PNNL

Abstract

Specific leaf area (SLA, leaf area per unit dry mass), is an index of plant carbon captured by photosynthesis and an important input into many terrestrial process models. However, the controls on and consequences of SLA variation are poorly understood, especially in high latitude, climatically-sensitive permafrost regions. To address this, we measured SLA and soil and topographic properties across a boreal forest permafrost transition, in which forest composition changed as permafrost deepened from 54 to >150 cm. Using replicated transects, we characterized both linear and threshold relationships between topographic and edaphic variables and SLA, and evaluated and expanded upon a conceptual model of environmental factors and vegetation patterns. We found that the depth of the soil active layer above permafrost (ALD) was highly correlated with SLA, for both coniferous and deciduous boreal tree species. Across a permafrost transition, intraspecific SLA variation was associated with a fivefold increase in NPP, suggesting that changes in ALD due to permafrost thaw could heavily influence ecosystem carbon accumulation. These empirical relationships and associated uncertainty can be incorporated into ecosystem models that use dynamic traits, improving our ability to predict ecosystem-level carbon cycling responses to ongoing climate change.