| Carya illinoensis is native to the United States and northern Mexico.Pecan is an oil tree with high economic and ecological benefits for both fruit and w ood species.In view of the excellent qualities（early fruiting,high yield,disease resistance）and significant economic benefits for plant,pecan has great promoti on potential in Chongqing mountainous area.There are great differences in gro wth and stress resistance among varieties,it is necessary to study the growth a daptability and photosynthetic physiological characteristics of pecan according to the characteristics of Chongqing mountainous area and natural resources conditi ons,so as to breed and develop excellent pecan varieties that adapt to the site characteristics of Chongqing mountainous area.In this study,8 pecan varieties i n Chongqing were used as research materials.In situ observation on phenology and growth adaptability of trees were investigated.The osmotic adjustment subst ances,chlorophyll content,leaf nitrogen content and photosynthetic nitrogen utili zation efficiency of trees were observed.The light response curve and CO2 resp onse curve were determined by using LI-6800 portable photosynthetic apparatus.This paper aims to explore the differences in growth adaptability,photosyntheti c capacity and physiology adaption among different varieties of pecan,and to cl arify the potential relationship between photosynthetic characteristics and other le af functional traits,and to provide a theoretical basis for the efficient cultivation and application.The primary research results are as follows:（1）Eight pecan varieties could normally complete the annual growth cycle under field conditions in Chongqing,and the average annual growth cycle lasted more than 240 days.The eight varieties can be divided into three types with t wo protogynous,five protandrous and one homogamous.The varieties that can be used as mutual pollination varieties are‘YLC12’בYLJ042’,‘YLC13’בY LJ042’,‘YLJ042’בYLC29’,‘YLC29’בMahan’,‘YLJ5’בMahan’.‘YLJ042’,‘YLJ5’and‘YLC29’could meet the pollination requirements of most varieties.（2）The growth characteristics were found to differ significantly among eigh t varieties.‘YLJ042’,‘YLC12’and‘YLC29’had relatively higher plant height,‘YLC13’and‘Mahan’had relatively higher crown ratio.The annual growth of plant height,ground diameter and branches of the eight varieties were 0.24～0.51m,3.55～6.25 mm and 0.16～0.23 m,respectively;the growth performance of‘YLC12’was the best,while that of‘YLJ5’was the worst.‘YLC35’,‘YLC13’and‘YLJ5’had relatively higher branch number,branch length and branch num ber,which occupied the space advantage of resource acquisition.The branch dia meter ratio of 8 varieties was 0.53～0.66,there were no signifycant differences b etween the varieties for branch diameter ratio,meaning that the capacity of adja cent branches to carry nutrients were approximately the same among eight varie ties.The branching rate of 8 varieties was 0.53～0.66,‘YLC10’and‘YLJ5’had relatively higher branching rate.‘YLC13’and‘Mahan’had relatively higher lea f aera,‘YLC35’had highest leaf area index,‘YLC35’and‘Mahan’had relativel y higher specific leaf area.（3）According to the field performance and the physiological and biochemic al indexes of different pecan varieties,the order of heat resistance of eight vari eties of pean from strong to weak was:‘YLC35’>‘Mahan’>‘YLC10’>‘YLC13’>‘YLJ042’>‘YLC12’>‘YLC29’>‘YLJ5’.The heat injury index（HII）was the highest in‘YLJ5’（0.43）and the lowest in‘YLJ042’（0.20）.The amount of growth was the highest in‘YLC35’and lowest in‘YLJ042’.‘YLC35’and‘M ahan’showed better performance over-summering,and could be used as heat res istant germplasms for further breeding and utilization.（4）The diurnal variation of photosynthesis was found to differ significantly among eight varieties in May and August,the Pn,stomatal conductance（GS）a nd transpiration rate（Tr）of the eight varieties showed two curve types of singl e peak and double peak in two months,while the diurnal variation of Cimostly showed V-shaped and W-shaped.‘YLC12’,‘YLC29’,‘YLC10’and‘Mahan’ap peared midday depression of photosynthesis in May,‘YLJ042’and‘YLJ5’had r elatively higher Pn,the peak value of‘YLJ042’and‘YLJ5’was 10.88 and 9.55μmol·mol-2s-1,respectively.In August,most varieties could overcome photosynt hetic“siesta”phenomenon except for‘YLC10’,‘YLC35’and‘YLC13’had rel atively higher Pn,the peak value of‘YLC35’and‘YLC13’was 12.26 and 13.38μmol·mol-2s-1,respectively.The daily mean value of Tr in August was higher than that in May,while the daily mean value of water use efficiency（WUE）i n August was lower than that in May.Compared with May,the daily mean val ue of Pn and Gs of most varieties increased in August,while the daily mean v alue Pn and GS of‘YLJ5’decreased by 32.10%and 48.39%respectively,and the daily mean value of Pn of‘YLJ042’decreased by 18.36%.The Tr,Gs and atmospheric temperature（Ta）were very important to the diurnal change of Pnamong the physiological and ecological factors.（5）The change of the Pn-PAR and CO2-PAR were completely similar in ei ght pecan varieties which showed a trend of rapid increase first and then stabili zed or declined.The photosynthetic characteristic parameters were found to diffe r significantly among eight varieties,the maximum net photosynthetic rate(Pmax)of eight varieties was 28.94～38.74μmol·mol-2s-1,the light compensation point（LCP）was 8.52～15.10μmol·mol-2s-1,and the light saturation point（LSP）was 1263.02～1684.10μmol·mol-2s-1.‘YLC35’and‘YLC13’had relatively higher Pmax,LSP,maximum carboxylation efficiency(Vcmax)and maximum electron transport rate(Jmax),meaning that their light efficiency and CO2 use efficiency potential were relatively strong.（6）There were differences in organic carbon(Cmass),mass-based and area-b ased leaf nitrogen concentration(Nmass,Narea),mass-based leaf potassium concent ration(Kmass),Chla,Chlb,chlorophyll content（Chl）,specific leaf weight（SLW）,leaf dry matter content（LDMC）,photosynthetic nitrogen utilization efficiency（PNUE）and total partition coefficients of leaf nitrogen in photosynthetic apparat us over the eight species.‘YLC35’had highest chlorophyll content,Nmass,PNU E and total partition coefficients of leaf nitrogen in photosynthetic apparatus.Th e Pmaxwas significant positively correlated with Chl,fraction of leaf nitrogen all ocated to carboxylation（PC）and PNUE,associated Pearson correlation coefficien t with 0.76,0.72,0.94,respectively.The correlation among PNUE and PC,SL W was significant positive and negative respectively,where the correlation coeff icients were 0.76 and-0.73,respectively.In summary,‘YLC13,‘YLC35’and‘Mahan’had better growth and photos ynthetic capacity than other pecan varieties,and were suitable for large-scale pr omotion in Chongqing. |
