Coupling Associations Between Plant Species Composition Traits And Biomass Carbon Sink Function And Mechanism Of Forests In The Greater And Lesser Khingan Mountains

The forest of the Greater and Lesser Khingan Mountains is an important ecological barrier in China,climate change and anthropogenic disturbance may change forest species composition and structure factors,resulting in a decline in forest quality,biodiversity and ecosystem functions.However,previous studies lacked of comprehensive and in-depth research on the responses of forest plant characteristics and functions under historical evolution,anthropogenic influences and climate change and decoupling of their complex coupling relationships,which also limits the proposal of scientific management measures to improve forest quality and functions.In this study,we used forests in the Greater and Lesser Khingan Mountains as the study plot.Firstly,the historical succession process and the potential mechanism of enhancing the carbon sink function of typical forests in Northeast China in the past 60 years were discussed based on the historical data combined with census data.Secondly,anthropogenic impacts represented by comparison between inside and outside the reserve,and climate change simulated by natural conditions of slope aspect,were used to illustrate the effects on forest plant composition characteristics and carbon sink function(including aboveground carbon storage and their stability)and further explore the underlying reason.Finally,the comparison of the effect of abiotic factors(geo-topographic factors)and human control(species,structure and functional diversity)on carbon stocks and stability provided a basis for revealing the potential for improvement of the carbon sink function.The preliminary conclusions are as follows:(1)The 60-year historical change of forest characteristics and functions: On the whole,the species and functional traits are more abundant over time,but the distribution uniformity did not change much,Pinus,Betula and Picea have always been in the dominant role with the ratio declining,but the proportion of other broad-leaved tree species such as Acer and Ulmus has continued to increase over time.The forest canopy trees tend to be shorter.The functional trait characteristics of forest community tended to be better photosynthetic,more water,soft-thin-broad-leaved and more N and P of leaves,but the potential maximum height of individual and the multifunction was lower.Aboveground carbon stocks are reduced and less resistant to decomposition,and in turn,carbon accumulates at a higher rate,making it more stable to cope with future climate change.The relationship among carbon stock and its stability,carbon accumulation rate and forest characteristics did not differ significantly over time,but the most important impact factors were the relative abundance of key species,the mean value of structural and functional traits and their interaction,while the contribution of diversity characteristics was least.(2)Differences due to natural forest protection: Our results showed that long-term conservation significantly altered the dominant species in the herb layer(80% of species),followed by shrub(58%)and tree layers(50%);there was a 1.6-8.0-fold increase in abundance in Corylus shrubs,Acer trees and Carex grass,but the amount of larch trees,Athyrium herbs and Lonicera shrubs in the reserve is only 1/10 to half of outside.In contrast,tree species diversity increased by 31% in the reserve,but nonsignificantly in shrub and herb layer.Forest protection in the reserve also led to the forest structural alteration with the observation of larger-sized trees and shorter herbs,but relatively sparse forests.The carbon storage increased significantly but the stability did not change significantly,with the strengthening of protection,the limiting factor on the function of carbon sink changed from tree height to DBH.(3)Differences under climate change: some species were more adaptable to climate warming,such as Salicaceae,Picea koraiensis,Corylus mandshurica,Spiraea salicifolia,Carex dispalata,Caldesia parnassifolia,Filipendula palmate.The amount of some other species decreased with climate change,such as Larix gmelinii,Vaccinium vitis-idaea,Rosaceae herb,Carex callitrichos and Sanguisorba officinalis.Climate warming induced lower trees,higher shrub and herbs,sparse forest,and higher shrub coverage,with more abundance and diverse trees,more diverse and even-distributed shrubs and richer and heterogeneous herbs.The aboveground carbon storage and stability had little change,and the key species of trees were the most crucial factors.The influence of geo-topographical factors was realized through the interaction with forest species and structural composition.(4)The effect of abotic factors and vegetation attributes and diversity on carbon storage and their stability: the influence of forest characteristics on carbon sink function is greater than abiotic factors(more than 5 times),characterized by leaf functional traits have a decisive role on the aboveground carbon stability,growing more in large leaf area,no hairiness,small specific leaf area,soft leaf trees is more conducive to the carbon stability increases,the more abundant and clutter distribution has a positive effect on carbon stability,and individual size of trees has a controlling effect on carbon stocks,which is 2 times more than other components.This study puts forward reasonable suggestions for achieving high carbon sequestration capacity and coping with future climate change,and provides a basis for forest management of NFPP.Overall,historical change,climate warming and human protection significantly changed plant species composition,structure and function traits.But for the improvement of carbon storage and their stability,the influence of external factors is far less than the management regulation of human,which need the scientific and optimal management on key tree species,structure and function traits regulation.