Table_1_Effect of Different Grain for Green Approaches on Soil Bacterial Community in a Karst Region.XLS

Soil bacteria participate in nutrient cycling above and below ground to promote ecosystem stability and health. However, the relationship of soil bacteria and environmental factors following the Grain for Green (GfG) program remains poorly understood in southwest China. Soil samples were collected from seven Grain for Green sites that had been revegetated for 15 years. Four of these sites were afforested with a different tree species: Zenia insignis (ZI), Toona sinensis (TS), Castanea mollissima (CM), and Citrus reticulate (CR). One site was revegetated with Zenia insignis and Guimu-1 elephant grass (ZG), and one with only Guimu-1 elephant grass (GM). The remaining site, abandoned cropland (AC), was left to regenerate naturally. Here, we used Illumina sequencing of 16S rRNA genes to explore how the Grain for Green project affected soil bacterial community. We found that Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were the dominant phyla in these soils. The dominant genera at each revegetation site were also different. The CM, ZI, TS, and AC sites were dominated by Micromonospora, ZG was dominated by Streptomyces, and CR and GM were dominated by Subgroup 6. The bacterial structure was most similar in AC and TS. Correlation analysis showed that the ratio of C:P had positive effects on KD4-96, Intrasporangiaceae, and Gaiella. The ratio of soil N:P was significantly positively correlated with Cupriavidus and Kribbella. The combination of planting Zenia insignis and Guimu-1 elephant grass had the best edaphic benefits, and the approach of planting Citrus reticulate and Toona sinensis needs to be improved. Redundancy analysis (RDA) revealed that plant Simpson index, and soil N:P contributed to 16 and 15.7% of the total variations in the soil bacterial community composition, respectively. Our results suggested that plant diversity (Simpson index) and soil stoichiometric ratio (N:P) were the important factors affecting the bacterial community, and phosphorus was the limiting factor of the bacterial community in the Grain for Green karst region. In the future, revegetation should be accompanied with phosphorus fertilizer and polycultures should be considered.

土壤细菌参与地上与地下的养分循环，助力生态系统的稳定与健康。然而，在中国西南地区，退耕还林（Grain for Green, GfG）工程实施后，土壤细菌与环境因子间的关联仍不甚明晰。本研究采集了7个已实施植被恢复15年的退耕还林样地的土壤样品：其中4个样地分别种植了不同的乔木树种——任豆树（Zenia insignis, ZI）、香椿（Toona sinensis, TS）、板栗（Castanea mollissima, CM）以及柑橘（Citrus reticulate, CR）；1个样地采用任豆树与桂牧1号象草（Guimu-1 elephant grass, ZG）混植模式；另1个样地仅种植桂牧1号象草（GM）；剩余1个样地为撂荒农田（AC），采取自然恢复模式。本研究通过16S rRNA基因的Illumina测序技术，探究退耕还林工程对土壤细菌群落的影响。研究结果显示，放线菌门（Actinobacteria）、变形菌门（Proteobacteria）、绿弯菌门（Chloroflexi）以及酸杆菌门（Acidobacteria）为各样地土壤中的优势菌门；不同植被恢复样地的优势菌属亦存在差异：CM、ZI、TS及AC样地的优势菌属为小单孢菌属（Micromonospora），ZG样地的优势菌属为链霉菌属（Streptomyces），CR与GM样地的优势菌属为亚群6（Subgroup 6）。AC样地与TS样地的细菌群落结构相似度最高。相关性分析表明，土壤碳磷比（C:P）对KD4-96、孢囊杆菌科（Intrasporangiaceae）以及盖亚菌属（Gaiella）具有显著正向影响；土壤氮磷比（N:P）与贪铜菌属（Cupriavidus）及克氏杆菌属（Kribbella）呈显著正相关。任豆树与桂牧1号象草混植的模式可带来最优的土壤生态效益，而柑橘种植与香椿种植的模式仍有待优化。冗余分析（RDA）结果显示，植物辛普森指数（Simpson index）与土壤氮磷比分别解释了土壤细菌群落组成总变异的16%与15.7%。本研究结果表明，植物多样性（辛普森指数）与土壤化学计量比（N:P）是影响细菌群落的关键因子，且磷元素为该退耕还林喀斯特区域土壤细菌群落的限制因子。未来的植被恢复工作应配合施加磷肥，并可考虑采用多物种混植的模式。