Effects Of Different Application Rates Of Biochar On The Soil N₂O Emission In Moso Bamboo Plantations And Associated Mechanisms

Moso bamboo?Phyllostachys edulis?is an important bamboo forest resource in the subtropics.China has the area of Moso bamboo forest of approximately 4.45 million hectares,accounting for 74%of the total area of Moso bamboo forest in China.Moso bamboo plantation has unique advantages and great potential in forest carbon sink and greenhouse gas emission reduction.However,the soil N₂O flux of bamboo forest is significantly higher than that of evergreen broad-leaf forest,and the management measures such as fertilization and ploughing will lead the soil nutrients loss and increase the soil N₂O emissions.Biochar application can increase soil nutrient content and significantly reduce soil N₂O emissions.However,the effects of different rates of biochar application on N₂O emissions from plantation soils and their mechanisms still remain unclear.This experiment was conducted in the intensively managed Moso bamboo plantation in the typical subtropical region of Hangzhou,Zhejiang Province.Through two years of field trial,the effects of different rates of biochar application(0 t ha^-1:control;5 t ha^-1:B5;15 t ha^-1:B15)on soil N₂O flux,temperature,moisture,pH,carbon and nitrogen pools,enzyme activity,gross nitrification,and denitrification rates in the Moso bamboo plantations were investigated.The relationship between soil N₂O flux and soil environmental factors in Moso bamboo plantations was explored,and the effects of different application rates of biochar on soil N₂O emissions in the Moso bamboo plantations and associated mechanisms were revealed.The main research results obtained are as follows:?1?The soil N₂O flux of Moso bamboo plantation shows a significant seasonal change in all treatments(0,5 and 15 t ha^-1),and the maximum of soil N₂O flux is in the summer,the minimum value is in the winter.Soil N₂O flux decreased with the increase of biochar application.Biochar treatments(5and 15 t ha^-1)significantly reduced the annual N₂O cumulative emission?P<0.05?in the first year,and there was no significant difference between different amounts of biochar treatments;biochar treatments was also significantly reduced the cumulative annual N₂O emission?P<0.05?in the second year,but there was a significant difference between two biochar treatments?P<0.05?.?2?Different rates of biochar application have no significant effect on the soil temperature in the Moso bamboo plantation.Compared with control,B5 and B15 treatment increased the soil water content of Moso bamboo plantation by 5.9%and 9.8%,respectively.Biochar input significantly increased soil pH?P<0.05?and it increased with the amount of biochar increase,but all biochar treatments showed a downward trend in the second year.Compared with the control,the WSOC content in the Moso bamboo plantation soil increased by 13.9%and 27.0%,the soil MBC content increased by12.4%and 15.1%,and the soil NH₄⁺-N content decreased by 9.2%and 13.0%,respectively,under the treatments B5 and B15.The content of soil NO₃^--N decreased by 16.7%and 19.0%respectively,soil WSON content decreased by 13.2%and 14.2%,and soil MBN content increased by 10.8%and 12.9%,respectively.?3?The activity of soil enzymes?invertase,urease and protease?showed a certain variation with temperature,generally reaching the lowest value in the winter and peak in the summer.Compared with the control,the B5 and B15 treatment in Moso bamboo plantation leads soil invertase activity decreased by 10.0%and 15.2%,soil urease activity decreased by 13.3%and 16.0%,soil protease activity decreased by 13.4%and 19.6%,respectively.Under the different treatment conditions of biochar(0,5and 15 t ha^-1),the soil gross nitrification and denitrification rates of Moso bamboo plantation showed seasonal changes,and the maximum rates of them all appeared in the summer,the minimum value in the winter.The soil gross nitrification and denitrification rates decreased with the increase of biochar application in the Moso bamboo plantation.Compared with the control,B5 and B15 treatment leads the soil gross nitrification rates decreased by 13.1%and 17.0%,respectively;the soil denitrification rates decreased by 18.6%and 27.6%,respectively.?4?The soil N₂O emission in the Moso bamboo plantation was significantly correlated to the soil temperature,WSOC,MBC,NH₄⁺-N,NO₃^--N,WSON,MBN concentration,urease activity,protease activity,nitrification rate and the denitrification rates?P<0.01?.In the treatments of B5 and B15,the soil N₂O emission was correlated to the soil temperature,NH₄⁺-N,NO₃^--N concentration,urease activity,protease activity,nitrification rate and the denitrification rates?P<0.01?.In the treatments of B5 and B15,the soil N₂O emission was correlated to the WSOC,MBC and WSON concentration?P<0.05?.