Hyperspectral technology has received great attention for estimating aboveground plant biomass. Corrections using ground spectrometer data have been proposed for more accurate integrated assessments of aboveground plant biomass. In this study, we sampled the aboveground plant biomass and the corresponding hyperspectral data from three types of alpine grassland ecosystems (alpine desert, alpine steppe, and alpine meadow) from the Qinghai-Tibetan Plateau to improve the biomass estimation accuracy. We used partial least squares regression and the vegetation indices (VIs) (using all two-band combinations (601*601combinations in all) involving 601 narrow bands between 400nm and 1000nm), and the optimal band combinations were used to calculate four most commonly used VIs. We found that the VIs are better than the least square method for alpine meadow, and that the most effective combinations were shown in the combinations of reflectance at the red edge (rather than red) and near-infrared bands(728nm,764nm). For alpine steppe and alpine desert, however, partial least squares regression is better than VIs. While the most important band for alpine steppe is between 600nm and 700nm in the red spectrum, the most important band for alpine desert is around 400nm. Our results can provide a theoretical basis for accurately estimating the aboveground plant biomass of different grassland types in the Qinghai Tibet Plateau.

Alpine grasslands are sensitive to grazing and atmospheric deposition of nitrogen (N). With the increase of N deposition, experimental investigations of the effects of grazing on alpine grassland vegetation with the background of N deposition are scarce. In this study, we examined the effects of overgrazing and overgrazing with N deposition on eco-physiologies of alpine grassland plants at the functional group level. We found that both overgrazing and overgrazing with N deposition obviously changed species composition and the dominance of three plant functional groups (PFGs) in alpine meadow and alpine steppe. Under overgrazing and overgrazing with N deposition treatment, forb tended to be predominant in the whole plant community, while grass and sedge dominance was obviously decreased. In addition, we found that the underlying eco-physiological processes that lead to forb-dominant were different under overgrazing and overgrazing with N deposition. Overgrazing with N deposition obviously tended to increase forb dominance both directly by selective herbivory and indirectly by enhancing forb photosynthetic capacity. Our results suggested that long-term overgrazing with N deposition will lead to a more favorable living environment for forbs, making the grassland community of alpine grasslands on the Qinghai-Tibetan Plateau likely shift to forb-dominant in the future.