Comparison of Daily Variations in Photosynthesis and Water-Consumption of Seedlings in Vigorous Growth Period of Three Tree Species from South China

Daily variations in photosynthesis and water-consumption in the seedlings were compared among three species by using Li-6400 photosynthetic system and by weighting potted seedlings. The experimental species included an endemic tree species (Zenia insignis) distributed in limestone area in south China and two other tree species (Evodia glabrifolia, Rhaphiolepis indica) commonly used for afforestation in limestone area. The results showed that R. indica and E. glabrifolia had similar or better ability to grow through photosynthesis and water conservation as compared with Z. insignis in vigorous growth periods. As for photosynthetic characteristics, the daily variation trend of net photosynthetic rate of seedlings from the three species was a “twin peaks” curve. R. indica had the highest net photosynthetic rate, reaching （11.709±0.392）μmol·m^-2·s^-1; E. glabrifolia took second place, and Z. insignis was at the lowest level. The parameter values on photoresponse curve indicated that R. indica had the most powerful ability to grow through photosynthesis, while Z. insignis and E. glabrifolia were similar to each other. As for the characteristic of water-consumption, the water-consumption in daytime and nighttime of Z. insignis was significantly higher than those of R. indica and E. glabrifolia. Water-consumption in daytime accounted for about 90% of the total consumption in the whole day. The water-consumption rate of the three species seedlings was comparatively low, between 2.91×10^-4 -4.28×10^-4 mol·m^-2·s^-1. Maximum water-consumption rate of E. glabrifolia was the lowest among them, while that of R. indica was slightly higher compared with Z. insignis, and the average ratio of the maximum water-consumption rate and the average water consumption rate was about 1.6.