Spectrum Of Plant Form And The Function In Forest Communities In Zheiiang Province Of Eastern China

Tree architecture represents trees' adaptance to environment.Previous studies have suggested that plant architectural strategies are dependent on variation of water,heat and light environment,and thus forming the global spectrum of plant form and the function of a given community.At local scale in forests,trees at different vertical levels have different patterns of architecture probably due to the light utilization and water transport.However,our understanding regarding local spectrum of tree form and the function of community,and the underlying mechanisms remains unclear.The research in this thesis was conducted in a Schima superba community(2 plots of 20×20 m2)and Liquidambar formosana community(2 plots of 20×20 m2)located in Tiantong and Putuoshan Island of Zhejiang Province,respectively.Within both communities,each individual was measured for architecture,light utilization and hydrualic traits including stem temperature.Tree architecture traits include tree height(H),crown area(CA),crown depth(CD).number of current year leaves(LN),proportion of vertical and horizontal branches(PVB and PHB),mean leaf area(MLA),petiole diameter and length(PD and PL),number of twig borne by first level branch(0BN),and number of first level branch borne by second level branch(1BN).Light utilization traits include maximum photosynthetic rate(Amax),light saturation point(LSP),light compensation point(LCP),stoma density(SD),and stomal conductance(Cond).Hydraulic traits include transpiration rate(Tr),wood density(WD),vessel diamter and density(VD and VDensity),sap flow(E),hydraulic conductivity(Kh),sapwood-specific hydraulic conductivity(Ks),leaf-specific hydraulic conductivity(Kl),Huber value(HV),and Huber value for petiole(HVleaf).Leaf economic traits include specific leaf area(SLA),leaf nitrogen content(N),leaf dry mass content(LDMC).Firstly,linear model was used to analyze the relationships between plant height and other architectural traits.Secondly,structural equation modeling(SEM)was employed to tease apart the effects of functional traits related to light utilization and water transport on tree height.In addition,we also tried to verify a compensation mechanism for light utilization and water transport based on the spatial architecture of leaves and branches through indirect effects on tree height.Finally,Principal Component Analysis(PCA)was used to reveal the relationships between hydraulic traits,photosynthetic traits,leaf economic traits and difference of stem temperature(?T),for the purpose to establish the spectrum of plant form and the function in forest communities.Following are the main results from this thesis:(1)Tree architecture showed significant variation along H.Specifically,PVB,CA,CD and VD significantly increased with increasing H,while OBN or 1BN significantly decreased.These results indicate that tall trees had bigger and more compact crown,but had loose anatomical structure.In addition,tall trees were characterized with bigger PL,PD,LA and LN in S.superba community,which further indicate the importance for plant vertical growth.(2)The SEM showed that traits related to light utilization and water transport including LSP,LCP,VD,LDMC,Tr and E had positive effects on H.However,trees could adjust their architecture to compensate for water transport via higher PVB,more convergent leaves and smaller LN,which enabled trees to have strong capability to capture light,and have bigger transpiration pull and VD to provide water for higher layers,and hence beneficial for trees' growth.By contrast,when equipped with higher PHB,more divergent leaves and bigger LN,plants had disadvantages to grow for having larger transportation resistance,smaller tranpiration pull and weaker ability for light utilization.(3)The physiological mechanisms for explaining H were different when all functional traits were considered.The effect value in S.superba community on plant height via light utilizaiton traits was strong than that via hydraulic traits.In contrast,the reverse was true for trees in L.formosana community.Thus,tree height in S.superba community was mainly limited by light resources,whereas tree height in L.formosana community was mainly influenced by water resources.(4)Evidences for local spectrum existed for H,LD and PHB among studied two communities.There was a spectrum along ?T-H dimension,and the individuals having big differences in stem temperature were clustered at one end,while individuals that represented small difference in stem temperature were clustered at the other end of the axes of H.In S.superba community,there were mainly two spectra along E-LSP-Amax-LD and N-Cond-PHB dimensions.The individuals which were representative of strong capacity of water transport and light utilization were clustered at one end,while traits that represented weak capacity of water transport and light utilization were clustered at the other end in each of the axes of LD and PHB.However,In L.formosana community,there were mainly two spectra along HVleaf-LD and E-PHB dimensions,which represented the capacity of water utilization.(5)When the whole plant spectrum for the two communities were combined together,leaf economic spectrum did not exist at the local scale,but there was a spectrum of plant form and function based on H.The acquisitive plants had high plant height,big crown and strong ability of light and water utilization.In contrast,conservative plants had low height,small crown and weak capacity of light and water utilization.In addition,there were four spectra,namely leaf hydraulic spectrum(LWP-HVleaf-Kl),spectrum of water and light utilization for LD(Kh-Cond-LD),spectrum of water and light utilization for PHB(N-HV-LDMC-PHB)and spectrum of water utilization for WD(HVleaf-WD).(6)Trees having different heights showed significant differentiation along the spectrum of plant form and function,and have completely different growth strategies.The traits which were representative of the acquisitive strategy were clustered at one end,while traits that represented the conservative strategy were clustered at other end in the tree height spectrum.Additionally,different life forms of community types were separated along this spectrum,with evergreen S.superba community having greater capacity of water utilization than deciduous L.formosana community.In conclusion,this thesis analyzed the relationships between light utilization traits,hydraulic traits and vertical architectural traits.Based on the research regarding vertical variation of tree architecture,I concluded that plant architecture's variation was a compensate strategy for their capcity of water utilization,and revealed the physiological mechanism for the variation of tree height from chacracters of light and water utilization in forest communities of Eastern China.Lastly,I combined all these functional traits together to build the local spectrum of plant form and function mainly based on tree height,providing a basis for the further understanding of community assembly.