Latitudinal Patterns And Influencing Factors Of Leaf Caloric Value Of Forest Ecosystem Along North-South Transect Of Eastern China

Leaf caloric value reflects the capacity of a leaf to fix and accumulate solar energy through photosynthesis.We systematically investigated the leaf caloric value of 920 plant species in 9 forests,representing a range of tropical to cold-temperate forests along the North-South Transect of Eastern China.In order to better reflect the capacity of leaves to capture solar radiation,we calculated leaf caloric value per area(ACV,KJ·cm-2)based on specific leaf area.In order to consider the community composition of plant species and their relative leaf biomass in the specific community,we calculated leaf gross caloric value(LCV,KJ·g-1)on three levels,species level,PFG level and community level.The goals were to explore the latitudinal patterns and influence factors of ACV and LCV at the levels of species,plant functional group,and community.Then we want to establish the relationship between LCV and gross primary productivity(GPP).The main findings of this study were as followed:(1)ACV ranged from 0.024 to 1.056 KJ cm'2 with an average of 0.151 KJ· cm-2.ACV declined linearly with increasing latitude along the transect.Altogether,the total variation in ACV at this large scale was explained by phylogenetic group(52.38%of variation),leaf element content(40.46%).Significant phylogenetic signals in ACV were observed not only within forest communities but also across the whole transect.This signal was stronger at higher latitudes,reflecting latitudinal change in the species composition of forest communities from complex to simple.We infer that climate influences spatial patterns in ACV by directly regulating the species composition of plant communities,as most plant species tolerate only a limited temperature range.(2)Our results showed that LCV for all species ranged from 12.85 to 22.15 KJ·g-1 with an average of 18.46 KJ·g-1.Plant functional groups had a significant influence on LCV,with trees>shrubs>herbs,conifers>broadleaved trees,and evergreens>deciduous trees.Unexpectedly,no apparent latitudinal trends of LCV at community level were observed,although LCV at the species level clearly decreased with increasing latitude.Use efficiency of LCV(CUE,g C KJ-1),defined as the ratio of GPP to total LCV at the community level,varied quadratic with latitude and was lower in the middle latitudes.Climate(temperature and precipitation)may explain 52.9%of the variation in spatial patterns of CUE,which was positively correlated with aridity.Our findings are the first large-scale report of the latitudinal patterns of LCV in forests at the species,plant functional group,and community levels and provide new insights into the relationship between LCV and ecosystem functions in forest communities.