Study Of Nutrients Transformation And Uptake Affected By Drying-rewetting In Soil-plant System

The change of precipitation and the improvement of irrigation lead to a more complex drying-rewetting process in soil,but the effects of different drying-rewetting patterns on nutrient availability have not been well investigated.In addition,there are few studies about nutrient dynamic change,transformation,and use efficiency during the drying-rewetting process.In this study,we set four drying-rewetting intensities（rewetting to 60%,45%,30%WHC respectively and a constantly moist control in60%WHC）and seven frequencies（soil experienced 0,1,2,3,4,6 and 8 drying-rewetting cycles,respectively）and explore the effects of different drying-rewetting patterns on soil nutrient availability.A pot experiment was set with two soil（grass,farm）,two plants（Alfalfa,Ryegrass）and two moist（drying-rewettting,constant moist）,and the dynamic changes of soil nutrients and plant growth and nutrient,nutrient conversion and use efficiency were investigated during the drying-rewetting process.The main conclusions were as follows:（1）The soil DOC consumption was promoted by drying-rewetting;and the drying-rewetting intensity had no significant effect on soil DOC consumption,while high frequency drying-rewetting promoted soil DOC consumption.Drying-rewetting promoted the consumption of NH₄⁺and the generation of NO₃^-.Mild drying-rewetting promoted the generation of NO₃^-,while severe drying-rewetting was more conducive to the stability of NH₄⁺.With the increase of drying-rewetting frequency,soil NO₃^-increased and NH₄⁺decreased gradually.Soil had a certain buffer effect on available P under drying-rewetting,and the variation range of available P was less than 20%under different drying-rewetting patterns.Available K was not affected by the drying-rewetting intensity,but decreased with the increase of drying-rewetting frequency.（2）The consumption rates of SOC and DOC in drying period were lower than those in rewetting period,and the drying-rewetting had no effect on SOC and DOC pool.The priming effect of rhizosphere on the decomposition of SOC and DOC was greater than the supplement effect of root exudates.The consumption rate of TN under drying period was lower than that in rewetting period in rhizosphere soil.The contents of NH₄⁺and NO₃^-increased in drying period while decreased in rewetting period,but NH₄⁺decreased and NO₃^-increased after drying-rewetting in rhizosphere soil.The consumption rates of TP in drying period were lower than rewetting phase in rhizosphere soil,but the consumption of TP decreased after drying-rewetting.Available P reduced in drying period and increased in rewetting period,but decline after drying-rewetting,available P in ryegrass rhizosphere was lower than alfalfa.The consumption rate of TK in drying period was lower than that in rewetting period,but reduced after drying-rewetting process.Available K increased in drying period and decreased in rewetting period,and the decrease of available K in rhizosphere soil during drying-rewetting was lower than that in constant moist.（3）The shoot height growth rate was lower in drying period than that in rewetting period,and plant shoot appeared a rapid growth phenomenon after rewetting,but the shoot height was lower in drying-rewetting than that in constantly moist treatment.The root length growth rate increased in drying period and decreased in rewetting period,the root length of alfalfa after drying-rewetting was the same as constantly moist treatment,while the root length of ryegrass in drying-rewetting was higher than constantly moist treatment.The aboveground and underground biomass of plants under drying-rewetting were lower than that under constant moist treatment.Plants could regulate the distribution of C,N and P under drying-rewetting:the C,N and P contents in root were higher than those in shoot during drying period;while the contents of N and P in shoot were higher than those in root after rewetting.Plants had no regulation effect on K distribution under drying-rewetting,and both the shoot and root K content in drying-rewetting were lower than that in constant moist treatment.（4）The reserves of plant C,P and K under drying-rewetting were all lower than those in the constant moist treatment;however,there was no significant difference in alfalfa nitrogen reserves between drying-rewetting and constant moist treatment.There was a strong correlation between nutrients uptake by plants and the decline in soil nutrients.The efficiency of nutrient transformation between soil and plant was reduced by drying-rewetting.The plant nutrients use efficiency of P and K was improved by drying-rewetting;however,the drying-rewetting had no significant effect on the use efficiency of N.