Effects of drought on the growth and resource use efficiency of two endemic species in an arid ecotone

Maintaining the stability of ecotone is a potential way to stop the expansion of arid areas, but little has known in many key arid ecotones. This study aimed to understand the responses of endemic species to drought conditions in an arid ecotone. A controlled experiment with different drought stress treatments (80%, 40% and 20% field water capacity (FC)) on two endemic species (Salix paraqplesia and Hippophae rhamnoides) was arranged in the ecotone between the Minjiang dry valley and mountain forest. Drought stress dramatically reduced the height, basal diameter, leaf number, biomass production and the accumulations of C, N and P of both species. An increase of belowground proportion was observed indicating higher root/shoot ratio under drought stress conditions, and drought further increased N and P use efficiencies and intrinsic water use efficiency (WUEi). Compared with S. paraqplesia under medium drought stress (40%FC), H. rhamnoides showed less change of morphology characteristics, higher P use efficiency, and WUEi due to better N sources. However, S. paraqplesia showed higher N use efficiency and WUEi under severe drought stress condition (20%FC) than H. rhamnoides. The results suggested that the expanding dry valley could seriously influence endemic species in the ecotone, and N-fixing plant such as H. rhamnoides could adapt to moderate drought stress better than non-N-fixing plant.