Responses in leaf functional traits and resource allocation of a dominant alpine sedge (Kobresia pygmaea) to climate warming in the Qinghai-Tibetan Plateau permafrost region

Assessing the influence of warming on leaf traits, carbon, and nutrient concentrations above and below ground to understand how the dominant sedge Kobresia pygmaea (C. B. Clarke) C. B. Clarke may respond and adapt to extant and future climate in the alpine meadow of the Qinghai-Tibetan Plateau. A warming experiment was conducted in the permafrost region of the Qinghai-Tibetan Plateau from 2008 to 2009. Two 2-year warming treatments (T1, annual warming of 2.1°C; T2, annual warming of 4.4°C) were used, and responses of leaf traits and above- and belowground carbon, nitrogen, and phosphorus concentrations of K. pygmaea were examined. The results show that both moderate (T1) and more extensive (T2) warming decreased leaf mass, leaf thickness, and vascular bundle size, and increased the mass-based photosynthetic rate (A_mass) and photosynthetic nitrogen use efficiency (PNUE). A moderate warming significantly decreased leaf carbon (C), nitrogen (N), and phosphorus (P), and root C and N concentrations of K. pygmaea. These decreases were even more pronounced under the more extensive warming. The decreases in leaf N and P were significantly larger than the decrease in leaf C concentration. Root P concentration increased more under the extensive than the moderate warming. The observed increase in leaf C:N ratio in the warming treatment indicates that enhanced temperature may increase the long-term nitrogen use efficiency of K. pygmaea leaves. This again suggests that K. pygmaea might adapt well to future climate warming, and that nitrogen might be a more important factor for K. pygmaea dominated alpine meadows under future climate warming.