植物内生枫香拟茎点霉促进水稻吸收和同化氮素的机理研究

Rice cultivation needs a lot of nitrogen fertilizers, among which only a small part is absorbed by rice plants and a large part is released into the ecosystem, causing the environmental pollution. Therefore, how to use the nitrogen fertilizers efficiently is an essential agricultural problem. Our previous studies have isolated and screened an endophytic fungus Phomopsis liquidambari strain B3, having a broad host range, which can significantly promote the nitrogen uptake and accumulation in rice and then increase the grain production. However, mechanisms underlying the excellent performance of endophytic fungus Ph. liquidambari B3 are still unknown. Based on the existing results, this project proposes three hypotheses here. Firstly, this endophytic fungus can improve the phytohormone levels in planta, which will then enhance the expressions of genes related to nitrogen transportation and nitrogen metabolism and increase root number of host plants. These will benefit the plant nutrient uptake. Secondly, the inoculation of endophytic fungus will increase the root secretion of rice, which will increase the total microbial numbers and activities. The increased microorganisms in soils can absorb and fix more nitrogen. Thus, these rhizospheric microorganisms enhance the total nitrogen content in the rice-endophyte symbiotic system. Finally, endophytic fungal inoculation can promote the rice plants to secrete more oxygen to the soil, which can accelerate the transformation of ammonia to nitrates catalyzed by ammonia oxidizing bacteria and mineralization of organic nitrogen by microorganism. And these processes will benefit the nitrogen absorbability of rice. In this project, the changes of phytohormones in rice plants will be measured. And the population changes of ammonia transforming microorganisms will be confirmed by high-throughput sequencing. Moreover, the oxidation-reduction potential and key enzyme activities in rhizospheric soils will be detected as well. Base on all these experiments, the mechanisms underlying how endophytic fungus Ph. liquidambari B3 promoting nitrogen uptake and assimilation of rice can be clarified. What’s more, the use of endophytic fungi can be a new approach to reduce the nitrogen fertilizer utilizations and increase the productions in rice cultivation.

水稻生产需要施加大量氮肥，其少部分被植物吸收，大部分均释放到生态系统造成污染。寻找氮肥高效利用的方法是重要生产问题。前期研究发现，广谱植物内生真菌枫香拟茎点霉B3 菌株可以显著促进宿主水稻的氮素吸收和积累并导致增产，其机理不清楚。结合前期研究基础，提出下面假说：首先，内生真菌提高了宿主激素含量，氮素转运蛋白和代谢酶的表达量增加，同时促进了宿主生根，增加了吸收面积；其次，内生真菌接种增加了宿主根系分泌物，因此提高了土壤微生物总量，微生物吸收和固持的氮素增加，减少了流失；根际土壤固氮微生物总量和活性也提高，扩大了体系氮源总量；第三，内生真菌增加宿主泌氧能力，增加土壤氨氧化和微生物矿化有机氮能力，有利于宿主对氮素的吸收。本项目拟检测接种后水稻体内激素的变化、采用高通量测序、比较根际氧化还原电位和土壤中关键酶活性等方法，阐明内生真菌促进水稻吸收和积累氮素的机理，将为减少水稻氮肥施用提供一个新思路。

水稻生产需要施加大量氮肥，其利用效率并不高。寻找氮肥高效利用的方法是重要生产问题。前期研究发现，植物内生真菌枫香拟茎点霉B3菌株（简称B3)可以显著促进宿主水稻的氮素吸收和积累并导致增产，其机理不清楚。本项目从三个方面开展研究。研究结果表明，首先，内生真菌接种引起的宿主激素变化导致其氮素吸收的增加。B3接种改变水稻体内生长素、细胞分裂素、乙烯的含量，激素变化导致铵转运蛋白、硝酸盐转运蛋白等关键基因表达量增加及硝酸还原酶、谷氨酰胺合成酶等酶活力增加，激素浓度改变也促进水稻根的生长，这些都有利于氮素吸收。其次，内生真菌定殖改变了水稻根际土壤微生物区系。用高通量测序表明，低氮条件下，B3接种组优化了根际微生物区系，氮、磷代谢基因功能加强。B3处理早期，土壤氨氧化细菌、氨氧化古菌、固氮菌的群落丰度增加，多样性改变。B3处理组水稻根系分泌物中可溶性糖、有机酸、游离氨基酸含量均显著高于对照组。用BIOLOG分析表明，低氮条件下，B3处理组土壤的平均颜色变化率、基质丰富度、代谢多样性、土壤酶活力均大于对照组。第三，内生真菌接种促进水稻根系泌氧，增强了氮素转化与吸收。与对照组相比，B3定殖的水稻根部有更大的通气组织面积，引起根系泌氧量和根际土壤氧化还原电位提高。生长素与乙烯参与介导这个过程。B3能在缺氧条件下提高水稻叶部的光合作用和可溶性糖积累，加速根系的厌氧和有氧呼吸，水稻根部产生了更多的ATP，有利于多种矿质元素的协同吸收。并且，B3诱导更多的碳水化合物向根部积累，有利于B3在根部的定殖。B3接种也加快了秸秆降解，提高了土壤中速效氮含量。本研究为农业上减少氮肥的使用提供了新的思路。总体上按期完成了研究工作，实现预期目的。目前已经发表12篇研究论文，其中SCI论文10篇，中文期刊论文2篇，另有部分论文在整理中。申请发明专利1件。博士生1人，硕士生2人参加本项目研究并撰写相关学位论文，获得相应学位。