三峡库区马尾松人工林土壤酶活性和微生物生物量对氮添加的季节性响应

Seasonal responses of soil enzyme activities and microbial biomass to nitrogen addition at different levels in Pinus massoniana plantation in the Three Gorges Reservoir area

以三峡库区马尾松人工林为对象,分析土壤微生物生物量、酶活性和养分含量对氮添加的初期响应规律,为预测该地区在大气氮沉降持续增加的背景下森林土壤的季节动态提供参考。结果表明:氮添加初期,中氮水平(60 kg hm^(-2)a^(-1))的氮添加处理使得各季节土壤β-1-4葡萄糖苷酶、N-乙酰氨基葡萄糖苷酶、酸性磷酸酶、多酚氧化酶、过氧化物酶活性均增加,高氮(90 kg hm^(-2)a^(-1))水平的添加处理增加了土壤有机碳、全氮和微生物生物量碳、氮、磷的含量和酸性磷酸酶及多酚氧化酶活性,降低了土壤pH值、全磷含量和β-1-4葡萄糖苷酶及N-乙酰氨基葡萄糖苷酶活性。土壤酶活性和微生物生物量存在明显的季节变化,秋季水解酶活性和微生物生物量碳、磷含量显著高于春夏两季,而氧化酶活性和微生物生物量氮含量则是春夏季较高。土壤酶活性与季节、土壤含水量、养分含量及微生物生物量碳氮磷含量存在显著的相关性,酶活性变化是多因子综合作用的结果,冗余分析表明土壤含水量、微生物生物量碳、氮、磷和全氮是驱动土壤酶活性的主要环境因子。氮沉降的持续增加会加速当地马尾松人工林土壤腐殖质的形成,增加有机碳的积累,导致土壤酸化,并产生磷限制。

Anthropogenic nitrogen(N)enrichment is a concern worldwide,as it affects almost every aspect of ecosystem function and composition.Many nitrogen(N)addition experiments have been well documented to decrease plant biodiversity across various terrestrial ecosystems.However,such generalizations about the impacts of nitrogen addition on soil enzyme activities and microbial biomass are lacking,especially in the Three Gorges Reservoir area,as a key sensitive ecological barrier of the middle and lower reaches of the Yangtze River.Therefore,we conducted nitrogen addition experiments in February 2019 in Pinus massoniana plantation in the Three Gorges Reservoir area of subtropical China.Soil samples were collected from three control plots(N_(CK)),three low-nitrogen addition plots(N_(low)),three middle-nitrogen addition plots(N_(middle)),three high-nitrogen addition plots(N_(high))in May,August and November,2019.We studied the soil enzyme activities,microbial biomass and nutrient content in response to nitrogen addition,which provided a theoretical basis for predicting soil seasonal dynamics in an increasing atmospheric nitrogen deposition background in the Three Gorges Reservoir area.The results show that,in the early stage of nitrogen addition,the medium nitrogen(60 kg hm^(-2)a^(-1))treatment increased the activities of β-1-4 glucosidase(BG),N-acetylglucosaminosidase(NAG),acid phosphatase(AP),polyphenol oxidase(PPO)and peroxidase(POD);the high nitrogen(90 kg hm^(-2)a^(-1))treatment increased the contents of soil organic carbon,total nitrogen,microbial biomass carbon(MBC),nitrogen(MBN),phosphorus(MBP),and the activities of AP,PPO,while decreased the soil pH,total phosphorus content and the activities of BG and NAG.There were significantly seasonal differences between soil enzyme activities and microbial biomass.Hydrolase activities,MBC and MBP contents in autumn were significantly higher than those in spring and summer,while oxidase activities and MBN contents were higher in spring and summer.Soil enzyme activities were significantly correlated with season,soil moisture content,soil nutrient,MBC,MBN,MBP.The change of soil enzyme activities is due to the comprehensive action of multiple factors.Redundancy analysis(RDA)showed that soil moisture content,MBC,MBN,MBP and total N greatly accounted for the variation in soil enzyme activities.The increasing nitrogen deposition will accelerate the formation of soil humus,increase organic carbon accumulation,lead to soil acidification,and produce phosphorus limitation in the local Pinus massoniana plantation.