Contribution Of Different Decomposer Groups To Litter Decomposition In Stream

Litter decomposition is an important ecological process of nutrient cycling and energy flow in freshwater ecosystems.Litter decomposition in streams is influenced by multiple decomposer groups,such as microorganism,meioinvertebrate and macroinvertebrate.At present,the research on the relative contribution of different decomposer groups to litter decomposition is not comprehensive enough.First,it is not clear whether the relative contribution of each decomposer group to the litter decomposition in streams is affected by the litter substrate quality.Secondly,the stream ecosystem is easily disturbed by human activities,such as eutrophication of water caused by excessive nitrogen and phosphorus emissions,which may also affect the contribution of various decomposer groups to litter decomposition.A forested headwater stream in Mt.Jinfo National Nature Reserve and the qingshui stream in the Shapingba district of Chongqing was selected as representatives of undisturbed stream and eutrophic stream to carry out litter decomposition research.Litter with different initial substrate quality was selected and litterbags of three different mesh sizes were set up to analyze the relative contribution of microorganisms,meiofauna and macrofauna to litter decomposition in streams with different nutritional status.The interaction mechanism among macroinvertebrate,meioinvertebrate and microorganisms in streams with different nutritional status and its influence on the decomposition process of litter with different initial substrate quality were analyzed by measuring the residual weight of leaves,the abundance of microorganisms(fungi and bacteria)and fungal biomass in the decomposition process and investigating the community composition of benthic fauna.The study found that(1)Litter decomposition rates were significantly different among different species in undisturbed stream: Alangium chinense(k=0.021 d-1)>Liquidambar acalycina(k= 0.006 d-1)> Machilus sp.(k=0.003 d-1).The order of decomposition rates of the three litters in eutrophic streams did not change,but the decomposition rates is about 3 times lower than that of undisturbed streams.Besides,the decomposition rate of native tree species in eutrophic streams is: Broussonetia papyrifera(k=0.011 d-1)> Erythrina variegata(k=0.006 d-1)> Ficus microcarpa(k=0.005 d-1),which were consistent with the matrix quality order indicated by P content and lignin /N in leaves.(2)Compared with undisturbed stream,Eutrophication of streams leads to the decrease of fungal biomass,abundance of fungi,and diversity of benthic animals.Meanwhile,the composition of feeding functional groups is changed,making deposit feeders become the dominant group in eutrophic stream,while the key groups involved in decomposition(shredder)almost disappeared.(3)Microorganisms are the main contributors in streams with different nutritional status.The interactions between benthic fauna with microorganisms are different in leaves with different qualities.In undisturbed streams,the presence of meiofauna significantly accelerated the decomposition of leaves with higher quality,while the presence of macrofauna significantly increase the decomposition rate of leaves with lower quality.Macro-and meioinvertebrates reduced the decomposition rate of leaves in eutrophic streams regardless of the quality of leaves.