Effects Of Free Air Temperature Increase On Rice Yield,Nitrogen Utilization,and Greenhouse Gases Emission From Paddy Field In Northeastern China

Northeastern is one of the most important rice production area in China,which is also one of the most significant areas affected by climate warming.Climate warming has changed the growth,dry matter accumulation and grain yield,and infulenced the absorption and utilization of nitrogen,and greenhouse gases emission from rice paddies.There are regional differences in the effect of climate warming on rice systems,and it needs to be further investigated how warming affects the yield,nitrogen utilization and greenhouse gas emissions of rice systems in Northeast China.Here,a field experiment using free air temperature increase（FATI）system was set up in Harbin,Heilongjiang Province from 2019 to 2020.By combined plot and ¹⁵N micro-area labeling experiment,we simulated anticipated warming to measure the effects of rice growth period,grain yield,nitrogen use efficiency and CH₄ and N₂O emissions.Through clarifying the important influencing factors which affect CH₄ and N₂O emissions,it can provide basis for rice sustainable production and environmental cost reduction.The main results were as follows:1)Warming shortened the total rice growth period.Under the treatment of warming,the pre-anthesis rice growth period was shortened by 6.5 days,the post-anthesis rice growth period was prolonged by 2.5 days,and the total growth period was shortened by 4.0 days.2)Warming showed a tendency to improve the photosynthetic performance of rice.The concentration transpiration rate,stomatal conductance and net photosynthetic rate of rice flag leaves had no significant difference between the treatments but indicated the increasing trend,which increased by6.1%,9.8%and 10.1%,respectively under warming treatment compared to control treatment.3)Warming increased dry matter accumulation and grain yield of rice.Warming increased the rice biomass and yield by 56.0%and 14.6%,respectively.Warming increased yield by 19.4%in 2019and 10.3%in 2020,which was mainly due to the increase of 1000-grain weight,grain number per spike and seed setting rate,while the difference is not significant（P>0.05）.4)Warming increasesed greenhouse gases emissions from paddy fields,and the main contribution is CH₄emission.Compared with control,warming increased the total CH₄emissions from rice fields by 30.3%,while only increased the total N₂O emissions by 13.4%.Warming significantly increased GHGE and GHGI by 29.1%and 14.9%,respectively.In addition,CH₄ contributed to GHGE by 96.5%.5)The ¹⁵N labelled micro-area experiment showed that warming increased significantly the total nitrogen uptake of rice increased significantly by 21.3%.The fertilizer nitrogen absorbed by rice decreased significantly by 12.5%and the nitrogen absorbed from the soil significantly increased by31.1%under warming treatment,resulting in 12.5%reduction in nitrogen recovery rate and 14.2%increase in nitrogen loss rate.In summary,climate warming shortened the growth period of rice in northeastern China,and tended to promote the accumulation of dry matter and increase yield of rice.At the same time,climate warming leads to the decrease of nitrogen use efficiency of rice,the loss of fertilizer nitrogen and the increase of greenhouse gases emissions from paddy fields,which increases the environmental cost of rice production.Under the climatic background in the future,we should give full play to the positive effect of climate warming on rice yield by selecting high-yielding cultivars,reasonably increasing population density,adjusting nitrogen application rate and optimizing nitrogen application schedule,which will be helpful for improving nitrogen use efficiency,reducing greenhouse gases emissions from paddy fields,and achieving sustainable rice production.