Assimilative branches and leaves of the desert plant Alhagi sparsifolia Shap. possesses a different adaptation mechanism to shade

Leaves and assimilative branches are crucial to the life cycle of Alhagi sparsifolia Shap. (Fabaceae), which grows in high-irradiance environments and is the main vegetation in the forelands of the Taklamakan Desert. This plant has an important role in wind protection and sand fixation at the oasis–desert transition zone. The morphology, physiology, and photosynthesis of A. sparsifolia leaves growing under low-light conditions have been extensively investigated. However, whether the plantʹs assimilative branches adapt similarly to low light levels is unclear, as are its specific light adaptation mechanisms. In this report, we characterized the biomass allocation, morphology, and chlorophyll a fluorescence of leaves and assimilative branches of A. sparsifolia. The results indicated that low-light conditions limited the normal growth of A. sparsifolia. The fraction of biomass allocated to leaves increased, whereas that to assimilative branches decreased. In addition, leaf thickness and assimilative branch diameter decreased, resulting in higher specific leaf area, specific assimilative branch length, and area for higher light absorbing and higher efficiency of light-usage. The assimilative branches and leaves were responded oppositely under low-light conditions in that leaves had lower photosystem II activity and assimilative branches had higher light-use efficiency to maximize light energy absorption for growth of A. sparsifolia.