Shifting plant species composition in response to climate change stabilizes grassland primary production

Abstract

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.

Responses of biomass allocation across two vegetation types to climate fluctuations in the northern Qinghai–Tibet Plateau

“…In this study, compared with the global root distribution (including desert grassland, temperate grassland, and tundra), we have only explored the vertical root distribution of alpine meadows and shrubs; thus, the species composition is different, ultimately leading to the major discrepancies in vertical root distribution between our study and previous studies. However, enhanced temperature could significantly decrease the soil moisture across different depths, especially at a depth of 10 cm (Liu et al, 2018). Furthermore, we found a shift in biomass toward the superficial layer across the two vegetation types, this result was not consistent with the result of a previous study conducted in an alpine meadow .…”

Plant phenological sensitivity to climate change on the Tibetan Plateau and relative to other areas of the world

“…It is noteworthy that the two study years differed in terms of weather, 2013 was dry and 2014 was wet (Liu et al. ), which may have caused the significant interactive effects of precipitation and year on plant phenology in this study. While warming had the largest effect on phenology in our study, precipitation influenced the response of functional groups to warming.…”

Thirteen‐year variation in biomass allocation under climate change in an alpine Kobresia meadow, northern Qinghai–Tibetan Plateau

“…Given that alpine ecosystems are nutrient poor, their soil nutrient supply largely depends on microbial decomposition and nutrient mineralization, and studies conducted on the Qinghai–Tibetan Plateau have shown that elevated temperature could significantly decrease the fungal abundance at 0–10 cm, but increase the fungal abundance in deeper soil (Zhang et al., ); thus, greater rates of mineral weathering and organic matter decomposition at greater depths promoted faster root growth at depth relative to that at 0–10 cm. Moreover, the maximum air temperature only significantly affected root biomass in the 0–20 cm soil layer, with little effect on root biomass in deeper soil layers, suggesting that the maximum air temperature might have significant effects on shallow‐rooted plants such as sedge, but limited or no effects on deep‐rooted plants such as forbs and grasses, because the root biomass of sedges, forbs and grasses in an alpine Kobresia meadow were mainly distributed in the 0–20 cm, 0–30 cm and 0–40 cm layers respectively (Liu et al., ). Meanwhile, previous studies have shown that belowground biomass is not only affected by environmental factors, but also by aboveground biomass of plant functional groups (Hutchings & John, ); this was not supported by our finding that the aboveground biomass of plant functional groups had little impact on belowground biomass across all depths, reflecting that the impact of maximum air temperature on belowground biomass was not mediated by aboveground biomass.…”