Effects Of Simulated Warming And Throughfall Reduction On Litter Decomposition In A Subtropical Evergreen Broad-leaved Forest

Plant litter is an essential component of carbon and nutrient pools in terrestrial ecosystems,contributing to energy flow and nutrient cycling in the ecosystem.With global climate change becoming increasingly concerning,it is vital to understand how different factors,such as warming and throughfall reduction,impact litter decomposition and the associated carbon and nitrogen cycles in terrestrial ecosystems.However,current research is still insufficient in determining how these factors affect the decomposition of various litter types,including single litters,mixed litters,and dead branches.Hence,accurately evaluating and predicting the effects of global climate change on the carbon and nitrogen cycle of terrestrial ecosystems remains a challenge.To address the current knowledge gaps,this study focused on the decomposition of six dominant tree species(Machilus pingii Cheng ex Yang、Daphniphyllum oldhami 、Daphniphyllum macropodum Miq and Cyclocarya 、Quercus acutissima Carr、Euonymus oxyphyllus Miq)under stimulated warming,throughfall reduction and their interaction in a mid-tropical evergreen broad-leaved forest located in Heishui Village,Huangwan Township,Emishan City,Sichuan Province of China.Specially,the decomposition of mixed litter of abovementioned species and the decomposed mixed litter of branches and leaves on the forest floor were also examined.The loss of mass,C,N,NDS(dissolved in neutral detergent),hemicellulose,cellulose and lignin were quantified after 3,6,12 and 18 months of litter decomposition.The results are as follows:(1)Initial nitrogen and hemicellulose content had a significantly positive impact on the decomposition rate of the litters,while the C/N ratio showed a significant negative correlation.The study also found that the decomposition rate of litters was significantly influenced by the decomposition rates of carbon,nitrogen,NDS,hemicellulose,cellulose and lignin.Interestingly,the study revealed that among all types of litters studied,the carbon release rate had the greatest influence on the decomposition rate.However,the effects of C components on the decomposition rate are largely depend on the litter type(evergreen,deciduous,or dead leaf).Specifically,NDS,lignin and cellulose regulated the decomposition rate in evergreen,deciduous and dead leaf types,respectively.(2)Antagonistic effects were occurred only in a few mixed litter types which often contained the Quercus acutissima Carr which has the least N content and slowest decomposition.In contrast,mixing effects were not found in most of mixed litter types.(3)It was found that the combination of warming and reduced rainfall did not have a significant effect on the decomposition rate of any of the eight single litter types tested.However,a significant effect of this combination was observed in the decomposition rate of certain mixed litter types.More specifically,warming promoted the decomposition rate of certain mixed litters with the lowest initial nitrogen content and slowest decomposition rate,whereas the combination inhibited the decomposition of some mixed litters containing the highest initial hemicellulose content and lowest lignin content.(4)Simulated warming and rainfall reduction,as well as their combined effect,did not result in a significant loss of mass,N,and lignin.However,they did have a significant impact on the rate of NDS loss.Specifically,rainfall reduction was found to inhibit the decomposition rate of C and NDS in dead branches and hemicellulose of Euonymus oxyphyllus Miq.On the other hand,warming was found to inhibit the decomposition rate of NDS of the same litter.Ultimately,the combination of warming and rainfall reduction had an even more pronounced effect,significantly inhibiting the decomposition rate of NDS and cellulose of Machilus pingii Cheng ex Yang.In summary,the decomposition rates of different chemical components play different roles in controlling decomposition among different litter types,with NDS,lignin,and cellulose being important carbon chemical attributes that affect the decomposition rates of evergreen,deciduous,and woody debris.Simulated warming,rainfall reduction,and their combination had no significant effect on the overall decomposition rates of litter,but they had a significant effect on the carbon release rate,NDS decomposition rate,hemicellulose decomposition rate,and cellulose decomposition rate of some types of litter.Importantly,this study demonstrates that the effects of warming and rainfall reduction on litter decomposition are strongly influenced by litter type,and that research on the decomposition of individual litter types cannot fully reflect the nutrient cycling process mediated by litter in forest ecosystems and its response to global climate change.