The Influence Mechanism of Vegetation Type on the Characteristics of nirS-Type Denitrifying Microbial Communities in Qinghai Lake Wetlands.

Soil denitrification is an important process in the emission of N2O, an atmospheric greenhouse gas. Environmental factors of different vegetation types are largely heterogeneous, which may directly or indirectly affect N2O fluxes. Through high-throughput sequencing of the nitrite reductase gene nirS, this study investigated the influence of vegetation type on the structure and diversity of denitrifying microbial communities in Qinghai Lake wetlands, China. The results showed that among the four vegetation types in the Qinghai Lake wetlands, Carex rigescens (CR) had the highest species richness index, and Leymus secalinus (LS) had the lowest species richness index. Species evenness followed the opposite trend. Proteobacteria were the main denitrifying bacterial phylum in the wetland soil of Qinghai Lake. There were 40 differential bacterial flora at different levels in the four vegetation types, most of which belonged to Proteobacteria. Magnetospirillum is a bacterium that differed significantly across the four vegetation types, and it was one of the main denitrifying taxa based on relative abundance in the LS vegetation type. Soil pH was the most important regulating factor of nirS-type denitrifying microbial community in Qinghai Lake wetland. In summary, the succession of vegetation types in the Qinghai Lake Wetlands changes the soil microenvironment and significantly affects the community structure and diversity of the denitrifying microbial communities. The large-area growth of CR might even increase the emission of nitrous oxide. This study can serve as a reference for further exploration of the N2O emission mechanism in the unique habitats of alpine wetlands.

[Changes of soil enzyme activities and nutrients across different succession stages of grazing alpine Kobresia grassland.] / æ”¾ç‰§é«˜å¯’åµ©è‰è‰åœ°ä¸åŒæ¼”æ›¿é˜¶æ®µåœŸå£¤é ¶æ´»æ€§åŠå »åˆ†æ¼”å˜ç‰¹å¾.

The variation of soil enzyme activity and relevance with soil nutrients was examined in multistable grazing alpine Kobresia grassland, including Gramineae-Kobresia humilis community, K. humilis community, K. pygmaea community at thickened stage, K. pygmaea community at cracked stage and forb-black soil type secondary bare land. The results showed that the vegetation coverage and aboveground biomass successively decreased with degenerative succession. The belowground biomass was the highest in the K. pygmaea community at thickened and cracked stages. The activities of soil sucrase, urease, cellulase, alkaline phosphatase and aryl sulfatase were higher at the surface soil layer (0-10 cm) than those at the subsurface soil layer (10-20 cm), while the pattern of chitinase activity was contrary. The activities of cellulase, alkaline phosphatase and aryl sulfatase were the highest in the Gramineae-K. humilis community and the lowest at the forb-black soil type secondary bare land, and they slightly increased during the thickened stage of K. pygmaea community. Chitinase activity was relatively high at the middle three stages, while urease and sucrase activity had an obvious increase in the forb-black soil type secondary bare land. Soil moisture, ammonium, alkali-hydrolyzable nitrogen, total nitrogen, total carbon and organic carbon successively decreased with degenerative succession, whereas the concentrations of nitrate and available phosphorus increased at the latter two succession stages. The activities of the other enzymes, except for chitinase, were significantly positively correlated with the soil available phosphorus, ammonium, alkali-hydrolyzed nitrogen, total carbon, and organic carbon, and negatively correlated with soil pH. The activities of cellulose, alkaline phosphatase and aryl sulfatase were significantly positively correlated with soil moisture and total nitrogen. The main factors affecting soil enzyme activity were available phosphorus and ammonium. Soil enzymes showed different evolutionary trends influenced by grazing degradation succession in the alpine grassland, with a synergistic effect with soil nut-rients. Moreover, severely degraded extreme environments may stimulate soil enzyme activities related to nitrogen and carbon transformation.

[Characteristics of artificial grassland plant communities with different establishment duration and their relationships with soil properties in the source region of three rivers in China].

This paper studied the biomass, species composition, and diversity index of artificial grassland plant communities with different establishment duration in the source region of the Three Rivers, and examined the relationships of soil physical and chemical properties with the changes of the plant community biomass and species diversity. The results showed that the species composition, functional group composition, and quantitative characters of the plant communities varied greatly. Soil moisture content increased with increasing species diversity, while soil bulk density was in adverse. Soil microbial biomass carbon significantly positively correlated with soil moisture and organic matter contents, but negatively correlated with soil bulk density. Soil organic carbon content had a "V" type change, which was consistent with the change pattern of soil moisture content, and decreased with increasing soil bulk density. Plant community biomass had significant positive correlations with the contents of soil nutrients and moisture, and the increase of the above- and below-ground biomass of plant communities promoted the increase of soil nutrient contents.