Analysis Upon Spatio-temporal Distribution Patterns Of Plant Diversity Over The Songnen Grasslands

There are obvious spatial and temporal distribution patterns of species diversity on Earth,such as the regular variation of species richness with latitude,longitude and altitude.Understanding the spatial and temporal distribution patterns of biodiversity can not only improve theoretical understanding of the global geographic distribution patterns of biodiversity and its mechanisms,but also provide important scientific basis and support for ecosystem management practices,such as the planning of nature reserves,and therefore has been widely concerned.Grassland is an important part of terrestrial ecosystem and serves as an important reservoir of species,with the essential function of maintaining biodiversity.Compared with other ecosystems,grassland has a relatively simple species composition and is therefore vulnerable to human disturbance.Songnen Grassland is the most important grassland ecosystem in the Northeast Plain of China,with good natural resource endowment and high plant diversity.Over the past 50 years,there has been a significant decline in grassland plant diversity in response to global climate change and increased human disturbance.In this study,based on the vegetation survey data and historical survey data literature of the project team in recent years,we calculated theαdiversity index andβdiversity index of Songnen grassland plants,used geostatistical Kriging spatial interpolation analysis method and Surfer spatial visualization technique to determine the regional distribution pattern ofαandβdiversity index of Songnen grassland,and based on multivariate statistical analysis method,we determined their key influencing factors.The classical power function model was used to fit the species-area relationship of plant spatial distribution in Songnen grassland,and the fitting effect was evaluated,and the key factors of environmental change and human activities affecting the species-area relationship in Songnen grassland were discussed.The main results of the study are as follows:（1）The temporal patterns ofαdiversity in Songnen grassland from 1963 to 2018 showed that plant species richness decreased by 63.3%.The decline rate of plant species richness was relatively high from 1963 to 1992,and the decline rate slowed down from 1992 to 2015,and species richness showed an increasing trend from 2015 to 2018.The spatial distribution pattern of plantαdiversity in Songnen grassland showed that,before 1992,the spatial heterogeneity of plant species richness in Songnen grassland was large,and the coefficient of variation reached81.11%.The high value area of species richness was mainly concentrated in the western boundary of Songnen Plain,while the low value area was mainly concentrated in the western hinterland.After 2015,plant species richness increased and the spatial coefficient of variation became smaller,about 47.76%.The spatial distribution pattern of plant species richness was different from that before 1992.The high-value areas were mainly concentrated in the inland of Songnen Plain,such as Suihua City,while the plant richness was lower in the west and its western border,such as Daqing City.The results of the analysis of factors influencing the spatial distribution pattern of plant species richness showed that soil and climate accounted for 25%（R²=0.25,p<0.001）of the total variation ofαdiversity in the spatial distribution pattern of plant species in this region.The contribution rate of significant soil indexes such as EC,Na⁺,Ca²⁺and p H reached 68.5%,and that of climatic drying index（AI）was 31.5%.In conclusion,soil salinization was the dominant factor affecting the spatial distribution ofαdiversity in Songnen grassland,followed by climatic dryness.（2）The results of the analysis of the spatial distribution pattern ofβdiversity in Songnen grassland showed that the turnover components ofβdiversity were significantly higher than those of the nested components in 2017 and 2018,and the turnover components accounted for89.2%of the totalβ-diversity in Songnen grassland,and the nested components accounted for10.8%.The results indicated that the spatial distribution pattern ofβdiversity in Songnen grassland was mainly dominated by turnover process,and species substitution was significant.High plantβdiversity areas were mainly concentrated in the northwest of the Songnen Plain,such as Daqing,Qiqihar,and Baicheng city.However,in 2018,Songyuan city in the hinterland of the Songnen Plain showed higher nested components,indicating that the species composition in the southern part of the Songnen Plain was similar.In 2017,effective accumulated annual temperature（ECT）and agricultural output（AOP）together accounted for 6%（R²=0.06,p=0.05）of the total variation ofβ-diversity spatial distribution pattern in Songnen grassland,and their contribution rates were 78.6%and 21.6%respectively.In 2018,mean temperature（MMT）,mean rainfall（MMP）,agricultural output（AOP）and soil p H accounted for 6%（R²=0.06,p=0.05）of the total variation ofβ-diversity spatial pattern in the sampled month,and their contribution rates were 30.0%,7.0%,29.5%and 32.9%,respectively.In conclusion,climate was the dominant factor affecting the spatial distribution of plantβdiversity in Songnen grassland,followed by human activities.Therefore,this study suggests that the potential mechanism of turnover replacement is attributable to climatic differences and differences in the intensity of human agricultural activities.（3）The spatial distribution of plant diversity in Songnen grassland was inconsistent with the classical power function model（R²=0.15,p<0.001）,indicating that the plant species-area relationship in this region was different from the classical theoretical paradigm.The results of species-area relationship fitting analysis showed that climate and soil salinization together accounted for 16.0%（R²=0.16,p=0.001）of the total variation in the degree of deviation.The contribution rates of significant soil indexes such as EC,Na+,HCO₃^-and Cl^-were up to 65.5%,and the contribution rates of climate indexes such as effective annual accumulated temperature（ECT）and average rainfall（MMP）in the sampled month were up to 34.5%.Therefore,the unique soil salinization characteristics of Songnen grassland-soda salinity is the main reason that may affect the deviation of the native plant species-area relationship from the classical power function theory model;followed by regional differences in climatic factors such as effective cumulative temperature and average annual precipitation.In summary,this study has accumulated experience in clarifying the spatial and temporal distribution patterns of plant diversity in the Songnen grassland region on a large scale,and the results have enriched the scientific understanding of the spatial and temporal distribution patterns of plant diversity in Songnen grassland,the key influencing factors and their possible driving mechanisms,and are expected to provide scientific support for the management of the Songnen grassland ecosystem,biodiversity conservation and the construction of regional biodiversity distribution pattern models.