Biomedical subjects

Boyd R. Strain

Publications and source records attributed to Boyd R. Strain.

3 recordsLinked to original sources

PubMed1999

Elevated CO(2) studies: past, present and future.

Increasing concentrations of atmospheric CO(2) are predicted to impact both current and future ecosystems. Elevated CO(2) is also predicted to affect biological processes at many levels of organization. In this overview, we summarize the responses of plants to elevated CO(2) including primary physiological and molecular responses, growth and reproductive responses, effects on plant-plant competition and interactions with other organisms, evolutionary responses, and effects at the ecosystem level. The objectives of this paper are to: (a) overview studies in this issue that were presented at a 1997 meeting entitled "Critical Assessment of the Response of Forest Ecosystems to Elevated Atmospheric Carbon Dioxide," which was sponsored by the Global Change and Terrestrial Ecosystems (GCTE) group of the International Geosphere Biosphere Program (IGBP), (b) review areas of recent progress in CO(2) research, (c) generalize patterns arising from past research, and (d) list critical areas of research for the future.

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PubMedDate not supplied

Direct and indirect effects of elevated CO(2) on whole-shoot respiration in ponderosa pine seedlings.

We determined the short-term direct and long-term indirect effects of CO(2) on apparent dark respiration (CO(2) efflux in the dark) in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings grown in 35 or 70 Pa CO(2) partial pressure for 163 days in naturally lit, controlled-environment chambers. Two soil N treatments (7 and 107 ppm total N, low-N and high-N treatments, respectively) were imposed by watering half the plants every 2 weeks with 15/15/18 fertilizer (N,P,K) and the other half with demineralized water. Direct effects of ambient CO(2) partial pressure on apparent dark respiration were measured during short-term manipulations (from minutes to hours) of the CO(2) environment surrounding the aboveground portion of individual seedlings. Short-term increases in the ambient CO(2) partial pressure consistently resulted in significant decreases in CO(2) efflux of seedling in all treatments. Efflux of CO(2) decreased by 3 to 13% when measurement CO(2) partial pressure was increased from 35 to 70 Pa, and by 8 to 46% over the entire measurement range from 0 to 100 Pa. No significant interactions between the indirect effects of growth CO(2) partial pressure and the direct effects of the measurement CO(2) partial pressure were found. Seedlings grown in the high-N treatment were significantly less sensitive to short-term changes in CO(2) partial pressures than seedlings grown in the low-N treatment. Apparent respiration tended to decrease in seedlings grown in elevated CO(2), but the decrease was not significant. Nitrogen had a large effect on CO(2) efflux, increasing apparent respiration more than twofold on both a leaf area and a leaf or shoot mass basis. Both the direct and indirect effects of elevated CO(2) were correlated with changes in the C/N ratio. A model of cumulative CO(2) efflux for a 160-day period demonstrated that, despite a 49% increase in total plant biomass, seedlings grown in the high-N + high-CO(2) treatment lost only 2% more carbon than seedlings grown in the high-N + low-CO(2) treatment, suggesting increased carbon use efficiency in plants grown in elevated CO(2). We conclude that small changes in instantaneous CO(2) efflux, such as those observed in ponderosa pine seedlings, could scale to large changes in carbon sequestration.

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PubMedDate not supplied

Effects of CO(2) enrichment on growth and root (15)NH(4) (+) uptake rate of loblolly pine and ponderosa pine seedlings.

We examined changes in root growth and (15)NH(4) (+) uptake capacity of loblolly pine (Pinus taeda L.) and ponderosa pine (Pinus ponderosa Douglas. Ex Laws.) seedlings that were grown in pots in a phytotron at CO(2) partial pressures of 35 or 70 Pa with NH(4) (+) as the sole N source. Kinetics of (15)N-labeled NH(4) (+) uptake were determined in excised roots, whereas total NH(4) (+) uptake and uptake rates were determined in intact root systems following a 48-h labeling of intact seedlings with (15)N. In both species, the elevated CO(2) treatment caused a significant downregulation of (15)NH(4) (+) uptake capacity in excised roots as a result of a severe inhibition of the maximum rate of root (15)NH(4) (+) uptake (V(max)). Rates of (15)NH(4) (+) uptake in intact roots were, however, unaffected by CO(2) treatment and were on average 4- to 10-fold less than the V(max) in excised roots, suggesting that (15)NH(4) (+) absorption from the soil was not limited by the kinetics of root (15)NH(4) (+) uptake. Despite the lack of a CO(2) effect on intact root absorption rates, (15)NH(4) (+) uptake on a per plant basis was enhanced at high CO(2) concentrations in both species, with the relative increase being markedly higher in ponderosa pine than in loblolly pine. High CO(2) concentration increased total (15)NH(4) (+) uptake and the fraction of total biomass allocated to fine roots (< 2 mm in diameter) to a similar relative extent. We suggest that the increased uptake on a per plant basis in response to CO(2) enrichment is largely the result of a compensatory increase in root absorbing surfaces.

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