The Photosynthetic Properties Of Hevea Brasiliensis And It Response To Drought Stress

Brazilian rubber tree (Hevea brasiliensis (Willd ex A. Juss)) is the most important rubber tree of artificial cultivation. At present, the cultivation of Brazilian rubber tree is the pillar-type industries in tropical China. In this study, grafted seedling and seedling of rubber tree were used as the plant materials, and the physiological and ecological properties of photosynthesis were researched under natural conditions, shading condition and drought stress condition respectively. The purpose is to find out the relationship between rubber tree's photosynthesis and the environmental factors (such as light intensity, temperature, atmospheric CO₂ concentration and the relative humidity), and offer some theoretical basis for studying physiological response mechanisms to drought stress, high-yield cultivation and drought resistance breeding. The main results are as following:1 For clear days, the diurnal variation of net photosynthetic rate (P_n) and transpiration rate (Tr) existed in H. brasiliensis are the two-peaked curve. The primary physiological and ecological factors that effect on P_n are stomatal conduction, water vapour pressure difference between leaf and air consistent, temperature and relative humidity. The depressions of Pn at noon mostly caused by strong light intensity, high temperature, and low RH after noon, decrease of stomatal conduction and photosynthetic capability, also included photo inhibition.2 The diurnal variation of light and CO₂ compensation point of H. brasiliensis are low at morning and evening, but high at noon. Light and CO₂ saturation point show a peak change, light saturation point is high in the morning or at noon, and CO₂ saturation point also is high in the morning. The diurnal variation of the light use efficiency, water use efficiency, apparent quantum yield and chlorophyll fluorescence parameters such as F_v/F_m and qP all are high in the morning and at evening, but low at noon, show a "U"curve changes, but non-photochemical quenching (NPQ) on the other way round, high at noon and show a down "U" curve changes. The diurnal change of apparen carboxylation efficiency and electron transport rate (ETR) is the two-peaked curve, consistent with the diurnal variation of P_n.