Abstract
The alpine grasslands on the Tibetan Plateau are sensitive and vulnerable to climate change. However, it is still unknown how precipitation use efficiency (PUE), the ratio of aboveground net primary productivity (ANPP) to precipitation, is related to community assembly of plant species, functional groups or traits for the Tibetan alpine grasslands along actual environmental gradients. We conducted a multi-site field survey at grazing-excluded pastures across meadow, steppe and desert-steppe to measure aboveground biomass (AGB) in August, 2010. We used species richness (SR), the Shannon diversity index, and cover-weighted functional group composition (FGC) of 1-xerophytes, 2-mesophytes, and 3-hygrophytes to describe community assembly at the species level; and chose community-level leaf area index (LAIc), specific leaf area (SLAc), and species-mixed foliar δ13C to quantify community assembly at the functional trait level. Our results showed that PUE decreased with increasing accumulated active temperatures (AccT) when daily temperature average is higher than 5 °C, but increased with increasing climatic moisture index (CMI), which was demined as the ratio of growing season precipitation (GSP) to AccT. We also found that PUE increased with increasing SR, the Shannon diversity index, FGC and LAIc, decreased with increasing foliar δ13C, and had no relation with SLAc at the regional scale. Neither soil total nitrogen (STN) nor organic carbon has no influence on PUE at the regional scale. The community assembly of the Shannon index, LAIc and SLAc together accounted for 46.3% of variance in PUE, whilst CMI accounted for 47.9% of variance in PUE at the regional scale. This implies that community structural properties and plant functional traits can mediate the sensitivity of alpine grassland productivity in response to climate change. Thus, a long-term observation on community structural and functional changes is recommended for better understanding the response of alpine ecosystems to regional climate change on the Tibetan Plateau.
Highlights
Soils in AMs were found to be more fertile with higher soil organic carbon (SOC) content than soils in ASs and desert-steppes, no difference in soil total nitrogen (STN) was found among the three alpine grassland types
The data presented in this study illustrated that climate primarily constrains precipitation use efficiency (PUE) of alpine grasslands on the Tibetan Plateau
Our results indicated that vegetation structural properties including species richness (SR), community assembly, plant composition of different functional groups, and plant functional trait diversity can mediate the response of productivity to changing climate regimes
Summary
Precipitation determines spatial and temporal variability in productivity of diverse temperate and alpine grasslands worldwide (Bai et al, 2008; Knapp & Smith, 2001; Sala et al, 2012; Sala et al, 1988; Shi et al, 2014; Yang et al, 2008). Most previous studies focused to examine the manner of productivity in response to changes in precipitation regimes (Bai et al, 2008; Gao et al, 2011; Hu et al, 2007; Paruelo et al, 1999; Sala et al, 1988; Yang et al, 2010); rare research has examined the potential and inherent regulating mechanisms of community assembly on ecosystem productivity
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