Abstract: Taking the 26-and 51-year-old artificial vegetation areas and the natural vegetation area in Shapotou region of southeast Tengger Desert as study sites, this paper measured the net photosynthetic rate (P_n) of algal crusts, and analyzed its relationships with crust water content (>100%, 40%-60%, and <20%), atmospheric CO₂ concentration (360 and 700 mg·L^-1), and air temperature (13 ℃, 24 ℃, and 28 ℃). The P_n of the crusts in the 26-and 51-year-old artificial vegetation areas and natural vegetation area was 3.4, 4.4, and 3.2 μmol·m^-2·s^-1, respectively, and the P_n in 51-year-old other two areas. Crust water content had significant effects on the P_n, which was significantly higher at medium water content (40%-60%) than at low (<20%) and high (>100%) water content. When the CO₂ concentration doubled (700 mg·L^-1), the P_n increased by 1.8-3.3 times at medium and high crust water content but had less change at low crust water content, compared with that under ambient CO₂ concentration (360 mg·L^-1). At medium and high crust water content, the P_n at 24 ℃ and 28 ℃ was 27%-66% higher than that at 13 ℃ (P<0.05), but at low crust water content, no significant difference was observed at the three  temperatures.

Key words: algal crust, photosynthesis, temperature, CO₂ concentration, global change, Great Xing’an Mountains, Larix gmelinii, throughfall characteristics.