▪ Abstract The primary effect of the response of plants to rising atmospheric CO2 (Ca) is to increase resource use efficiency. Elevated Ca reduces stomatal conductance and transpiration and improves water use efficiency, and at the same time it stimulates higher rates of photosynthesis and increases light-use efficiency. Acclimation of photosynthesis during long-term exposure to elevated Ca reduces key enzymes of the photosynthetic carbon reduction cycle, and this increases nutrient use efficiency. Improved soil–water balance, increased carbon uptake in the shade, greater carbon to nitrogen ratio, and reduced nutrient quality for insect and animal grazers are all possibilities that have been observed in field studies of the effects of elevated Ca. These effects have major consequences for agriculture and native ecosystems in a world of rising atmospheric Ca and climate change.

More Efficient Plants : a consequence of rising atmospheric CO2

. In the first part of this review, I discuss how we can predict the direct short-term effect of enhanced CO2 on photosynthetic rate in C3 terrestrial plants. To do this, I consider: (1) to what extent enhanced CO2 will stimulate or relieve demand on partial processes like carboxylation, light harvesting and electron transport, the Calvin cycle, and end-product synthesis; and (2) the extent to which these various processes actually control the rate of photosynthesis. I conclude that control is usually shared between Rubisco (which responds sensitively to CO2) and other components (which respond less sensitively), and that photosynthesis will be stimulated by 25–75% when the CO2 concentration is doubled from 35 to 70 Pa. This is in good agreement with the published responses. In the next part of the review, I discuss the evidence that most plants undergo a gradual inhibition of photosynthesis during acclimation to enhanced CO2. I argue that this is related to an inadequate demand for carbohydrate in the remainder of the plant. Differences in the long-term response to CO2 may be explained by differences in the sink-source status of plants, depending upon the species, the developmental stage, and the developmental conditions. In the third part of the review, I consider the biochemical mechanisms which are involved in ‘sink’ regulation of photosynthesis. Accumulating carbohydrate could lead to a direct inhibition of photosynthesis, involving mechanical damage by large starch grains or Pi-limitation due to inhibition of sucrose synthesis. I argue that Pi is important in the short-term regulation of partitioning to sucrose and starch, but that its contribution to ‘sink’ regulation has not yet been conclusively demonstrated. Indirect or ‘adaptive’ regulation of photosynthesis is probably more important, involving decreases in amounts of key photosynthetic enzymes, including Rubisco. This decreases the rate of photosynthesis, and potentially would allow resources (e.g. amino acids) to be remobilized from the leaves and reinvested in sink growth to readjust the sink-source balance. In the final part of the review, I argue that similar changes of Rubisco and, possibly, other proteins are probably also involved during acclimation to high CO2.

Rising Co2 Levels and Their Potential Significance for Carbon Flow in Photosynthetic Cells

AGPase, ADP glucose pyrophosphorylase
GS, glutamine synthetase
GOGAT, glutamate : oxoglutarate amino transferase
NADP-ICDH, NADP-dependent isocitrate dehydrogenase
NR, nitrate reductase
OPPP, oxidative pentose phosphate pathway
3PGA, glycerate-3-phosphate
PEPCase, phosphoenolpyruvate carboxylase
Rubisco, ribulose-1,5-bisphosphate carboxylase/oxygenase
SPS, sucrose phosphate-synthase

