Abstract: Understanding the drought tolerance and water consumption of plants is significant for selecting suitable tree species for vegetation restoration in arid and barren sites. In this study, we measured those characteristics of two-year-old seedlings of three common afforestation species, Cephalomappa sinensis, Cinnamomum camphora, and Lysidice rhodostegia, in the karst mountains of Southwest Guangxi. The water consumption characteristics were measured by pot seedling weight method, and photosynthetic characteristics were measured by LI-6400XT photosynthetic system under different soil drought stress levels. The results showed that net photosynthetic rate (P_n), stomatal conductance (G_s), and transpiration rate (T_r) of the three species decreased with increasing drought stress. The intercellular CO₂ concentration (C_i) tended to decrease, and then significantly increased during severe drought (SD) stress. By contrast, the stomatal limitation value (L_s) tended to increase, then significantly decreased during SD (P<0.05). Stomatal factor led to the decrease of P_n under light drought (LD) and moderate drought (MD) stress, while non-stomatal factor caused P_n to decrease under SD stress. Water use efficiency (WUE) of C.sinensis during LD was the highest, but decreased significantly under SD. The WUE of C. camphora and L.rhodostegia  tended to increase as soil drought stress increased, with the highest values appearing during MD. The WUE of both species significantly decreased during SD stress (P<0.05). The daily total water consumption of all the species decreased with increasing drought stress, with that of L. rhodostegiabeing the highest under the same soil water content. The diurnal variation of water consumption rate of all the three species was a single peak curve, while the maximum peak differed in different periods of drought stress. The average water consumption rate of L. rhodostegia in the daytime was the highest under LD and MD. During SD stress, the average water consumption rate ofC. sinensis in the daytime was the highest, followed by L. rhodostegia. A subordinate function analysis showed that the comprehensive drought tolerance was in the order of C. sinensis>C. camphora>L. rhodostegia. The subordinate function weighted average values of all the three species were between 0.3 and 0.5, indicating that the three species had moderate resistance to soil drought stress.

Key words: drought stress, photosynthetic characteristics, water consumption, water use efficiency, subordination function method.