Abstract: Water-carbon exchange process and major influencing factors of Robinia pseudoacacia plantations in the Yangjuangou watershed of the Chinese Loess Plateau were measured at leaf scale, to explore the variations of watercarbon exchange with slope aspects and stand ages and analyze the potential effects of nutrient contents in leaves on watercarbon exchange process. The results showed that: (1) 11- and 27-year-old R. pseudoacacia were at different growing stages. The former had a higher intensity of watercarbon exchange than the latter. (2) The proportion of R. pseudoacacia individuals with higher net photosynthetic rate, water use efficiency, stomatal conductance and intercellular CO₂ concentration was greater on semisunny slope than on sunny slope, suggesting that semisunny slope was more suitable for R. pseudoacacia growth. (3) The variation patterns of N and K contents in different quadrats were as follows: semi-sunny slope>sunny slope, 27-year-old>11-year-old, indicating that R. pseudoacacia grew better on the semisunny slope than on the sunny slope, mature R. pseudoacacia grew better than juvenile R. pseudoacacia. The differences of K content in leaf in different quadrats were significant, suggesting that K content in leaf was sensitive to the changes of slope aspect and stand age. Therefore, compared with the sunny slope, the semisunny slope with more suitable hydrothermal condition should be considered as priority for establishing R. pseudoacacia plantation, and the reforestation on soils with enriched available K could be a potential way for improving plant’s water use efficiency. These results are significantly instructive for the improvement of Grain for Green Project and the management of existing plantations in the arid and semi-arid regions.

Key words: grain yield., wheat, irrigation regime, photosynthesis, middle growth stage, water consumption