稻草和三叶草分解对微型土壤动物群落的影响

EFFECTS OF CLOVER AND STRAW DECOMPOSITION ON SOIL MIRCOFAUNAL COMMUNITY

有机物的施用能够促进土壤肥力和生物群落的发展,然而有机物组成或质量对土壤生物尤其是土壤动物的影响仍需要更多的研究。本研究将稻草和三叶草秸秆分别与土壤混合培养,在分解开始后的第14、35和70天分析土壤可溶性有机物、微生物生物量和微型动物群落的变化。结果表明,与稻草相比,三叶草秸秆提高了土壤活性有机碳和氮的含量。此外,三叶草对食细菌微型动物如原生动物和食细菌线虫有较强的促进作用,表明低碳氮比有机物促进了细菌主导的土壤食物网的发展。与三叶草相比,稻草提高了微生物生物量碳和微生物碳氮比,对土壤硝态氮的生物固持作用明显;稻草还刺激了线虫群落内的食真菌者、植食者和捕杂食者,提高了微型动物群落的多样性、成熟度和结构复杂性,说明高碳氮比的有机物更利于真菌主导食物网结构的形成。总之,通过秸秆种类的选择可调控土壤氮素的有效性及土壤生物食物网结构,有助于协调土壤氮素的生物转化过程和植物吸收之间的矛盾。

Organic amendments can significantly improve soil fertility and increase the soil biota in both number and activity. However, little attention has been given to impact of composition or quality of the organic substances on soil biota communities, especially on soil microfauna. In order to explore effects of the application of different crop residues on composition of the soil microbial food web, and to harmonize the contradiction between biological mineralization and fixation of soil nitrogen and plant N uptake, investigations were conducted of responses of soil labile carbon, nitrogen and soil microfauna （ nematodes and protozoan ） to amendment of different crop residues through in-lab microcosm incubation. Dynamics of soil dissolved organic carbon （DOC） , dissolved organic nitrogen （DON） , microbial biomass carbon （MBC） and nitrogen （ MBN ） , soil microfauna （ protozoa and nematodes ） were monitored in soils amended with rice straw or clove, following 14, 35 and 70 days of incubation. Results show that, compared with rice straw, clover significantly （p 〈 0.05 ） increased the contents of DOC and DON, especially the contents of DON, NO3-N and MBN along similar rising trends during the 70-day incubation period. However, the amendment of clover led to lower MBC and microbial C ： N ratios, but higher number of amoebae and flagellates than the amendment of rice straw did （p 〈 0.05 ） , particularly flagellates, of which the increase in number reached a significant level, after incubation for 14 d and 35 d （p 〈 0.05） . In addition, quality of the residue significantly affected the number of nematodes, which was significantly higher in the soil amended with clover than in the soil amended with rice straw. The number of nematodes rose continuously with the incubation going on in the soil amended with clover, while it stayed almost unchanged in the soil amended with rice straw. Concomitantly, relative abundance of the nematode trophic groups was also significantly affected by type of the residue （p 〈 0.05 ） , for example, relative abundance of bacterivorous nematodes and nematode channel ratio （ NCR ） were significantly higher in the soil amended with clover than with rice straw, while relative abundances, Shannon diversity, maturity index （ ∑MI 2-5 ） , and structure index （SI） of fungivorous nematodes, herbivorous nematodes and omnivorous nematodes were markedly lower in the former than in the latter （p 〈 0.05 ） . Clover displayed a strong stimulating effect on soil bacterivores, like protozoa and nematodes, which indicates that organic amendment low in C ： N ratio improves the structure of bacteria- dominated soil microbial food web. In contrast to clover, rice straw with higher C ： N ratio stimulated fungivores, herbivores and omnivores in the nematode community, increasing their proportions, and diversity, maturity and structural complexity of the nematode community, which further indicates that organic substances with high C ： N ratio promotes the structure of fungi-dominated microbial food web. In short, both quality and composition of the organic amendment have remarkable impacts on composition of soil carbon and nitrogen, abundance of soil microfauna, and structure and diversity of the soil microfaunal community. The use of appropriate types of crop residue may serve the purpose of manipulating size and composition of the soil microbial food web within a short period of time. Further studies should be done with more attention to research and validation of relative importance of composition of crop residue amended and some other soil abiotic factors through a longer term field experiment, so as to have a better understanding of the mechanism of type of organic amendment regulating the structure and functions of soil biota.