土壤盐胁迫下植物对同种幼苗的“庇护”及根际作用机理

Whether seedling could successfully establish in a stressful environment is crucial for plant population dynamics due to its higher vulnerability to environmental constraints. Although it is well documented that adult plants can facilitate their neighboring seedlings via canopy shading or micro-climate amelioration or herbivore removal under stressful conditions, how rhizosphere of adult plants play a role in affecting the establishment of their conspecific seedlings is poorly understood. .The overall goal of this grant project is to examine whether and how adult plants affect their conspecific seedlings via rhizosphere connection under soil salt stress environment. The central hypotheses of this project are: (1) adult plants may enrich soil organic matter, nutrient elements (e.g. nitrogen and phosphors), and soil microbes (e.g . soil arbuscular mycorrhizal fungi) around their rhizosphere forming a “resource-island”, and their neighboring conpspecific seedlings may share this “resource-island”; (2) adult plants may promote their conspecific seedlings to develop arbuscular mycorrhizal symbiosis by providing AMF “inoculum”, and may share nutrients through mycorrhizal network. Specific objectives of this project are: (1) to characterize the rhizosphere soil of adult plants and to investigate the enrichment of soil organic carbon and nutrients and soil microbes in the rhizosphere along a salinity gradient; (2) to quantify the neighbor effects of adult plants on their conspecific seedlings via rhizosphere by establishing “neighbor effect experiment” along the salinity gradient, and by conducting a common garden experiment in greenhouse; (3) to test how rhizospheric factors mediates the effects of adult plants on their conspecific seedlings, and whether arbuscular mycorrhizal fungi play a role in these effects by using root compartment facility and stable isotope tracing. .The significance of this project is, for the first time, that demonstrates the roles of rhizosphere of adult plants in nursing their conspecific seeedlings under soil salt stress, and the contribution of arbuscular mycorrhizal fungi. Understanding how adult plants facilitate their conspecific seedlings through rhizosphere could be an important mechanism that leads to re-establish a plant population under degraded stress environments.

幼苗能否成功定植是胁迫环境中植物种群建立和维持的关键环节。研究表明,胁迫环境下成体植物对同种幼苗的定植有重要促进作用，对其解释目前主要围绕冠层效应（如遮阴、改善小气候、驱赶害虫等）开展，而根际效应有待揭示。本项目拟研究“土壤盐胁迫下成体植物是否及如何通过根际‘资源岛’促进同种幼苗的成长”。项目计划（1）沿土壤盐分梯度建立样地，研究成体植物根际“资源岛”的特点；（2）沿盐分梯度建立成体植物-幼苗邻体实验，研究成体邻体植物整体（包括地上部分和地下部分）、根际（通过冠外拽消除冠层效应）和无成体邻体植物三种情况下同种幼苗的生长，分析成体植物是否通过根际“资源岛”效应来“庇护”同种幼苗；(3) 通过根际隔离和稳定性同位素示踪实验，剖析成体植物根际因子对同种幼苗的影响。结果将揭示成体植物根际对幼苗“庇护”的根际机理及丛枝菌根的作用，对加深认识植物种内相互作用机制和指导胁迫环境下种群的建立都有重要意义。

幼苗能否成功定植是胁迫环境中植物种群建立和维持的重要环节。研究表明胁迫环境下成体植物对同种幼苗的建立有重要促进作用，对其解释目前主要围绕冠层效应（如遮阴、改善小气候、驱赶害虫等）开展，而根际效应有待揭示。本项目围绕土壤盐胁迫下成体植物是否和如何通过根际“资源岛”效应“庇护”同种幼苗的成长这一科学问题，开展了以下研究：（1）沿土壤盐分梯度建立样地，研究成体植物根际“资源岛”的特点；（2）沿盐分梯度建立成体植物-幼苗邻体实验，研究成体邻体植物整体（包括地上部分和地上部分）、根际（通过冠外拽消除冠层效应）和无成体邻体植物三种情况下同种幼苗的生长，分析成体植物是否通过根际“资源岛”效应来“庇护”同种幼苗；(3) 通过根际隔离和同位素示踪实验，剖析成体植物根际因子对同种幼苗的影响。经4年研究，完成了项目计划的研究内容和目标, 重要研究进展如下：（1）发现土壤盐胁迫下成体植物根际对同种幼苗具有“呵护”效应，与幼苗单种群相比，成体植物-幼苗共存系统中，幼苗的成活率和生长显著得到促进；而且成体植物对的幼苗这种“呵护”效应，根际效应显著大于冠层效应。（2）阐明成体植物通过逐渐形成的“资源岛”和“生物岛”是其对邻近同种幼苗产生抚育效应的重要原因，与裸地相比成体植物的根际盐分含量下降，土壤有机物含量和土壤微生物丰富度增加，丛枝菌根（AM）真菌繁殖体（如孢子密度）增加；成体植物根际土壤显著提高幼苗成活率和AM共生体的形成。（3）揭示出土壤盐胁迫下成体植物通过AM菌丝网络“呵护”同种幼苗。分子生物学证明成体植物和幼苗的AM真菌群落相似，稳定性同位素证明成体植物与幼苗根际之间形成菌丝网络（CMN），成体植物根际积累的养分（如氮素）可通过CMN被幼苗利用，从而促进幼苗生长。邻体实验表明，在有菌丝网络CMN连接的成体植物-幼苗体系，随着盐分胁迫增强，RII由负值转变为正值（竞争转为互惠）。