Effects Of Nitrogen Addition And Litter Increase Or Decrease To Moist Evergreen Broad-leaved Forest Soil Respiration And Soil Carbon And Nitrogen

The generally increasing atmospheric deposition of N in the world can continuously affect the growth of forest vegetation,which in turn leads to an increase or decrease in the amount of forest litter.Litter is an important source of soil C,and changes in the input of fresh litter can have a strong effect on the decomposition and transformation process of the original C of the soil,namely the priming effect.Therefore,the effect of N deposition on the C cycle of forests has a direct effect?impact of N increase on soil C?and indirect effect?change of soil C caused by changes in litter input?.In this study,the wet evergreen broad-leaved forest in Yuping District of western China was taken as the research object.A two-factor interaction experiment was designed based on the application of N and litter changes.Twenty-two 20 m×20 m plots were established and divided into 3 plots.N levels?4 replicate plots per level?:control,low N,and high N(0,50,150 kg N hm^-2 a^-1),9 plots 2 m×per plot 2 m quadrats,divided into 3 treatments,namely,original withering,increasing withering,and withering?with no change in litter,50%increase,and 50%reduction?,N application from January 2014,and litter processing from 2015 Beginning in July.The experiment simulated the increase of N deposition 50%,150%,and the increase of 50%and 50%of the fresh litter input,and studied the soil respiration and soil C,N responses in the wet evergreen broad-leaved forest.To provide a theoretical basis for a more in-depth understanding of the potential impact of atmospheric N deposition on forest C revenue and soil C and N,and to provide reference for fertilization and litter management in forestry production practices.The following main findings are drawn.?1?From July 2015 to December 2017,the cumulative total litterfalls of CK,LN,and HN were 1.29,1.29,and 1.34 kg m^-2,respectively,and N had no significant effect on litterfall.The 10 cm soil temperature averages 12.9°C,the highest temperature occurs at21°C in July,the lowest month occurs at 6.0°C in January,and the average annual humidity in 0-5 cm soil is 55.6%.N has no significant effect on soil temperature and humidity.?2?Application of N significantly reduced the soil respiration rate,and the decrease of soil respiration rate was caused by the treatment of withering.The increase of soil respiration rate resulted in the increase of the respiration rate.Application of N significantly suppressed soil C emissions in the wet evergreen broad-leaved forest.The cumulative soil C emissions for the two sites from January 2016 to December 2017 were CK,LN,and HN of 1915,1431,and 1579 g C m^-2,respectively.The Q₁₀ of soil respiration was 2.60.No significant effect of N application and litter increase or decrease on Q₁₀ was found.?3?Application of N significantly reduced soil pH.Soil pH of CK,LN,and HN in A layer were 3.50,3.44,and 3.36,respectively.Soil pH values of CK,LN,and HN in layer B soil were 3.91,3.86,and 3.73,respectively;litter treatment had no significant effect on soil pH.?4?The soil TOC content increased with the increase of N fertilizer application;The ROC content in soil increased with the increase of N application amount,and the effect of litter increase or decrease was not significant.N application and litter increase or decrease had no significant effect on the EDOC in A and B layers.?5?N application and litter increase or decrease had no significant effect on the TN content in A and B layers.The average TN content in A and B layers was 44.5 g kg^-1 and9.9 g kg^-1,respectively,which was higher than the average in China.The soil TN content was 1.54 g kg^-1.Both NH₄⁺-N and NO₃^--N increased significantly with the increase of N application,and both applied N and time effects were significant,indicating that N can significantly increase the inorganic N content in soil and increase the inorganic N content.The rate increases.Withering treatment significantly increased soil NH₄⁺-N content.?6?N application and litter increase or decrease had no significant effect on soil MBC in A and B layers,but the results of?LSD?comparison showed that applying N reduced MBC,that is,CK>LN>HN;The decrease in MBC and the increase in the percentage of MBC increase,ie,-L<0L<+L.Application of N effect on A layer of soil MBN play a significant inhibitory effect,so in the A soil soil MBN increased with the application of N levels increased,N increased the use of microorganisms to reduce the use of N.This study showed that N application significantly inhibited soil respiration in the wet evergreen broad-leaved forest and significantly increased TOC content in HN-treated soil.Litter increase and decrease treatment increased and decreased soil respiration respectively,and soil TOC in+L treatment.The significant decrease in the content indicates that the increase in litter input yields a positive priming effect and promotes the decomposition of the original soil organic matter.Application of N significantly affected the soil inorganic N content and significantly reduced the soil pH,causing a potential impact on soil microbial communities.