Community assembly and functional leaf traits mediate precipitation use
efficiency of alpine grasslands along environmental gradients on the Tibetan
Plateau
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