Results (<i>P</i>-values) of repeated measures analysis of variance (RMANOVA) on the effects of warming (W), year (Y), and their interactions on gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem CO₂ exchange (NEE).

<p>Results (<i>P</i>-values) of repeated measures analysis of variance (RMANOVA) on the effects of warming (W), year (Y), and their interactions on gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem CO₂ exchange (NEE).</p

Inter-annual patterns of gross ecosystem productivity (GEP) (a), ecosystem respiration (ER) (b), and net ecosystem CO₂ exchange (NEE)(c) in control and warming treatments from 2012 to 2014.

<p>C: Control, W: Warming. Different capital letters indicated significant different (P<0.05) among years in same treatments; different small letters indicated significant different (P<0.05) among different treatments in same years.</p

Results (<i>P</i>-values) of repeated measures analysis of variance (RMANOVA) on the effects of warming (W), sampling date (D), and their interactions on gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem CO₂ exchange (NEE).

<p>Results (<i>P</i>-values) of repeated measures analysis of variance (RMANOVA) on the effects of warming (W), sampling date (D), and their interactions on gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem CO₂ exchange (NEE).</p

Intra-annual patterns of gross ecosystem productivity (GEP) (a, b, c), ecosystem respiration (ER) (d, e, f), and net ecosystem CO₂ exchange (NEE) (g, h, i) in 2012 (left panels), 2013 (middle panels) and 2014 (right panels).

<p>C: Control, W: Warming.</p

Total aboveground biomass (a), graminoid biomass (b), forb biomass (c), and ratio of graminoid and forb (d) in alpine meadow during 2012–2014 growing seasons.

<p>C: Control, W: Warming.</p

Temporal patterns of soil temperature and soil moisture in control and treatment plots in alpine meadow.

<p>C: Control, W: Warming. (a): Intra-annual patterns of soil temperature; (b) Intra-annual patterns of soil moisture; the dotted line indicate the period of spring drought in each year; (c): Inter-annual patterns of soil temperature; (d): Inter-annual patterns of soil moisture.</p

The relationships between ecosystem CO₂ fluxes: gross ecosystem productivity (GEP) (filled cycles and solid lines), ecosystem respiration (ER) (filled triangles and dashed lines), and net ecosystem CO₂ exchange (NEE) (open cycles and dotted lines), and aboveground biomass: total biomass, graminoid biomass, forb biomass, and biomass ratio of graminiod/forb across 2012 to 2014.

<p>The relationships between ecosystem CO₂ fluxes: gross ecosystem productivity (GEP) (filled cycles and solid lines), ecosystem respiration (ER) (filled triangles and dashed lines), and net ecosystem CO₂ exchange (NEE) (open cycles and dotted lines), and aboveground biomass: total biomass, graminoid biomass, forb biomass, and biomass ratio of graminiod/forb across 2012 to 2014.</p

Temporal dependence of gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem CO₂ exchange (NEE) on soil moisture and soil temperature across the three growing seasons.

<p>Temporal dependence of gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem CO₂ exchange (NEE) on soil moisture and soil temperature across the three growing seasons.</p

Differential response of alpine steppe and alpine meadow to climate warming in the central Qinghai–Tibetan Plateau

Recently, the Qinghai–Tibetan Plateau has experienced significant warming. Climate warming is expected to have profound effects on plant community productivity and composition, which can drive ecosystem structure and function. To explore effects of warming on plant community productivity and composition, we conducted a warming experiment using open top chambers (OTCs) from 2012 to 2014 in alpine meadow and alpine steppe habitat on the central Qinghai–Tibetan Plateau. We measured aboveground net primary productivity (ANPP), community composition and species diversity under ambient and two levels of artificially warmed conditions across three years. Our results showed that warming significantly stimulated plant growth in the alpine meadow, but reduced growth on the alpine steppe. The increase of ANPP in alpine meadow was a result of an increase of plant height under warming. Warming-induced drought conditions were primarily responsible for the observed decrease of ANPP in an alpine steppe. Plant community composition and species diversity were not influenced by warming in alpine meadow. Alternatively, in alpine steppe, cover of graminoids and forbs significantly declined while legumes substantially increased under warming, subsequently resulting in rapid species losses. Changes in soil moisture were responsible for observed changes in graminoids and legumes in the alpine steppe. Overall, experimental results demonstrated that warming had a positive impact on plant community structure and function in alpine meadow and had a negative impact on these characteristics in an alpine steppe. This work highlights the important role of soil moisture for regulating plant productivity and community composition response to warming in the alpine steppe. In particular, the deep-rooted, drought resistant plants may increase in a warmer future in the central Qinghai–Tibetan Plateau. These changes may reduce habitat quality for the local community of grazers because many of the species that increased are also unpalatable to grazers