The structure and function of alpine grassland ecosystems, including their extensive soil carbon stocks, are largely shaped by temperature. The Tibetan Plateau in particular has experienced significant warming over the past 50 y, and this warming trend is projected to intensify in the future. Such climate change will likely alter plant species composition and net primary production (NPP). Here we combined 32 y of observations and monitoring with a manipulative experiment of temperature and precipitation to explore the effects of changing climate on plant community structure and ecosystem function. First, long-term climate warming from 1983 to 2014, which occurred without systematic changes in precipitation, led to higher grass abundance and lower sedge abundance, but did not affect aboveground NPP. Second, an experimental warming experiment conducted over 4 y had no effects on any aspect of NPP, whereas drought manipulation (reducing precipitation by 50%), shifted NPP allocation belowground without affecting total NPP. Third, both experimental warming and drought treatments, supported by a meta-analysis at nine sites across the plateau, increased grass abundance at the expense of biomass of sedges and forbs. This shift in functional group composition led to deeper root systems, which may have enabled plant communities to acquire more water and thus stabilize ecosystem primary production even with a changing climate. Overall, our study demonstrates that shifting plant species composition in response to climate change may have stabilized primary production in this high-elevation ecosystem, but it also caused a shift from aboveground to belowground productivity.

Satellite data indicate significant advancement in alpine spring phenology over decades of climate warming, but corresponding field evidence is scarce. It is also unknown whether this advancement results from an earlier shift of phenological events, or enhancement of plant growth under unchanged phenological pattern. By analyzing a 35‐year dataset of seasonal biomass dynamics of a Tibetan alpine grassland, we show that climate change promoted both earlier phenology and faster growth, without changing annual biomass production. Biomass production increased in spring due to a warming‐induced earlier onset of plant growth, but decreased in autumn due mainly to increased water stress. Plants grew faster but the fast‐growing period shortened during the mid‐growing season. These findings provide the first in situ evidence of long‐term changes in growth patterns in alpine grassland plant communities, and suggest that earlier phenology and faster growth will jointly contribute to plant growth in a warming climate.

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g r f o r m e t Seasonal and inter-annual variations in CO 2 fluxes over 10 years in an alpine shrubland on the Qinghai-Tibetan Plateau, China The shrubland acted as a net CO 2 sink with a negative NEE (−74.4 ± 12.7 g C m −2 year −1 , Mean ± S.E.). The mean annual gross primary productivity (GPP) and annual ecosystem respiration (RES) were 511.8 ± 11.3 and 437.4 ± 17.8 g C m −2 year −1 , respectively. The classification and regression trees (CART) analysis showed that aggregated growing season degree days (GDD) was the predominant determinant on variations in monthly NEE and monthly GPP, including its effect on leaf area index (LAI, satellite-retrieved data). However, variations in monthly RES were determined much more strongly by LAI. Non-growing season soil temperature (T s ) and growing season length (GSL) accounted for 59% and 42% of variations in annual GPP and annual NEE, respectively. Growing season soil water content (SWC) exerted a positive linear influence on variations in annual RES (r 2 = 0.40, p = 0.03). The thermal conditions and soil water status during the onset of the growing season are crucial for inter-annual variations of carbon fluxes. Our results suggested that an extended growing season and warmer non-growing season would enhance carbon assimilation capacity in the alpine shrubland.