Xia Jiangbao

Critical responses of photosynthetic efficiency in Campsis radicans (L.) Seem to soil water and light intensities

Campsis radicans (L.) Seem is one of the main forestation tree species in semi-arid loess hilly region. Using the CIRAS-2 portable photosynthesis system, the light-response of the photosynthetic efficiency parameters of three-year-old C .radicans leaves, such as net photosynthetic rate (P N ), transpiration rate (Tr), water use efficiency (WUE), and light use efficiency (LUE), were studied under different soil water conditions in order to explore the effects of soil water stress on photosynthesis and the suitable soil water content for water-saving irrigation of this liana. Soil water and light intensity needed by the growth and development of C .radicans were analyzed. The results show that P N , Tr, WUE, and LUE of the leaves had threshold value to soil water and photosynthetically-active radiation (PAR). The nonrectangular hyperbola model was used to simulate light-response curve and the convexity was about 1. With the increase of soil relative water content of field capacity (Wr, ranged from 20.1% to 71.1%), the light compensation point declined while light saturation point, the maximum P N and apparent quantum yield increased. When Wr was about 71.7%, the light compensation point was at the minimum (21.61μmol/m 2 /s) and the light saturation point was at the maximum (1400 μmol/m 2 /s). In order to maintain the normal plant growth and have higher P N , LUE, and WUE synchronously, the range of Wr was from 49.5 to 71.1%. The optimum Wr was 71.1%, and the minimum Wr was 28.2% for the normal growth of C .radicans . The high P N and WUE were recorded when PAR ranged from 800 to 1600 μmol/m 2 /s and the light saturation points ranged from 800 to 1400 μmol/m 2 /s. The peak value of LUE was found when PAR ranged from 100 to 300 μmol/m 2 /s, indicating that the C. radicans had high adaptability to light conditions. Key words : Campsis radicans, soil water content, photosynthetically-active radiation, photosynthetic efficiency, water use efficiency.

Photosynthesis responses to various soil moisture in leaves of Wisteria sinensis

A study was conducted to determine the fitting soil moisture for the normal growth of two-year-old W. sinensis (Sims) Sweets by using gas exchange technique. Remarkable threshold values of net photosynthetic rate (Pn), transpiration rate (Tr) and water use efficiency (WUE) were observed in the W. sinensis leaves treated by various soil moisture and photosynthetic available radiation (PAR). The fitting soil moisture for maintaining a high level of Pn and WUE was in range of 15.3%–26.5% of volumetric water content (VWC), of which the optimal VWC was 23.3%. Under the condition of fitting soil moisture, the light saturation point of leaves occurred at above 800μmol·m−2·s−1, whereas under the condition of water deficiency (VWC, 11.9% and 8.2%) or oversaturation (VWC, 26.5%), the light saturation point was below 400μmol·m−2·s−1. Moreover, the light response curves suggested that a special point of PAR occurred with the increase in PAR. This special point was considered as the turning point that indicated the functional transition from stomatal limitation to non-stomatal limitation. The turning point was about 600, 1000, 1000 and 400 μmol·m−2·s−1, respectively, at VWC of 28.4%, 15.3%, 11.9% and 8.2%. In conclusion, W. sinensis had higher adaptive ability to water stress by regulating itself physiological function.