Anna W. Schoettle

Role of phosphorus and nitrogen in photosynthetic and whole plant carbon gain and nutrient use efficiency in eastern white pine

SummaryIn white pine (Pinus strobus) seedlings grown in five forest soils from New York State, net photosynthetic capacity (Amax) plant-1 was correlated with total foliar N plant-1 (r2=0.57), but was more highly correlated with total foliar P plant-1 (r2=0.82). There was no relationship (r2<0.01) between Amax [g leaf]-1 and foliar N [g leaf]-1 for the pooled data set, but there was a significant (P<0.001), but weak (r2=0.20) positive relationship between Amax [g leaf]-1 and foliar P [g leaf]-1 across all soils. However, within two of the five soils leaf N concentration was a significant (P<0.05) determinant of photosynthetic capacity. Due to differences in soil nutrient availabilities a large range in foliar P:N ratio (0.02–0.15) was observed, and the proportion of leaf P:N appeared to control Amax [g leaf N]-1. Whole plant nitrogen (NUE) and phosphorus (PUE) use efficiencies were well correlated with whole plant P:N ratio. In addition, NUE was well correlated with Amax [g leaf N]-1 and PUE was well correlated with Amax [g leaf P]-1. However, NUE was not well correlated with PUE, and Amax [g leaf N]-1 was not well correlated with Amax [g leaf P]-1. These results indicated that P and/or N limitations were important components of photosynthetic nutrient relations in white pine grown in these five soils and suggest that both P and N and their proportions should be considered in analyses of photosynthesis-nutrient relations.

Coupling biochemical and biophysical processes at the leaf level: an equilibrium photosynthesis model for leaves of C3 plants

The paper presents a generic computer model for estimating short-term steady-state fluxes of CO2, water vapor, and heat from broad leaves and needle-leaved coniferous shoots of C3 plant species. The model explicitly couples all major processes and feedbacks known to impact leaf biochemistry and biophysics including biochemical reactions, stomatal function, and leaf-boundary layer heat- and mass-transport mechanisms. The ability of the model to successfully predict measured photosynthesis and stomatal-conductance data as well as to simulate a variety of observed leaf responses is demonstrated. A model application investigating physiological and environmental regulation of leaf water-use efficiency (WUE) under steady-state conditions is discussed. Simulation results suggest that leaf physiology has a significant control over the environmental sensitivity of leaf WUE. The implementation of a highly efficient solution technique allows the model to be directly incorporated into plant-canopy and terrestrial ecosystem models.

Causes and Consequences of Variation in Conifer Leaf Life-Span

Species with mutually supporting traits, such as high N{sub mass}, SLA, and A{sub mass}, and short leaf life-span, tend to inhabit either generally resource-rich environments or spatial and/or temporal microhabitats that are resource-rich in otherwise more limited habitats (e.g., {open_quotes}precipitation{close_quotes} ephemerals in warm deserts or spring ephemerals in the understory of temperate deciduous forests). In contrast, species with long leaf life-span often support foliage with low SLA, N{sub mass}, and A{sub mass}, and often grow in low-temperature limited, dry, and/or nutrient-poor environments. The contrast between evergreen and deciduous species, and the implications that emerge from such comparisons, can be considered a paradigm of modern ecological theory. However, based on the results of Reich et al. (1992) and Gower et al. (1993), coniferous species with foliage that persists for 9-10 years are likely to assimilate and allocate carbon and nutrients differently than other evergreen conifers that retain foliage for 2-3 years. Thus, attempts to contrast ecophysiological or ecosystem characteristics of evergreen versus deciduous life forms may be misleading, and pronounced differences among evergreen conifers may be ignored. Clearly, the deciduous-evergreen contrast, although useful in several ways, should be viewed from the broader perspective of a gradient in leaf life-span.

Effects of O3 and acidic rain on photosynthesis and growth in sugar maple and northern red oak seedlings

Two-year-old sugar maple Acer saccharum and northern red oak Quercus rubra seedlings were exposed to all combinations of several levels each of ozone (O3) and simulated acidic rain. Deposition rates and amounts of simulated rain were normal for eastern North America (12·5 mm of rain twice per week) and levels of acidity in the various treatments ranged between pH 5·6 and 3·0. Plants were exposed to O3 for 7 h per day on 5 d per week. Concentrations of O3 were constant and ranged between 0·02 and 0·12 μl litre−1 in the various treatments. Ozone treatments caused significant declines in net photosynthesis in both species, with the largest reductions observed (30% in maple and 20% in oak) after two months in the highest O3 treatment (0·12 μl litre−1). Reductions in growth as a result of O3 treatments occurred in sugar maple, but apparently due to the relatively short duration of the pollution treatments, growth reductions were not observed in red oak. Chlorophyll contents in sugar maple leaves increased as a result of O3 exposure. Simulated acidic rain treatments had no effect on either net photosynthesis or growth in either species and no interactive effects of the two pollutants were observed. The results of this study suggest that sugar maple and red oak are relatively insensitive to acidic rain over the course of a single growing season, but potential long-term effects are unknown. These two species were sensitive to relatively low concentrations of O3, and ambient levels of O3 in eastern North America could be having significant deleterious effects on sugar maple and red oak in the field.

Acid Rain and Ozone Influence Mycorrhizal Infection in Tree Seedlings

Atmospheric pollution may be causing reduced growth and increased mortality of trees in forests in Europe and North America. Acid rain and ozone are the two pollutants most frequently mentioned as causal agents in the forest decline problem. One plant-environment interface where atmospheric pollution may be having an impact is the symbiotic association between roots and soil fungi known as mycorrhizae. Mycorrhizae are essential for the survival and growth of most forest tree species in the natural environment. Mycorrhizal fungi can affect the nutrient uptake and translocation, water uptake, root morphology, carbon metabolism and disease resistance of the host plant. In specific instances, mycorrhizal infection has been observed to enhance tree growth increase seedling survival or protect plants from root disease. Therefore, sensitivity of the mycorrhizal association to atmospheric pollution could be harmful to forest trees and might influence the decline of forests.