Analysis of reflectance can be used to estimate foliar concentrations of photosynthetic pigments, thus providing information on the physiological status of green plants. We compared several methods of reflectance analysis for the capacity to differentiate among effects of fertilization treatments across different irradiances on seedlings of Engelmann spruce (Picea engelmanii Parry ex Engelm.). Seedlings were grown in two light treatments (0 and 60% shade) and three nitrogen (N) treatments (10, 25 and 100 mg N l-1) for one growing season, after which foliar reflectance of the needles was measured. Five indices were tested: R550 (% reflectance at 550 nm); red edge position; the ratio R698:R760; the structure independent pigment index (SIPI); and the photochemical reflectance index (PRI). Both the light and nutrient treatments significantly affected foliar chlorophyll a and b and carotenoid concentrations. Among the indices tested, R550, red edge position and R698:R760 ratio were related to chlorophyll concentration, and were significantly affected by both light and N treatments. Both SIPI and PRI were related to chlorophyll and carotenoid concentrations. Among these relationships, PRI was affected by both treatments, whereas SIPI was sensitive to N treatment but not to light treatment. All five indices were weakly but significantly correlated with growth as measured by dry weight.

Summary• Carbon sequestration has focused renewed interest in understanding how forest management affects forest carbon gain over timescales of decades, and yet details of the physiological mechanisms over decades are often lacking for understanding long-term growth responses to management.• Here, we examined tree-ring growth patterns and stable isotopes of cellulose (d 13 C cell and d 18 O cell ) in a thinning and fertilization controlled experiment where growth increased substantially in response to treatments to elucidate physiological data and to test the dual isotope approach for uses in other locations.• • Tree-ring isotopic records, particularly d 13 C cell , remain a viable way to reconstruct long-term physiological mechanisms affecting tree carbon gain in response to management and climate fluctuations.

The success in clinical trials of the anti-cancer drug, Taxol(R), obtained from the bark of Pacific yew (Taxus brevifolia Nutt.), has raised interest in cultivation and regeneration of this little-known species. Pacific yew is shade-tolerant and it is not known whether the foliage can tolerate the high solar irradiances found on an open forest regeneration site or a nursery. Acclimation of Pacific yew to sun and shade was studied by comparing foliar physiology and morphology of male and female trees growing in full sun or shade. Interspecific foliar acclimation to sun was studied by comparing sun-grown English yew (Taxus baccata L.) with Pacific yew. No sex-specific acclimation was found in foliar physiology or morphology in either species. Sun-grown foliage of Pacific yew and English yew differed with respect to light harvesting, transpiration, stomatal conductance, leaf structure, stomatal distribution and foliar N concentrations and contents. Chlorophyll a fluorescence measurements indicated that shade-grown foliage of Pacific yew had larger and more efficient light harvesting systems than sun-grown foliage. Rates of CO(2) uptake and transpiration were similar in sun- and shade-grown foliage indicating acclimation of photosynthesis to the growth irradiance. Specific leaf area was significantly higher in shade-grown foliage of Pacific yew than in sun-grown foliage and was diagnostic of the light environment in which the foliage grew. Foliar N concentrations were not significantly different between sun- and shade-grown leaves of Pacific yew but sun-grown foliage had a higher N content. Physiological and morphological adjustments of Pacific yew foliage conferred tolerance to both high light and shade, enabling the trees to survive in a variety of light environments and indicating that Pacific yew is suited to nursery cultivation and regeneration of open sites.

Leaf-level physiological processes were studied in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) to determine whether apparent increases in stand-level water use efficiency (WUE) observed in response to nitrogen (N) fertilization were attributable to foliar N effects on carbon fixation rates or on stomatal control of water loss. Photosynthesis and transpiration were measured at different light intensities and ambient CO(2) molar fractions and comparisons were made between current-year shoots with average foliar N concentrations of 1.58% (High-N) and 1.25% (Low-N). Photosynthetic rates and foliar N concentrations were positively correlated. In response to light, photosynthesis and stomatal conductance were closely coupled and a similar coupling was observed in response to different ambient CO(2) concentrations. Partitioning the photosynthetic responses into mesophyll and stomatal components indicated that foliar N altered mesophyll conductance but not stomatal control of water loss. High-N shoots had significantly greater rates of photosynthesis and transpiration than Low-N shoots and, as a result, instantaneous WUE did not differ significantly between High-N and Low-N shoots.