Study On The Difference Of Plant Growth Condition Under Urban-Rural Gradients From Field Sampling And Remote Sensing

Cities are considered as natural laboratories for studying vegetation responses to global changes.Plant functional traits of leaf(PFT-L)that varies with environmental conditions can provide a reliable and convenient indicator of the impacts of urbanization on plant growth.However,previous studies can't explain the complex effects of urbanization on vegetation growth systematically,as field measurement researches can't well indicate the distribution pattern,and the remote sensing studies were poor explained for their mechanism.Our study has explored the different effects of urbanization on vegetation growth along urban-rural gradients using field observations and remote sensing analysis.Field observations compared the PFT-Ls of Camphor(Cinnamomum bodinieri)trees along urban-rural gradients.Meanwhile,multi-source remote sensing data along the urban-rural gradients for Changsha were used to analyze the differentiation of vegetation indexes(Normalized Difference Vegetation Index,NDVI;Enhanced Vegetation Index,EVI),photosynthetic indexes of vegetation(Solar-induced chlorophyll fluorescence,SIF;Gross Primary Productivity,GPP;Net Photosynthetic,PSN),canopy structure indexes of vegetation community(Fraction of Photosynthetically Active Radiation,FPAR;Leaf Area Index,LAI),soil properties indicators,air quality indexes,and meteorological indexes.Main results are as following:(1)Vegetation indexes,photosynthetic indexes of vegetation,canopy structure indexes of vegetation community showed a significant increasing trend along urban-rural gradients(p<0.001).This result showed that the vegetation growth at different urbanized region(urban,suburban,rural)were differently affected by urbanization.In urban region,annual change rates of all the indexes above were generally decrease,while slight increase in the core vegetated region suggested that urbanization has enhanced vegetation growth in urban region.And GPP was significantly correlated with most of the environmental factors(e.g.,available nitrogen,total nitrogen,sulfur dioxide,ammonia,evapotranspiration,specific humidity),and the correlation was significantly different in different regions along the urban-rural gradients.(2)There were significant differences for leaf area(LA),leaf perimeter(LP),leaf width(LW),secondary axis length(SL),leaf circularity(LC)and leaf aspect ratio(LAR)between different regions along the urban-rural gradients.And specific leaf area(SLA)showed a very significant increasing trend along the urban-rural gradient.Leaf dry mass(LDM)had a very significant positive correlation with LA,LP,leaf length(LL),LW,primary axis length(PL)and SL on all urbanized regions,and the correlations were generally lower in suburban areas.SLA is highly correlated with all the PFT-Ls except LC and LAR in suburban region.(3)GPP is highly correlated with meteorological indicators and PFT-Ls of camphor tree in the urban-rural gradients.PFT,Ls along urban-rural gradients can be used to simulate GPP better,and the goodness of multivariate model fit is 0.905.Cross-scale analysis showed that urbanization has affected the leaf economic spectrum(LES)of plants,and a general shift from the 'quick investment-return' to the'slow investment-return' type was observed with the urbanization.Cities are harbingers of future global change and considered as natural laboratories for studying vegetation responses to these changes.In this cross-scale study,multi-source data along urban-rural gradients were used to explore vegetation growth responses to urbanization.Our study provided an empirical foundation for understanding the response of vegetation to future global change.