Photosynthesis and respiration rates depend on leaf and root morphology and nitrogen concentration in nine boreal tree species differing in relative growth rate

摘要

The interspecific relationships between leaf and root metabolism, chemistry and morphology were investigated in high and low light conditions for the young seedlings of 9 boreal tree species (Populus tremuloides, Betula papyrifera, Betula alleghaniensis, Larix laricina, Pinus banksiana, Picea glauca, Picea mariana, Pinus strobus and Thuja occidentalis) that differed in relative growth rate (RGR). Light saturated net photosynthesis (Asat), whole-plant nitrogen (N) uptake rates, leaf and root respiration and morphology, and RGR all varied in parallel among the 9 species when grown in 5% or 25% of full sunlight. RGR, Asat, leaf and root respiration (Rd), and N uptake rate per unit root mass or length differed significantly between species. Asat, leafand root Rd and N uptake rates were all correlated with species traits, such as seed mass, leaf life span and shade-tolerance rankings. Mass-based Asat was greater in conifer seedlings raised under low light conditions compared with high light conditions. In contrast, area-based Asat was higher for plants grown in high light conditions, especially in the deciduous species. Once adjusted for differences in plant mass, leaf or root respiration rates did not differ for plants grown in either light environment. Interspecific variation in RGR was positively correlated with rates of photosynthesis, respiration and N uptake. Leaf photosynthesis and respiration rates were correlated to specific leaf area and leaf N concentrations. Root respiration rates, N uptake rates, specific root length (root length per root dry mass) and root N concentrations were all highly correlated with each other. It is suggested that a close coupling exists of tissue-level metabolism, chemistry and structure with whole-plant performance and species ecophysiological and life-history traits.