Photosynthetic Physiological Characteristics And Distribution Of Photosynthate During Cone Growth Of Pinus Koraiensis

Carbon assimilation and photosynthate allocation among plant organs is critical to determine vegetative and reproductive growth.The change of environmental conditions will not only affect the photosynthesis of trees,but also affect the allocation pattern of resources,and then affect trade off between reproductive and vegetative growth of trees.Korean pine（Pinus koraiensis）is not only a precious native timber species,but also a high-quality edible nut tree species in China and even in the world.It has strong apical dominance,masting behaviors and fruiting only at the top of the crown.The relationship between individual vegetative and reproductive growth and its regulation is an important scientific and technical problem related to Korean pine nut production.Exploring the photosynthetic physiology and resource allocation mechanism of Korean pine cone development and its response to management measures is helpful for us to establish accurate cultivation measures of Korean pine,to provide theoretical basis for promoting the fruiting of Korean pine.Thus,this study took the fruiting Korean pine stock trees was taken as the object,through the control experiments of girdling and defoliation,using stable isotope ¹³C labeling tracer technique,photosynthetic gas exchange and chlorophyll fluorescence analysis technique,combined with the determination of physiological and biochemical indexes,the differences of photosynthetic physiological characteristics of reproductive and vegetative branches and photosynthetic physiological changes during cone development of Pinus koraiensis were compared and analyzed.The law of photosynthate distribution and utilization of Korean pine nut development was analyzed,the source of nutrients needed for cone development was identified,and the photosynthetic physiological characteristics and photosynthate distribution mechanism of Korean pine cone development were revealed.Meanwhile,the management measures of fruit thinning and fertilization were used to explore the regulation and response mechanism of photosynthetic physiological characteristics and photosynthate distribution to fruit thinning and fertilization in Pinus koraiensis,so as to provide a theoretical basis for enriching the theory of resource allocation and promoting the fruiting of Korean pine.The main results are as follows:（1）The diurnal and seasonal changes of photosynthetic parameters of reproductive branches and vegetative branches showed similar changes,but the net photosynthetic rate of vegetative branches was significantly higher than that of reproductive branches.The diurnal variation of net photosynthetic rate（Pn）and stomatal conductance（Gs）of the two branch types showed a typical“double-peak”curve,while the diurnal variation of intercellular CO₂concentration（Ci）showed a"V"trend.And"stomatal limitation"was the main limiting factor of photosynthesis of the two branch types of Korean pine.The Pn,Gs,Ci,water use efficiency（Wue）and chlorophyll content of current and 1-year-old needles of vegetative and reproductive branches increased at first and then decreased,which reaching the maximum in August.The carboxylation efficiency（CE）,CO₂ saturation point（CSP）and photorespiration rate（R_p）of reproductive branches were lower,indicating that the needles of reproductive branches had strong utilization of low CO₂ concentration,while the dark respiration rate（R_d）of vegetative shoots was low,and the maximum net photosynthetic rate(P_max)and light saturation point（LSP）were higher,indicating that vegetative branches had high utilization of strong light and low respiratory consumption rate.（2）The photosynthates of Pinus koraiensis could not meet the growth and development of cones,which need the supply of other photosynthates.Girdling limited the growth and development of branches and cones.And girdling significantly reduced the growth of needles and branches,the accumulation of biomass and non-structural carbohydrate concentration,and prevented the development of cones.The effect of defoliation on branch growth and cone development is limited.With or without defoliation,girdling treatment led to cone abortion,branch stop growth or death.（3）The photosynthates of Pinus koraiensis will be transported and distributed to cones only after meeting the growth demand of vegetative branches.By using ¹³CO₂ isotope tracer technique to label vegetative branches for 4 h and 24 h respectively,higherδ¹³C was detected in needles,branches and cones of unlabeled reproductive branches,and significantly higher than that of branches of unlabeled treatment.After 4 h and 24 h of isotope labeling,the enrichment of ¹³C assimilates of 4.5%and 45.4%were detected in reproductive branches,respectively.However,after 4h of ¹³CO₂ isotope labeling in the whole plant,only 2%of ¹³C assimilates were allocated to cones,regardless of whether or not fruiting ¹³C assimilates were distributed in vegetative growth,which also indicated that there was a strong competition between reproductive growth and vegetative growth of Korean pine.（4）The photosynthetic capacity of the needles on reproductive and vegetative branches decreased significantly due to reducing the intensity of reproductive organ sink by fruit thinning,while the accumulation of photosynthates increased significantly.Fruit thinning treatment significantly decreased Pn,Gs,transpiration rate（Tr）,chlorophyll content and chlorophyll fluorescence parameters of reproductive and vegetative branches.The Pn of the needles of the two branch types had a significant positive correlation with Gs,Tr and chlorophyll content,while a significant negative correlation with the initial fluorescence（F0）.The chlorophyll content had a significant positive correlation with the chlorophyll fluorescence parameters and a significant negative correlation with Ci.The concentration of soluble sugar,starch and non-structural carbohydrate in needles increased significantly due to the decrease of sink intensity,which led to the increase of photosynthate accumulation in source leaves.The electron transport in the process of photosystemⅡwas also blocked by the decrease of library intensity,and the enzyme activity of PSⅡreaction center was destroyed accordingly.（5）The photosynthetic physiological characteristics and nutrient concentration of Pinus koraiensis showed a positive response to fertilization,and its growth and seed setting were significantly increased.No matter the single application of N,P,K fertilizer or the combined application of NP and NPK significantly promoted the DBH,crown width growth of Korean pine,significantly increased the seed setting rate and cone yield per tree.The effects on the growth and fruiting of Korean pine were NPK>NP≥N>P>K>CK.Compared with the control,the DBH,seed setting rate and cone yield of Korean pine treated with NPK increased by 27.7%,121.2%and 158.3%,respectively.Fertilization significantly increased the contents of Pn,Gs,Tr,Wue and chlorophyll,as well as the concentrations of soluble sugar,starch,non-structural carbohydrates and nutrients in Korean pine.The chlorophyll content of annual and annual needles increased gradually with the extension of time,while the concentration of non-structural carbohydrates in needles and branches decreased at first and then increased with time,and the concentration was the lowest in August.Fertilization significantly increased the concentrations of corresponding nutrient elements in needles,branches and trunks,indicating that Pinus koraiensis was sensitive to fertilization.Conclusion,the photosynthetic and nutritional relationship between vegetative and reproductive growth of Pinus koraiensis has different patterns.（1）the photosynthetic rate of the first round of unfruited vegetative branches adjacent to the fruiting reproductive branches was significantly higher than that of the reproductive branches.The photosynthates of reproductive branches could not meet the demand of the growth and development of cones and branches,and need the input support of photosynthates from adjacent vegetative branches.However,the photosynthates of vegetative branches first meet the needs of their own vegetative growth before they are transported outward,indicating that the demand for photosynthates for reproductive growth will be strongly competitive in the allocation of resources for vegetative growth.（2）The production,output and distribution of photosynthate in Korean pine needles will change due to the decrease of sink absorption formed by fruit thinning,that is,production decreases,output decreases and accumulation increases.The increase of nutrition supply caused by fertilization can improve the comprehensive photosynthetic capacity and the ability to supply vegetative growth and reproductive growth of Korean pine needles,and increase the vegetative and reproductive growth.Those results indicated that the state of vegetative and reproductive growth could be regulated by regulating the balance of resource allocation between vegetative and reproductive growth.