、N-acetylglucosaminidase(NAG)、Leucine aminopeptidase(LAP)、Acid phosphatase(ACP)in the 10-20 cm soil layer.Ryegrass monoculture significantly increased the DOC∶DON ratio in the 0-20 cm soil layer and raised pH in the 10-20 cm soil layer.It markedly reduced DON,NH4+-N,NO3--N,DON∶AP ratio in both soil layers,as well as TP and DOC in the 0-10 cm layer(p<0.05).Microbial biomass trends were similar to those observed with alfalfa,but ryegrass also significantly enhanced the carbon-transforming enzyme activities in the 0-10 cm soil layer and phosphorus-transforming enzyme activities in the 10-20 cm layer.Mixed planting significantly increased pH and DOC∶DON ratios in the 0-10 cm and 10-20 cm soil layer,while markedly reducing DOC,DON,NH4+-N,NO3--N,TP,AP,and the DON∶AP ratio in both soil layers(p<0.05).This treatment maintained microbial biomass at levels comparable to CT and significantly higher than those in the monoculture treatments,while significantly enhancing phosphorus-transforming enzyme activities.[Conclusion]The regulatory mechanisms of soil enzyme activities differ among cover crop types,mainly reflected in the 10-20 cm soil layer.Leguminous cover crops enhance the activities of soil carbon-,nitrogen-,and phosphorus-transforming enzymes by increasing soil nitrogen content,regulating the stoichiometric ratios of DOC∶DON and DON∶AP of available nutrients,and altering the nutrient acquisition pathways of soil microbial communities.Gramineous cover crops enhance the activities of soil nitrogen-and phosphorus-transforming enzymes by increasing soil carbon content and changing DOC∶DON and DOC∶AP ratios.Mixed planting balances soil nutrient stoichiometry and maintains a high soil microbial biomass.In the short term,mixed planting is an optimal measure for maintaining microbial biomass and improving soil health,whereas alfalfa monoculture is optimal for increasing soil nutrient content and promoting internal cycling of soil nutrients.