人工固沙植被凋落物对土壤微生物群落组成及代谢多样性影响

With the succession of artificial plantation in the semi-arid regions of China, increases in diversity and productivity of plant community have promoted the restoration of sandy soil ecosystem. The structure and function of soil microbial community can be affected by the plant litters during this process. The changes in soil microbial community will in turn influence the diversity and productivity of plant community via microbe-mediated feedback. Nevertheless, the mechanisms of micro-mediated plant-soil feedback during the artificial plantation succession have not been well understood to date. With the aim of revealing the alterations in soil microbial composition and catabolic diversities during different successional stages of the artificial plantation and the feedback of such alterations to the artificial plantation, active sand-dunes (control), stable sand-dunes with 13-year-old and 30-year-old artificial Caragana microphylla shrubs and natural C. microphylla shrubs in Horqin sandy land will be studied. Soil samples and plant litters will be collected under the canopies of C. microphylla. The genetic and catabolic diversities of soil microbial communities will be determined by using 454 pyrosequencing technique and MicroResp plates, respectively. By analyzing the changes in the quality and quantity of plant litters and soil organic carbon fraction during different successional stages of the artificial plantation, the direct and/or indirect influences of alterations in plant litter quality and quantity resulting from the changes in composition of the artificial plantation on soil microbial diversities will be illuminated. As a useful biotic index of soil quality, the variations in the genetic and catabolic diversities of soil microbial communities will reflect the restoration phase of sand-dune ecosystem following the artificial plantation establishment. In addition, this study will help us to better understand the mechanism of microbe-mediated plant-soil feedback, and further provide theoretic evidence for promoting the stability of sandy soil ecosystem.

随着人工固沙植被的演替，物种多样性和生产力提高，促进了沙地土壤生态的恢复。此过程中，人工植被能通过凋落物影响土壤微生物群落的结构和功能。土壤微生物的变化能通过对植物的反馈影响植物群落多样性和生产力。然而目前人工植被演替过程中土壤微生物参与的"土壤-植物反馈"机制尚不清楚。本研究以科尔沁沙地流动沙丘（对照）、种植13和30年的小叶锦鸡儿人工固沙植被与天然小叶锦鸡儿植被为对象，采用高通量测序和MicroResp板技术分别测定人工植被演替前期和后期土壤微生物群落的遗传和代谢多样性，揭示不同演替阶段人工固沙植被冠层下土壤微生物群落变化；结合分析不同演替阶段凋落物质量及土壤有机碳组分的差异，阐明人工植被通过凋落物对土壤微生物群落多样性的直接和/或间接影响。本研究拟通过土壤微生物多样性反映人工植被对沙丘土壤生态系统的恢复水平，为探明土壤微生物对人工植被的反馈机制、提高沙丘土壤生态系统稳定性提供理论依据

本项目在内蒙古科尔沁沙地选取种植12年（代表演替前期）和30年（代表演替后期）的小叶锦鸡儿人工林为对象，研究我国北方半干旱沙化地区人工固沙林定植后凋落物质和量随恢复年限增长的变化特征及其对土壤有机碳组分、土壤微生物群落组成和代谢多样性的影响。结果显示：.1、小叶锦鸡儿灌丛下凋落物的质和量在不同演替阶段表现出显著差异。演替后期凋落物的生物量、木质素含量、碳氮比和碳磷比均显著高于演替前期，而含氮量和含磷量则表现出相反趋势。凋落物中（半）纤维素含量在不同演替阶段没有显著变化。.2、土壤总有机碳含量随小叶锦鸡儿种植年限的增长而显著增高，其中热水溶有机碳占土壤总有机碳的比重表现出相似趋势。与演替前期相比，冷水溶有机碳占土壤总有机碳的比重在演替后期下降了50-67%。.3、土壤微生物群落在丰度、组成和代谢功能等三个方面在演替后期发生明显变化。土壤细菌的运算分类单位（OTU）在小叶锦鸡儿不同演替阶段没有显著差异；演替后期土壤真菌的OTU比演替前期高出一倍。不同演替阶段土壤微生物群落的相对丰度在门水平上没有显著差异，但α-变形菌纲中Sphingomonas、Balneimonas、Phenylobacterium和Novosphingobium，放线菌门中Mycobacterium和Pseudonocardia，担子菌门中Geastrum和接合菌门中Mortierella的相对丰度都随着种植年限的增长不断增高，而β-变形菌纲则表现出相反的趋势。主成分分析和冗余分析表明，演替前期土壤微生物群落代谢糖类和氨基酸类碳源的能力较强，演替后期土壤微生物群落偏好代谢芳香酸类和有机酸类碳源，这与易分解有机碳或较难分解有机碳分别占土壤总有机碳的比重在不同演替阶段的变化有关。.本研究初步揭示了科尔沁沙地人工固沙林演替过程中凋落物质和量、土壤有机碳及其组分和土壤微生物群落组成和代谢功能间的内在关系，为深入研究我国北方半干旱沙化地区植被恢复过程中植被演替和土壤微生物群落的相互作用奠定了基础。同时，对于不同演替阶段凋落物质量和土壤养分有效性的分析反映了演替后期植物必需养分的匮乏，为研究和制定半干旱地区人工固沙林长期经营管理策略中的养分管理方案提供了理论依据。