环境因子对花生根瘤菌遗传多样性和分布的影响机制研究

It is important to study the relationship between peanut rhizobium biodiversity and environmental factors for it could have significace to improve the symbiotic nitrogen fixation ability of peanut – rhizobium symbiotic system. Most study for peanut rhizobium diversity focused on isolate peanut rhizobium from different sampling sites and different peanut cultivars, their work enriched the rhizobium diversity and facilitated studying the peanut rhizobium characteristics. However environment factors and peanut cultivar affection limited our understanding to the relationship of peanut rhizobium diversity and richness distributed in soil and nodules. In this study our study focuses on compare the rhizobium diversity isolated from the same peanut cultivar and the rhizobium of soil samples and thus could reveal the objective function of environmental factors. We have collected the soil samples, nodules and isolated the rhizobium from peanut nodules from 19 sampling sites which environmental factors are different, and the primary phylogenetic relationships for part of rhizobium have been analyzed in our previous study. Next, we will determine the accurate taxonomy positioin for all the rhizobia isolated in this study through multilocus sequence analysis of three housekepping genes. And the species composition and richness of all the rhizobium species distributed in soil samples and the peanut rhizosphere soils will be uncovered through culture-independent methods. Finally we will reveal the concret affection mechanism of environmental factors through its affection on the rhizobium biogeographical distributioin, competitive nodulation abilities and so on. Thus this study will put forward scientific proof for the selection of peanut rhizobium adjust different environmental factors and improve the competitiveness nodulatioin abilities for peanut rhizobium used in agronomy.

研究花生根瘤菌遗传多样性与环境因子关系对充分发挥花生共生固氮作用有重要意义。之前工作对不同地域、不同品种花生根瘤菌的分离鉴定，丰富了其多样性，为了解不同花生根瘤菌特点打下基础，然而环境因素和宿主的双重选择性，限制了对花生根瘤菌多样性及丰度和土壤中实际丰度相关性的客观认识。本研究针对同一花生品种，结合根瘤菌分离和样点土壤中根瘤菌多样性分析，对客观揭示环境因子作用机制具有重要意义。前期研究完成了对环境条件差异较大的19个样点根瘤及土壤样品采集、根瘤菌分离及部分菌株的初步系统进化分析。后续实验拟采用持家基因多位点分析方法确定这些菌的具体分类地位，用未培养研究方法分析样点土壤、花生根际土壤中根瘤菌物种组成及丰度。最终从环境因子对根瘤菌生物地理分布、竞争结瘤能力等方面深度揭示环境因子的具体作用机制。这一研究将为生产上适应不同环境花生根瘤菌的选育和提高花生根瘤菌竞争结瘤能力提供科学依据。

当前对花生根瘤菌多样性的研究一般基于对不同地域、不同品种花生根瘤菌的分离鉴定，而环境和宿主的双重选择，限制了对花生根瘤菌多样性与环境因子关系的客观认识。因此，本研究主要针对两个花生品种，结合根瘤菌分离和样点土壤中根瘤菌多样性分析，客观揭示了环境因子作用机制。（1）针对两个花生品种，从全国21个样点采集根瘤、分离保藏根瘤菌1500余株，发现中国花生根瘤菌多样性异常丰富，分布于40个种，其中有28个潜在新种群，新种群数量占比70%，其中本研究首次发现的花生根瘤菌分布于16个种群，极大丰富了花生根瘤菌种质资源。（2）对花生根瘤菌的物种分布与环境因子相关性分析表明，AP、pH是影响花生根瘤菌分布的主要土壤因子，最暖季降水量、湿季平均温度、年降水量是影响其分布的主要气候因子。（3）对花生品种与根瘤菌物种进行相关性分析表明，花生品种对根瘤菌的选择性不显著。样点花生根瘤菌物种组成主要受环境因子影响，花生根瘤菌剂的推广主要考虑其对环境因子的适应性。（4）基于rpoB高通量测序定种分析的免培养研究表明，花生根际土壤中优势慢生根瘤菌的OTU（>1%）中仅有1个被分离得到，表明可能存在大量在土壤中占优势的花生根瘤菌新种质资源。（5）通过实验分析表明，环境因子不仅影响根瘤菌在土壤中的丰度及存活率造成其在自然环境中的生物地理学分布，还影响到根瘤菌的竞争结瘤能力，导致根瘤内根瘤菌的多样性及丰度差异。本研究评价了环境因子对根瘤菌的影响机制，揭示了不同区域的优势花生根瘤菌物种组成及丰度，为高效根瘤菌的筛选和应用范围具有指导意义。