“蚯蚓-菌根-玉米”微生态系统对盐碱地氮磷循环的驱动机理

Earthworms, as ecosystem engineering, can improve soil physical and chemical properties. Arbuscular mycorrhizal(AM) fungi can significantly alleviate salt stress in plants. In the present work, the micro-ecosystem made up of earthworm, AM fungi and maize was designed to improve soil physical, chemical and biological properties in the saline and alkaline soil. The interaction between earthworm and mycorrhiza on soil structure improvement, which could drive the nitrogen and phosphorus cycling in the saline and alkaline soil will be studied from these three sections: (1) the interactive effect of earthworm and AM fungi on soil structure, which could improve the salt tolerance of maize root, will be determined by testing soil water, soil structures and root biochemical changes. (2) The interaction between earthworm and AM fungi on soil nitrogen and phosphorus cycling will be studied by determining of its origin using stable isotopes (15N and 33P ). RT-PCR method will be used to determine the express of NH4+ transporter、NO3- transporter and P transporter gene maize root, which can explain the interactive effect of earthworm and AM fungi on maize root and shoot N, P content in the saline and alkaline soil. (3) 454 sequencing method will be used to determine the interactive effect of earthworm and AM fungi on the regulation of soil microorganisms, which can drive the nitrogen and phosphorus cycling in the saline and alkaline soil and increase the nitrogen, phosphorus content in maize shoot and root. All these results will gives useful benchmark information for describing the saline and alkaline soil evolution rule and the ecological function of soil biota.

本研究利用蚯蚓改良土壤理化性质和菌根提高植物耐盐的特性，构建了用于盐碱地改良的“蚯蚓-菌根-玉米”微生态系统，并研究其原位接种改良盐碱地土壤结构，进而驱动氮磷矿化和转运的生态过程，具体如下：（1）通过测定土壤结构、土壤水分及根系生理指标，揭示蚯蚓菌根互作改良盐碱土壤结构，提高根系耐盐性的生理机制；（2）通过15N和33P同位素标记法，及测定根系NH4+ transporter、NO3- transporter和P transporter基因定量表达，揭示蚯蚓菌根互作对盐碱地土壤氮磷矿化及玉米吸收氮磷的影响；（3）通过测定土壤理化特性和根系生理指标，结合454高通量测序等方法揭示田间原位接种“蚯蚓-菌根-玉米”微生态系统调控盐碱地土著微生物群落，进而促进土壤氮磷矿化和玉米吸收氮磷的生态过程。研究结果对于揭示盐碱地土壤演变规律和土壤生物的生态功能具有重要意义。

本研究利用蚯蚓改良土壤理化性质和菌根提高植物耐盐的特性，构建了用于盐碱地改良的“蚯蚓-菌根-植物”微生态系统，同时研究了其原位接种驱动盐碱地土壤改良和氮磷循环的作用机制，研究结果对于揭示盐碱地土壤演变规律和土壤生物的生态功能具有重要意义。本项目的主要结果如下：（1）中度和重度盐碱土条件下玉米生长显著受到抑制。在轻度盐碱地中，玉米通过促进P、K、Mg、Cu、B和Mn等养分吸收，进而增加玉米生物量。中盐度和重盐度条件下，土壤含盐量、Na吸附比和地上部Na含量增加，显著减少玉米K、P、N、Ca、Mg、Cu和Mn等养分吸收从而抑制玉米生长；（2）重度盐碱胁迫下，蚯蚓和AM真菌可以协同改良盐碱土物理结构，提高玉米生理盐适应性，促进玉米生长。蚯蚓和AM真菌协同降低土壤含盐量、增加土壤大团聚体比例和渗透调节能力，从而提高玉米养分吸收和光合作用，促进高盐碱胁迫下玉米生长；（3）蚯蚓和AM真菌在菌丝际可以协同提高盐碱土氮素有效性从而促进玉米氮吸收。蚯蚓和AM真菌菌丝可以改善土壤物理结构和调控土壤氮功能微生物如固氮菌(nifH)，氨氧化细菌(AOB amoA)和反硝化细菌(nirS，nirK和nosZ)，促进盐碱土氮素的转化；（4）蚯蚓产生的蚯蚓粪通过调控与氮循环有关的微生物促进15N标记的秸秆矿化分解从而提高盐碱土壤氮素有效性，并通过促进玉米根系中高亲和硝酸根转运蛋白基因的表达，促进玉米根系吸收15N-NO3-。蚯蚓粪还可以通过提高有机质含量并调控土壤真菌群落结构重塑土壤大团聚体微观结构，进而通过改善根际微环境(例如降低土壤含盐量和pH，改善团聚体微结构及提高氮养分有效性)调控玉米根系ABA介导的MAPK信号转导途径以及与三羧酸循环有关的代谢物等增加玉米根系耐盐性，最终影响玉米地上部与光合作用、氨基酸代谢和ABA合成有关的通路途径，并通过调控激素信号转导途径促进叶片气孔关闭和通过激活MAPK信号转导途径提高玉米对非生物胁迫的抗性。