Characteristics Of Typical Forest Plant Diversity And Its Impact Mechanism On Soil Carbon Sink Function In Northeast China

Northeast forest is the largest state-owned forest region in China,and its ecosystem carbon sink function is considered crucial to achieving the carbon neutrality goal.In this study,8 permanent sample plots with a total area of 16.2 ha were established in the Northeast Forest Zone,and a total of over 50000 woody plants were investigated,forming a coupling relationship between plant diversity and forest soil carbon sink in the Northeast Forest Zone.This study analyzed the characteristics and influencing factors of plant diversity in Northeast China.The effects of plant diversity,mycorrhizal types,community structure,soil physicochemical properties,and land use types on soil carbon capture and stability were emphatically explored.The research results showed as follows:1)The average Richness of woody plants was 10.75,the average Simpson index was 0.72,the average Shannon-Wiener index was 1.69,and the average Pielou evenness index was 0.76in the forests of Northeast China.The average mingling degree（M）of of woody plants was0.57,and the stand was medium mixed.The average uniform angle index（W）was 0.54,and the stand was aggregated distribution.The average neighborhood comparison（U）was 0.51,and the stand was median state.The results of variance partitioning analysis showed that the interaction of individual size,forest spatial structure characteristics and geoclimate contributed the most to the changes in woody plant diversity in Northeast China,with an interpretation value of 36.6%.Redundancy analysis showed that latitude,mingling degree,and uniform angle index were significant factors causing diversity changes.The above factors can be adjusted to achieve the protection of woody plant diversity in Northeast China.2)The vertical structure of a forest ecosystem is a key factor in its functioning,including arbors,shrubs,herbs,and the regeneration layer.Through a detailed investigation of the individual size,community characteristics,and plant diversity of arbors,shrubs,herbs,and regeneration layers in the Shuanghe National Nature Reserve and Dobukur National Nature Reserve in the Daxing’anling forest region,the coupling relationship between plant diversity and community structure characteristics was analyzed by redundancy analysis and variance partitioning analysis,and the most important individual and community characteristics indicators affecting diversity changes were ranked.The diameter and height of trees were only50%of those in 1970s,and the richness of arbors and herbs was about 50-60%higher than that in Huzhong Nature Reserve of the central Daxing’anling.The results of redundancy analysis showed that the tree height in the regeneration layer had the greatest explanatory power for the diversity differences in the Shuanghe Nature Reserve,and the arbors height in the arbors layer had the closest relationship with the changes in plant diversity in the Dobukur Nature Reserve（p<0.05）.3)Poplar afforestation can significantly affect the stability of soil carbon sequestration.The results showed no significant difference in soil organic carbon（SOC）respirational decomposition rate between farmland and shelterbelt forests but a 15.8%higher SOC concentration in shelterbelt forests（p<0.05）.The poplar shelterbelts reduced the temperature sensitivity(Q₁₀)by 15.4%（p<0.05）,with deeper soils a more significant reduction in Q₁₀.No significant humidity sensitivity（Hs）（linear gradients）differences were found in farmland and shelterbelt forests.Partitioning of the RDA ordination-based variation showed that SOC stability(Hs and Q₁₀)of farmland was more affected by geo-climate.In contrast,the SOC stability of shelterbelt forests was greatly influenced by soil properties.Our findings manifest that the above-mentioned SOC changes can improve shelterbelt forest carbon sequestration function by prolonging the SOC lifespan in soil by at least 7%and SOC concentration by>15%.This should be included in the future to assess the underground soil carbon impact of Three-North shelterbelts in China and provide data supports for the estimation of similar forest stands in other parts of the world.4)Based on the permanent plots of the experimental forest of Northeast Forestry University,tree richness and arbuscular mycorrhizal（AM）experiments were settled and soil organic carbon（SOC）and glomalin-related soil protein carbon（Total,TG-C and easily extracted,EEG-C）,stability(heterotrophic respiration,Rh,temperature sensitivity,Q₁₀ and humidity sensitivity,Hs),in situ soil CO₂,CH₄,N₂O fluxes,and CAZymes were measured.We found high tree richness induced 16-126.6%higher SOC,TG-C,Rh,and in situ N₂O flux.AM dominant plots had 34-39%higher SOC and Rh than the ectomycorrhizal plots.The richness and AM’s effects in 0-1 m soils were more evident than 0-20 cm soils.Richness directly improved C stability,while richness-AM-decreased-CAZymes favoured the C accrual,and glycoside hydrolases,polysaccharide lyases,carbohydrate esterases,glycosyl transferases,auxiliary activities,and carbohydrate-binding modules cooperated in the regulation.In addition,the accumulation of aggregate carbon in soil is crucial for nutrient availability and mitigation of global climate change.Through the study of plant diversity and mycorrhizal types on soil aggregate carbon capture and stability,we found that high tree richness induced 7-64%higher aggregate carbon,mean weight diameter and geometric mean diameter.AM dominant plots had 7-94%higher aggregate carbon,mean weight diameter and geometric mean diameter than the ECM plots.The aggregates carbon sink stability of surface and deep soil were most affected by mycorrhizal dominance,and the compensation effect of plant diversity had improved the explanatory power of deep soil aggregate carbon stability.High tree richness significantly increased the carbon content of macroaggregates,microaggregates and silt and clay in surface and deep soil.The important values of ECM trees were significantly negatively correlated with the carbon content of macroaggregate,microaggregate,and silt and clay,and the stability of aggregates.The important values of AM trees were significantly positively correlated with the carbon content of macroaggregate,microaggregate,and silt and clay,and the stability of aggregates.5)Through the analysis of the effects of species diversity,forest spatial structure,tree size,soil physicochemical properties,and geoclimate on soil carbon capture and stability in the northeastern forest of China,we found that soil carbon capture and stability was most affected by woody plant richness,and the compensation effect of plant diversity had the greatest explanatory power on soil carbon stability.High tree species richness significantly increased SOC and Rh;In addition,the stand spatial structure also had an important impact on the soil carbon sink stability.The mingling degree and uniform angle index were significantly positively correlated with SOC,Rh,and Hs.Geoclimate can have a significant direct impact on SOC,Rh,and Hs,and can also indirectly affect SOC,Rh,and Hs by affecting tree species richness and soil properties.The research results provide data support for improving the management of forest soil carbon sink function at the regional level.The above relevant results provide basic data for forest management in Northeast China.The purpose of this study is to provide theoretical basis for the synergistic improvement of forest tree diversity,key species effects,and soil carbon sink functions in Northeast China,and will also help provide data support for relevant forest schemes in the future"carbon dioxide peaking"and"carbon neutrality"in Northeast China.