Climate warming drives a shift in alpine meadow ecosystem plant community: implications for ecosystem carbon cycling
Climate warming is expected to have a large impact on plant community composition and productivity in tundra and alpine ecosystems, which in turn might induce a range of biogeochemical feedbacks. Temperature rising in the Qinghai-Tibet Plateau is proved to be earlier and higher than other areas in the same latitude. Net ecosystem exchange (NEE) of alpine meadow was positively responds to the climate warming. In addition to the abiotic factors, species composition also would affects the ecosystem productivity. We therefore hypothesize a change in species composition, and the composition change could contribute to the positive response of NEE to warming.
After two years of experimental warming, species number, Shannon-Wiener, Simpson and evenness had no significant change, but ecosystem CO2 fluxes were significantly elevated. Warming changed the community structure by reducing the importance value (IV) of the dominant sedge species by 4.4%, increasing and sum IV of grass and forbs by 4.9%. Community structure change increases the ecosystem carbon uptake on the basis of higher net photosynthesis and light use efficiency in forbs than in sedge. The decrease in IV of sedge and increase in IV of forbs and grasses could also contribute to the stimulation in ecosystem uptake because ecosystem CO2 fluxes showed positive correlation with sum IV of forbs and grass but negative correlation with IV of sedge. The threshold value of importance value for converting the ecosystem from a net carbon uptake to a net release is 0.698 for sedge and 0.256 for grass and forbs. The results suggest that warming-induced shifts toward forbs and grasses will maintain the ecosystem function in terms of carbon sink in alpine meadow ecosystem in a permafrost region of Qinghai-Tibet Plateau.