Atmospheric nitrogen deposition in China displays a pronounced southeast-northwest gradient, with a range of ～35 kg·hm-2·a-1 in southern and central China and ～7.55 kg·hm-2·a-1 in the northwest. With the Grain for Green project, the environment of Loess Plateau has been greatly improved in the past decades. Little is known about how nitrogen deposition impacts the soil microbial communities in plantations in this region. In order to investigate the responses of diversity and structure of soil microbial community in Pinus tabuliformis plantations to nitrogen addition on Loess Plateau, China, we used high-throughput sequencing of 16S ribosomal RNA genes of bacteria and ITS genes of fungi to investigate the effects of nitrogen addition (200 kg N·hm-2·a-1) on the bacterial and fungal community over a 40-year chronosequence of coniferous P. tabuliformis plantation forests. After nitrogen addition, the Shannon diversity of both bacteria and fungi significantly increased in the 25-year-old stand, while the abundance-based coverage estimator of bacteria increased significantly in the 40-year-old stand. Nitrogen addition enhanced the relative abundance of Bacteroidetes in the 40-year-old stand and that of Acidobacteria/Zygomycota in the 25-year-old stand. In contrast, the relative abundance of Thaumarchaeota was reduced by nitrogen addition in the 40-year old stand. The effects of nitrogen addition were stronger on bacterial than on fungal community structure as indicated by the results from non-metric multidimensional scaling analysis. Moreover, the effects of nitrogen addition were stronger in the 25-year-old stand than in the 40-year-old stand. These results indicated that the effects of nitrogen addition on microbial community structure diminished over time in temperate forests on Loess Plateau, China. The stronger effects of nitrogen addition was found on the community structure of bacteria than that of fungi, and on the microbial community structure in the 25-year-old stand than in the 40-year-old stand. Our findings suggested that forest ecosystem at a certain stage (～40-year old) would be less sensitive to disturbance such as nitrogen addition than young forests.
中国南方及中部为高氮沉降区(～35 kg·hm-2·a-1),氮沉降量向西北依次递减(～7.55 kg·hm-2·a-1).黄土高原区历经几十年的退耕还林还草而面貌一新,但该区域人工林土壤微生物群落结构对氮素添加响应的研究还鲜有报道.本研究以黄土丘陵区不同林龄油松人工林为研究对象,应用Illumina HiSeq测序技术对细菌16S rDNA和真菌ITS进行序列测定与分析,探讨根际土壤细菌和真菌群落结构组成对土壤氮添加(施用量为200 kg N·hm-2·a-1纯氮)的响应,旨在探究我国西北黄土丘陵区油松人工林根际土壤微生物多样性及群落结构对定量氮添加的响应.结果表明: 氮添加显著增加了25年龄林地细菌和真菌Shannon多样性,显著增加了40年龄林地细菌丰度指数.氮添加显著增加了40年龄林地拟杆菌门的相对丰度和25年龄林地酸杆菌门及接合菌门的相对丰度,但显著降低了40年龄林地奇古菌门的相对丰度.非度量多维尺度分析结果显示,氮添加对土壤细菌群落结构组成的影响程度大于真菌,对25年龄林地微生物群落结构组成的影响程度大于40年龄林地.表明不同林龄油松人工林根际土壤微生物的多样性及群落结构对土壤氮添加响应具有差异性.相对于真菌群落结构组成,细菌群落结构组成对氮添加更敏感;相对于40年龄林地,25年龄林地根际土壤微生物的群落结构组成对氮添加更敏感.因此,黄土高原区人工林地生态系统演替到一定阶段(40年左右),比幼龄林地生态系统更能承受外界较大的氮添加扰动.
Keywords: Loess Plateau; diversity; soil microbial community composition; temperate forest..