| The forest ecosystem in Changbai Mountain is the most typical forest ecosystem with vertical gradient distribution of vegetation in East Asia.It is also one of the most sensitive to global climate change and well-preserved forest ecosystems in China.The incline in the topography has made this region an ideal place for studying the growth and ecophysiology of alpine trees along an elevational gradient.The responses of tree growth and physiological characteristics to elevation gradient can reflect the adaptability of trees to environmental variations and help predict their responses to future climate changes.The sapling stage is an important part of the plant life.As the main tree species in Changbai Mountain,Pinus koraiensis Sieb.et Zucc.,Quercus mongolica Fisch.Ex Ledeb.,Acer ukurunduense Trautv.&C.A.Mey.,Tilia amurensis Rupr.and Betula platyphylla Suk.have great ecological service values.At present,studies on the physiological and growth characteristics of saplings of these tree species along the elevation gradient are rarely reported.This study systematically measured the annual growth,biomass allocation,leaf photosynthetic,leaf reflectance spectrum and leaf structure characteristics of saplings of this five tree species at different elevations in Changbai Mountain nature reserve.The purpose of this study was to analyze the responses of growth characteristics and leaf properties of different tree species along elevation gradient,to compare the differences of responses among species,and to compare the biotic and abiotic factors which affecting the growth of different species.The understanding of life history strategies of each species is also help to better understanding of the inner mechanism of species diversity maintenance,and provides theoretical basis for the sustainable management of mountain forests in this region.The data provided in this study will also contribute to the accurate estimation of forest carbon reserves and the further improvement of the plant functional character database in this region.The results and conclusions are as follows:(1)In P.koraiensis and mixed broadleaved forests(PBMF)and evergreen coniferous forests(ECF),the biomass of current-year needles,current-year branches and one-year-old needles of P.koraiensis saplings,as well as their ratios to the total biomass,increased with the increase of elevation respectively.The growth parameters in PBMF were larger than those in ECF.These indicated that in two different kinds of forest type,the annual growth of P.koraiensis saplings increased with the increase of elevation,and the climate warming may not be conducive to the growth of P.koraiensis saplings.Moreover,the annual growth of P.koraiensis saplings in PBMF was significantly higher than that in ECF.(2)Results of redundancy and correlation analysis showed that the 13 needle properties and 10 environmental parameters could explain 42.26%and 45.11%of the variation in growth of P.koraiensis saplings in PBMF.The growth of sapling of P.koraiensis in PBMF was significantly correlated with leaf properties such as leaf water potential and saturated light intensity,but also significantly correlated with the average annual atmospheric temperature,average annual atmospheric humidity,annual accumulated temperature,annual precipitation,atmospheric pressure and other environmental factors.The 13 needle properties and 10 environmental parameters could explain 40.95%and 33.27%of the variation in growth of P.koraiensis saplings in ECF.The growth of saplings of P.koraiensis in ECF was significantly correlated with leaf properties such as leaf total phosphorus content,leaf total carbon content and light saturation rate,but also significantly correlated with the average annual atmospheric temperature,average annual atmospheric humidity,annual accumulated temperature,annual precipitation,soil moisture content,soil total phosphorus content and other environmental factors.The physiological plasticity of P.koraiensis saplings is greater than its growth and morphological plasticity.(3)Biomass of leaves,current-year branches and one-year-old branches of Q.mongolica saplings and the ratios to total biomass decreased with the increase of elevation,indicating that the climate warming may be conducive to the growth of Q.mongolica saplings in this area.Results of redundancy and correlation analysis showed that the 16 needle properties and 10 environmental parameters could explain 42.91%and 34.18%of the variation in growth of Q.mongolica saplings.Leaf properties such as chlorophyll content,total nitrogen content and apparent quantum efficiency,as well as environmental factors such as average annual atmospheric temperature,average annual atmospheric humidity,annual accumulated temperature,annual precipitation,atmospheric pressure and soil pH value significantly affected the growth of Q.mongolica saplings.The physiological plasticity of Q.mongolica sapling is greater than its growth and morphological plasticity.(4)The carotenoid index and the structure independent pigment index of saplings of A.ukurunduense,T.amurensis and B.platyphylla increased with the elevation;total biomass,leaf biomass to total biomass and new branch biomass to total biomass decreased with the increase of elevation.These indicated that the environmental pressure of saplings of these three species increased with the increase of elevation,and the annual growth decreased with the increase of elevation.The climate warming may be beneficial to the growth of these three tree species.(5)The saturated light intensity of B.platyphylla sapling is greater than that of A.ukurunduense and T.amurensis;the dark respiration rate and the apparent quantum efficiency of B.platyphylla sapling were increased and decreased with the increase of elevetion,respectively.However,there were no significant differences between dark respiration rate and apparent quantum efficiency of saplings of A.ukurunduense and T.amurensis from various elevations.These suggested that under a warming climate,B.platyphylla saplings would have a competitive advantage over A.ukurunduense and T.amurensis in areas with high light intensity such as forest edges or forest Windows.The light compensation point and water use efficiency of young A.ukurunduense decreased and increased with the increase of elevation,respectively.The results showed that under the climate warming situation,the light intensity needed for the balance of photosynthesis and respiration increased and the water use efficiency decreased,which made the young trees of A.ukurunduense have no competitive advantage over the other two tree species.The water use efficiency of T.amurensis saplings decreased with the increase of elevation,indicating that it was more competitive than A.ukurunduense and B.platyphylla in the future climate warming. |
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