关键词: 施氮, 退化草地, 土壤微生物, 分子生态学网络

Abstract:

【Objective】 Nitrogen input affects the sustainability of the global grassland ecosystem. Paying attention to the soil microbial community and its molecular ecological network can provide a theoretical basis for grassland degradation restoration. 【Method】 Taking Songnen degraded Leymus chinensis grassland as the research object, the molecular ecological network of soil microbial community was constructed by applying high-throughput sequencing and random matrix network construction with and without nitrogen treatment. To explore the effects of nitrogen management on the soil microbial community structure and network in degraded Leymus chinensis grassland, the key microbial changes in the microbial network structure under the condition of nitrogen addition was studied, and the interaction between microorganisms during the process were investigated, and the conditions for external nitrogen addition key points and regularity of soil bacterial dynamic change were analyzed. 【Result】 At the level of phylum classification, there were 22 bacterial phylum in nitrogen-applied grassland and 23 without nitrogen. The 7 phylum were the dominant phylum of the nitrogen-applied and non-nitrogen-applied grasslands. Among them, Proteobacteria was the phyla containing the largest number of OTUs, accounting for about 30.46% of the total sequence. The next largest genus was about 30.15% of the total sequence. The genus Gemmatimonadetes was the third genus containing OTUs, accounting for 8.14% of the total sequence. Actinomycete accounted for about the total 6.15% of the sequence, while Chloroflexi, Bacteroidetes and Nitrospirae accounted for 17.16% of the total sequence. The relative abundances of Proteobacteria, Actinomycota and Bacteroides in soil microorganisms in nitrogen-applied grassland were significantly higher than those in non-nitrogen applied grassland soil; The relative abundances of Proteobacteria, Actinomycete and Bacteroidetes were significantly higher than the soils of nitrogen-applied grassland (P<0.01), and no significant difference was found between the nitrogen application and non-nitrogen treatment of other bacteria. The forward connection ratio, the average path length, the average clustering coefficient, and the modularity of the characterizing network were all significantly lower than the nitrogen-free treatment (P<0.001). In the molecular ecological network of soil, there were 16 modular hubs without nitrogen treatment (Zi>2.5, Pi≤0.62), and there were 6 modular hubs under nitrogen treatment, all of which belong to Acidobacteria, Gemmatimonadetes and Actinomycete. Nitrogen application led to changes in soil microbial species relationships, which in turn changed the overall soil ecological network. 【Conclusion】 Nitrogen application reduced the complexity and tightness of soil network structure of degraded grassland, and reduced the relative abundance of Acidobacteria and Chloroflexi in degraded grassland, while which improved the relative abundance of Proteobacteria, Actinomycete and Gemmatimonadetes. The number of microbial key species (OTU) in soil decreased from 16 (no nitrogen application) to 6 and there was no overlapping OTU in both soils, indicating that nitrogen application regulated key species of its community network and thus changes its molecular ecological network.

Key words: nitrogen application, degraded grassland, soil microbe, molecular ecology network