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Light-emitting diode (LED) technology shows promise for supplementing photosynthetically active radiation (PAR) in forest nurseries because of the potential reduction in energy consumption and an ability to supply discrete wavelengths to optimize seedling growth. Our objective was to examine the effects of light spectra supplied by LED and traditional high-pressure sodium (HPS) lamps on growth and physiology of Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) and Engelmann spruce ( Picea engelmannii Parry ex Engelm.) seedlings. We used three latitudinal sources for each species: British Columbia (BC), Idaho (ID), and New Mexico (NM). Container seedlings were grown for 17 weeks in the greenhouse under an 18 h photoperiod of ambient solar light supplemented with light delivered from HPS or LED. In general, seedlings grown under LED had significantly greater growth, gas exchange rates, and chlorophyll contents than those seedlings grown under HPS. The growth and physiological responses to supplemental lighting varied greatly among species and seed sources. Generally, LED-grown seedlings from BC had the greatest growth and tissue dry mass followed by ID and NM populations. Compared with HPS, the significant increase in seedling growth and concomitant energy savings with LED (29% energy consumption relative to HPS) demonstrates the promise of using LED as PAR supplemental lighting for container seedling production. [ABSTRACT FROM AUTHOR]

High nitrogen (N) concentrations and high NH4+:NO3− ratios that are characteristic of heavily eutrophic and constructed wetlands may be detrimental to the growth and establishment of macrophytes in wetlands formed in the oil sands reclamation areas. This study investigates the effects of N form on the physiology, growth, and root expansigenous honeycomb aerenchyma structure of Acorus americanus (Raf.) Raf., an important macrophyte targeted for wetland reclamation in Canada. Three populations of A. americanus were grown in aerated solution culture and provided for up to 3 months with two different concentrations of N (2 mmol·L−1, 8 mmol·L−1) as NH4+, NO3−, or NH4+ + NO3−. Fresh mass and physiological parameters including gas exchange, chlorophyll fluorescence, stomatal traits, nitrogen and chlorophyll concentration, root morphology, and aerenchyma structure were examined. The effects of N form were concentration-dependent. At 2 mmol·L−1 N, NH4+ + NO3− plants had higher fresh mass, photosynthetic rates, number of first-order roots, root diameter, and maximum root length than those provided solely with NH4+ or NO3−. At 8 mmol·L−1 N, both NH4+ and NH4+ + NO3− treatments had a negative impact on growth, net photosynthesis, and chlorophyll concentrations, and they also led to thinner and shorter roots with necrotic tips, a significant reduction in fractional root porosity, and a denser aerenchyma with smaller lacunae. The results indicate that high levels of NH4+-N may negatively affect the establishment of A. americanus plants in constructed wetlands through its impact on growth, net photosynthesis, and root morpho-anatomy. [ABSTRACT FROM AUTHOR]

A fundamental aspect of the carbon cycle is the exchange of carbon between plants and the atmosphere. It is, therefore, important to understand factors that affect differences in gas exchange and carbon balance within and among species. Concentrations of nonstructural carbohydrates are often used as a proxy for carbon balance. We determined diel patterns of leaf carbohydrate concentrations in relation to irradiance (sun vs. shade) in seedlings and mature trees of two sympatric oak species (Quercus virginiana Mill. and Quercus hemisphaerica Bartram ex Willd.). For seedlings, we also measured leaf gas exchange. Higher sun exposure significantly increased photosynthesis and carbohydrate concentrations in both species. Carbohydrate concentrations of seedling leaves showed strong diel fluctuations, whereas concentrations in mature tree leaves did not. This contrast might be attributed to faster carbohydrate export from leaves of mature trees. The difference in sink strength between seedlings and adults may be related to the decreasing ratio of leaf mass to plant mass with ontogeny, increasing the demand for carbohydrates per unit leaf mass. Seedlings and mature trees are clearly functionally different and care must be taken when extrapolating results from seedling experiments to mature trees. [ABSTRACT FROM AUTHOR]