Landscape And Climate-driven Changes In Plant Diversity And Carbon Sink In The Heilongjiang River Basin

The Heilongjiang River Basin is an important region for biodiversity conservation,carbon sink function maintenance and black soil productivity protection in high latitude regions of the world.In the past few decades,the Chinese part of the basin has undergone a large-scale conversion of grasslands,wetlands and forests to arable land,leading to a series of ecological problems in the basin.In addition,due to its location in the middle and high latitudes,the ecological functions of the basin will be under the dual pressure of climate change and human disturbance in the future,making related problems more serious.In this process,changes in land use,plant species composition and distribution,and carbon sink function will be affected by future climate change and human disturbance.Therefore,it is urgent to reveal the relevant diverse-carbon sink function landscape thresholds and future multi-scenario change trends at the regional level.In this study,we analyzed the spatial pattern of landscape and assessed the spatial distribution of landscape ecological risks in the Heilongjiang River Basin,and quantified the indicator role and threshold effect of landscape characteristics driven by land use on plant diversity and carbon sink.To explore the coupling effects of human disturbance and future climate on plant diversities and carbon sink risks,and to reveal the inter-specific differences in soil carbon sink and nutrients of key species on the basis of determining the influence of suitability distribution of key species.Combined with the change of land use and plant function group under future climate scenarios,the impacts of plant diversity and the potential of carbon sink enhancement in the Heilongjiang Basin were quantified.The preliminary conclusions are as follows:(1)The main land use types in China are forest(46.6%),farmland(26.7%)and grassland(19.3%).Among the landscape level indexes,the land use area index,landscape ecological risk index(LERI),landscape fragmentation index(PD and ED)had the largest explanations for the differences in plant diversity,carbon sink and soil physical and chemical properties.Among the land use types,the landscape characteristics of forest,farmland and grassland explained the plant diversity,carbon sink and soil physical and chemical properties the most.The increase of forest area,the decrease of farmland and grassland area,the decrease of landscape ecological risk index and the decrease of landscape fragmentation degree are accompanied by the increase of plant diversity,biomass carbon and soil C/N.Threshold effect is mainly manifested in the proportion of forest area(%),shape index,aggregation index,landscape diversity and landscape risk index,that is,when these indexes are higher or lower than the threshold value,carbon sink and plant diversity will change dramatically.The relevant thresholds are: forest area is greater than 16.7%,landscape aggregation index(AI)is greater than 64.1%,DIVISION index should be less than 0.65,and landscape richness on the whole,namely landscape types,can be as high as 5.The allocation and regulation of landscape pattern can also be realized by adjusting the landscape pattern of forest,farmland and grassland.It is suggested that in Songnen Plain,where the landscape ecological risk is highest,the construction of urban greening and shelter forest should be continued,and increasing the proportion of forest area is an important measure to reduce the risk.(2)Human disturbance related to land use can significantly affect the response of plant diversity and carbon sink to future climate in this region.Under different climate change scenarios,plant diversity,biomass carbon and total carbon storage increased by8%-31%,17%-21% and 4%-7% in the region as a whole,but soil carbon and nitrogen storage decreased by 2%-5%.Locally,plant diversity and total carbon storage in the southern part of the Songnen Plain and the eastern Hulunbuir Grassland are at risk of reduction,and the risk level is up to Level 3.Regional biomass carbon is mainly affected by rainfall,with little risk of reduction.Soil carbon and nitrogen stocks had the highest risk of reduction,accounting for 79.5%-98.4% of the entire basin area.Land use related anthropogenic disturbances increased the risk of loss of plant diversity,biomass carbon,and total carbon stocks under climate change(the increases were reduced to 4-9%,11-14%,and 3-6%),and reduced the risk of loss of soil carbon and nitrogen stocks in forested areas.(3)Differential responses of key plant species in this region under future climate conditions.MaxEnt model in this study simulated the distribution of 16 key species in this region: Betula platyphylla,Populus spp.,Ulmus pumila,Larix gmelinii and Pinus sylvestris were mainly affected by precipitation,and their contribution rates were 12%-43%,while Juglans mandshurica,Phellodendron amurense,Quercus mongolica,Fraxinus mandshurica,Pinus koraiensis,Picea spp.and Deyeuxia angustifolia were both affected by temperature and precipitation,and their contribution rates were 11%-27% and 10%-37%,respectively.The distribution probability of Alnus hirsuta is affected by precipitation and forest distribution,and the contribution rates are 10%-32%and 10%,respectively.The distribution of Salix rosmarinifolia is influenced by precipitation,wetland distribution and altitude.The contribution rates were 29%,19%and 13%,respectively.The suitable distribution area decreased: Betula platyphylla,Quercus mongolica,Larix gmelinii,Salix rosmarinifolia and Deyeuxia angustifolia,decreased 20%-50%.Little change in the suitable distribution area are: Fraxinus mandshurica,Ulmus pumila and Alnus sibirica;Suitable distribution area increased are:Juglans mandshurica,Phellodendron amurense,Populus spp.,Pinus koraiensis,Picea spp.and Pinus sylvestris,especially Pinus koraiensis,with an increase of up to 350%.The geographical distribution expanded: Juglans mandshurica,Phellodendron amurense,Populus spp.,Pinus koraiensis,Picea spp.;The species moving to the southeast are Betula platyphylla,Pinus sylvestris and Alnus sibirica.The species that moved to the northwest were Quercus mongolica and Deyeuxia angustifolia.The suitable distribution area of Fraxinus mandshurica became dispersed,Ulmus pumila moved eastward,Larix gmelinii moved southward,and Deyeuxia angustifolia moved westward.(4)The influence of tree species on mineral soil properties is of great regional difference,while the influence of needle and broadleaf difference is of great consistency.Studies on 14 tree species and 6 sites showed that soil SOC and TN in broad-leaved forest were 30-50% higher than those in coniferous forest,and the contribution of aggregates accounted for 75-77% of the increase in soil SOC and TN in broad-leaved forest.The main reason for the increase of SOC and TN in broad-leaved forest is that the increase of the number and stability of soil aggregates in broad-leaved forest enhances the protection of SOC and TN.Among them,the concentrations of SOC and TN in aggregates increased by 30-50%;The relative mass of particle aggregates increased by 50%,and that of non-aggregates(silt and clay)decreased by 14%.The uncertainty of the above coniferous and broad-leaved differences was relatively low(4.2%): the broad-leaved forests had higher SOC and TN accumulation than the coniferous forests in the areas with less clay content,higher altitude and precipitation,more mandshurica mandshurica and fewer poplar trees.(5)The simulation results of land use change under future climate scenarios show that forest area will increase,grassland and farmland will decrease,and urban area will expand first and remain unchanged after 2045.This will result in a 7% to 11% increase in plant diversity and a 9% increase in biomass carbon from 2025 to 2100 under future climate scenarios.The simulation results of plant functional group change under future climate scenarios show that the area of broad-leaved forest in the Heilongjiang Basin will increase,and the area of coniferous forest will increase first,and remain unchanged after 2050.This would result in a 5% increase in soil carbon and nitrogen stocks between2025 and 2100 compared with current climate scenarios.In conclusion,climate change and land use affect plant diversity and carbon sink in the Heilongjiang River Basin by changing the suitability distribution of key species and vegetation composition through landscape characteristics.This has the potential to increase plant diversity and carbon sink in the Heilongjiang Basin by 5%-11% in future scenarios.Therefore,under future climate change,there is little risk of major ecological functions changing,but there is a threshold effect on the impact of landscape characteristics on these functions,and relevant studies should be strengthened in the future.