This review first summarizes the numerous studies that have described the interaction between the nitrogen supply and the response of photosynthesis, metabolism and growth to elevated [CO2]. The initial stimulation of photosynthesis in elevated [CO2] is often followed by a decline of photosynthesis, that is typically accompanied by a decrease of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), an accumulation of carbohydrate especially starch, and a decrease of the nitrogen concentration in the plant. These changes are particularly marked when the nitrogen supply is low, whereas when the nitrogen supply is adequate there is no acclimation of photosynthesis, no major decrease in the internal concentration of nitrogen or the levels of nitrogen metabolites, and growth is stimulated markedly. Second, emerging evidence is discussed that signals derived from nitrate and nitrogen metabolites such as glutamine act to regulate the expression of genes involved in nitrate and ammonium uptake and assimilation, organic acid synthesis and starch accumulation, to modulate the sugar-mediated repression of the expression of genes involved in photosynthesis, and to modulate whole plant events including shoot–root allocation, root architecture and flowering. Third, increased rates of growth in elevated [CO2] will require higher rates of inorganic nitrogen uptake and assimilation. Recent evidence is discussed that an increased supply of sugars can increase the rates of nitrate and ammonium uptake and assimilation, the synthesis of organic acid acceptors, and the synthesis of amino acids. Fourth, interpretation of experiments in elevated [CO2] requires that the nitrogen status of the plants is monitored. The suitability of different criteria to assess the plant nitrogen status is critically discussed. Finally the review returns to experiments with elevated [CO2] and discusses the following topics: is, and if so how, are nitrate and ammonium uptake and metabolism stimulated in elevated [CO2], and does the result depend on the nitrogen supply? Is acclimation of photosynthesis the result of sugar-mediated repression of gene expression, end-product feedback of photosynthesis, nitrogen-induced senescence, or ontogenetic drift? Is the accumulation of starch a passive response to increased carbohydrate formation, or is it triggered by changes in the nutrient status? How do changes in sugar production and inorganic nitrogen assimilation interact in different conditions and at different stages of the life history to determine the response of whole plant growth and allocation to elevated [CO2]?

https://www.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3040.1999.00386.x

The interaction between elevated carbon dioxide and nitrogen nutrition: the physiological and molecular background

Plant responses to atmospheric CO2 enrichment with emphasis on roots and the rhizosphere.

summary
Because of their prominent role in the global carbon balance and their possible carbon sequestration, trees are very important organisms in relation to global climatic changes. Knowledge of these processes is the key to understanding the functioning of the whole forest ecosystem which can he modelled and predicted based on the physiological process information. This paper reviews the major methods and techniques used to examine the likely effects of elevated CO2 on woody plants, as well as the major physiological responses of trees to elevated CO2. The available exposure techniques and approaches are described. An overview table with all relevant literature data over the period 1989-93 summarizes the percent changes in biomass, root/shoot ratio, photosynthesis, leaf area and water use efficiency under elevated CO2. Interaction between growth, photosynthesis and nutrition is discussed with a special emphasis on downward regulation of photosynthesis. The stimulation or reduction found in the respiratory processes of woody plants are reviewed, as well as the effect of elevated CO2 on stomatal density, conductance and water use efficiency. Changes in plant quality and their consequences are examined. Changes in underground processes under elevated CO2 are especially emphasized and related to the functioning of the ecosystem. Some directions for future research are put forward.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1994.tb03961.x

Tansley Review No. 71 Effects of elevated atmospheric CO2on woody plants

Lycopersicon esculentum Mill. cv Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO2 concentrations (330 or 900 microliters per liter) for 10 weeks. Tomato plants grown at 900 microliters per liter contained more starch and more sugars than the control. However, we found no significant accumulation of starch and sugars in the young leaves of L. esculentum exposed to high CO2. Carbon exchange rates were significantly higher in CO2-enriched plants for the first few weeks of treatment but thereafter decreased as tomato plants acclimated to high atmospheric CO2. This indicates that the long-term decline of photosynthetic efficiency of leaf 5 cannot be attributed to an accumulation of sugar and/or starch. The average concentration of starch in leaves 5 and 9 was always higher in L. esculentum than in L. chmielewskii (151.7% higher). A higher proportion of photosynthates was directed into starch for L. esculentum than for L. chmielewskii. However, these characteristics did not improve the long-term photosynthetic efficiency of L. chmielewskii grown at high CO2 when compared with L. esculentum. The chloroplasts of tomato plants exposed to the higher CO2 concentration exhibited a marked accumulation of starch. The results reported here suggest that starch and/or sugar accumulation under high CO2 cannot entirely explain the loss of photosynthetic efficiency of high CO2-grown plants.

