Priming Effect On Soil Carbon By Abnormal Litter

Extreme weather events such as ice storms and typhoons have severely disrupted the forest ecosystem,resulting in a large number of abnormal litters such as fallen fresh leaves,broken branches,and broken stems.The input of abnormal litter into the soil carbon pool will accelerate or inhibit the decomposition of soil organic carbon,producing positive or negative priming effect on soil organic carbon,and then influence the forest carbon cycle process.However,the current researches on this process are still very scarce.In this study,four common tree species in southern subtropical forests,Pinus massoniana,Castanopsis fissa,Castanopsis chinensis,and Machilus chekiangensis,were selected as the experimental materials.We collected the ¹³C-labled fresh leaves of plants and added them on the surface of soil.Three different addition amounts with dry weight of 50 g（L）,25 g（M）,and 12.5g（S）were set,as well as two different treatment methods with firing and non-firing.In this study,a 110-day indoor incubate experiment was conducted.And we measured the CO₂ efflux,¹³C abundance,and changes in soil carbon during the incubation.The main conclusions are as follows:（1）The carbon efflux patterns of abnormal litter with different addition amounts were similar,which showed a rapid increase in the early stage,a decline in fluctuations afterwards,and a stable low level in the later stage.88.75-94.92%of the carbon efflux process occurred in the early and mid-term（0-45 d）,indicating that most of the decomposition of abnormal litter was completed in a short period of time.During the entire 110-day incubation,67.86-95.31%of the carbon in abnormal litter was released into the atmosphere in the form of C-CO₂.（2）The priming effect of different addition amounts of abnormal litter on soil organic carbon was mainly divided into three stages.In the early stage（0-7 d）,each treatment group showed a strong negative priming effect,and the intensity of the negative priming effect increased with the increase of addition amounts.After that,the negative priming effect of each treatment group gradually decreased（7-35 d）.In the middle and late stages of the incubation（35-110 d）,the priming effect tended to be stable.The priming effect of P.massoniana with M and S treatments,dropped slowly to 0 and disappeared,while other treatment groups all turned to positive priming effect.After 110-day incubation,the OC and the ¹³C value of the top soil added with abnormal litter increased slightly compared to the control group,while the OC and ¹³C value of the deep soil were almost unchanged.（3）The difference in the carbon efflux process and priming effect dynamic of P.massoniana were small under different treatment methods.However,the carbon efflux process and priming effect dynamic of C.fissa,C.chinensis and M.chekiangensis after firing changed a lot.The carbon efflux rate of the firing treatments was significantly lower than that of the non-firing treatments in the early stage（P<0.05）.The priming effect of the firing treatments was all positive during the incubation.During the entire 110-day incubation,55.82-84.23%of the carbon in abnormal litter in the firing treatments was released into the atmosphere in the form of C-CO₂,while that of the non-firing treatments was 71.70-94.32%.After 110-day of incubation,the OC content andδ¹³C value of the top soil increased slightly,and the increment of firing treatments was larger than that of non-firing treatments.However,the OC content andδ¹³C value of the deep soil were almost unchanged.In summary,the input of abnormal litter into forest soil will increase the organic carbon content of the top soil in a short term without affecting the deep soil.Most of the carbon produced by its decomposition was released into the atmosphere in the form of C-CO₂.The firing treatment can change the priming effect of abnormal litter on soil carbon and reduce the release of carbon from litter to the atmosphere.These results deepen the understanding on the influence of abnormal litter in the forest carbon cycle and provide scientific avidences for the management of the southern subtropical forest ecosystem under the background of global climate change.