亚热带杉木人工林土壤胞外酶活性对隔离降雨的季节响应

摘要

Soil enzymes play an essential role in nutrient mineralization and their activity is an exceptional indicator for predicting the capacity of soil to supply nutrients to plants.In soil organic matter decomposition,soil extracellular enzymes catalyze the rate-limiting step and their catalysis,production,and degradation rates are regulated by moisture.Due to global warming,precipitation in the mid-subtropical region is decreasing,which profoundly affects the forest ecosystems;however,research in this field is relatively scarce.To investigate how soil extracellular enzyme activity (EEA) responds to altered precipitation regime,we conducted this study to measure the effects of experimental reduction in rainfall by 50％ on the soil physicochemical properties,extracellular enzyme activity,and nutrient availability in surface soil samples from a Cunninghamia lanceolata forest ecosystem,collected in dry and wet seasons.These extracellular enzymes were carbonacquisition enzymes,including β-glucosidase (3G),cellulose hydrolysis (CBH),phenol oxidase (PHO),and peroxidase (PEO).The results showed that the overall enzyme activities of the wet season samples were higher than those of the dry season samples.Irrespective of the season,except for PHO in the dry season samples,the activities of almost all soilenzymes,especially 3G,significantly increased after treatment.Redundancy analysis indicated that the EEA patterns were mainly driven by soil moisture,NO3--N,and dissolved organic carbon (DOC) in the dry season,and by microbial biomass carbon,DOC,and NH4+-N in the wet season.Our results suggested that the EEA in the carbon cycle in the mid-subtropical region would increase with reduction in precipitation.This may be because,despite the precipitation exclusion experiment,moisture did not become a limiting factor owing to the high rainfall in the mid-subtropical region.Alternatively,it could be a response or adaptation strategy of EEA to the adverse environmental change of precipitation reduction.Our study could have implications for carbon and nutrient cycling under changes in precipitation in the near future.%土壤酶在养分矿化过程中起着至关重要的作用,是预测土壤向植物提供养分能力的特殊传感器.土壤酶的催化、生产和降解速率受水分调节,而全球气候变暖所引起的降水减少将对中亚热带地区森林生态系统造成深刻影响,但是关于中亚热带杉木人工林土壤酶活性对降水变化响应的研究还是相对匮乏.通过隔离降雨模拟实验减少50％的降水,探究干湿两季中亚热带杉木人工林表层土壤的理化性质、胞外酶活性和有效养分对降水减少的响应.研究的胞外酶有:参与碳循环的β-葡萄糖苷酶(βG)、纤维素水解酶(CBH)、酚氧化酶(PHO)、过氧化物酶(PEO).冗余分析结果显示:干季时的土壤酶活性主要是受土壤含水量、硝态氮和可溶性有机碳(DOC)的影响,湿季则主要受微生物量碳、DOC和铵态氮的影响.湿季的土壤酶活性总体大于干季的土壤酶活性.除了干季的酚氧化酶外,无论干季或是湿季,几乎所有土壤酶活性在降水减少后均有所提高,其中3G活性变化最为显著.这可能是因为中亚热带地区降水丰富,尽管进行了隔离降雨处理,但水分仍然未达到限制水平;也可能是酶活性对降水减少这种不利的环境变化做出的响应或适应策略.本研究也为未来气候变化降水减少下对预测碳循环和养分循环提供了一定的科学依据.