摘要:

Abstract.Climate change will include correlated increases in temperature and atmospheric CO2concentration (Ca). Rising temperatures will increase the ratio of photorespiratory loss of carbon to photosynthetic gain, whilst rising Cawill have an opposing effect. The mechanism of these effects at the level of carboxylation in C3photosynthesis are quantitatively well understood and provide a basis for models of the response of leaf and canopy carbon exchange to climate change. The principles of such a model are referred to here and used to quantitatively examine the implications of concurrent increase in temperature and Ca. Simulations of leaf photosynthesis show the increase, with elevation of Cafrom 350 to 650 μmol mol‐1, in light saturated rates of CO2uptake (Asat) and maximum quantum yields (φ) to rise with temperature. An increase in Cafrom 350 to 650 μmol mol‐1can increase Asatby 20% at 10°C and by 105% at 35°C, and can raise the temperature optimum of Asatby 5°C. This pattern of change agrees closely with experimental data. At the canopy level, simulations also suggest a strong interaction of increased temperature and CO2concentration. Predictions are compared with the findings of long‐term field studies. The principles used here suggest that elevated Cawill alter both the magnitude of the response of leaf and canopy carbon gain to rising temperature, and sometimes, the direction of response. Findings question the value of models for predicting plant production in response to climate change which ignore the direct effects of rising Caand the modifications that rising Caimposes on the temperature response of net

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01439.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.In the first part of this review, I discuss how we can predict the direct short‐term effect of enhanced CO2on photosynthetic rate in C3terrestrial plants. To do this, I consider: (1) to what extent enhanced CO2will 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 CO2concentration 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 CO2may 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 adirectinhibition 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.Indirector ‘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 dur

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01440.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Very little attention has been directed at the responses of tropical plants to increases in global atmospheric CO2concentrations and the potential climatic changes. The available data, from greenhouse and laboratory studies, indicate that the photosynthesis, growth and water use efficiency of tropical plants can increase at higher CO2concentrations. However, under field conditions abiotic (light, water or nutrients) or biotic (competition or herbivory) factors might limit these responses. In general, elevated atmospheric CO2concentrations seem to increase plant tolerance to stress, including low water availability, high or low temperature, and photoinhibition. Thus, some species may be able to extend their ranges into physically less favourable sites, and biological interactions may become relatively more important in determining the distribution and abundance of species. Tropical plants may be more narrowly adapted to prevailing temperature regimes than are temperate plants, so expected changes in temperature might be relatively more important in the tropics. Reduced transpiration due to decreased stomatal conductance could modify the effects of water stress as a cue for vegetative or reproductive phenology of plants of seasonal tropical areas. The available information suggests that changes in atmospheric CO2concentrations could affect processes as varied as plant/herbivore interactions, decomposition and nutrient cycling, local and geographic distributions of species and community types, and ecosystem productivity. However, data on tropical plants are few, and there seem to be no published tropical studies carried out in the field. Immediate steps should be undertaken to reduce our ignorance of this critical area.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01441.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Photosynthesis by many marine phytoplankton algae is saturated by the inorganic C concentration in air‐equilibrated sea water. These organisms appear to use an active inorganic C transport process (CO2‐concentrating mechanism) which increases the CO2concentration around rubisco and saturates this enzyme with CO2and suppresses its oxygenase activity. A minority of marine phytoplankton algae have photosynthetic characteristics more suggestive of diffusive CO2entry; the inorganic C concentration present in sea water does not saturate photosynthesis by these organisms. Theoretical considerations, tested when possible against observation, suggest that the organisms with a CO2‐concentrating mechanism could have a lower cost of photons, nitrogen, iron, manganese and molybdenum to achieve a given rate of carbon accumulation by the cells than is the case for the organisms with diffusive CO2entry. Zinc and selenium costs may show the reverse effect. The increased sea‐surface inorganic C, and CO2concentrations which will result from anthropogenic increases in atmospheric CO2content are predicted to increase the rate of photosynthesis, and of growth when other resources are abundant, and to reduce, or reverse, the higher resource (photons, nitrogen, iron, manganese and molybdenum) cost of a given rate of CO2assimilation in organisms with CO2diffusion relative to those which have CO2concentrating mechanisms and do not repress them at higher inorganic C concentrations. These effects may well alter species composition, and overall resource cost of growth, of phytoplankton; any influence that these effects may have on CO2removal from the atmosphere are severely constrained by other trophic levels and, especially, oceanic circulation patterns. Changed sea‐surface temperatures are unlikely to qualitatively alter these co

