Abstract: The assimilation of CO₂ in the woody tissue of stems is an important but always overlooked part in plant carbon budgets. In this study, the LI-6400XT portable photosynthesis measurement system and a special photosynthetic leaf chamber (P-Chamber) were used to measure stem photosynthesis of seven woody species in the same habitat, and to compare water use efficiency between leaves and stems. Our results showed that stem photosynthesis could offset CO₂ emission from stem respiration by 67.8%-122.5%, thereby effectively reducing plant carbon loss. Stem photosynthesis accounted for 2.9%-23.5% of gross photosynthesis in leaves. Moreover, water use efficiency in stems was as high as 12.5 times of leaves. Our results indicated that the role of stem photosynthesis in maintaining plant carbon balance could not be ignored. It is necessary to consider the contribution of stem photosynthesis to predict the dynamics of carbon cycle under the background of climate change.

Key words: stem photosynthesis, stem respiration, carbon cycle, desert ecosystem, life history strategy.