Comparison of energy partitioning between artificial pasture and degraded meadow in three-river source region on the Qinghai-Tibetan Plateau: A case study

摘要

To reveal the differences in energy exchange between a degraded alpine meadow (DM) and an artificial pasture (AP, that was artificially planted with Elymus nutans on the ploughed degraded meadow), the energy partitioning and its biophysical controls were compared between the two study sites in the Three-River Source Region (TRSR) on the Qinghai-Tibetan Plateau. The mean maximum leaf area index (LAI) for AP and DM was 2.66 and 1.08 m(2) m(-2), respectively. The net radiation (R-n) sensible heat flux (H) latent heat flux (lambda E), and soil heat flux (G) showed similar seasonal changes for the two study sites; no obvious differences in energy partitioning were noted between AP and DM during the non-growing season. However, during the growing season, R-n of DM was about 5.4% higher than that of AP, although almost the same downward shortwave and longwave radiation was received at both sites. Moreover, the mean albedo (alpha) of DM was lower by 0.02 than that of AP, and the mean soil surface temperature of DM was 4.1 degrees C lower than that of AP. The partitioning of available energy into H and lambda E of DM differed markedly from those of AP, and the lambda E/R-n ratio of DM was 16.4% higher than that of AP, whereas the H/R-n ratio of the former was 20.9% lower than that of the latter during the growing season. The growing season (annual) mean Bowen ratio (beta) was 0.69 +/- 0.04 and 0.90 +/- 0.03 (2.38 +/- 0.09 and 2.93 +/- 0.12) at DM and AP, respectively, indicating that more available energy of DM was used for lambda E in comparison with that for AP. The difference in vegetation was considered to be the major factor leading to differences in the energy partitioning between the two sites. The results of the case study suggest that meadow degradation increases water loss through evapotranspiration and that enlarging the area of artificial pasture can increase the plant productivity and improve the water conservation capacity in this region.