Effects of light intensity treatments on photosynthetic characteristics in Tetrastigma hemsleyanum

Abstract

Tetrastigma hemsleyanum has obvious pharmacological effects on inhibitting tumor cell proliferation and migration clinically. It is on the verge of extinction with the increasing demand over the past decade, so bionic planting is imperative to meet the medical needs. In this paper, we explored suitable light intensity conditions for the T. hemsleyanum growth by consideration that T. hemsleyanum grows in the forest wildly and is sensitive to strong light. Two-year-old T. hemsleyanum cuttings were shaded with different gradients treatment as test materials. The shading gradients were set as full light(ck), shade 30%, 50%, 70% and 90%. The responses of photosynthetic characteristics to light intensity were analyzed in different growth stages (rapid growth period and slow growth period). Following indicators were also measured:contents of photosynthetic pigments were determined by 95% alcohol extraction; light photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci) and transpiration rate (Tr) were measured by LI-6400XT portable photosynthesis system; light response curve (LSP), light compensation point (LSP), quantum efficiency (AQE), dark respiration rate (Rd) and maximum net photosynthetic rate (Pmax) were calculated, and the light response curve was fitted. Results showed that trends of chlorophyll a (Chla), chlorophyll b (Chlb), total chlorophyll (Chl) and carotenoid (Car) were increased with the increase of shade gradients, but the contents of photosynthetic pigment changed little in different periods; most photosynthetic indices also showed increasing trends with the increase of shading gradients, reached the maximum values in the treatment of 70% shade, then reduced, the values of rapid growth period (Pn was 4.19 μmol·m-2·s-1, Gs was 53.54 mol·m-2·s-1, Tr was 0.98 mmol·m-2·s-1, LSP was 340.49 μmol·m-2·s-1, AQE was 0.18 mol·mol-1, Rd was 1.20 μmol·m-2·s-1 and Pmax was 5.34 μmol·m-2·s-1) were 41.67%~67.26% higher than those of slow growth period (Pn was 1.74 μmol·m-2·s-1, Gs was 17.53 mol·m-2·s-1, Tr was 0.36 mmol·m-2·s-1, LSP was 159.28 μmol·m-2·s-1, AQE was 0.06 mol·mol-1, Rd was 0.70 μmol·m-2·s-1 and Pmax was 2.45 μmol·m-2·s-1); Ci and LSP showed trends of decreasing first and then tending to be stable. It showed that the photosynthetic activity decreased and plant growth slowed down with unsuitable environmental conditions such as strong light, high temperature and low humidity. The analysis of results indicated that the growth of 70% shading was appropriate in different growth periods. This paper discussed the relationship between physiological characteristics and light intensity of T. hemsleyanum in different growth periods, enriches the research results of physiological aspects, and provided basic theory for artificial cultivations and under-forest-cultivation.