Photosynthesis, transpiration and water use efficiency of four plant species with grazing intensities in Hunshandak Sandland, China

In order to explore the response patterns of gas exchange to the increased grazing intensity and to test whether or not plants have compensatory growth under animal grazing disturbance, we have conducted this experiment in Hunshandak Sandland of Northern China. Changes in net photosynthetic rate (Pn), transpiration rate (E), and water use efficiency (WUE) of four plant species (Cleistogenes squarrosa, Agropyron cristatuni, Artemisia ftigida, Potentilla acaulis) in four grazing intensities, non-, light-, moderate- and high-grazed plots were investigated. Pn of all four species increased from non-grazed plots to moderate-grazed plots then decreased under high-grazed conditions. However, P. acaulis increased its Pn from moderately grazed plots to high-grazed plots, suggesting a strong compensatory photosynthetic growth. Transpirations of the four species elevated considerably with the increase of grazing intensity. Except for Artemisia frigida, WUE of others increased significantly from non-grazed plots to moderately grazed plots then decreased in high-grazed plots. Our results indicate that, while a sharp decrease in leaf areas and aboveground biomass, photosynthetic growth and WUE were enhanced under moderate level of grazing. With a level of grazing increased, the plant functions were declined as a result. Therefore, grassland in Hunshandak Sandland fails to support the present stocking rate. (C) 2007 Elsevier Ltd. All rights reserved.