氮添加对巴音布鲁克高寒湿地土壤微生物量和酶活性的影响

随着全球氮沉降速率的快速增加,已对陆地生态系统微生物群落活性和代谢产生了深刻的影响。因此迫切需要了解全球气候变化敏感区土壤中微生物量和酶活性对氮添加的响应。为此,以中亚干旱区巴音布鲁克高寒湿地为研究对象,在保护良好的高寒湿地选择沼泽(S)、沼泽草甸(SM)和草甸(M)3种湿地类型布设野外原位氮添加试验(施氮浓度分别为0、8、16 kg N hm^-2 a^-1),探究短期氮添加对土壤微生物生物量碳(MBC)、微生物生物量氮(MBN)、微生物生物量碳/氮(MBC/MBN)、微生物商(QMB)、土壤蛋白酶、脲酶、碱性磷酸酶、H₂O₂酶和蔗糖酶活性的影响。结果表明:(1)高寒湿地不同湿地类型土壤微生物量和酶活性存在显著差异,其中SM土壤MBC、MBN、MBCN、QMB较S和M区高,对酶活性而言,SM和M区土壤蛋白酶和碱性磷酸酶活性较高,M区H₂O₂酶和脲酶活性较高。(2)氮添加显著增加了3种湿地类型中土壤MBC和MBN,其中MBC增加了7.00%-119.00%,MBN增加了8.03%-38.26%。氮添加仅显著增加了S和SM区土壤MBC/N和QMB (增加了24.68%-113.10%),但抑制了M区土壤MBC/N和QMB (抑制了8.93%-10.36%)。(3)氮添加显著增加了3种湿地类型土壤中脲酶、蛋白酶和H₂O₂酶活性,分别增加了7.25%-59.63%、4.71%-58.55%和34.70%-157.27%。但是氮添加对土壤碱性磷酸酶活性无显著影响。对蔗糖酶而言,N1处理增加了S区土壤蔗糖酶活性(增加了58.58%),而N2处理显著降低了22.72%。氮添加对SM和M区蔗糖酶活性无显著影响。(4)结构方程模型的结果显示,氮添加直接增加了土壤微生物量和酶活性。而随着湿地类型的变化(S-SM-M)直接和间接(通过pH)增加了酶活性;湿地类型的变化还通过影响pH、有机碳和有效养分间接增加了土壤微生物量。总之,氮添加和湿地类型可直接或间接的影响着土壤微生物量和酶活性。其中,土壤pH和有机碳是微生物量和酶活性变化的主要影响因素。本研究可为中亚干旱区高寒湿地应对未来气候变化的措施的制定提供技术参考。

Effects of nitrogen addition on soil microbial biomass and enzymatic activity in Bayinbuluk alpine wetland

With the rapid increase of global nitrogen deposition rate, it had a profound impact on the activity and metabolism of microbial community in the terrestrial ecosystem. Therefore, it is urgent to understand the response of soil microbial biomass and enzyme activity to nitrogen addition in the sensitive areas of global climate change. Therefore, taking Bayinbuluk alpine wetland in the arid region of the Central Asia as the research object, this study selected 3 types of well protected alpine wetlands:Swamp (S), Swamp meadow (SM) and Meadow (M), and arranged field in situ nitrogen addition experiments (nitrogen application concentrations are 0, 8 and 16 kg N hm^-2 a^-1, respectively). The aim is to explore the effects of short-term nitrogen addition on soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass carbon/nitrogen (MBC/MBN), microbial quotient (QMB), soil protease, urease, alkaline phosphatase, H₂O₂ enzyme and sucrase activities. Results showed that:(1) there were significant differences in soil microbial biomass and enzyme activities among different wetland types in alpine wetland. The MBC, MBN, MBC/N and QMB in the SM were higher than those in S and M. For enzyme activities, soil protease and alkaline phosphatase activities in the SM and M were higher, and H₂O₂ enzyme and urease activities in M were higher. (2) Nitrogen addition significantly increased soil MBC and MBN in the 3 wetland types, in which MBC increased by 7.00%-119.00% and MBN increased by 8.03%-38.26%. Nitrogen addition only significantly increased soil MBC/N and QMB in S and SM area (increased by 24.68%-113.10%), but inhibited soil MBC/N and QMB in M area (inhibited by 8.93%-10.36%). (3) Nitrogen addition significantly increased the activities of urease, protease and H₂O₂ in the soil of the 3 areas, by 7.25%-59.63%, 4.71%-58.55%, and 34.70%-157.27%, respectively. However, nitrogen addition had no significant effect on soil alkaline phosphatase activity. For sucrase, N1 treatment increased soil sucrase activity in the S area (increased by 58.58%), N2 treatment significantly decreased by 22.72%, while nitrogen addition had no significant effect on sucrase activity in SM and M area. (4) Results of structural equation model (SEM) showed that nitrogen addition directly increased soil microbial biomass and enzyme activity. With the change of wetland type (S-SM-M), soil enzyme activity increased significantly and indirectly through pH; Changes in wetland types also indirectly increased soil microbial biomass by affecting pH, organic carbon and available nutrients. In conclusion, nitrogen addition and wetland type can directly or indirectly affect soil microbial biomass and enzyme activity. Soil pH and organic carbon are the main influencing factors of microbial biomass and enzyme activity. This study can provide technical reference for the formulation of measures to deal with future climate change in alpine wetlands in arid areas of the Central Asia.