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 (Nmass) or leaves with very long life-span and small Nmass 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-Ålesund (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 Nmass tended to increase along the climatic gradient with decreasing growing season and lower temperatures. In evergreen shrub species, both leaf life-span and leaf Nmass 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.