Relationship between Net CO₂ Assimilation and Dry Weight Accumulation in Field-Grown Tobacco

Abstract

To assess the variability of net photosynthetic CO2 exchange per unit leaf area and to construct budgets for stands of field-grown tobacco (Nicotiana tabacum, Connecticut Broadleaf), a number of short-time measurements were made on all available leaf positions on two varieties using a hand-held transparent chamber for conducting gas exchange measurements on leaves. Measurements of net CO2 exchange were carried out on 18 separate days during a 35-day period, beginning 22 days after the seedlings were transplanted to the field. Gas exchange assays on leaves were conducted under ambient conditions of temperature and light intensity at all times of day. Solar radiation was monitored throughout the period, and losses of respiratory CO2 from stems, roots, and leaves (in the dark) were estimated. A estimation of a carbon budget; and (c) whether one could determine from a carbon budget why one variety produced more dry weight than the other. This investigation has demonstrated the usefulness of the C02-depletion method of assaying net CO2 exchange in field studies, and clearly established the close relationship between net CO2 exchange and dry weight accumulation.We have been involved in a continuing effort to modify genetically the biochemistry of C3 plants to produce tobacco mutants with decreased photorespiration and greater than normal rates of net CO2 assimilation per unit of leaf area (1,2,10,16). To confirm that varieties with superior rates of net photosynthesis under controlled conditions of the laboratory or greenhouse perform similarly in the field, an accurate yet convenient method of measuring net CO2 uptake under field conditions was sought. Most recently, we adapted the C02-depletion system described by Clegg et al. (5,13) to tobacco leaves in the field. It is based on the short-time measurement of the decrease in CO2 concentration in a portable, hand-held transparent chamber clamped over the leaf. This method permitted the convenient assay of large numbers of samples, and the results proved to be reliable and reproducible.It became apparent from our experience and from that of others that a limited number of instantaneous measurements of rate of

Effects of CO2 and O2 on Photosynthesis and Growth of Autotrophic Tobacco Callus

“…The chamber was flushed (1 L min-') with moistened gas of known composition, and measurements were begun by closing the stopcocks and removing gas samples at intervals ofseveral minutes through the serum stopper with a hypodermic syringe. Assimilation of CO2 was determined from the rate of CO2 depletion (10). Gas flushing was resumed, and measurements of CO2 depletion repeated several times to ensure that the rates were constant.…”

Selection of Nicotiana tabacum Haploids of High Photosynthetic Efficiency

“…It has been suggested that crop production could be increased by improving the photosynthetic efficiency (19,28).Although in some cases there is not a clear correlation between net photosynthesis and crop yield (9, 12), some reports show a clear positive correlation between net CO2 assimilation and dry weight accumulation (7,21,29).A great variability in photosynthetic ability is found in different species as well as within different cultivars of the same species.Differences in the CO2 assimilation rate have been observed in soybean (8), maize (14), tobacco (28), alfalfa, and cotton. This variability indicates the possibility of selecting plants with higher photosynthetic efficiency.…”

“…Although in some cases there is not a clear correlation between net photosynthesis and crop yield (9, 12), some reports show a clear positive correlation between net CO2 assimilation and dry weight accumulation (7,21,29).…”

Factors Affecting Expression of Enhanced Catalase Activity in a Tobacco Mutant with O2-Resistant Photosynthesis

“…Thus, photosynthesis was examined in some leaves in bright light and in some under overcast conditions. The measurements on wild-type and M7 plants were made from 0930 until about 1300 using a brief (20 s) CO2 depletion determination made with a Plexiglas cuvette that enclosed 0.8 dM2 of leaf area clamped over a leaf (10). A randomized system was used to determine the sequence in which plants in each line were measured on each of 8 d during a 19-d period.…”