Physiological consequences of height-related morphological variation in Sequoia sempervirens foliage

This study examined relationships between foliar morphology and gas exchange characteristics as they vary with height within and among crowns of Sequoia sempervirens D. Don trees ranging from 29 to 113 m in height. Shoot mass:area (SMA) ratio increased with height and was less responsive to changes in light availability as height increased, suggesting a transition from light to water relations as the primary determinant of morphology with increasing height. Mass-based rates of maximum photosynthesis (A_max,m), standardized photosynthesis (A_std,m) and internal CO₂ conductance (gi,m) decreased with height and SMA, while the light compensation point, light saturation point, and mass and area-based rates of dark respiration (R_m) increased with height and SMA. Among foliage from different heights, much of the variation in standardized photosynthesis was explained by variation in gi, consistent with increasing limitation of photosynthesis by internal conductance in foliage with higher SMA. The syndrome of lower internal and stomatal conductance to CO₂ and higher respiration may contribute to reductions in upper crown growth efficiency with increasing height in S. sempervirens trees.