Biologic Markers of Air-Pollution Stress and Damage in Forests (1989) / Chapter Skim
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Carbon Allocation Processes as Indicators of Pollutant Impacts on Forests Trees
Carbon Allocation Processes as Indicators of Pollutant Impacts on Forests Trees
Pages 293-302
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From page 293... ...
ABSTRACT The physiological processes linking carbon assimilation and net primary production in forest trees offer a broad spectrum of reference points for documenting, evaluating, and predicting the effects of atmospheric pollutants on forests. Measurements of photosynthesis, dark respiration, leaf maintenance costs, energy storage reserves, secondary metabolites associated with plant resistance to pathogens, dry matter partitioning, and patterns of annual radial growth of forest trees represent useful indicators of pollutant effects that encompass levels of detection ranging from short term mechanistic processes to longer term responses that integrate seasonal or multi-year effects.
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From page 294... ...
Some components of carbon allocation pathways that provide useful endpoints in evaluating mechanisms of action and implications for impacts of air pollutants on growth potential of forest trees (after McLaughlin, 1988a) .l,2 reduced translocation, and changes in patterns of storage, mobilization, and utilization of energy storage reserves.
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From page 295... ...
The exchange of carbon, both photosynthetic uptake and respiratory losses, by foliage of forest trees has been an obvious focal point in many studies aimed at evaluating tree growth potential. With respect to air pollutant impacts, changes in photosynthesis particularly have figured prominently in efforts to understand the concentration threshold for physiological responses (Botkin et al., 1972)
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From page 296... ...
and may deplete as much or more carbon from available energy pools as reduced photosynthesis. Increased dark respiration may be particularly significant when coupled with reduced rates of Pn, and in fact, reduced Pn may be a consequence of increases in light respiration, a component of the assimilation process that has received little emphasis with respect to pollutant effects.
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From page 297... ...
Storage and Mobilization. With respect to evaluating impacts of air pollutants on tree production potential, the storage reserves provide a potentially useful and temporally integrative indicator of the carbohydrate economy of the tree and its capacity both to meet the energy demands of annual growth cycles and to resist insects and disease.
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From page 298... ...
Observed response patterns at the stem level can provide testable hypotheses about basic physiological processes strongly influencing growth of a species as well as likely causal factors leading to disruption of the growth process (McLaughlin et al., 1987~. Several summary points can be made regarding the use of carbon allocation pathways to identify and diagnose responses of trees to air pollutants: (1)
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From page 299... ...
Within this context an analytical framework can be suggested that first documents the magnitude anti patterns of change in a biological indicator or indicator system and then tests both the physiological basis of the measured response as well as its consequences at successively higher levels of whole plant integration. The physiological basis must be understood to address adequately the causal relationships and the range of possible consequences, while the more integrative measures help document the range and probabilities of actual responses observed under field conditions.
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From page 300... ...
1980. Photosynthesis and needle elongation responses of Pinus strobes clones to low level sulfur dioxide exposures.
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From page 301... ...
In Proc. Commission of European Communities Workshop Interrelationships between Above and Below Ground Influences of Air Pollutants on Forest Trees.
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From page 302... ...
Amundson 1985. Ambient levels of ozone reduce net photosynthesis in tree and crop species.
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