Effects Of Biochar Application On Nutrients Uptake Of Cunninghamia Lanceolata Seedlings And Soil Nutrients Under Simulated Nitrogen Deposition

In recent years,changes in nutrient cycling in forest ecosystems caused by N deposition have aroused widespread concern.Biochar,as a new soil conditioner,plays an important role in changing soil pH,improving soil nutrient availability(such as N,P),and increasing C sequestration.However,little is known about how biochar and its interaction with N deposition may influence the concentration of nutrients on the soil and plants.In order to study how N deposition and biochar application affect soil nutrients,soil microbial biomass and different organs'nutrients of Cunninghamia lanceolata(Lamb.)seedlings(1-year-old),we applied additional N deposition and biochar treatments in field plots.We applied three levels of additional N deposition:Ambient N deposition without added nitrogen(nitrogen control,N₀),a low level of added N deposition(ambient plus 40kg·ha^-1·yr^-1,N₁),and a high level of added N deposition(ambient plus 80 kg·ha^-1·yr^-1,N₂).We applied within each N treatment three levels of biochar:0(biochar control,B₀),12(B₁),and 36(B₂)t·ha^-1.This study simulates the effects of increased nitrogen deposition on nutrient cycling in the soil and seedlings and explores how biochar interaction with N addition may influence it.This study aims to provide theoretical guidance for the reasonable cultivation of seedlings and the sustainable management of it.(1)The addition of biochar and nitrogen,under each level,had no significant effect on total biomass and stem biomass of Cunninghamia lanceolata(Lamb.).The root biomass significantly increased but foliar biomass decreased with biochar application and the foliar biomass also increased significantly with N addition,which caused biomass allocation of seedlings changed.At each level of nitrogen deposition,biochar application significantly increased the root-shoot ratio,with an increase range from 68.7 to 144.6%.However the higher nitrogen deposition significantly decreased the root-shoot ratio.(2)The foliar C,P,K,Ca,and Mg concentration all increased with biochar application.The foliar N concentration increased only at the lower biochar application level but decreased at the higher biochar application level.At biochar control(B₀),the N deposition significantly increased the foliar N concentration with an increase of 48.9-51.2%but had no significant effect on the remaining nutrients concentration of the foliar.It can be seen that in the early stage of seedling growth,the application of BC treatment increased the absorption of P,K,Ca,and Mg elements in the seedling leaves,resulting in an imbalance of nutrients and a reduction in the biomass of the leaves.(3)In this study we found that BC application increased soil pH(compared with B₀treatment)with an average increase of 14.4%;N deposition treatment decreased soil pH(compared with N₀ treatment).Application of biochar significantly increased the concentration of soil available P,available K,and NO₃^--N,but had no significant effect on soil available N and NH₄⁺-N.The concentration of soil total elements also generally increased with application of biochar.Biochar addition alone significantly increased the C:N and C:P ratio in the soil,the increase from 13.4%to 31.0%and 8.3%to 9.9%respectively.The N:P ratio in the soil decreased with application of biochar.Compared with N₀B₀ treatment,N addition alone significantly increased soil N content,and available N,NH₄⁺-N,NO₃^--N contents are generally increased by 34.10%,26.8%,and 182.5%respectively.The C:N ratio in the soil decreased with the increase of N addition,but there were no difference of N:P ratio in the soil between each level of N deposition.Pearson correlation analysis showed that available nutrients in the soil correlated positively with concentration of soil total nutrients.(4)The MBC content increased first and then decreased with the increase of biochar application.MBN and MBP both increased with application of biochar,with average increases of 30.5%and 19.9%,respectively.At each level of biochar application rate,the higher N addition rate significantly increased the soil MBP content but significantly decreased the MBC and MBN contents.There was no significant difference in MBN:MBP ratio between each level of biochar application.Compared with the treatment without biochar application,higher biochar application rates significantly decreased MBC:MBN and MBC:MBP ratio,with an average reduction of 23.9%and 21.9%,respectively.In the biochar control(B₀),the higher N addition rate significantly reduced soil MBC:MBN ratio,compared with lower N addition rate.Compared with double control(N₀B₀),the higher N addition rate decreased MBC:MBP and MBN:MBP ratio,with an average reduction of 46.1%and 31.5%,respectively.