氮沉降对缙云山柑橘林不同季节土壤微生物群落结构的影响

土壤微生物积极参与生态系统的物质循环和转化.人类活动造成全球氮沉降量激增,引起土壤微生物群落结构和功能的改变,进而导致生态系统失衡.2014年6月—2015年5月在缙云山柑橘林建立野外模拟氮沉降试验样地,原位设置4个施肥水平:对照(N0,0 g·m~(-2)·a~(-1))(以N计,下同)、低氮(N20,20 g·m~(-2)·a~(-1)),中氮(N4 0,40 g·m~(-2)·a~(-1))和高氮(N60,60 g·m~(-2)·a~(-1)).施氮处理2 d后,采用磷脂脂肪酸(PLFA)标记法和ACE(Automated Soil CO_2Exchange Station,UK)自动土壤呼吸监测系统对土壤微生物群落结构、土壤温湿度进行测定.研究表明:(1)不同季节土壤微生物对氮沉降的响应各异,春季氮沉降抑制土壤微生物量,夏、秋、冬季N40处理提高了土壤微生物量,N20、N60表现为抑制土壤微生物量;氮沉降对土壤温度有显著影响,但对土壤湿度影响不明显(p0.05).(2)土壤微生物丰富度指数和Shannon-Wiener多样性指数在中氮沉降条件下达最大;Pielou均匀度指数则表现不一致,春季和夏季在中氮浓度下最大,秋季在高氮处理下最大,冬季则在低氮处理下最大.(3)土壤温度与放线菌呈显著负相关(p0.01);土壤湿度与细菌和总PLFA呈显著正相关(p0.01),与放线菌呈显著正相关(p0.05).综合分析表明,土壤微生物受土壤温度和含水量的共同影响,氮沉降降低了土壤微生物含量,此研究结果支持了氮沉降抑制土壤微生物的认识.

Effects of simulated nitrogen deposition on soil microbial community structure in different seasons of Citrus Forest in Mt. Jinyun, Chongqing

Soil microorganisms are of great significance to element circulation and transformation in ecosystems. The great increase in nitrogen deposition caused by human activities could change the structure and function of soil microbes, and then disturb the balance of ecosystem. An on-site experiment was conducted in citrus forest of Mt. Jinyun from June 2014 to May 2015. Nitrogen treatments were designed at four levels:control (N₀, 0 g·m^-2·a^-1), low nitrogen (N₂₀, 20 g·m^-2·a^-1), moderate nitrogen (N₄₀, 40 g·m^-2·a^-1) and high nitrogen (N₆₀, 60 g·m^-2·a^-1). The influences of fertilization on the structure of soil microbial community and soil temperature and moisture were investigated by using phosphorus lipid fatty acids (PLFAs) and automated soil CO₂ exchange station, respectively. The results showed that the response of soil microorganisms to nitrogen deposition varied with seasons greatly. Generally, nitrogen deposition decreased soil microbial population from all treatments in spring and from the treatment of N₂₀ and N₆₀ in summer, autumn and winter, but increased the soil microbial biomass from N₄₀ treatment in summer, autumn and winter. Moderate nitrogen treatment significantly increased microbial richness and diversity, while the responses of the Pielou evenness index to nitrogen deposition changed with seasons. The maximum values of the Pielou evenness index were observed in autumn under high nitrogen treatment and in winter under low nitrogen treatment, but in spring and summer under medium nitrogen concentration. There was a significantly negative correlation between soil temperature and actinomycetes. Soil moisture was positively correlated with bacteria, total PLFA and actinomycetes. Therefore, it is concluded that soil microbes were affected by soil temperature and moisture content, but nitrogen deposition could reduce soil microbial biomass. Thus, our experimental results clearly confirmed the insight that nitrogen deposition restrained soil microorganisms.