不同光强处理对三叶青光合特性的影响

为探讨适宜三叶青Tetrastigma hemsleyanum生长的光强环境，并为其人工栽培和林下栽培提供基础，以2年生三叶青扦插苗为试验材料，对它们进行不同梯度的遮光处理，梯度设置为全光照（ck），遮光30%，50%，70%和90%，研究光强对三叶青不同生育时期（快速生长期与高温缓慢生长期）的光合特性的影响。采用体积分数为95%乙醇浸提法测定三叶青叶片中光合色素，利用LI-6400XT便携式光合系统测定仪测定叶片净光合速率（P_n），气孔导度（G_s），胞间二氧化碳摩尔分数（C_i）和蒸腾速率（T_r）等指标，计算光饱和点（L_SP），光补偿点（L_CP），量子效率（A_QE），暗呼吸速率（R_d）和最大净光合速率（P_max），并拟合光响应曲线。结果表明:随着遮光程度的增加，叶绿素a，叶绿素b，总叶绿素和类胡萝卜素总体上呈现上升趋势，但是在不同生育时期变化不大；多数光合指标亦随遮光程度增加而呈现增长趋势，多在遮光70%时达到最大值之后下降，且快速生长期（P_n为4.19 μmol·m-2·s-1，G_s为53.54 mol·m-2·s-1，T_r为0.98 mmol·m-2·s-1，L_SP为340.49 μmol·m-2·s-1，A_QE为0.18 mol·mol-1，R_d为1.20 μmol·m-2·s-1，P_max为5.34 μmol·m-2·s-1）比高温缓慢生长期（P_n为1.74 μmol·m-2·s-1，G_s为17.53 mol·m-2·s-1，T_r为0.36 mmol·m-2·s-1，L_SP为159.28 μmol·m-2·s-1，A_QE为0.06 mol·mol-1，R_d为0.70 μmol·m-2·s-1，P_max为2.45 μmol·m-2·s-1）数值高41.67%~67.26%；C_i和L_SP呈现先下降后趋于稳定趋势，表明高温缓慢生长期的强光、高温、低湿等环境条件使其光合活跃度下降，对植株生长产生胁迫。综合试验结果得出结论，不同生育时期三叶青均在遮光度70%的条件下生长适宜。

Effects of light intensity treatments on photosynthetic characteristics in Tetrastigma hemsleyanum

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 (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i) and transpiration rate (T_r) were measured by LI-6400XT portable photosynthesis system; light response curve (L_SP), light compensation point (L_SP), quantum efficiency (A_QE), dark respiration rate (R_d) and maximum net photosynthetic rate (P_max) 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 (P_n was 4.19 μmol·m-2·s-1, G_s was 53.54 mol·m-2·s-1, T_r was 0.98 mmol·m-2·s-1, L_SP was 340.49 μmol·m-2·s-1, A_QE was 0.18 mol·mol-1, R_d was 1.20 μmol·m-2·s-1 and P_max was 5.34 μmol·m-2·s-1) were 41.67%~67.26% higher than those of slow growth period (P_n was 1.74 μmol·m-2·s-1, G_s was 17.53 mol·m-2·s-1, T_r was 0.36 mmol·m-2·s-1, L_SP was 159.28 μmol·m-2·s-1, A_QE was 0.06 mol·mol-1, R_d was 0.70 μmol·m-2·s-1 and P_max was 2.45 μmol·m-2·s-1); C_i and L_SP 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.