Leaf-trait variation of tundra plants along a climatic gradient: an integration of responses in evergreen and deciduous species

To understand response patterns of leaf traits in tundra plants against decreasing annual season length comprehensively, a graphic model based on carbon balance theory was presented. The model predicted that leaves with very short life-span and high nitrogen concentration (N-mass) or leaves with very long lift-span and small N-mass will be dominate under the conditions of a short growing season. To test this prediction, leaf life-span and other leaf traits of 26 tundra species were compared among four sites selected along a gradient of climatic harshness: a subalpine site at Abisko in northern Sweden, two nearby mid-alpine sites at Latnjajaure with early and late snowmelt, and a site at Ny-Alesund (Svalbard) in the High Arctic. In herbaceous and deciduous shrub species, leaf life-span and/or leaf mass per unit area (LMA) tended to decrease, and leaf N-mass tended to increase along the climatic gradient with decreasing growing season and lower temperatures. In evergreen shrub species, both leaf life-span and leaf N-mass tended to increase under harsh conditions, but the response pattern of LMA was less clear. Deciduous species produced short-lived leaves with a low construction cost and probably high photosynthetic potential, whereas evergreen species produced long-lived leaves. The contrastive patterns of leaf-trait variation between the deciduous and evergreen plants observed in this study were concordant with the prediction of the model.