Abstract: Stem photosynthesis (P_g) is an alternative and significant carbon source, playing a crucial role in plant survival under extreme environment. The main aims of this study were to quantify stem and leaf photosynthesis, find out the main drivers of P_g, and estimate the contributions of P_g to plant individual carbon balance of two dominant species Haloxylon ammodendron and Tamarix ramosissima in Gurbantunggut Desert. A Li-Cor 6400 portable photosynthesis system and a special chamber were used to measure leaf and stem photosynthesis. Ancillary measurements included leaf/stem functional trait (chlorophyll content, water content, leaf/stem area, carbon/nitrogen content, etc.) and environmental factors (air temperature and humidity, photosynthetically active radiation, soil temperature, and soil water content). Our results showed that P_g of H. ammodendron and T. ramosissima was 2.37 and 0.98 μmol·m^-2·s^-1, P_g refixation CO₂ of stem respiration by 65%-76% and 57%-77% in H. ammodendron and T. ramosissima. P_g was influenced by photosynthetically active radiation, air temperature, soil temperature and water vapor deficit. P_g assimilation CO₂ accounted for 8.2%-16.6% and 3.6%-8.3% of CO₂ assimilation of H. ammodendron and T. ramosissima, respectively. The maximum value appeared at noon when temperature was high. There might be fundamental defects if we ignore the contribution of branch photosynthesis when predicting carbon process of desert ecosystem under the background of climate change.

Key words: desert plant, stem photosynthesis, drought stress, adapting strategy