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Dominant species and ecosystem gas exchange in temperate grassland under different land use patterns |
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| Affiliation: | Key Laboratory of Traditional Chinese Medicine Protection and Utilization of Beijing City, Beijing Normal University, State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, College of Resources Science & Technology, Beijing Normal University, Beijing 100875, China |
| Abstract: | Aims Ecosystem carbon uptake or release is influenced by land uses. However, few quantitative studies have been made to give accurate explanations. Based on field measurements of gas exchange and water relations at the leaf scale and the ecosystem scale in temperate grasslands locating in northern China, we aim to 1) clarify the difference in carbon exchange between the leaf scale and the ecosystem scale in different land uses; 2) understand how human activities influence the carbon pools at the ecosystem scale by analyzing changes in gross primary productivity (GPP) and ecosystem respiration (Reco); and 3) explore whether water condition in semi-arid steppe restricts CO2 absorption at the ecosystem level. Methods We selected three dominant spcies, Stipa grandis, Artemisia frigida and Leymus chinensis, based on quadrat surveys. Some ecophysiological indexes were measured using a modified LI-6400 in the sample plots of three land use patterns: enclosed plots, mowed plots and grazed plots. We calculated net ecosystem CO2 exchange (NEE), GPP, Reco and water use efficiency (WUE) with the measured results. All data were analyzed using one-way ANOVA and t-test of SPSS. Important findings By comparing the carbon exchange of dominant species at the ecosystem scale, we found that carbon exchange varies with change of land use. NEE and GPP of the ecosystem in the grazed plots are different from those in the enclosed plots and the mowed plots, and GPP is more dependent on Reco. In grazed plots, the diurnal change of NEE shows C uptake, but in the other two plot types it appears to release C. The phenomenon that negative net photosynthetic rate (Pn) returns to positive values from midday to dusk should be a special reaction of plants living in grasslands to protect themselves under high light and temperature conditions. There is no difference in WUE at the ecosystem scale, but the tendency of evapotranspiration (ET) is not the same; nevertheless, the degree of fluctuation of WUE for the same species at the leaf scale is largest in the grazed plots and smallest in the enclosed plots. |
| Keywords: | dominant species gas exchange grassland use pattern temperate grassland water use efficiency |
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