COMPARISON ON LEAF-WATER-RELATION OF TWO SHRUB SPECIES IN A SOUTH CHINA
两种南亚热带林下灌木叶片水分特性的比较研究

The water relations of leaves for two understory shrubs, Rhodomyrtus tomentosa and Evodia lepta in a south subtropical forest were studied. The experiment was conducted at two sites in Ding Hu Shan mountain, Guangdong Province. The "open site" was on the top of back-hill near the office of Reserve Station,and the "middle site" was downwarded about 30m on the same hill. Stomatal conductance and water potential were measured by stable porometer(Li-cor 1600) and PMS pressure chamber respectively. Water potential components were calculated from pressure-volume curves.The daily courses of stomatal conductance in two plants from local time 7:00 to 17:00 showed a pattern of single peak. The time with maximum stomatal conductance in a day varied depending on seasons, it shifted to an earlier time from March to October. The highest average stomatal conductance was found in summer, and the lowest in winter. A midday depression of stomatal conductance was observed at the open site in August. In all cases at these two sites, and in nursery site, R. tomentosa had a higher stomatal conductance than E lepta.Water potential went down from dawn and reached its minimum at noon,then raised back again in the evening. The trend of high water potential in March and August and low one in December was in consistent with the change of wet and dry season. Diurnal and seasonal patterns of water potential were not different between the two shrubs, but R. tomentosa possessed relatively higher water potential at dawn and midday than E. lepta in dry season.The relationship between stomatal conductance and leaf water potential was regarded as a hyperbola for this two plants. In August, the minimum water potential was still kept over the osmotic potential at zero turgor. No significant difference in the capacity of osmotic adjustment was found between the two species although they showed a different stomatal conductance pattern.