氮添加对不同坡度退化高寒草甸土壤细菌多样性的影响

Effect of nitrogen addition on soil bacterial diversity in alpine degraded gras slands of differing slope

选取三江源区果洛州不同坡度退化程度相近的高寒草甸,进行氮添加试验,运用Miseq PE250测序技术对土壤细菌16s rDNA进行序列测定和分析,探讨3个氮添加水平低等量氮添加(LN,2 g N·m^-2)、中等量氮添加(MN,5 g N·m^-2)、高等量氮添加(HN,10 g N·m^-2)对不同坡度退化草地土壤细菌多样性的影响。结果表明:放线菌门(Actinobacteria)、变形菌门(Proteobacteria)是研究区草地土壤中最主要的两大类群。缓坡地与陡坡地土壤细菌个别丰度极低的门以及61.4%以上(包括未鉴定的细菌属)细菌属存在显著差异(P<0.05)。不同施氮水平对退化高寒草地各细菌门以及大部分细菌属影响不显著,对一些丰度较低的属的影响显著(P<0.05),且在不同坡度所响应的细菌属不同。无论是缓坡地还是陡坡地,氮添加对退化高寒草甸土壤细菌群落结构存在显著差异(P<0.05),土壤微生物丰富度和多样性整体上呈现出随着施氮量增加先减少后增加的趋势,中等量氮添加显著降低了土壤细菌丰富度和多样性,高水平氮添加显著抑制了土壤细菌的丰富度和多样性的下降(P<0.05),说明氮添加对细菌多样性的影响具有阈值限制性。

The aim of this study was to determine the effects of nitrogen addition on the bacterial community in soils in degraded alpine meadows with different slopes in Guoluo Prefecture,in the Sanjiangyuan Region.Degraded grasslands with different slopes were supplemented with nitrogen at three levels:low nitrogen(LN,2 g N·m^-2),medium nitrogen(MN,5 g N·m^-2),high nitrogen(HN,10 g N·m^-2),and the effects on soil bacterial diversity were determined.The 16s rDNA region of soil bacteria was sequenced and analyzed using Miseq PE250 sequencing technology.Actinomycota and Proteobacteria were the two main bacterial classes in the grassland soil in the study area.Individual phyla with extremely low abundance in soil and those with high abundance(>61.4%),including unidentified bacterial genera,differed significantly between gentle slope and steep slope regions(P<0.05).Different nitrogen addition levels did not significantly effect on the relative abundance of bacterial phyla and most bacterial genera in degraded alpine grassland,but had significant effects on some less abundant genera(P<0.05).On both gentle and steep slopes,the overall soil microbial richness and diversity tended to initially decrease and then increase with increasing nitrogen addition.The HN treatment inhibited the decrease of soil bacterial richness and diversity.The effect of nitrogen addition on bacterial diversity was threshold-limited.Among the three treatments,the MN treatment significantly reduced soil bacterial richness and diversity(P<0.05)