生长季不同月份平茬对柠条人工林地土壤细菌群落特性的影响

柠条是豆科锦鸡儿属植物栽培种的通称，其中，中间锦鸡儿是中国西北地区重要的生态恢复型柠条灌木，平茬是促进柠条植株再生的重要手段。为了探讨生长季不同月份平茬对柠条人工林地土壤细菌群落结构和多样性的影响，基于Illumina Hiseq测序平台对宁夏盐池荒漠草原人工柠条林生长季不同月份平茬土壤细菌16S rDNA基因V3~V4区片段进行了序列测定，结合土壤理化因子，分析了人工柠条生长季不同月份平茬土壤细菌群落多样性与土壤理化因子的相关性。结果表明：变形菌门、放线菌门、酸杆菌门、绿弯菌门是生长季4-10月平茬的柠条人工林地土壤的优势细菌门，7个不同月份平茬分组之间在变形菌门、放线菌门、芽单胞菌门、己科河菌门、硝化螺旋菌门存在差异，其中第一优势细菌门变形菌门排序为：Y9>Y8>Y4>Y5>Y7>Y6>Y10，9月最高，为29.74%，显著高于10月（P<0.05），其他各月之间差异不显著（P>0.05）；5月平茬的放线菌门相对丰度最高，且显著高于4、6、7、8、9月（P<0.05）；9月平茬的酸杆菌门丰度最低。土壤细菌多样性指数也在不同月份平茬之间具有一定差异，细菌群落丰富度指数依次为：Y8>Y7>Y4>Y5>Y6>Y9>Y10，多样性较高的是4、6月平茬，9月平茬显著低于其他各月（P<0.05）。冗余分析（RDA）表明，不同月份平茬影响柠条人工林地土壤细菌分布的主要土壤环境因子是全磷、速效氮、有机质。放线菌纲、酸微菌纲与土壤pH正相关；α变形菌纲与土壤有机质正相关；δ-变形菌纲与含水量、全钾呈显著正相关；γ-变形菌纲、芽单胞菌纲与有机质、速效氮、全磷呈显著正相关。综合分析，平茬各月土壤细菌群落特性存在差异，土壤细菌优势菌群分布丰富、土壤养分含量较高的柠条旺盛生长季的4-8月平茬优于生长期末的9-10月，对于维持柠条的生态效益和开发利用柠条饲草料具有实际参考价值。

Effect of cutting time during the growing season on the soil bacterial community under an artificial Caragana intermedia plantation

Caragana intermedia is a shrub that plays an important role in ecological restoration in Northwest China， and cutting is an effective measure to promote its regeneration. In this study， we determined the effect of the cutting time of an artificial C. intermedia plantation on the desert steppe of Ningxia on the soil bacterial community. The artificial C. intermedia plantation was cut at seven different times： April （Y4）， May （Y5）， June （Y6）， July （Y7）， August （Y8）， September （Y9）， and October （Y10）. Soil samples were collected， and DNA extracted from the soil samples was sequenced using the Illumina Hiseq sequencing platform. The sequence data were analyzed to determine differences in soil bacterial community structure， species composition， and diversity characteristics among the treatments. The dominant phyla in soil samples were Proteobacteria， Actinobacteria， Acidobacteria， Chloroflexi. The abundance of Proteobacteria， Actinobacteria， Gemmatimonadetes， Rokubacteria， and Nitrospirae differed among the seven sampling times. The different cutting time were ranked， from highest abundance of the dominant bacterial phylum Proteobacteria to lowest， as follows： Y9>Y8>Y4>Y5>Y7>Y6>Y10. The proportion of Proteobacteria was highest in Y9 （29.74%）， and significantly higher than that in Y10 （P<0.05）， but not significantly different among the other treatments （P>0.05）. The highest relative abundance of Actinobacteria was in Y5， and was significantly higher than that in Y4， Y6， Y7， Y8， and Y9 （P<0.05）. The lowest abundance of Acidobacteria was in Y9. The treatments were ranked， from highest bacterial community abundance index to lowest， as follows： Y8>Y7>Y4>Y5>Y6>Y9>Y10. The diversity index of soil bacteria differed among treatments. Bacterial diversity was highest in Y4 and Y5， and was significantly lower in Y9 than in the other treatments （P<0.05）. Redundancy analyses showed that the main soil environmental factors affecting the distribution of the soil bacteria in different treatments were soil total phosphorus， available nitrogen， and soil organic matter. Presence of Actinobacteria and Acidimicrobiia was positively related to soil pH； presence of Alphaproteobacteria was positively related to soil organic matter； presence of Deltaproteobacteria was significantly positively correlated with soil water content and total potassium； and Gammaproteobacteria and Gemmatimonadetes were positively correlated with soil organic matter， available nitrogen， and total phosphorus. Thus， the cutting time significantly affected the soil bacterial community structure. The dominant bacterial community in the soil was richly distributed and the nutrient content in soils was higher when C. intermedia was cut in April-August， the vigorous growth period， than when it was cut in September-October. These results have practical significance for maintaining ecological benefits and developing Caragana forage.