Environmental Responses Analysis Of Radial Growth Of Quercus Aliena Var.acutiserrata And Quercus Variabilis In Qinling Mountains

Oak forests is an important forest resource in China.It not only has ecological and social benefits such as carbon sequestration,water storage,oxygen supplement and recreation,but also can provide economic values such as woods and corks.However,the main environmental factors and mechanisms affecting the growth of oak forests in China are not clear.In this paper,the Quercus aliena var.acutiserrata and Q.variabilis in three locations of Qinling Mountains(the north-south boundary zone in China)are the main research objects.Based on tree-ring chronologies and field survey information,the radial growth dynamics of two oak trees at different altitude gradients and their relationship with climate,and the dynamic change of the basal area increments of the oaks and their relationships with environmental factors such as climate,tree age,competition,density and topography were studied;finally,the biomass and productivity of single tree and oak stands were estimated based on the existed biomass allometric models.In order to provide theoretical guidance for the managements and protection of oak resources in China.The main results are as follows:(1)15 residuals chronologies of the Q.aliena var.acutiserrata and Q.variabilis were established at different altitudes in Qinling Mountains.The tree rings growth-climate analysis showed that the response of oak trees at different altitudes on the northern slope of Taibai Mountains(TBS)in the central Qinling Mountains was relatively consistent.Individual tree radial growth was positively correlated with the precipitation and Palmer Drought Severity Index from May to July of current year,but with May-July Monthly saturated vapor pressure deficit,average temperature and maximum temperature are inversely related.The responses of the oak trees growth to climate change in eastern(Baotianman,BTM)and western(Xiaolongshan,XLS)Qinling were various across different altitudes,but they were all affected psitively by the precipitation in June and negatively by the temperature in June.(2)Mixed effect models of individual tree diameter increments of the Q.aliena var.acutiserrata and Q.variabilis were established.Taking into account the random factors of individual trees and plots,time series autocorrelation(first-order autoregression and moving average model,ARMA)and heteroscedastic structure(power function),linear mixed effect models of the individual tree basal area increment(BAI)were carried out for the two oaks,as proven to outperform the general linear models.At the same time,it was found that precipitation has a significantly positive effect on the BAI of the oak trees in the central and western Qinling Mountains,and has a significantly negative effect on the BAI of the Q.aliena var.acutiserrata trees in the eastern Qinling Mountains;temperature has a significantly positive effect on the BAI of oak trees in the western Qinling Mountains,and has a significantly negative effect on the eastern Qinling Mountains,but has no significant impact on the central Qinling Mountains.The competition between trees is the main limiting factor for the growth of oaks in the Qinling Mountains,and the age of the trees and the initial DBH both have a significant effect on the growth of Qinling oak trees.For example,the initial DBH has a significantly positive correlation with the oak trees in the central and eastern Qinling Mountains and a significantly negative correlation with the oak trees in the western Qinling Mountains.The BAI of oak trees at all altitudes showed an increasing trend with increasing age.(3)The biomass and productivity of oak forests in different regions were compared.Allometric equation fitting results show that,overall,the order of biomass of Q.aliena var.acutiserrata forests was Taibai Mountains in central Qinling> Baotianman in eastern Qinling>Xiaolong Mountains in western Qinling;and the average biomass of Q.variabilis forests in Taibai Mountains was lower than that in Baotianman;the ratios of trunk biomass in Q.aliena var.acutiserrata(51.3%-56.0%)were higher than that of Q.variabilis(42.6%-46.7%),and the ratios of leaf biomass in Q.aliena var.acutiserrata(1.1%-1.7%)are lower than Q.variabilis(2.5%-2.8%).Quercus forests in Qinling region had the highest biomass or productivity in the70-year-old forest.(4)Using provenance experiments,the pattern of carbon assimilation and carbon allocation of the Q.variabilis saplings across various provenances was revealed.The low-latitude provenance(Hunan Chengbu)had the highest individual average biomass,while the provenance of Henan Neixiang is the lowest.The root-shoot ratios of Q.variabilis saplings were all larger than those at oak natural forests in Qinling Mountains,and the sequence of root-shoot ratios was Pinggu(PG)> Zigui(ZG)> Neixiang(NX)> Chengbu(CB)> Taibai Mountain(TBS)>Baotianman(BTM).The maximum net photosynthetic rate(Pmax)of the provenances at low latitudes(Hunan Chengbu)was highest when compared with other provenances.The primary conversion efficiency of light energy of photosystem Ⅱ(Fv/Fm)of various provenances was not inhibited by light.There is no sign of physiological stress,and the PSⅡ light energy heat dissipation and light protection ability were comparable among different provenances.In summary,the precipitation during the growing season can promote the radial growth of oak trees at all altitudes in Qinling,and the high temperature during the growing season can inhibit its growth.In addition,competition,tree age and initial DBH also have a significant effect on the radial growth of oak trees.Among them,competition is the most important limiting factor.The age and DBH of trees had positive or negative effects on the radial growth of oak trees at different periods.The radial growth,high growth,carbon accumulation and photosynthesis parameters of the high-latitude Q.variabilis were lower than those of low-latitude provenance after southward migration,which indicates that the response of growth and carbon accumulation to climate warming was not rapid and sensitive for Q.variabilis saplings.In addition,the ring width indices(RWI)of natural oak forests in Qinling Mountains had no obvious upward trend during the climate warming and drying period,indicating that the age,DBH and competition factors of oak trees have a greater impact on their growth than climate change in Qinling Mountains.