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.

摘要干旱-湿润交错带环境稳定是控制干旱区不断扩散的潜在途径, 但相关研究较为缺乏。为了解岷江干旱河谷－山地森林交错带植物对干旱胁迫的生长适应机制, 以交错带两种典型乡土植物(高山柳Salix paraqplesia和沙棘Hippophae rhamnoides)为研究对象, 研究其在不同程度干旱胁迫条件下的形态生长、生物量生产、N和P积累与利用格局。干旱胁迫明显降低了两种植物的株高、基径和叶片数等形态特征, 减小了生物量生产以及C、N和P的积累, 改变了生物量以及C、N和P的分配格局, 但提高了N和P利用效率。尽管高山柳具有相对较高的N利用效率, 但是沙棘在干旱胁迫条件下可以维持较高的生长和较大的P利用效率, 可以更好地适应于干旱环境。这些结果表明干旱区的持续扩散将严重影响交错带植物的生长, 同时交错带植物也具有相对较强的适应干旱胁迫的潜力, 可以通过改变资源分配格局和提高限制养分利用效率以适应恶劣的生存环境。