氮添加对天山高寒草原土壤酶活性和酶化学计量特征的影响

为探究氮添加对高寒草原生态系统土壤酶活性的影响,于2018年在中国科学院巴音布鲁克草原生态系统研究站,选择4个氮添加水平(对照,N0,0 kg·hm^-2·a^-1;低氮,N1,10 kg·hm^-2·a^-1;中氮,N3,30 kg·hm^-2·a^-1;高氮,N9,90 kg·hm^-2·a^-1),开展土壤酶活性对氮添加响应的研究,分析土壤酶活性对氮添加的响应特点,土壤酶化学计量比以及土壤酶活性与土壤环境因子的关系。结果表明:与对照相比,氮添加在N3水平显著增加β-1,4葡萄糖苷酶(βG)、β-D-纤维二糖水解酶(CBH)和β-1,4木糖苷酶(βX)酶活性(P<0.05),N1和N3水平显著增加碱性磷酸酶(AKP)活性(P<0.05),N3水平显著降低多酚氧化酶(PPO)活性(P<0.05),氮添加对亮氨酸氨基肽酶(LAP)活性影响不显著,N3水平下显著增加N-乙酰-β-D氨基葡萄糖苷酶(NAG)活性(P<0.05)。相关分析表明,8种土壤酶活性均与土壤有机碳(SOC、NAG除外)和总磷(TP)显著相关,与土壤总氮(TN)不相关。研究区土壤酶活性C∶N∶P化学计量比为1∶1∶1.2,与全球生态系统的土壤酶活性C∶N∶P的比值1∶1∶1相偏离,表明该研究区土壤微生物生长受磷素限制。冗余分析(RDA)进一步揭示出土壤有机碳和土壤全磷含量是影响土壤酶活性的主要因子。

Effects of nitrogen addition on soil enzyme activities and ecoenzymatic stoichiometry in alpine grassland of the Tianshan Mountains

The effects of nitrogen (N) addition on activities of soil carbon (C),N,and phosphorus (P) circulation-related enzymes were investigated in an alpine grassland ecosystem in 2018.A long-term simulated N addition experiment was initiated at the Bayinbuluk Grassland Ecological Research Station of the Chinese Academy of Sciences in 2009;four N fertilizer treatments were applied at different sites: control (N0,0 kg·hm^-2·a^-1),low nitrogen (N1,10 kg·hm^-2·a^-1),moderate nitrogen (N3,30 kg·hm^-2·a^-1),and high nitrogen (N9,90 kg·hm^-2·a^-1).In the present study,stoichiometric ratios of soil ecological enzymes and the relationships between soil enzyme activities and environmental factors were analyzed.Our results revealed the following.Compared with N0,N3 treatment significantly increased β-1,4-glucosidase (BG),cellobiohydrolase (CBH) and β-1,4-xylosidase activities (βx) (P<0.05).N1 and N3 treatments obviously increased phenol oxidase (PPO) activity (P<0.05).N3 treatment obviously increased β-1,4-N-acetylglucosaminidase (NAG) activity (P<0.05).No N treatment affected L-leucine aminopeptidase activity (LAP).Correlation analysis showed that activities of all soil enzymes were positively correlated to soil organic C (SOC) content (except NAG) and total phosphorus (TP) content but were not to total nitrogen content.Soil ecoenzymatic C∶N∶P stoichiometry in the study area was 1∶1∶1.2,which is inconsistent with the global 1 ∶1 ∶1 pattern.This result suggests that soil microbial growth in the studied grasslands is limited by P content.Canonical redundancy analysis indicated that SOC and TP were the dominant factors affecting soil enzyme activity.