西北荒漠绿洲过渡带土壤细菌结构和氮代谢对梭梭恢复的响应

探究植被恢复过程中土壤微生物群落结构和氮代谢变化,是认识陆地生态系统生物地球化学过程的重要环节。然而,关于干旱区荒漠人工植被种植后土壤微生物功能的研究鲜有报道。选择西北荒漠绿洲过渡带建植时间序列(3、6、11、19、28a和46a)梭梭(Haloxylon ammodendron)林为研究对象,取冠层下表层土样(0-10 cm),流动沙地(Ms)作为对照,采用高通量测序技术,探究土壤细菌群落多样性、结构、氮代谢及功能基因对梭梭恢复的响应,考察土壤细菌群落结构变化的关键驱动因子。结果表明,放线菌门(Actinobacteriota)和变形菌门(Proteobacteria)是所有样地的优势细菌类群。Shannon指数随梭梭种植年限增加显著增加,表明梭梭建立显著提高了土壤细菌群落多样性。样本层级聚类分析显示不同年限梭梭林土壤细菌群落被分为3个小组,非度量多维尺度(NMDS)分析表明梭梭的建立显著改变了土壤细菌群落结构。Spearman相关性分析显示土壤含水量(SM)、有机碳(SOC)、速效磷(AP)和速效钾(AK)显著影响土壤细菌群落结构,且呈显著正相关。土壤细菌氮代谢主要以同化和异化硝酸盐还原为主,硝酸盐还原基因(NRG)丰度是氨氧化基因(AOG)的17.5-126.9倍,表明反硝化速度快于硝化速度。NRG/AOG随梭梭种植年限增加而下降,表明梭梭生长有助于土壤氮的积累。研究结果有助于对干旱荒漠生态系统恢复过程中植物-土壤相互作用方面的理解。

Responses of soil bacterial structure and nitrogen metabolism to Haloxylon ammodendron restoration in an oasis-desert ecotone of northwestern China

Studying the changes in soil microbial community structure and nitrogen metabolism in the process of vegetation restoration is an important part for better understanding the biogeochemical processes in terrestrial ecosystems. However, there are very few reports on the functional potential of soil microorganisms after planting artificial vegetation in arid deserts. We selected Haloxylon ammodendron plantations along an age sequence (3-, 6-,11-, 19-, 28-, and 46-years) for research, sampled surface soil (0-10 cm) under the canopy, and took the moving sandy land (Ms) as the control in an oasis-desert ecotone in northwestern China. We used high-throughput sequencing to explore the responses of soil bacterial diversity, structure, nitrogen metabolism, and functional genes to the restoration of H. ammodendron, and to investigate the key driving factors of soil bacterial community structure change. The results showed that Actinobacteriota and Proteobacteria were the main dominant phyla in all plots. Shannon diversity index increased significantly with plantation ages (P < 0.05), indicating that the establishment of H. ammodendron plantations improved the soil bacterial diversity. The Chao richness indices tended to increase with the restoration of vegetation. Hierarchical clustering analysis showed that soil bacterial communities in different plantation ages were divided into three groups, and bacterial communities from the same revegetation site were grouped together. Non-metric multidimensional scaling (NMDS) analysis indicated that the establishment of H. ammodendron plantations on moving sandy land significantly changed the structure of soil bacterial communities (P < 0.01). Spearman correlation analysis showed that soil organic carbon (SOC), moisture content (SM), available phosphorus (AP), and available potassium (AK) significantly affected the structure of bacterial communities and showed a significant positive correlation (P < 0.05). Other environmental factors like electrical conductivity, total carbon, and available nitrogen had no significant effect on soil bacterial community structure. Assimilatory and dissimilatory nitrate reductions were the main parts of nitrogen metabolism. The predicted proportions of hydroxylamine oxidase (hao), reductase (hcp), and ammonia monooxygenase (amo) associated with nitrification were low, especially in the moving sandy land, with an average abundance of 8.9×10^-5%. The abundance of nitrate-reduction genes (NRG) was 17.5-126.9 times that of ammonia-oxidization genes (AOG), indicating that the reaction rate of denitrification was faster than that of nitrification. NRG/AOG decreased with plantation ages, indicating that the growth of H. ammodendron contributed to the accumulation of soil nitrogen. Our study provides an overview of soil bacterial community during the restoration of H. ammodendron and insights into the critical roles of functional genes in the nitrogen cycle. The findings might improve better understanding of plant-soil interactions in arid desert ecosystem restoration.