Architectural plasticity and growth responses of Hippophae rhamnoides and Caragana intermedia seedlings to simulated water stress

The objective of this controlled experiment was to compare the ability of Hippophae rhamnoides L. (Sea buckthorn) and Caragana intermedia Kuang & H.C. Fu (Intermediate peashrub), both perennial temperate deciduous shrubs, to acclimate to a water deficit by architectural plasticity and growth responses. Their changes in branching pattern parameters, and in dry matter accumulation and allocation, were recorded after 2 years of exposure to four different water supply levels: normal precipitation, slight drought, drought and extreme drought. Their branching patterns showed that H. rhamnoides tended to expand horizontally, with more, shorter, thinner branches and a larger branch angle, whereas C. intermedia tended to grow perpendicularly with fewer, longer, thicker branches and a smaller branch angle. The overall bifurcation ratio and stepwise bifurcation ratio R1:2 of H. rhamnoides were comparatively steady; in contrast, those of C. intermedia increased markedly with an increase in water supply. The different adaptation strategies in biomass distribution pattern under different water supply treatments indicated that C. intermedia made a relatively high investment in root growth, especially in deeper roots, and in its changes in bifurcation ratio under water stress. H. rhamnoides grown under ample water supply was distinguished by its fast growth and relatively high investment in branches and leaves. The study revealed the ability of C. intermedia to adapt to a wider range of water stress by architectural plasticity and growth responses.