Effects Of Genetic Evolution On Grain Yield,Root Morphology And Physiology In Mid-season Japonica Rice And Methane Emission In Paddy Soil

Methane is one of the main greenhouse gases and it plays an important role in global warming.Paddy soil is a main source of methane emissions,thereby controlling methane emission has a crucial role to play in global climate change.Rice is a key factor affecting the methane emissions in paddy soil.However,the effect of genetic improvement(GE)of rice cultivars on methane emission has not been clearly understood.In this study,12 typical mid-season japonica rice cultivars(including super rice)applied in rice production in Jiangsu province during the last 60 years were selected and were classified into six types of 1950s,1960s,1970s,1980s,and 1990s in the 20th century and since the 2th century according to their application decades.The effects of GE on grain yield,root morphology and physiology in mid-season japonica rice and methane emission in paddy soil were investigated.The main results were as follows:1.GE significantly increased grain yield.The increase in total spikelets contributed greatly to yield increase,and the increase in total spikelets was mainly due to the increase in spikelets per panicle,especially in modern super rice cultivars.During 1950s to 1990s,filled grain rate in rice increased with GE,but it was much lower in super rice cultivars released after 2000s,and this might be the main reason limiting further yield increase for those super rice cultivars.GI also significantly increased dry matter accumulation at some key growth stages,such as booting stage,heading and maturity.2.GE gradually increased root dry weight,root shoot ratio,root length,root number,root diameter,root bleeding sap,root oxidation activity,total absorbing surface area and active absorbing surface area in mid-season japonica rice.The concentrations of malic acid,succinic acid and acetic acid exuded from roots increased significantly,while those of tartaric acid and citric acid decreased significantly,with GI at booting and heading stages.GE improved root morphology and physiology of mid-season japonica rice.3.Similar trends of methane emission fluxes were found among different rice types during whole growth period.There were two emission peaks,one was 15 d after transplanting,and the other was from booting to heading stage.GE significantly decreased total methane emission amount during whole growth period,and it also decreased global warming potential(GWP)of methane and GWP per unit grain production.During early growth period,there were no significant differences in methane emission fluxes among rice types,and GI significantly decreased methane emission fluxes during mid and late growth period in rice.4.Total methane emission amount significantly and negatively correlated and grain yield and biomass at maturity.Root morphology(dry weight,root length,root number),root physiology(root oxidation activity,active absorbing surface area and root bleeding sap)and the concentrations of organic acids exuded from root(malic acid,succinic acid,acetic acid,citric acid and tartaric acid)at booting and heading stages had close relationships with total methane emission amount and methane emission fluxes at the corresponding stages.5.Significant effects of N amount on total methane emission amount and methane emission fluxes were observed in paddy soil,and they varied with rice cultivars.It might be that N amount affected root morphology(dry weight,root length,root number),root oxidation activity and the concentrations of organic acids exuded from root and then further affected grain yield and methane emission in rice.