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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。
Atmospheric nitrogen deposition is one of the most important phenomena of global change. A series of ecological problems caused by the increasing sedimentation volume have become increasingly serious. Grassland, as one of the main types of terrestrial ecosystem, responds to the atmospheric nitrogen deposition not only in the changes of vegetation and community dynamics, but also in the underground ecological processes. In addition, most of the world’s grassland ecosystems are facing different degrees of degradation. Nitrogen in grassland is a useful attempt to seek grassland restoration. This paper reviews the research progress on the effects of atmospheric nitrogen deposition and nitrogen input on soil microbial characteristics (microbial biomass, microbial biomass, microbial respiration, microbial diversity and soil enzymes) of grassland ecosystem. The results show that: Nitrogen favors an increase in the number of bacteria, but has little or no effect on the number of fungi. Long-term nitrogen application reduced soil microbial biomass, but the effect of short-term nitrogen application was uncertain. The effects of nitrogen application on soil microbial respiration in grasslands depend on the amount of carbon sources available to the microorganisms. The increase of carbon input into underground plants can promote the respiration of soil microorganisms and the decrease of input of underground organic matter inhibits the respiration of microorganisms. (4) Nitrogen application changed the composition of community structure and substrate utilization of soil microorganism, which showed a negative effect on soil microbial diversity. ⑤Nitrogen increased the activity of β-glucosidase, phosphatase and most of the glycosidases, reducing the activity of urease. So far, there is still great uncertainty about the effects of nitrogen on grassland microbial characteristics. In the future, long-term experimental studies on the effects of nitrogen input on grassland ecosystems should be carried out to study the effects of nitrogen on respiration of soil microorganisms and reasonable Determine the nitrogen saturation threshold of sustainable development of grassland ecosystem in our country, and further improve and develop a new method to measure soil microbial diversity.