Quantifying the physiology of structurally complex arctic vegetation and implications for ecosystem function in a shrubbier tundra

As conditions become more favorable in some arctic regions for shrub growth, shrubs will not only expand laterally, but they will grow thicker and taller, altering the physical structure of the canopy. The increase in surface roughness and canopy complexity accompanying the advancement of shrub species requires a more detailed understanding of the within-canopy distribution of leaf traits for ecosystem-level carbon models. Some leaf traits like photosynthesis and leaf N content are linked strongly to respiration. In complex canopies (LAI>1) shrubs may optimize resources based on light availability, with more invested in sun-exposed leaves at the top and less in the shaded understory. By measuring leaf traits throughout the canopy, vertical patterns of respiratory carbon exchange can be extrapolated. Variation in canopy leaf traits must also be compared to that resulting from environmental drivers as well as inter-specific differences between shrubs to account for the relative magnitude of its effect on the carbon budget. Preliminary data indicate that there is substantial variation between Betula nana and Salix pulchra shrub canopies across four study sites with contrasting soil temperature, moisture, and pH, active layer depth, and snowmelt regimes. Additionally, decreases in the photosynthetic capacity of leaves under lower light are observed in complex canopies.