Photosynthetic Physiology Of An Endangered Plant Tetracentron Sinense Oliv.

Tetracentron sinense Oliv.,the only tall deciduous tree in the family Tetracentraceae,is listed as the second-level national protected plant.In this paper,Li-6400 portable photosynthetic apparatus was used to estimate the light response,CO₂ response and specific leaf area of different diameter classes of T.sinense and that in different habitats,and then the photosynthetic physiological and ecological characteristics of T.sinense and its adapatablity to habitats were analyzed,and the endangered factors and effective protection and management strategies related to photosynthesic physiology were discussed,which can provide a scientific basis for the effective protection and management of T.sinense germplasm resources.The main results are as follows.1.Photosynthetic physiology of different diameter classes of T.sinense individualsThe net photosynthetic rate of different diameter classes was higher in spring compared to spring and autumn.In spring and summer,the minimum P_n appeared in the individuals of J3 diameter-class,while the minimum was in J1 diameter-class in autumn;the maximum all in J5 diameter-class in spring,summer and autumn.The light compensation points?LCP?of different diameter-classes individuals ranged from 17.52to 31.76?mol·m^-2·s^-1,and their light saturation points?LSP?were above 562 to706.62?mol·m^-2·s^-1,indicating that the T.sinense resistance to negative light.In the CO₂ response,the photosynthetic capacity and adaptability of individuals in J2 and J5 were relatively stronger,while that in J4 and J1 were poor.In each season,the T.sinense individuals can adapt to the higher light intensity by reducing the specific leaf area?SLA?to protect the photosynthetic structures of leaves from destruction.The SLA in the individuals of J2 diameter-class were higher than that in other diameter-classes,indicating the lower photosynthetic capacity and adaptability;while the SLA in J5 diameter-classes was relatively less,indicating the stronger photosynthetic capacity.2.Photosynthetic physiology of the T.sinense and their associated species in different habitatsThe diurnal variation of the T.sinense Pn and Tr in the forest gap and forest edge showed a"double peak"curve.For its associated trees,the diurnal variation of Pn and Tr in the forest edge and under the forest was a“double peak”curve,but the diurnal variation of the T.sinense Pn and Tr under the forest showed a"single peak"curve.the LSP,LCP and Pmax of T.sinense in forest gap were greater than that in forest edge and under the forest.In the forest edge,the photosynthetic capacity of T.sinense was less than that of Pterocarya stenoptera,while the same as that of Acer franchetii.Under the forest,the photosynthetic capacity of T.sinense was less than its associated trees.The results showed that the ecological range of T.sinense to light is narrower and photosynthetic capacity is lower than that of its associated species in the forest edge and under the forest,causing it to be at a disadvantage in interspecific competition.In the forest gap,the Pmax,CE,C_iast and R_p of T.sinense were relatively higher than those in forest edge and under the forest.In forest edge and under the forest,CE,R_p,LCP and LSP of Pterocarya stenoptera were the greatest,followed by Acer truncatum and T.sinense.The results showed that the adaptation range of the CO₂ and the accumulation of photosynthetic products of T.sinense in forest gap were the greatest compared to in forest edge and under the forest,and were less than those of its associated species in forest edge and under the forest.The specific leaf area?SLA?of the T.sinense in different habitats varied with the light environment.Under strong light conditions,the SLA will be reduced to protect the photosynthetic structures of leaves from direct light.Under lower light conditions,the SLA of the T.sinense will increase to strengthen the photosynthetic capacity of the leaves.