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The Impact of Climate Warming on Alpine Grassland Ecosystem |
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Update time: 07-19-2009 |
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The IPCC reported that if the atmospheric CO2 concentration rises at a rate of 0.1%/a, annual averaged temperatures during 2071-2100 on the Qinghai-Tibetan Plateau will increase by 3.3-8.4 ℃ during the summer months and by 3.2-10.9℃ during the winter months compared with those during 1961-1990. Nighttime temperatures in the Qinghai-Tibetan Plateau show higher trends of growth than daytime temperatures. Little information is available by which we can assess how the grassland on the plateau will react to this change, thus simulated warming experiments have been performed in this region in order to understand the possible effect of ongoing climate warming on the vast grasslands on the plateau.
1. The effects of simulated warming on the phenology and above-ground biomass
Open Top Chambers (OTC) are commonly employed to study the effect of climate warming on ecosystems. Four 30×30 m sites that had been fenced in since 1999, with 16 plots laid within, in a 4×4 matrix. A complete factorial experimental design was established within each site, where warming was simulated using fiberglass OTC. The OTC, which were 1.5 meters in diameter and 40 centimeters high, were made with 1.0 mm thick Sun-Lite HP (Solar Components Corporation, Manchester, NH, USA) fiberglass. The slanted sides are designed to maximize both the transmittance of incoming radiation and the trapping of heat. Monthly air temperatures (average air temperatures at 5 cm, 10cm and 20cm above-ground) in the OTC’s increased by 1.64 ℃, 1.96 ℃, 1.67 ℃, 1.69 ℃, 1.18 ℃, and 0.67 ℃ over the control plots, respectively.
The phenological phases of the alpine meadow are affected significantly by increased temperatures. The growing phase of plant populations inside the OTC’s was delayed, on average, by 4.95 days. Beginning times for all phenological phases advanced, but ending times were delayed. This was especially true for the beginning of the fruit-bearing phase, which was advanced by 2.84 days, while the end of the vegetative phase, after the bearing of fruit, was delayed 5.74 days. However, the contrary was true for the florescence phase, with its beginning time delayed, and its ending time advanced. Perhaps this is due to the fact that the energy obtained during the sunlight hours, and the amount of sunshine available, was reduced by the fiberglass of the OTC’s.
Almost all alpine meadow species could be categorized into graminoids, sedges, and forbs. The aboveground biomass of most gramineous plants such as Koeleria cristata, Festuca ovina, Festuca rubra, Poa sp., Stipa aliena, Elymus mutans increased. The aboveground biomass of most sedgy plants such as Kobresia humilis, Carex sp., Scirpus distigmaticus also increased. However, the contrary is true for forbs such as Gentiana straminea, Saussurea superba, Thalictrum alpinum, Gueldenstaedtia diversifolia, Gentiana farreri, Taraxacum sp., Potentilla bifurca and Potentilla nivea. Consequently, the aboveground biomass of graminoid and sedge species inside OTC’s increased by 12.3% and 1.18% over the control, respectively. However, in contrast, the aboveground biomass of forbs decreased by 21.13%. Numerous impacts on the phenology, growth, and physiological state of the vegetation in the plots have been observed. For example, forbs in heated plots show significant reductions in aboveground biomass. However, in our study, a simulated experiment on the alpine meadow on the Qinghai-Tibetan Plateau, forbs in heated plots showed a significant increase in aboveground biomass.
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