Soil Nitrogen Cycling Rates In Poyang Lake Wetland Soil Under Different Drought Conditions

The availability of nitrogen is a key factor limiting the primary productivity of terrestrial ecosystems.Since the ¹⁵N isotope dilution method has been proposed,it has become the only effective method for analyzing soil nitrogen cycling rates,and has been widely used to calculate soil nitrogen cycling rates.Based on published literature data on the determination of soil nitrogen cycling rate in China using ¹⁵N isotope dilution method,it has been found that many studies focused on forest,grassland and farmland soils;and the impact factors of soil nitrogen cycling rate include pH,TN,TC,C/N,NH₄⁺-N and NO₃^--N.There are few studies research on the effects of nitrogen cycling rate on wetland soils.Poyang Lake wetland is an important freshwater wetland system in China,but extreme droughts in the Poyang Lake area have occurred frequently in recent years,and the annual drought duration has gradually increased.Carrying out“the soil nitrogen cycling rates under different drought conditions and its influencing factors”can provide a scientific basis for the comprehensive management of Poyang Lake wetland.In this paper,based on the sampling of surface soil?0²0 cm?in the typical vegetation of Poyang Lake wetland?Phragmites,Carex and Phalaris?,and simulates severe drought?30%WHC?maximum water holding capacity??,moderate drought?50%WHC?and optimum water?80%WHC?by indoor water control experiment.The soil nitrogen cycling rate was calculated by pairing ¹⁵NH₄NO₃?NH₄¹⁵NO₃,and analyze the difference of soil drought conditions and explore the influencing factors.The results show that:?1?There were significant differences in soil nitrogen cycling rates under different vegetation types.The overall trend of soil nitrogen cycling rate in the three vegetation belts was:Phragmites>Carex>Phalaris,showing a trend of accelerating along the lake to the slope.Soil nitrogen cycling rate,including soil gross mineralization rate,gross nitrification rate,NH₄⁺fixed rate and NO₃^-fixed rate in the Phalaris(1.15 mg N kg^-1d^-1?1.27mg N kg^-1d^-1?0.24 mg N kg^-1d^-1?0.79 mg N kg^-1d^-1)and Carex(3.45 mg N kg^-1d^-1?1.88 mg N kg^-1d^-1?2.62 mg N kg^-1d^-1?3.11 mg N kg^-1d^-1)the difference was not significant,but both were significantly lower than the Phragmites(18.266 mg N kg^-1d^-1?4.275 mg N kg^-1d^-1?13.65 mg N kg^-1d^-1?5.24 mg N kg^-1d^-1).?2?Soil nitrogen cycling rates were significantly different under different drought conditions.Soil nitrogen cycling rate,including soil gross mineralization rate,gross nitrification rate,NH₄⁺fixed rate and NO₃^-fixed rate in the 30%WHC(3.90 mg N kg^-1d^-1?1.26 mg N kg^-1d^-1?3.70 mg N kg^-1d^-1?0.46 mg N kg^-1d^-1)and 50%WHC(5.81mg N kg^-1d^-1?1.15 mg N kg^-1d^-1?4.73 mg N kg^-1d^-1?0.73 mg N kg^-1d^-1),the difference was not significant,but both were significantly lower than 80%WHC(13.16 mg N kg^-1d^-1?5.01mg N kg^-1d^-1?8.08 mg N kg^-1d^-1?7.95 mg N kg^-1d^-1).?3?In soil physicochemical properties,oil moisture,NH₄⁺,vegetation type,soil C/N,and NO₃^-were the influencing factors of soil nitrogen cycle rates in Poyang Lake Wetland,and soil moisture?p=0.008?is the main influence factor of nitrogen cycling rate.There was no significant difference in soil AOA abundance and gross nitrification rate.Soil AOB abundance was positively correlated with gross nitrification rate,indicating that AOB played a major role in the soil nitrification rate of Poyang Lake wetland.