Abstract: To understand the responses of photosynthesis in Salix psammophila and Caragana korshinskii, two shrub species commonly distributed in the water and wind erosion crisscross region on the Loess Plateau, to precipitation alteration, a manipulated precipitation experiment (control, water addition by 45%, and water reduction by 50%) was conducted. Leaf water relation, photosynthetic capacity, leaf morphological structure and nutrient concentration were measured after three years precipitation manipulation. For Salix, there was no difference of predawn leaf water potential among treatments during both dry and wet season, while midday leaf water potential showed significant responses to both water  addition and reduction during the dry season. For Caragana, both predawn and midday leaf water potential significantly decreased by water reduction, and showed no response to water addition. The light-saturated photosynthetic rate (A_max) in Salix during the dry season and Caragana during both dry and wet  changed for the treatments of water addition and reduction. The enhanced A_max in Salixby water addition during dry season was attributed to improved biochemical properties, while the decreased A_max in Salix during dry season was mainly related to increased CO₂ diffusion limitation. For Caragana, the increasedA_max by water increase during the dry season was attributed to decreased stomatal limitation, and to decreased CO₂ diffusion limitation and biochemical limitation during the wet season, respectively. The decreased A_max of Caraganaby water reduction during both seasons was related to increased biochemical limitation. Specific leaf mass, N and P contents of both species did not respond to water addition and reduction, indicating that the variation of A_max by water availability was not related to leaf structure and nutrient limitation. These results provide reference for evaluating the adaptability of both shrub species and modeling water and carbon cycling under future climate change.

Key words: Yangtze estuary, Collichthys lucidus, suitability index, correlation analysis.