The Respiration Characteristic Of CWD(Coarse Woody Debris) Decomposition And Its Influence Factors In Subtropical Forests

Coarse woody debris（CWD）plays an important role in forest ecosystem function because it contains a large stock of carbon（C）and nutrients and affects both carbon and nutrient cycling.The carbon release during CWD decomposition(R_CWD)process is an important component that cannot be ignored in the carbon budget of forest ecosystems.Meanwhile,the decomposition of CWD（and thus carbon release）is a complex ecological process,and it affected and driven by a series of factors which including environment factors（e.g.,temperature,moisture content,light condition and nitrogen deposition）,initial quality and biological community characteristics.In this study,we conducted field-based and lab-control experiment to investigate the respiration patterns of different tree species CWD and its affects factors during CWD decomposition process in Lushan Mountain of subtropical China.Results from the decomposition of CWD in situ field-based experiments showed that:The R_CWDof Lithocarpus glaber（LI）,Platycarya strobilacea（PL）and Cryptomeria japonica（CR）followed a similar seasonal fluctuation pattern.The annual R_CWD of PL was generally higher than that of LI and CR.While,the Q₁₀of LI（2.73）were higher than those in the CR（2.67）and PL（2.46）.There were significant relationships between T_CWD and R_CWD for each tree species,which were described by an exponential function.CWD temperature and moisture content explained about 42.9-59.2%and 11.7-16.6%of the total variation in R_CWDamong different tree species.To test the HFA hypothesis for CWD decomposition,we quantified the respiration of CWD(R_CWD)for different tree species over a two-year study period.We used a dynamic chamber method to monitor R_CWD over time in two reciprocal translocation field experiments involving CWD of the same decay stage from three tree species,and determined the effects of changes in CWD temperature and CWD moisture content on R_CWD.The three tree species used were Cryptomeria japonica（CR）,Platycarya strobilacea（PL）and Acer davidii（AC）.We found that R_CWD exhibited a distinct seasonal pattern,and it was predominantly controlled by CWD temperature and microbial.The temperature sensitivity of R_CWD,as indicated by Q₁₀,ranged from 2.35-2.94,which varied among tree species and field sites.The R_CWD,Q₁₀ and microbial below PL and AC in the“home field”were higher than those in the“visiting field”,while the R_CWD,Q₁₀ and microbial below CR were the opposite.CWD temperature explained over 50%of the total variation in R_CWDamong different tree species and field sites,but no significant relationship was found between R_CWD and CWD moisture.The existence or magnitude of the HFA effect observed for CWD decomposition in this study was directly explained by the difference in soil microbial community between home and visiting field that were a result of differences in CWD quality among the three species and in soil nutrients between the two field site（forest types）.Altitudinal gradients could be a useful tool for examining the influence of temperature on the decomposition process in the natural environment.Here,we conducted a field-based experiment along an altitudinal gradient（215,430,834,and 1400 m a.s.l.）to investigate the respiration of CWD(R_CWD)of Pinus taiwanensis Hayata（PT）and Cinnamomum camphora（Linn.）Presl（CC）in response to temperature change over a 24-month period in subtropical China.We found that altitude gradient significantly declined R_CWD,with its effect further amplified by increasing altitude.The temperature sensitivities of R_CWD to CWD temperature as indicated by Q₁₀were increased with altitude,and it generally expressed as altitude 1400m>altitude 834m>altitude 430m>altitude 215m.We conducted a field-based experiment to investigate the effects of photodegradation on the respiration of CWD(R_CWD)of Cunninghamia lanceolata（CL）,Schima superba（SS）,and Cinnamomum camphora（CC）over a 24-month period in subtropical China.And we also determined the effects of changes in CWD temperature and moisture content on R_CWDof the three tree species.We found that photodegradation significantly accelerated R_CWD,with its effect further amplified by increasing temperature.The temperature sensitivities of R_CWD to CWD temperature as indicated by Q₁₀were increased by photodegradation treatments.The CWD temperature can explain over 70%of the variation in R_CWDamong different tree species and treatments.We conducted a field-based experiment to investigate the respiration of CWD(R_CWD)of Cunninghamia lanceolata（Lamb.）Hook.and Cinnamomum camphora（L.）Presl.in response to elevated UV-B radiation and N deposition over a 24-month period in subtropical China.We found that UV-B and N treatment,alone or in combination,significantly accelerated R_CWD,with their effect further amplified by increasing temperature.Moreover,the combined treatment（UV-B+N）far exceeded the sum of the individual effects of UV-B and N treatments.Our study indicated that CWD decomposition depended on tree species,CWD temperature and moisture content,and CWD quality were the important factors affecting CWD decomposition.HFA in CWD decomposition depended on tree species,and microbial community,CWD temperature and CWD quality were the main factors affecting CWD decomposition and determining HFA.The several important drivers of global environmental change（elevated UV-B,photodegradation,N deposition,and temperature increase）would work synergistically to accelerate CWD decomposition in forest ecosystems.