Gas exchange and water use efficiency of three native tree species in Hunshandak Sandland of China

Only three tree species, i.e. Ulmus pumila, Malus baccata, and Prunus padus, are distributed in Hunshandak Sandland (HS) in Inner Mongolia, China. Field studies of gas exchange and chlorophyll (Chl) fluorescence of these three tree species were conducted in three and periods of growth season 2002. Net photosynthetic rate (P-N), transpiration rate (E), stomatal conductance (g(s)), and F-v/F-m of U. pumila were higher than in M. baccata and P. padus, especially in the midday. Hence M. baccata and P. padus were more sensitive to high temperature and irradiance than U. pumila in HS. This may be a reason for wide distribution of U. pumila in HS. M baccata and P. padus are adapted to the back slope of fixed dune, because the micro-habitat is relatively cool and less irradiated than the slope facing sun. Water use efficiency (WUE) of U. pumila was lower than that of M baccata and P. padus, and thus U. pumila does not form forests in this region, because the soil is dry.