Driving Effect Of Warming And Fertilization On The Loss Of Gaseous Reactive Nitrogen Species In Rice And Wheat Fields

Climate warming is an indisputable reality.Studies have consistently demonstrated that it can significantly enhance the loss of gaseous active nitrogen in agro-ecosystems.Rice-wheat rotation represents an important planting method in the middle and lower reaches of the Yangtze River.It is an urgent and practical problem to reduce the loss of rice-wheat farmland gaseous active nitrogen under warming conditions.Slow-release fertilizers and organic fertilizer substitution exhibit promising potential in mitigating gaseous active nitrogen loss in rice and wheat fields,owing to their gradual nutrient release and reduced availability of nitrogen for consumption.However,current conclusions are primarily based on realistic environmental conditions,without considering the uncertainties that may arise from warming,such as its potential impact on mineralization（organic fertilizers）,release（slow and controlled-release fertilizers）,and soil nitrogen conversion.Therefore,in this study,the effects of slow-release fertilizers（SRF,100%replacement）and organic fertilizer（OF,20%replacement）replacement on gaseous active nitrogen loss in rice-wheat fields were studied under two environmental conditions:increasing temperature（T）and non-increasing temperature（N）,using an open warming platform in the field and conventional fertilization（CF）as the control.The reasons behind the changes were analyzed through an examination of soil physicochemical properties and functional microorganisms,while also assessing the effects of warming fertilization on crop yield and nutrient uptake.The primary research findings are as follows:（1）The wheat yield under warming treatment was 8.90%lower than that of the non-warming control,while the wheat yield under three fertilization treatments remained similar despite temperature variations.In contrast to the wheat yield,SRF and OF treatments exhibited consistent yields regardless of increased temperature conditions,whereas CF treatment showed a tendency towards decreased rice yield（15.28%）compared to no increased temperature control.In addition,the rice yield under SRF treatment increased by4.28%and 18.44%compared with CF treatment,respectively,while OF treatment showed similar yields to CF treatment.The nutrient content and uptake of wheat and rice were inconsistent due to dry matter accumulation at maturity.However,the replacement treatment of slow-release fertilizers was beneficial to increase the nitrogen uptake of wheat plants under warming,which increased by 29.57%compared with conventional fertilizer.In addition,both SRF and OF treatments were beneficial to increase the nitrogen uptake of rice plants under warming.The results indicate that soil fertility was not significantly affected by increasing temperature,while fertilization had a significant impact on the inorganic nitrogen content of the soil.Compared with CF treatment,SRF and OF treatment increased soil inorganic nitrogen content,and SRF treatment had the highest soil inorganic nitrogen content under the two temperature conditions.Furthermore,both SRF and OF treatments tended to increase the contents of soil organic matter,total nitrogen,available phosphorus and available potassium at the same temperature.（2）Under the same fertilization treatment,the seasonal ammonia volatilization loss in wheat fields under warming treatment was higher than that under control without warming,with an average increase of 55.39%,but the difference between SRF treatments did not reach a significant level.Furthermore,both SRF and OF treatments exhibited reduced seasonal ammonia volatilization losses compared to CF treatment at both temperatures.Notably,the SRF treatment resulted in significantly lower seasonal ammonia volatilization losses than both CF and OF treatments at both temperatures.In addition to the influence of ammonium nitrogen content in soil during the basal and overwintering fertilizer periods,ammonia volatilization loss in wheat fields is also closely related to nitrate nitrogen content during the overwintering fertilizer period and soil urease activity during the jointing-booting fertilizer period.The results also showed that warming fertilization had a significant effect on N₂O emission in wheat fields.Warming significantly promoted N₂O emission in wheat fields treated with CF and OF,which increased 40.57%（CF）and 27.47%（OF）,respectively,compared with the same fertilization treatment without warming.Under the same temperature conditions,seasonal N₂O emissions from OF and CF treatments are comparable but higher than those of SRF treatment.The difference is significant under increasing temperatures.Ammonium nitrogen content in soil at base fertilizer stage and jointing booting stage,nitrate nitrogen content in soil at overwinter fertilizer stage,urease activity in soil,copy number of nir S gene,and contents of p H,SOM and TN in soil were the main reasons for the differences in N₂O emissions.（3）Under the same fertilization treatment,the seasonal ammonia volatiles loss of rice fields under warming treatment was significantly higher than that under no warming control.The increase was approximately 39%（CF）,71%（SRF）and 37%（OF）for the three fertilization treatments,respectively.In addition,the ammonia volatilization loss of CF treatment was significantly higher than that of OF and SRF treatments at the same temperature.Moreover,the SRF treatment exhibited the lowest ammonia volatilization loss at both temperatures and was significantly lower than that of OF treatment.The concentration of ammonium nitrogen in surface water during the basal fertilizer and tillering stages,nitrate nitrogen content in soil during the tillering stage,urease activity of soil during the basal fertilizer stage,soil p H,and copy number of AOA gene were identified as key factors influencing ammonia volatilization loss in paddy fields.The results indicate that warming significantly increased N₂O emissions from organic fertilizers（OF）and chemical fertilizers（CF）treatments,but had no significant effect on the N₂O emission of SRF.Furthermore,compared to CF treatment,OF treatment has notably stimulated N₂O emission in paddy at the same temperature,with an increase of 114.70%（non-warming）and 48.84%（warming）,respectively;whereas SRF treatment has substantially reduced N₂O emission by 79.52%（non-warming）and 81.87%（warm）.The soil nitrate nitrogen content during the tiller and ear fertilizer stages,ammonium nitrogen concentration in surface water during these same stages,soil urease activity during base and ear fertilization periods,as well as soil p H and SOM contents were the main driving factors of N₂O emission difference under different treatments.The above analysis suggests that replacing slow and controlled release fertilizer and organic fertilizer can effectively maintain rice yield stability,improve nitrogen uptake and utilization under climate warming.However,this replacement cannot mitigate the potential negative impact of climate warming on wheat production.Moreover,the replacement treatment of slow and controlled release fertilizer is conducive to reducing gaseous active nitrogen loss in rice-wheat fields,while replacing with organic fertilizer only has a limited effect on ammonia volatilization loss in these fields and may increase N₂O emissions.Conversely,substituting organic fertilizers only has a limited effect on reducing ammonia volatilization losses in these fields while increasing N₂O emissions specifically within rice fields.The findings can serve as a foundation for devising strategies to mitigate the loss of gaseous active nitrogen in rice-wheat fields under climate warming,while highlighting the need to remain vigilant about the detrimental impact of climate warming on wheat yield.