模拟氮沉降增加对不同树种土壤微生物群落结构的影响

Influence of simulated nitrogen deposition enhancement on soil microbial community of different tree species

土壤微生物作为生态系统分解者,在物质循环和能量流动中起着重要作用。人类活动引起的氮沉降增加会直接或间接改变土壤微生物结构和功能,最终影响生态系统物质循环和能量流动。于2012年5月起每月月初添加硝酸铵模拟不同梯度氮沉降(5.6、15.6、20.6 g N·m^(-2)·a-1),2013年4月中旬(雨季)和10月中旬(旱季)运用磷脂脂肪酸(PLFAs)法研究氮沉降对马尾松(Pinus massoniana)、海南红豆(Ormosia pinnata)、荷木(Schima superba)和马占相思(Acacia mangium)4个树种土壤微生物群落结构的影响。结果表明:随氮沉降水平的增加,土壤微生物总PLFAs降低,但细菌仍然是土壤微生物的优势类群。旱季土壤微生物PLFAs高于雨季。土壤微生物与土壤含水率、p H和总氮具有显著相关性。雨季土壤微生物主要受p H和含水率影响,而旱季土壤微生物主要受养分的影响。氮沉降胁迫下,固氮树种海南红豆和马占相思土壤微生物PLFAs高于其他树种。采样时间、氮水平和树种对土壤微生物(总土壤微生物、细菌、真菌和放线菌)PLFAs有显著影响,但没有显著改变土壤F/B值。因此,在研究氮沉降对土壤微生物的影响时,需综合考虑氮沉降时间效应、氮沉降水平和不同树种的影响,以便更好地为环境保护以及生态系统可持续发展等提供科学依据。

As decomposers,soil microbes play great roles in material circulation and energy flow in ecosystems. Elevated nitrogen deposition caused by human activities can directly or indirectly change the structure and function of soil microbial community,and then influence the material circulation and energy flow in ecosystems. From May 2012,nitrogen deposition was simulated in laboratory with ammonium nitrate at three levels monthly（ 5.6,15.6,20.6 g N·m^（-2）·a^（-1）） at the beginning of every month,and the effects of nitrogen deposition on soil microbial community structure were investigated by phospholipid fatty acids（ PLFAs） method in the middle of April（ rainy season） and October（ dry season） 2013 with one pine species and three broad leaf species,namely Pinus massoniana,Ormosia pinnata,Schima superba and Acacia mangium. The results showed that with the increase of nitrogen level for all tree species,total soil microbial PLFAs decreased,but bacteria were still the dominant microorganisms. The soil microbial PLFAs in dry season were higher than those in rainy season at all the tested nitrogen levels for all the tree species. Soil microorganisms related significantly to soil water content,soil p H and total nitrogen.In rainy season,soil microbes were mainly influenced by the soil p H and soil water content,but by soil nutrient in dry season. Under the stress of nitrogen deposition,soil microbial PLFAs of nitrogen fixation plants（ O. pinnata and A. mangium） were higher than those of the other two species. Sampling time,nitrogen levels and tree species all had significant influences on soil microbial（ total soil microorganisms,bacteria,fungi and actinomycetes） PLFAs,but had no impacts on the ratio of fungal to bacterial PLFAs（ F / B）. The timing effect,the nitrogen deposition level and the effect of tree species should be taken into integrated consideration when studying the effects of nitrogen deposition on soil microorganisms,to provide a scientific basis for the environment protection and the sustainable development of ecological system.