Effects Of Soil Warming And Precipitation Exclusion On Soil Respiration Of Chinese Fir Plantation And Its Mechanismin Mid-subtropical China

Climate change is truly a global issue,which has got unprecedented concern and a wareness across the international community.The climate warming and changing precipitation pattern,as two remarkable features of climate change,exert a strong effect on terrestrial ecosystem carbon cycle.Subtropical evergreen broad-leaved forest in China is one of the most important forest carbon sink on the global scale.Studying the impact of climate change on subtropical forest ecosystem is great significance.We stimulated global change in young Chinese fir(Cunninghamia lanceolata)plantation in Sanming Research Station of Forest Ecosystem and Global Change,Fujian,China.Four treatments were set to simulate global climate change including control,warming(5?),precipitation exclusion(exclusion 50%precipitation)and the interaction of warming and precipitation exclusion.We focused on the effects of temperature and precipitation changes on soil respirations from different components in young Chinese fir plantation.Also,we examined how soil warming and precipitation exclusion influenced soil enzyme activities,microbial community structure and laboratory incubation to further explain the mechanism of soil carbon emissions.This study will benefit sustainable management of subtropical forests under the background of global change.The main results showed below:(1)We explored the response of soil respiration from different components to warming and precipitation exclusion in young Chinese fir plantation in preaent study.Besides soil temperature and moisture,nutrient composition of different season is also the dominated factors to soil respiration.Results showed that,compared with CT,W and WP treatment significantly increased annual soil respiration fluxes by 16%and 9.1%.However,P treatment significantly reduced 10.3%of the annual soil respiration fluxes.This indicated that warming increased soil respiration due to accelerate the decomposition of soil organic carbon and decrease the microbial biomass carbon and nitrogen.P treatment reduced the DOC content and soil microbial biomass carbon and nitrogen that inhibited soil respiration.W and WP treatment significantly increased the total heterotrophic respiration fluxes by 19.2%and 19%respectively.P treatment had no significant effect on heterotrophic respiration fluxes.Distict from heterotrophic respiration,W treatment increased by 10.2%the total autotrophic respiration fluxes.Nevertheless,the P and WP treatment decreased the total autotrophic respiration fluxes by26.5%and 8.1%respectively indicating that the physiological activity of plant root is more sensitive to precipitation pattern changed.(2)We also studied the response of soil enzyme activity and microbial community structure to warming and precipitation exclusion.It revealed that the temperature and moisture were the main factors to the changes of enzyme activity.At the time of low temperature with less rainfall,the warming would significantly promote the activity of BG and CBH.However,the moisture stress would appeare under warming and precipitation exclusion causing greater inhabitation to BG and CBH activities than warming alone.Under the high temperature and rainy climate,the enzyme activity is dominated by moisture effects.Shifts in temperature and moisture would change the microbial community structure,and warming treatment significantly reduce the total PLFA biomass,bacterial biomass and fungal biomass in present study.The inhibitory effect of warming on fungi was stronger than bacteria,and Gram-positive bacteria(GP)was the dominated bacterial community.But warming treatment and precipitation exclusion would further inhibit bacteria.It indicated that soil respiration rate and carbon emission decreased as time goes by in this study.The main reasons was the increase of carbon cycle-related enzyme activity and the decrease of soil microbial community biomass.It is still the main influencing factors to the soil carbon emission whether the microbial community and plant adapt to the environment change under the backgroud of warming and changing precipitation pattern in the future.(3)The results showed that warming and adding moisture significantly promoted the mineralization of soil organic carbon.The effect of temperature on the mineralization of soil organic carbon was greater than that of moisture.The soil organic carbon mineralization in the control plot was greater than the warming plots.Soil Q10 is positively correlated with soil moisture content.Increasing temperature increases the enzymes activity of BG,CBH,and NAG,increasing energy and nutrient that improving soil heterotrophic respiration,but enzyme activity and microbial communities were easier to be inactivated when the temperature surpassed 40? and 30?.