| Global climate change caused by greenhouse gas emissions is one of the main threats facing the current ecosystem.As one of the important measures to alleviate global climate change,forests have attracted widespread attention from all walks of life.China's subtropical region is a key area for planted forest cultivation,and studying the carbon-water relationship of planted forests in this area has also become a key research direction for sustainable plantation management.According to the status quo of forest resources,how to make use of the carbon sequestration effect of existing forests is the main problem to be solved by current academic circles.To this end,this study took the representative Chinese fir plantations in the subtropical regions as the research object,selected 8 sample plots in the test forest,and arranged canopy nitrogen(N),understory vegetation removal(UR),nitrogen+understory vegetation removal(N+UR)and control treatments(CK)have 16 plots(4 replicates for each treatment)to study soil respiration,soil characteristics,stand water consumption and water use efficiency of Chinese fir plantations under each treatment.The purpose of the dynamic change characteristics is to systematically study the relationship between“vegetation-soil-atmosphere”and explore the changes in the carbon-water relationship of the planted forest ecosystem in response to nitrogen addition and removal of understory vegetation measures.Provide basic data on managing the carbon-water balance of planted forests in subtropical regions and coping with changes in the carbon-water relationship under global climate change.Through one-year test monitoring(November 2018-October 2019),the following main research results have been obtained:(1)N and UR treatments have a significant promotion effect on the soil respiration rate(P<0.05),which can increase the rate by 41.91%and 8.30%respectively.According to the Pearson correlation analysis,the respiration rate and total nitrogen(TN),The carbon-nitrogen ratio(SOC/TN)and catalase activity(CA)have a significant correlation(P<0.05),and N treatment can reduce 54.30%and 17.27%of TN content in rainy and dry seasons.N and UR treatments.It can increase 58.99%and 56.65%of SOC/TN in the rainy season,and decrease the ratio of 13.10%and 21.90%in the dry season(P<0.05),but N and UR treatments have no significant effect on CA(P>0.05).(2)The trunk sap flow of Chinese fir under all treatment measures showed a unimodal or bimodal curve,and there were seasonal differences(P<0.05),from the annual scale analysis,the sap flow rate between different seasons and weather.The average and peak values are summer>autumn>spring>winter,sunny>rainy days.Each treatment has the greatest impact on the sap flow rate in autumn(P<0.05).Compared with the control group,N treatment can reduce the sap flow rate in autumn 69.75%of the average flow rate,which increased 24.31%of the average value in rainy days,while the UR treatment could increase the average value of 41.70%and 90.90%in sunny and rainy days respectively.N and UR treatments had an effect on the average daily water consumption and stand transpiration of Chinese fir trees.The water consumption will have an inhibitory effect,and the water consumption is expressed in spring and winter<summer,autumn,sunny day>rainy days.The annual cumulative water consumption under each treatment measure is 731.76(CK)mm,428.03(N)mm,and 671.33(UR)mm and 403.61(N+UR)mm.(3)During 2016-2019,the tree biomass under each treatment measure increased by4.62kg/m2-10.99kg/m2,with an average annual growth rate of 9.36%-25.45%,among which the tree biomass under N treatment increased.The UR treatment will slow down the growth rate of fir.The water use efficiency of fir under each treatment measure is 14.90(CK)kg C/m3H2O,10.62(N)kg C/m3H2O,8.28(UR)kg C/m3H2O and 12.63(N+UR)kg C/m3H2O,and both N and UR treatments have inhibitory effects on it.The above analysis shows that nitrogen application can increase the intensity of soil respiration and accelerate the growth rate of trees,while removing understory vegetation can increase the transpiration rate of trees,but at the same time it will slow down the growth of trees,and both treatment measures will reduce the water content of fir usage efficiency.Therefore,in the practice of forestry production,you can choose to retain the understory vegetation and control the amount of nitrogen fertilizer applied in summer and autumn to achieve the purpose of promoting the growth of fir and improving the water use efficiency of the plantation. |
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