外源氮输入对草地土壤微生物特性影响的研究进展

大气氮沉降作为全球变化的重要现象之一,沉降量不断增加所带来的一系列生态问题日趋严重.草地作为陆地生态系统的主体类型之一,对大气氮沉降的响应不仅体现在地上植被生长和群落动态的变化,其地下各种生态过程的变化更加值得关注.此外,世界范围内的草地生态系统大部分面临不同程度的退化,草地施氮是寻求草地恢复的有益尝试.综述了大气氮沉降和人为施氮引起的外源氮输入变化对草地生态系统土壤微生物特性(微生物数量、微生物量、微生物呼吸、微生物多样性和土壤酶)影响的研究进展,研究表明:①施氮有利于细菌数量的增加,但对真菌数量的影响甚微或是降低真菌的数量.②长期施氮降低土壤微生物量,但短期施氮的影响效应具有不确定性.③施氮对草地土壤微生物呼吸的影响效应取决于微生物可获得的碳源的量.输入地下的植物碳量增加促进土壤微生物呼吸,输入地下的有机质减少则抑制微生物呼吸.④施氮改变了土壤微生物的群落结构组成和底物利用方式,对土壤微生物多样性的影响表现出负效应.⑤施氮提高了β-葡糖苷酶、磷酸酶和大部分糖苷酶的活性,降低了脲酶的活性.迄今为止,施氮对草地土壤微生物特性的影响效应仍存在很大的不确定性,今后的研究中应开展氮输入对草地生态系统影响的长期试验研究、加强对土壤微生物呼吸的影响研究以及合理确定我国草地生态系统可持续发展的氮饱和阈值,并进一步完善和发展测量土壤微生物多样性的新方法.

Advances in the Influence of External Nitrogen Input on Soil Microbiological Characteristics of Grassland Ecosystem

Atmosphere nitrogen deposition is becoming an important phenomenon of global change, and results in a series of ecological problems. As one of the main terrestrial ecosystems, grassland ecosystem is more sensitive to the change of atmosphere nitrogen deposition, as is not only reflected by the growth of aboveground plant and the change of plant community, but also paid close attention due to the change of multiple belowground processes. Besides, most of grasslands worldwide have suffered degradation at different degrees, so the input of nitrogen fertilization has become a beneficial try to restore the degraded grassland. Here, the influences of external nitrogen input on soil microbe characteristics of grassland ecosystem are presented. The results indicated that nitrogen input was favorable to the increase of bacteria number, but had little effect on or even decreased the number of fungi. Long term nitrogen input decreased the soil microbial biomass, while short term nitrogen input may increase, decrease or have no effect on microbial biomass. The influence of nitrogen input on soil microbial respiration depends on the magnitude of available carbon which microbial needed. Nitrogen input would change the structure diversity and function diversity of soil microbe, and have a negative effect on soil microbial diversity. Nitrogen input increased the activities of the β-glucosidase enzyme and phosphatase enzyme, but decreased the activity of the urease enzyme. So far, the researches about the influences of nitrogen input on soil microbe characteristics still have a lot of uncertainties. Therefore, the long-term field studies, the research about the soil microbial respiration and the threshold quantity of nitrogen level which was appropriate to restoration of the grassland should be strengthened in the future studies. Besides, the new technologies and methods to determine the soil microbial diversity are also expected to develop.