| In order to know the distribution of non-structural carbohydrate(NSC)in mature rubber trees,and the effect of stem water storage during the first canopy leaf flushing period,we measured NSC concentration of surface tissues(leaves,branches,bark and sap wood)of rubber trees from October 2017 to February 2019,and monitored the sap flow patterns of the trunk and root bases during the first canopy leaf flushing period.At the same time,NSC concentration changes in branches and leaves of young trees which adjacent to mature trees were measured and compared with mature rubber trees during the overwintering period in 2018(2018.11-2019.2).The main results are as follows:(1)Mature rubber trees will accumulate NSC gradually in leaves,bark and trunk at the beginning of winter when whether got cold and drought.At the beginning of March,when rubber trees grow theirfirst new canopy leaves and shoots,the concentration of NSC in branches,bark and trunk both decreased because they were used to support the growth of new leaves and shoots,which is like previous studies on rubber trees.Also,like that of other tropical and temperate deciduous species.At the peak of growing season(from August to October),the NSC concentration in leaves and bark decreased,probably due to rubber production and harvest or may be phloem damage caused by tapping,because it is also the peak harvest time.(2)The NSC concentration of leaves and branches of young rubber trees was closely related to temperature and sunshine duration during wintering period.The NSC concentration of leaves and branches decreased at low temperature and short sunshine day.Leaves in young trees seem to be damaged and their carbon assimilation ability declines after low temperature day,at which time,lead NSC concentration cannot be improved with the increase of temperature and sunshine in short term.Meanwhile branches NSC concentration of young rubber trees kept increased during wintering period,which was like the strategy of temperate evergreen tree species.However according to the results of previous studies,this accumulation strategy might also be related to different characteristics of "source"/"sink" of young trees and mature trees and different transport characteristics of NSC.It is also possible that the growth of young rubber trees was limited in cold and drought environments so that NSC content increased.(3)After the budding stage,the sap flow of rubber trees began to fluctuate obviously,and nighttime sap flow gradually become vigorous.That’s because rubber trees have just experienced short-term winter drought before leaf flushing,and that’s why they replenished water at night.That’s the adaptation of rubber trees to the water requirement of producing new leaves and shoots.It was found that the sap flow dynamics monitored on the crown and trunk bases of rubber trees showed there was time lag during the process of sap flow initiation,increase and decrease in the growth period of the first canopy leaves,which indicated that the stem water storage did play a role at the time.The diurnal process of water storage and release water in rubber tree trunks varies during the first Ieaf growth period.Results shows that amount of trunk release water was highest at the discoloration and stabilization period,reach 2.07±0.72 kg/d,but the contribution rate to transpiration is the lowest for 9.93%. |
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