柑橘菌根根外菌丝释放球囊霉素相关土壤蛋白的特性及其相关功能研究

Citrus trees are mostly planted in poor soil hills and mountains. Citrus has shallow root systems with less root hair and strongly depends on mycorrhizal symbiosis associated with arbuscular mycorrhizal fungi (AMF) for taking up soil nutrient and water. Glomalin, a special glycoprotein, mainly secreted and released by AMF hyphae. In general, glomalin is hydrophobic and almost insoluble in its native status. Glomalin in soils is operationally defined as glomalin-related soil protein (GRSP), which plays important roles on soil aggregate structure and carbon pool cycling and has been one of the most hot topics among plant-fungus-soil interaction research. It is unknown the release and the related functionings of GRSP by hyphae. The present project will explore these GRSP released characteristics through extraradical mycorrhizal hyphae and related functionings of root glomalin and GRSP in citrus. An artificially constructed two-compartment or three-compartment growth rhizobox will be used to confine fungal hyphae and roots in its own compartment, in order to study the characteristics of GRSP released by extraradical mycorrhizal hyphae and hyphal bridge in situ between plants with or without their destruction, and the distributed characteristics of GRSP in the roots and rhizosphere. The present study will also clarify the effects and the functionings of both GRSP released by extraradical hyphae and exogenous GRSP treatments on soil aggregate stability and soil and/or root carbon pools. The expected results will have insights into understanding the characteristics of extraradical hyphal released GRSP and the functionings of GRSP in soil aggregate structure and soil organic carbon cycling. These results will provide theoretical and technical support for the application of GRSP in improving soil structure and fertility and management of GRSP in citrus orchards.

我国柑橘多种植在贫瘠丘陵山地，根系浅，少根毛，依赖丛枝菌根真菌（AMF）共生吸收土壤养分和水分。球囊霉素主要是由AMF菌丝释放的一种难溶于水、性质稳定的特殊糖蛋白，在土壤中亦称球囊霉素相关土壤蛋白（GRSP），对土壤团聚体结构和碳库循环具有重要作用，是植物-真菌-土壤交叉研究国际热点。目前关于菌丝释放GRSP及这种释放的功能尚不清楚。本项目以根外菌丝释放的GRSP为对象，通过盆栽及自制能分隔菌丝和根系的二室或三室生长箱，接种AMF或添加外源GRSP，探明柑橘砧木枳菌根根外菌丝原位或破坏后及株间建立的菌丝桥对GRSP释放和在根际根段间的分布特征，菌丝释放的GRSP和外源GRSP对土壤团聚体稳定性及根系和土壤碳库的效应和作用机制。预期结果能明确根外菌丝释放GRSP的特性及与菌丝着生状况的关系和在土壤团聚体结构和有机碳储存循环中的作用机制，并为橘园土壤结构改良、地力提升和GRSP管理提供依据。

球囊霉素是丛枝菌根真菌（AMF）菌丝和孢子释放的一种难溶于水、性质稳定的糖蛋白，在土壤中亦称球囊霉素相关土壤蛋白（GRSP），是植物-真菌-土壤交叉研究国际热点。本项目重点研究了柑橘常用砧木枳菌根根外菌丝释放球囊霉素的特点及其功能。首次在国际上将GRSP分成易提取球囊霉素相关土壤蛋白（EE-GRSP）和难提取球囊霉素相关土壤蛋白（DE-GRSP）。利用二室根箱，揭示DE-GRSP是一种性质顽固的球囊霉素，由EE-GRSP周转而来，而EE-GRSP是性质活跃、新生成的球囊霉素。接种AMF均不同程度提高了根室和菌丝室各GRSP成份含量，且EE-GRSP和DE-GRSP的贡献明显高于根系菌根侵染；菌丝单独存在条件下团聚体稳定性是多个因子的综合贡献，且GRSP对柑橘团聚体稳定性起主要贡献。PVC定期顺时针旋转处理成功模拟了菌根根外菌丝破坏，且这种破坏显著地抑制了EE-GRSP和T-GRSP的形成，并进一步地削弱了GRSP对团聚体稳定性的功效，最终负面影响植物生长。利用分根根箱，证明了接种室与非接种室间有潜在的根系和土壤球囊霉素的系统性特征。居于三室根箱，揭示EE-GRSP和DE-GRSP能够固持C，其中EE-GRSP固持0.775～1.370 mg C/g，占土壤碳库的6.03～10.67%，DE-GRSP固持1.243-2.304 mg C/g，占土壤碳库的12.33～18.65%。菌根真菌能够通过EE-GRSP和DE-GRSP来固持C，且能增加土壤碳库的量，但这种效应受菌根真菌种类的影响。外源EE-GRSP能够作为一种潜在的植物/土壤调节剂，促进枳实生苗的生长、改善土壤结构以及刺激土壤C的积累和相关酶活性，以1/2 EE-GRSP呈现了最好的处理效应。本研究为橘园土壤结构改良、地力提升和GRSP管理提供依据。