Geographic Variation Of Morphology,Anatomy And Biomass Dynamics Of Tree Fine Roots

Fine root(diameter<2 mm)morphological and anatomical traits could influence the survival and growth of trees,fine root biomass(FRB),production(FRP)and turnover(FRT)plays critical roles in carbon balance and nutrient cycling in forest ecosystem.Thus,studies on the geographic variation of fine root morphological and anatomical traits and FRB dynamics along nature environmental gradients at large scale have important implications on predicting the response and mechanisms of trees and forest ecosystem in the context of global change.This study investigated the spatial variation of tree fine root morphological and anatomical traits and FRB dynamics at large scale,in order to explore the possible responses of tree fine root system to future climate change.At the individual level,we sampled Ginkgo biloba and Eucommia ulmoides from different climate region(5 study sites from subtropical to temperate climate were Shaoguan in Guangdong Province,Zhengzhou in Henan Province,Taiyuan in Shanxi Province,Yinchuan in Ningxia Hui Autonomous Region,and Shenyang in Liaoning Province),to study the geographic variation of morphological and anatomical traits of leaf and 1st order root.At stand level,we analysed the geographic variation of absorptive(diameter<0.5 mm)and fine(diameter<2 mm)root biomass,production and turnover of Fraxinus mandschurica in different sites(from south to north:Wandianzi in Fushun in Liaoning Province,Maoershan in Shangzhi in Heilongjiang Province and Dailing in Yichun in Heilongjiang Province)in Northeast China.At regional level,we summarized published data,and detected the spatial variation of FRB,FRP and FRT of coniferous,broadleaved and total forests in China.Our results showed that:1.At individual level,mean annual precipitation(MAP)played the dominant role in the spatial variation of morphological and anatomical traits of leaf and 1st order root of G.biloba and E.ulmoides.Specific leaf area(SLA),stomtal and leaf vein density,and the diameter of 1st order root of both species were positively correlated with MAP,while leaf thickness,specific root length(SRL)decreased along the MAP gradient.In both species,there were negative correlation between SLA and SRL,leaf thickness and the diameter of 1st order root,while the xylem cell number of leaf and 1st order root were positively correlated,indicating the coordinated variation between leaf and 1st order root in different environment.At drier site,the thicker leaf,lower stomatal and leaf vein density would reduce water transpiration,and the thinner root and cortex layer would improve water uptake,while at the moist site,the higher SLA,stomatal and vein density could improve the maximum photosynthetic rate,and the more xylem cell in both leaf and 1st root could improve the maximum vertical water conductivity to balance the transpiration and photosynthesis.These results showed the tight relationship between leaf and root in water uptake,transportation and transpiration,and the plasticity of structure and function of the two organs along environment gradients.2.At stand level,biomass and production of absorptive and fine root of F.mandschurica showed great variation among sites in Northeast China.Biomass and production of absorptive and fine root biomass in Dailing were nearly twice as much as that in Wandianzi.However,the variation of turnover and morphological traits(SRL and tissue density)of absorptive and fine root were quite little between different sites.Mean annual temperature(MAT)was the dominant climatic factor driven the spatial variation of absorptive and fine root biomass and production of F.mandschurica.Both biomass and production of absorptive and fine root were negatively correlated with MAT,while turnover and morphological traits of absorptive and fine root were not significantly correlated with any climatic variable.These results indicating that F.mandschurica may tend to increase production and biomass rather than adjust morphological traits or lifespan of absorptive and fine root in the colder site to meet the demand of soil resource of aboveground growth.The ratio of absorptive root biomass to fine root biomass varied little(47-52%)along the MAT gradient,but was significantly lower in deeper soil layer(26-56%),implicating that the ratio was mainly influenced by soil physical and chemical properties rather than climatic factors.3.At regional level,FRB,FRP and FRT displayed obvious geographic variation in Chinese forests,and the variation patterns were mainly characterized by MAP.FRB of coniferous,broadleaved and total forests were 224.3 g m-2,317.2 g m-2 an 278.3 g m-2,respectively,and FRP were 320.5 g m-2 a-1,387.2 g m-2 a-1 and 366.8 g m-2 a-1,and FRT were 1.30 a-1,1.11 a-1 and 1.19 a-1.Our estimation of FRB of Chinese forests were lower than that in other region and global average,while FRP and FRT were close to,if not higher the estimation of other region and global average.Possible reasons were Chinese forests were younger(stand age was 40.1a in average)and grown in a relative drier climate than other regional or global forests.FRB,FRP and FRT increased with increasing MAP,possibly due to the relative large variation of precipitation(41%)compared to temperature(14%)in growing season(from May to September).These indicated that the shift of spatial-temporal pattern of precipitation in future would deeply influence fine root biomass dynamics and the carbon and nutrient cycling driven by fine root dynamics of forest ecosystems in China.The strong influence of MAT on FRB,FRP and FRT of forests in China were different with the variation patterns of fine root variables in F.mandschurica dominated by MAT in northeast China,indicating that temperature rather than precipitation was the key limiting factor in colder region.In summary,from fine root morphology and anatomy at tree individual level to regional FRB dynamics in Chinese forests,obvious geographic variation,which were tightly related with climatic factors,were displayed.However,the key influential variable on tree fine root structure and function maybe different for different species in different region,indicating the diversity of adaption strategies of tree fine root system to environmental change.These findings would help our understanding and predicting the response of individual tree growth and forest ecosystem cycling to future climate change.