干旱区生态环境知识资源中心

The diurnal variation of photosynthetic characteristics for Buxus microphylla and Sophora davidii in the karst desertification area of Southern China were measured by using Lcpro+ photosynthetic apparatus of England on sunny days. The results showed that the net photosynthetic rate and transpiration rate of Buxus microphylla and Sophora davidii increased with the increase of light radiation and temperature. In order to protect themselves, partial stomata were closed initiatively or passively, which resulted that the intercellular CO2 concentration and leaf moisture were decreased, the photosynthetic rate and transpiration rate were relatively declined and it was appeared a more obvious or lagged "midday break" phenomenon. The diurnal mean value of net photosynthetic rate for Buxus microphylla was 2.66 +/- 0.69 mu mol CO2.m(-2).s(-1) which was much lower than Sophora davidii (7.32 +/- 3.87 mu molCO(2).m(-2).s(-1)), this basically accords with the rule that the comprehensive photosynthetic efficiency of leguminosae vegetation is higher than buxaceae. The most active time of photosynthetic physiological characteristic for Buxus microphylla was at 8:00, and the reason for the lower photosynthetic activity in other time periods may be related to its intolerance to strong light and high temperature, while the photosynthetic characteristic of Sophora davidii was relatively high throughout the day. 8:00 was one of the best time for the assimilation of Buxus microphylla and Sophora davidii. There was a great difference in water use efficiency between Buxus microphylla and Sophora davidii in other periods, but there was a cross change trend of "high-low-high-low". On the whole, Buxus microphylla has the characteristic of low photosynthetic rate, low transpiration rate and low water use efficiency, Sophora davidii has the characteristic of high photosynthetic rate, high transpiration rate and low water use efficiency, the diurnal mean value of water use efficiency for Sophora davidii (1.52 +/- 0.84 mu molCO(2).mmol(-1)H(2)O) was slightly higher than Buxus microphylla (1.40 +/- 0.78 mu molCO(2).mmol(-1) H2O). Planting plant under the special environment background of rocky desertification, we must fully consider the photosynthetic characteristics at different time points and take necessary measures (such as shading and replenishing water) to increase its water use efficiency and explore potential ecological and economic values. According to the characteristics of photosynthesis adaptation for Buxus microphylla and Sophora davidii at different times, it is of great theoretical and practical significance to develop forestry resources and restore vegetation in the karst areas.