Study On Phenological Storage Mechanism Of Non-structural Carbohydrates In Young Trees Of Typical Trees In Beijing

In order to reveal the phenological rhythm storage mechanism of non-structural carbohydrates at the organ and whole plant levels,young trees of four typical tree species in Beijing,Pinus tabulaeformis,Platycladus orientalis,Robinia pseudoacacia and Populus davidiana,were selected as study objects.We measured and analyzed the phenological rhythm changes of component content and sugar starch ratio of non-structural carbohydrates（NSC）,and monitored environmental factors,plant growth indexes and physiological parameters to study their correlation with these influencing factors.The research results showed that:（1）The growth trend of plant height and ground diameter of all tree species is consistent,showing a single peak,reaching the peak in summer phenology phases.The bud opening phase in spring and deciduous phase in autumn promoted biomass allocation of above-ground organs and supporting organs,while the peak period of summer phenology inhibited biomass allocation of above-ground organs.The order of magnitude of specific leaf area for each tree species was P.davidiana>R.pseudoacacia>P.tabulaeformis>P.orientalis.The patterns and trends of organ biomass allocation differed among tree species（P<0.05）.The allocation of leaf biomass of evergreen tree species was 2.8 times that of deciduous tree species,and the proportion of leaf biomass allocation was the highest at the peak period of leaf unfolding phase.The biomass allocation of twigs fluctuates greatly in spring phenological phase,reaching a maximum value of 32.05%at the early stage of leaf unfolding phase.The biomass allocation of trunk was highest at the bud burst stage and the early leaf unfolding phase,and the proportion of trunk and thick roots in the whole plant reached 39.01%and 22.53%,respectively.Throughout the whole observation period,the fine roots of deciduous tree species fluctuated violently.During the reproductive growth phase,the biomass allocation of branch decreased sharply to 5.93%,while the biomass of leaves increased continuously.（2）The photosynthetic fluorescence parameters and leaf water potential of all tree species showed significant interspecific differences（P<0.05）.As the phenological rhythm progressed,photosynthetic parameters were higher in the fully leaf unfolding and leaf growth capping phases and lower in the leaf discoloration phase,with the photosynthetic parameters of deciduous tree species being about 3.2 times higher than those of evergreen species.The difference in chlorophyll fluorescence parameters between evergreen and deciduous tree species ranged from 7.02%to 26.24%,which were larger in the growth capping,fruit maturing and leaf discoloration phases of each tree species,and decreased during the deciduous phase from 9.64%to 98.41%（P<0.05）.Among each parameter,F_v/F_mchanged the least,with a mean value of more than 0.8.The general trends of the phenological rhythm changes of F_m,ψ_o,φ_Eoand PI_ABSwere consistent,with a"unimodal"trend.The order of the magnitude of leaf water potential of each tree species was:P.tabulaeformis>P.orientalis>R.pseudoacacia>P.davidiana,and the maximum leaf water potential was observed in the autumn phenology of cone maturing,first fruit shedding and leaf discoloration phases,and there was a significant decrease in leaf water potential in the summer growth capping and autumn defoliation phases,with a decrease from 22.70%to 57.51%.（3）Significant differences（P<0.05）were found in total amount and fractions of NSC of different organs and whole plants of each tree species.Deciduous and evergreen species adopted different carbon storage strategies,and the fluctuations of NSC and fractions of deciduous species were significantly higher than those of evergreen species.The general trend of phenological rhythm changes of soluble sugar and sugar starch ratio were similar,and the total amount of NSC and starch were similar,all showing a"single valley type".The total NSC of the whole plant fluctuated from 88.68 mg/g to 135.42 mg/g for each tree species,with sharp fluctuations in spring and autumn,and gentle fluctuations in summer.The differences in total amount of NSC and fractions of different organs were greatest at the leaf bud burst phase,and then gradually decreased with phenological rhythm.The total amount of NSC in aboveground and underground organs reached the lowest at the first leaf unfolding and beginning of leaf defoliation.The total NSC of leaves reached the lowest level（82.22 mg/g）in autumn during leaf defoliation,and the old leaves were lower than the new leaves.Branchlets reached the lowest level in the first leaf unfolding and leaf defoliation,and the extreme difference reached 65.73 mg/g.The main stem and thick root reached the lowest at the first leaf unfolding,which were 80.06 mg/g and 80.38 mg/g,respectively.Fine roots reached the lowest value（85.95 mg/g）in autumn deciduous phase.The NSC and component content and sugar starch ratio of xylem of different organs were generally higher than those of phloem,about 31.30%higher,with significant differences between the two parts at the leaf bud burst and leaf spreading phases.（4）There were significant correlations（P<0.05）between total amount and fractions of NSC of each tree species and various growth indexes,physiological parameters and environmental factors.Among the growth indexes,the correlation of aboveground organs,root shoot ratio and specific leaf area is stronger than other growth indexes,and pearson correlation coefficient was up to 0.968（P<0.05）.The correlation between evergreen tree species and their growth indexes were stronger than that of deciduous tree species.Each tree species generally showed significant positive correlations with photosynthetic parameters.Among all the chlorophyll fluorescence parameters,F_v/F_mandφ_Eohad the strongest leaf water potential had the weakest correlations with NSC components and sugar starch ratio.In the principal component analysis of environmental factors,the first two axes had cumulatively explained 79.18%of the total variation,and sunshine duration（0.927）,temperature（0.891）and solar radiation（0.810）were the main influencing factors.Correlation analysis revealed that each tree species has a strong correlation with temperature,solar radiation and sunshine duration,with the highest coefficient of 0.938（P<0.01）.The variation of NSC was mainly influenced by starch content and its percentage（89.61%,P<0.001）.There were interspecific differences in the correlation among NSC,starch,soluble sugar and sugar starch ratio.Tree species,phenology and their interactions all highly significantly effected the total amount of NSC and components and sugar starch ratio（P<0.001）.Among them,tree species had a greater effect on starch and NSC,phenology had a greater effect on soluble sugars,and their interaction had a greater effect on the sugar starch ratio.To sum up,the growth indexes,physiological parameters,NSC and its components,and sugar starch ratio of trees had significant interspecific differences and obvious phenological rhythm characteristics.Tree species of different life forms adopt different phenological rhythm carbon storage strategies,and many factors affect the phenological rhythm storage of NSC in trees.The above results can provide an information basis for further study on the interannual variation of plant phenology and the dynamics of stress factors related to carbon storage,and the development and evaluation of ecosystem models of Beijing urban forest under the background of climate change.