Alterations in the physiology of CO₂ exchange in tomato plants grown in CO₂-enriched atmospheres

Abstract

Young, greenhouse-grown tomato plants were transferred to growth cabinets where they were maintained in normal air (0.03% CO2) or in air enriched to 0.1 or 0.5% CO2. CO2 enrichment increased net assimilation rate but decreased leaf area ratio. As a result, relative growth rate was greatest at 0.1% CO2 and was less in 0.5% CO2 than in 0.03% CO2. Gas exchange measurements were made on the third true leaf of plants from different CO2 regimes. They indicated that growth under conditions of CO2 enrichment affected photosynthesis at an early stage of leaf development (leaf plastochron index (PI) = 5) but not at a later stage (PI = 10.5). The effects were linked to changes in mesophyll resistance, not stomatal resistance. At PI = 5 and under equivalent test conditions of irradiance and CO2 concentration, net photosynthesis tended to be increased following growth in 0.1% CO2 but was decreased or unchanged by 0.5% CO2. Young leaves developed in 0.1% CO2 were less subject to photosynthetic inhibition by atmospheric oxygen and had low CO2 compensation points. CO2 enrichment also affected the activities of the enzymes ribulose-1,5-bisphosphate carboxylase and glycolic acid oxidase and the enzyme responses corresponded well with the gas exchange responses. The results indicate that photosynthetic adaptations may occur in response to the concentration of CO2 present during growth, and that enrichment to concentrations much above 0.1% CO2 may be detrimental to net photosynthesis and growth rate.

Acclimation of Two Tomato Species to High Atmospheric CO2

“…Azcon-Bieto (2) reported that the accumulation of soluble sugars in wheat leaves was correlated to the inhibition of photosynthesis. Except for leaf 5 of L. esculentum sampled at 0800 h at week one, our study found no substantial accumulation of sugars during the first 5 weeks of treatment for L. esculentum (Figs. 2, C and G, 3, C and G), suggesting that the rapid decline of the relative growth rate and photosynthesis could not be attributed to sugar accumulation.…”

“…In a recent study, Yelle et al (21) showed that the beneficial effects of CO2 enrichment on the relative growth and photosynthetic rates were not maintained as tomato plants matured. Photosynthesis of leaf 5 was 37% higher than ' Research supported by Conseil des Recherches en Peche et AgroAlimentaire du Quebec and by the Fonds pour la Formation de Chercheurs et l'Aide a la Recherche. the control plants after 1 week of CO2 enrichment, but thereafter decreased.…”

“…However, the long-term effects of high CO2 levels on the physiological and biochemical behaviors of tomato plants need to be studied further. Many species lose their photosynthetic efficiency when subjected for an extended period to high concentrations of CO2 in the atmosphere (5,9,12), and become gradually less efficient in the use ofthe added CO2. In a recent study, Yelle et al (21) showed that the beneficial effects of CO2 enrichment on the relative growth and photosynthetic rates were not maintained as tomato plants matured.…”

Acclimation to High CO2 in Bean

“…Generally, CO2 enrichment increases total dry weight and yield when light, temperature, and water are not limiting growth. Elevated CO2 has the greatest impact on the plant organs developing during the treatment period (1,10,12). Experiments with soybeans (10) show that CO2 enrichment only increases yield when applied during reproductive growth and not when applied during vegetative growth.…”

“…Experiments with soybeans (10) show that CO2 enrichment only increases yield when applied during reproductive growth and not when applied during vegetative growth. Older leaves seem less responsive to high CO2 than young leaves (1,12), and differences between vegetatively growing plants in high and ambient CO2 diminish with prolonged treatment (1). Leaf thickness increases with high C02 treatment (17) which may bias area-based photosynthetic measurements.…”