Study On Dynamics Of The Decomposition Of Mixed Litters And The Colonization Of Macroinvertebrates In A Headwater Stream Of Changbai Mountain In Winter

In the natural stream ecosystem,the leaf litters usually exist in the form of mixture.The research based on a single species cannot well explore the real state of decomposition of the leaf litters in the stream ecological system,therefore,the aim to indicate the relationship between the species composition and diversity of the leaf litters and the decomposition of the leaf litters is especially crucial.Annually,about 70% of the streams in the Changbai Mountains are frosted with manifest seasonal freeze-thaw characters from November to April.However,the dynamic of mixed decomposition of the leaf litters in the process of seasonal freezing and thawing is unclear.In order to reveal the relationship between leaf litter decomposition and colonization of macroinvertebrates in the stream during the winter,this research used the way of litter decomposion bags to carry out a 187-days investigation for monoculture and mixing leaf litters such as Tilia amurensis,Acer mono and Quecus mongolica in a headwater stream of the Changbai Mountains.The main conclusions are as follows:(1)In the pre-freezing period,the mass losses were significantly different among those three kinds of leaf litters in monoculture(P < 0.05),whose decomposition rates descended as A.mono,T.amurensis,and Q.mongolica.However,there were no significant difference among those mixing litters(P > 0.05).In the freezing period,the mass loss rate of the Q.mongolica was apparently lower than that of A.mono and T.amurensis(P < 0.05).Meanwhile,A.mono and T.amurensis did not have an obvious difference(P > 0.05).Moreover,the mass loss rates of A.mono and T.amurensis were the highest in the mixed treatment groups and also significantly higher than the rest of mixed treatment groups(P < 0.05),but the difference between the remaining mixed treatment groups were not significant(P > 0.05).In the thawing period,the mass loss rate of the Q.mongolica was significantly lower than that of A.mono and T.amurensis(P < 0.05),and the differences between A.mono and T.amurensis were not significant(P > 0.05).However,there were no significant difference among the mixed treatment groups(P > 0.05).(2)In the pre-freezing period,the litter mixing effects occurred in the bags with T.amurensis and Q.mongolica,and the litter mixing effects on shredders were poor.In the freezing period,the litter mixing effects occurred in the bags with A.mono and T.amurensis,and the mixing effects on shredders were significant.(3)In the litter decomposition process,the collectors are the most important functional feeding groups,followed by the shredders and predators.Among those three kinds of leaf litters in monoculture,the relative abundance of the collectors was the highest among the litter of Q.mongolica,up to 65.4%,and the relative abundance of the shredders and predators was 15.5% and 13.1% respectively.In the mixed treatment groups,the relative abundance of the collectors was the highest among the litters of A.mono and T.amurensis,up to 54.9%,and the relative abundance of the shredders and predators was 21.9% and 16.8% respectively.(4)Bray-Curtis similarity analysis and NMDS analysis showed that,in the pre-freezing period and freezing period,there was a significant difference in the structure of macroinvertebrates community in the decomposition bags of different leaf litters.In the thawing period,macroinvertebrates community had the highest similarity.It indicated that macroinvertebrates have certain selectivity to food and habitat in the pre-freezing and freezing period.In the freezing period,the highest value of each functional feeding group density and biomass was found in the mixed bag with A.mono and T.amurensis,which suggested that the combination of A.mono and T.amurensis provides the best food source and habitat choice for macroinvertebrates.