Leaf Delta Research Articles

Ecophysiological responses of woody plants to past CO(2) concentrations.

An approach is detailed for calculating historical rates of CO(2) uptake and water loss of leaves from measurements of leaf delta(13)C composition and climatic information. This approach was applied to investigate leaf gas exchange metabolism of woody taxa during the past 200 years of atmospheric CO(2) increase and in response to the longer-term atmospheric CO(2) increases plants experienced over the Pleistocene. Reconstructed net assimilation rates and water use efficiencies increased in response to increasing atmospheric CO(2) concentrations in both sets of material, whereas stomatal conductance, showing the combined responses of changes in stomatal density and leaf assimilation rates, was generally less responsive. Woody temperate taxa maintained a nearly constant c(i)/c(a) ratio in response to the increase in atmospheric CO(2) concentrations over both timescales, in part, as a result of changes in stomatal density. The reconstructed leaf-scale physiological responses to past global climatic and atmospheric change corroborated those anticipated from experimental work indicating the adequate capacity of experiments, at least at the scale of individual leaves, to predict plant responses to future environmental change.

Photosynthesis and water-use efficiency of sugar maple (Acer saccharum) in relation to pear thrips defoliation.

An experimental introduction of pear thrips (Taeniothrips inconsequens Uzel), a major defoliator in sugar maple (Acer saccharum Marsh.) forests in northeastern North America, was conducted in a field plantation to determine if compensatory gas exchange occurs in response to feeding damage by this piercing-sucking insect. Sugar maple trees were enclosed in netting (167 micro m mesh) and pear thrips adults were introduced before leaf expansion in the spring. Pear thrips reduced whole-tree leaf area by approximately 23% and reduced leaf size (both mass and area) by 20% in the upper crown. Measurements of net CO(2) assimilation rate (A(net)) and stomatal conductance (g(s)) were made on tagged foliage that was later analyzed for stable carbon isotope composition (delta(13)C) to provide estimates of short- and long-term leaf water use efficiency (WUE). Pear thrips feeding reduced A(net) for fully expanded leaves by approximately 20%, although leaf chlorophyll content and leaf mass per unit area were apparently not affected. Comparison of A(net), g(s), instantaneous WUE and leaf delta(13)C between damaged and control trees as well as visibly undamaged versus moderately damaged foliage on pear thrips-infested trees indicated that there were no effects of pear thrips feeding damage on WUE or leaf delta(13)C. Long-term WUE among sugar maple trees in the field plantation, indicated by leaf delta(13)C analysis, was related to shorter-term estimates of leaf gas exchange behavior such as g(s) and calculated leaf intercellular CO(2) concentration (C(i)). We conclude that pear thrips feeding has no effect on leaf WUE, but at the defoliation levels in our experiment, it may reduce leaf A(net), as a result of direct tissue damage or through reduced g(s). Therefore, even small reductions in leaf A(net) by pear thrips feeding damage may have an important effect on the seasonal carbon balance of sugar maple when integrated over the entire growing season.

Correlations between Carbon Isotope Discrimination and Leaf Conductance to Water Vapor in Common Beans

Carbon isotope discrimination (Delta) was measured in the field on 10 cultivars of common bean (Phaseolus vulgaris L.). There was substantial variation (more than 2 per thousand) in leaf Delta values and these differences were maintained between vegetative and reproductive developmental stages. These bean lines also exhibited substantial differences in leaf conductance to water vapor, and again these differences were maintained across developmental stages. The differences in leaf conductance were positively correlated with Delta values, whether conductance was measured as total leaf conductance or as the individual conductances of either upper or lower leaf surfaces. The observed differences in leaf conductance were not associated with differences in stomatal density. There were small differences among bean lines in their leaf Kjeldahl nitrogen contents, which is interpreted as indicating that photosynthetic capacity among bean lines was similar. Thus, because Delta values and leaf conductance were positively correlated, these data suggested that there may have been differences among bean lines in the extent to which stomata limited photosynthetic gas exchange rates.