The Effect Of Alternate Wetting And Drying Irrigation On Nitrogen Absorption Of Rice And Soil Nitrogen Transformation

Nitrogen(N)is the most important nutrient element for crops,and its transformation process in soil is affected by N absorption of crops and soil physicochemical properties deeply.Alternate wetting and drying irrigation is one of the important water-saving measures of rice,which will have a significant impact on rice growth and soil environment.Both of crops N uptake and soil N transformation will be affected significantly by alternative wetting and drying irrigation,but there are few studies to combine both.In this study,a culture experiment by root-box was established to explore the relationship between N absorption of rice and N transformation of soil under alternative wetting and drying irrigation.The experiment included two water managements:Alternate wetting and drying irrigation(AF)and Conventional Flooding(CF).Under two treatments,to analyse:1)The variation characteristics of N accumulation,yield,leaf photosynthesis and root of rice;2)The differences of nitrification potential(NP),denitrification capacity(DC),abundance of nitrifiers(AOA and AOB),abundance of denitrifiers(nirK and nirS-type)and community structure ofdenitrifiers in rhizosphere and non-rhizosphere of surface(0～10 cm),middle(10～20 cm)and bottom(20～30 cm)soil layers,and attempted to correlate the soil N transformation and rice N uptake.The main results and conclusions are as follows:(1)The growth of rice was affected significantly by water management.Compared with CF treatment,the yield,N accumulation,photosynthesis characteristics,root characteristics,effective panicle and 1000-grain weight of rice was decreased significantly under AF treatment.The yield and nitrogen accumulation of rice was reduced by AF treatment through reducing the root absorptive capacity,effective panicle and net photosynthetic rate of rice.(2)The NP in rhizosphere was lower than that in non-rhizosphere which was inhibited significantly by rice roots.The large absorption of NH4+ by rice roots was the main reason that the NP in rhizosphere was inhibited by roots.The results of correlation analysis showed that nitrogen accumulation of rice was negatively correlated with NP in rhizosphere of all soil layers.The inhibition of roots on NP in rhizosphere was decreased by AF treatment through reducing nitrogen accumulation and absorption of NH4+ of rice.(3)The abundance of AOA in rhizosphere of surface and middle soil layer was significantly higher than that in non-rhizosphere,and it was more sensitive to roots than AOB.The growth of AOA could be stimulated by roots,but the correlation between the abundance of AOA and NP in rhizosphere was not strong.The abundance of AOB was was significantly correlated with NP in non-rhizosphere(0.482,P<0.01),it was the main driver of NP in non-rhizosphere.The NP in non-rhizosphere was affected significantly by AF treatment through affecting the abundance of AOB.(4)Under CF treatment,the DC in rhizosphere was lower than that of non-rhizosphere at jointing stage,but higher at flowering stage.The DC in rhizosphere was inhibited by rice roots at jointing stage,but promoted at flowering stage.The DC in rhizosphere of AF treatment was higher than that of CF treatment at jointing stage,but lower than that of CF treatment at flowering stage.Therefore,the inhibition or promotion of rice roots on DC in rhizosphere was slowed down under AF treatment,which was related to the effect of AF treatment on nitrogen uptake and root growth of rice plants,and the difference in abundance and community structure of denitrifiers.(5)The abundance of nirS-denitrifiers was more sensitive to roots than that of nirK-denitrifiers,and its growth was stimulated by roots.The abundance of nirK-denitrifiers was more sensitive to water management than that of nirS-denitrifiers,and its growth was limited under AF treatment.The results of RDA have showed that the community structure of nirK-denitrifiers was significantly different between rhizosphere and non-rhizosphere.The results of PERMANOVA have showed that water management could explain the variations of nirS-denitrifiers community structure significantly in surface and bottom soil layers(14.37%,3.86%).The difference in abundance and structure of nirK-,nirS-denitrifiers between rhizosphere and non-rhizosphere was one of the main factors which have caused the difference response of DC to water management.In conclusion,compared with CF treatment,the nitrogen uptake of rice was reduced under AF treatment.In addition to affecting the morphology,photosynthesis and nitrogen uptake of plant,AF treatment has also weakened the inhibition of roots on NP and DC in rhizosphere at jointing stage which increased nitrogen loss.Therefore,we should pay attention not only to the stress of water on rice under AF treatment,but also to the regulation of nitrification and denitrification in rhizosphere to reduce soil N loss.