Abstract:

Diurnal net photosynthetic and transpiration rates of six plant species on the Loess Plateau were measured in the field during May, July, and September 2002. Photosynthetic characteristics of these species were quantified by applying a model of net photosynthesis and stomatal conductance to the field data. The results indicated that the model could explain up to 79% and 59% of the variation in the net photosynthetic rate and stomatal conductance, respectively. Hippophae rhamnoides and Artemisia capillaris had higher net photosynthetic rates than the other species because these species had high biochemical photosynthetic efficiencies whereas the other species had low photorespiration coefficients. An afternoon depression in photosynthetic rates in Robinia pseudoacacia, Hippophae rhamnoides L. subsp. sinensis Rousi, Artemisia gmelinii and A. capillaris was explained by decreased stomatal conductance, and, in Malus pumila and Caragana korshinskii, the reduction was due to decreased biochemical photosynthetic capacity. These field results provide a basis for future laboratory studies to better understand the ecophysiological properties of these plants.