Effects of acidification on nitrogen allocation in rice-soil system and N2O emission
Soil acidification is a significant factor constraining rice production in China.Severe soil acidification can lead to imbalance in crop-soil nitrogen(N)transformation,which reduces rice yields and increases environmental risks.However,there is a lack of systematic research related to the impact of soil acidification on N transformation,allocation,and N losses in rice-soil systems.In this study,rice-soil systems with four soil acidity treatments were investigated:neutral(pH 7,CK),weakly acidic(pH 6,T1),moderately acidic(pH 5,T2),and strongly acidic(pH 4,T3).Differences in rice yield,N accumulation,N metabolic enzyme activities,N use efficiency,N balance,and nitrous oxide(N2O)emissions were compared.With increasing soil acidity,N accumulation,utilization efficiency,and yield of rice plants displayed trends of increase followed by decrease.Correlation analysis indicated that N accumulation at the jointing stage was significantly positively correlated with the activities of nitrate reductase(NR),glutamine synthetase(GS),glutamate synthetase(GOGAT),and glutamate dehydrogenase(GDH)in leaves,as well as GS and GOGAT activities in stems.Similarly,N accumulation at the flowering stage was significantly positively correlated with NR,GS,GOGAT,and GDH activities in panicles compared to the CK treatment.N2O cumulative emissions in the T1,T2,and T3 treatment groups were reduced by 20.3%,58.0%,and 76.7%,respectively.The N2O emissions per unit yield exhibited a decreasing trend followed by an increase.N balance analysis showed that,compared with CK,the apparent loss of N in the T2 and T3 treatments was reduced by 15.8%and 21.1%,respectively;rice N uptake was reduced by 1.5%and 15.3%,respectively;soil inorganic N residue was increased by 41.2%and 88.2%,and the N surplus rate was increased by 2.2 and 7.1 percentage points,respectively.When soil acidification develops to moderately and strongly acidity levels,it could reduce N accumulation,utilization efficiency,and yield by inhibiting N metabolism processes in the stem and leaves at the nodulation stage,and in the panicles at the flowering stage,respectively.Soil acidification reduced cumulative N2O emissions and N2O emission per unit yield.In addition,moderately and strongly acidity level soils raised environmental risks by reducing rice N uptake and increasing pre-planting soil inorganic N content,leading to higher soil inorganic N residue and N surplus rates.
soil acidificationriceN use efficiencyyieldN2Osoil N balance
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