PHOTOSYNTHESIS AND RESPIRATION RATES DEPEND ON LEAF AND ROOT MORPHOLOGY AND NITROGEN CONCENTRATION IN 9 BOREAL TREE SPECIES DIFFERING IN RELATIVE GROWTH-RATE

1. To test several hypotheses about acclimation and adaptation of phot osynthesis and respiration to differing light conditions, we investiga ted the interspecific relationships between leaf and root metabolism, chemistry and morphology in high and low light conditions for young se edlings of nine boreal tree species that differ in relative growth rat e (RGR). 2. Light-saturated net photosynthesis (A(sat)), whole-plat ni trogen (N) uptake rates, leaf and root respiration and morphology, and RGR all varied in parallel among the nine species when grown in both 5% and 25% of full sunlight. RGR, A(sat), leaf and root respiration (R -d), and N uptake rate per unit root mass or length differed significa ntly among species, ranking (from high to low): Populus, Betula and La rix SPP (all deciduous) and then to five evergreen conifers (Pinus, Pi cea and Thuja spp,), which were generally comparable in these measures . 3, A(sat), leaf and root R-d and N uptake rates were all correlated (r approximate to 0.8 to 0.9) with species traits, such as seed mass, leaf life span and shade-tolerance rankings. Mass-based A(sat) was gre ater in conifer seedlings raised in low than high light. In contrast, area-based A(sat) was higher for plants grown in high than low light, especially in the deciduous species. Once adjusted for differences in plant mass, leaf or root respiration rates did not differ for plants g rown in low vs high light. 4, Interspecific variation in RGR was posit ively correlated (r approximate to 0.9) with rates of photosynthesis, respiration and N uptake. Leaf photosynthesis and respiration rates we re correlated to specific leaf area and leaf N concentrations (r appro ximate to 0.9). Root respiraristi rates, N uptake rates, specific root length (root length per root dry mass) and root N concentrations were all highly correlated with each other (r approximate to 0.8 to 0.9). These data suggest a close coupling of tissue-level metabolism, chemis try and structure with whole-plant performance and species ecophysiolo gical and life-history traits.