水稻根系形态生理对稻田甲烷排放的调控及其生理机制

Rice roots play a key role in methane emission in paddy fields. However, the regulatory effects of morphological and physiological traits of rice roots on methane emission and their physiological mechanisms have not been clearly understood. The heterotrimeric G protein is an important regulatory protein and involved in rice root growth and morphogenesis. With three G protein related mutants and their wild type rice cultivars with similar growth period as materials, the project is designed to investigate: (1) The changes of cumulative methane emission during whole growth period and dynamic characteristics of methane emission fluxes at key growth stages in paddy fields; (2) The changes of root morphology (root number, length, density, diameter, weight and aerenchyma) and physiology (the root oxidation activity, total and active absorption area, and the contents of organic acids, amino acids in root bleedings and exudates) at key growth stages and their relationships with methane production and emission in paddy fields; (3) The regulatory effects of nutrient management (including wheat straw returning to the paddy field), water management and exogenous chemicals on root morphology and physiology and methane emission. This study is expected to elucidate the physiological mechanisms of morphological and physiological traits of rice root on methane emission in paddy fields and put forward the cultivating approaches to regulating methane emission in paddy fields through the regulation of morphology and physiology of rice roots.

水稻根系是影响稻田甲烷排放的关键因素之一，但水稻根系形态生理对稻田甲烷排放的调控作用及其机理仍不十分清楚。水稻G蛋白是参与根系生长与形态建成的重要调节蛋白。本项目拟以已获得的生育期相近的3组G蛋白突变体及其野生型水稻为材料，研究：(1)全生育期及关键生育期（分蘖中期、穗分化期、抽穗期、乳熟期和成熟期）稻田甲烷排放通量和排放总量的变化规律；(2)关键生育期水稻根系形态（根数、根长、根长密度、根直径、根重、根体积和根系通气组织结构等）和生理（根系氧化力、吸收表面积、根系伤流液和分泌物中有机酸组分及浓度等）的变化特征及其与稻田甲烷排放的关系；(3)营养(含秸秆还田)、水分管理和外源化学物质对水稻根系形态生理和稻田甲烷排放的调控作用。通过上述研究，以期揭示水稻根系形态生理影响稻田甲烷排放的生理机制，提出通过调控根系形态生理调控稻田甲烷排放的栽培技术途径，为稻田甲烷减排提供理论和实践依据。

水稻根系是连接植物与土壤和土壤微生物的重要纽带，对产量形成和稻田甲烷(CH4)排放均具有重要影响。但水稻根系与土壤微生物的互作并影响稻田CH4排放的机理尚不清楚。本项目以不同水稻品种（含转基因株系）为材料，较为系统地研究了：1）参与编码G蛋白的OsRGA1基因对水稻光合产物分配和CH4排放的影响；2）不同水稻品种根系形态生理及根系与根际土壤互作影响CH4排放的机理；3）水稻品种演进对光合产物分配和稻田CH4排放的影响；4）氮肥运筹、干湿交替灌溉和脲酶/硝化抑制剂等栽培措施对CH4排放的调控。主要结果如下：1）穗分化期CH4排放差异是造成不同品种CH4排放总量差异的主要原因，水稻茎鞘非结构性碳水化合物含量/根系分泌总碳含量（NSC/TOC）是驱动CH4排放的主要因素，OsRGA1基因可以调控光合产物用于根系生长和根沉积的分配比例，减少根系分泌碳底物，提高NSC/TOC比值，有利于水稻高产低排。2）根系分泌物中苹果酸、柠檬酸和琥珀酸可提高甲烷氧化菌丰度和活性，促进CH4氧化。3）水稻品种改良提高了穗分化期光合产物向根系生长和产量形成的分配比例，有效增强穗分化期水稻根系形态与活力，促进根际土壤中CH4氧化，降低稻田CH4排放。4）适量增施穗肥可促进根系泌氧，刺激根际土壤中的CH4氧化，提高pmoA/mcrA比值，减少稻田CH4排放。尿素配施硝化抑制剂或脲酶抑制剂可显著提高水稻产量，降低CH4排放。5）干湿交替灌溉有利于提高水稻根干重和根系氧化力。干湿交替灌溉条件下施用硝化抑制剂能进一步降低CH4排放。以上研究结果表明，选用合适品种或通过栽培措施促进有利于运输至根系的光合产物用于根系生长、提高根系泌氧能力并促进根分泌有机酸进而增强根际土壤CH4氧化、有效减少稻田CH4排放。研究结果对水稻高产绿色栽培具有重要的理论和实践价值。