Acclimation of Two Tomato Species to High Atmospheric CO2 I. Sugar and Starch Concentrations

Lycopersicon esculentum Mill. cv Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO(2) concentrations (330 or 900 microliters per liter) for 10 weeks. The elevated CO(2) concentrations increased the initial ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity of both species for the first 5 weeks of treatment but the difference did not persist during the last 5 weeks. The activity of Mg(2+)-CO(2)-activated Rubisco was higher in 900 microliters per liter for the first 2 weeks but declined sharply thereafter. After 10 weeks, leaves grown at 330 microliters per liter CO(2) had about twice the Rubisco activity compared with those grown at 900 microliters per liter CO(2). The two species showed the same trend to Rubisco declines under high CO(2) concentrations. The percent activation of Rubisco was always higher under high CO(2). The phosphoenolpyruvate carboxylase (PEPCase) activity measured in tomato leaves averaged 7.9% of the total Rubisco. PEPCase showed a similar trend with time as the initial Rubisco but with no significant difference between nonenriched and CO(2)-enriched plants. Long-term exposure of tomato plants to high CO(2) was previously shown to induce a decline of photosynthetic efficiency. Based on the current study and on previous results, we propose that the decline of activated Rubisco is the main cause of the acclimation of tomato plants to high CO(2) concentrations.

/pdf/acclimation-of-two-tomato-species-to-high-atmospheric-co2-ii-ri2iiwd7u6.pdf

Acclimation of two tomato species to high atmospheric CO2. II. Ribulose-1,5,-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase

Lycopersicon esculentum Mill. CV. Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO2 concentrations (330 or 900 µmol·m -3 ) for 10 weeks. The elevated CO2 concentration increased the relative growth rate (RGR) of L. esculentum and L. chmielewskii by 18% and 30%, respectively, after 2 weeks of treatment. This increase was not maintained as the plant matured. Net assimilation rate (NAR) and specific leaf weight (SLW) were always higher in C02-enriched plants, suggesting that assimilates were preferentially accumulated in the leaves as reserves rather than contributing to leaf expansion. Carbon dioxide enrichment increased early and total yields of L. esculentum by 80% and 22%, respectively. Carbon exchange rates (CER) increased during the first few weeks, but thereafter decreased as tomato plants acclimated to high atmospheric CO 2. The relatively constant concentration of internal C02 with time suggests that reduced stomatal conductance under high CO 2 does not explain lower pho- tosynthetic rates of tomato plants grown under high atmospheric CO 2 concentrations. Leaves 5 and 9 responded equally to high CO2 enrichment throughout plant growth. Consequently, acclimation of CO 2-enriched plants was not entirely due to the age of the tissue. After 10 weeks of treatment, leaf 5, which had been exposed to high CO 2 for only 10 days, showed the greatest acclimation of the experiment. We conclude that the duration of exposure of the whole plant to elevated CO2 concentration, rather than the age of the tissue, governs the acclimation to high CO 2 concentrations.

/pdf/duration-of-co2-enrichment-influences-growth-yield-and-gas-3hav6hcde5.pdf

Duration of CO2 enrichment influences growth, yield, and gas exchange of two tomato species.

Annual greenhouse tomato production under a sequential intercropping system using supplemental light

Interactions between root-zone temperature and light levels on growth, development and photosynthesis of Lycopersicon esculentum Mill. cultivar ‘Vendor’

Marc J. Trudel

Papers

Acclimation of Two Tomato Species to High Atmospheric CO2 I. Sugar and Starch Concentrations

Acclimation of two tomato species to high atmospheric CO2. II. Ribulose-1,5,-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase

Duration of CO2 enrichment influences growth, yield, and gas exchange of two tomato species.

Annual greenhouse tomato production under a sequential intercropping system using supplemental light

Interactions between root-zone temperature and light levels on growth, development and photosynthesis of Lycopersicon esculentum Mill. cultivar ‘Vendor’