Comparison of drought strategies of three co-existing woody plants by their hydraulic structures

This paper investigates the physiological characteristics for drought resistance among three main afforestation woody species (ie Robinia pseudoacacia L., Quercus variabilis Blume, Platycladus orientalis (L.) Franco) in lithoid mountainous areas in north China. Variations in their gas exchanges and water relations were comparatively measured during withholding water and subsequent rewatering of potted seedlings. The results showed that: 1) under wellwatered conditions, black locust (R. pseudoacacia) had the strongest photosynthesis, the greatest stomatal conductance and water consumption among the three species. 2) However, black locust was most sensitive to soil drying among the three species, its photosynthesis and stomatal conductance rapidly declined. 3) On being rewatered, both gas exchanges and water relations were able to be rapidly recovered in all three species, among which black locust and cork oak (Q. variabilis) had faster recovery than arborvitae (P. orientalis). 4) Stomatal conductance (gs) of black locust changed rapidly when percentage loss of hydraulic conductivity (PLC) varied. By contrast, gs of cork oak and arborvitae changed much slower in response to soil moisture and PLC. In summary, black locust is able to rapidly assimilate and accumulate carbohydrates in wellwatered conditions, however, when drought came, it sharply shut down its stomata and even shed leaves to prevent excessive loss of water. To the contrast, the other two species could maintain fairly high photosynthesis in intermediate drought stress, especially arborvitae. Soil moisture condition in the lithoid mountainous areas could restrict the development of black locust forests.