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01442.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The global uptake of CO2in photosynthesis is about 120 gigatons (Gt) of carbon per year. Virtually all passes through one enzyme, ribulose bisphosphate carboxylase/oxygenase (rubisco), which initiates both the photosynthetic carbon reduction, and photorespiratory carbon oxidation, cycles. Both CO2and O2are substrates; CO2also activates the enzyme. In C3plants, rubisco has a low catalytic activity, operates below its Km(CO2), and is inhibited by O2. Consequently, increases in the CO2/O2ratio stimulate C3photosynthesis and inhibit photorespiration. CO2enrichment usually enhances the productivity of C3plants, but the effect is marginal in C4species. It also causes acclimation in various ways: anatomically, morphologically, physiologically or biochemically. So, CO2exerts secondary effects in growth regulation, probably at the molecular level, that are not predictable from its primary biochemical role in carboxylation. After an initial increase with CO2enrichment, net photosynthesis often declines. This is a common acclimation phenomenon, less so in field studies, that is ultimately mediated by a decline in rubisco activity, though the RuBP/Pi‐regeneration capacities of the plant may play a role. The decline is due to decreased rubisco protein, activation state, and/or specific activity, and it maintains the rubisco fixation and RuBP/Piregeneration capacities in balance. Carbohydrate accumulation is sometimes associated with reduced net photosynthesis, possibly causing feedback inhibition of the RuBP/Piregeneration capacities, or chloroplast disruption. As exemplified by field‐grown soybeans and salt marsh species, a reduction in net photosynthesis and rubisco activity is not inevitable under CO2enrichment. Strong sinks or rapid translocation may avoid such acclimation responses. Over geological time, aquatic autotrophs and terrestrial C4and CAM plants have genetically adapted to a decline in the external CO2/O2ratio, by the development of mechanisms to concentrate CO2internally; thus circumventing O2inhibition of rubisco. Here rubisco affinity for CO2is less, but its catalytic activity is greater, a situation compatible with a high‐CO2internal environment. In aquatic autotrophs, the CO2concentrating mechanisms acclimate to the external CO2, being suppressed at high‐CO2. It is unclear, whether a doubling in atmospheric CO2will be sufficient to cause a de‐adaptive trend in the rubisco kinetics of future C3plants, producing higher catalytic a

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01443.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Only a small proportion of elevated CO2studies on crops have taken place in the field. They generally confirm results obtained in controlled environments: CO2increases photosynthesis, dry matter production and yield, substantially in C3species, but less in C4, it decreases stomatal conductance and transpiration in C3and C4species and greatly improves water‐use efficiency in all plants. The increased productivity of crops with CO2enrichment is also related to the greater leaf area produced. Stimulation of yield is due more to an increase in the number of yield‐forming structures than in their size. There is little evidence of a consistent effect of CO2on partitioning of dry matter between organs or on their chemical composition, except for tubers. Work has concentrated on a few crops (largely soybean) and more is needed on crops for which there are few data (e.g. rice). Field studies on the effects of elevated CO2in combination with temperature, water and nutrition are essential; they should be related to the development and improvement of mechanistic crop models, and designed to test their predicti

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01444.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Herbaceous C3plants grown in elevated CO2show increases in carbon assimilation and carbohydrate accumulation (particularly starch) within source leaves. Although changes in the partitioning of biomass between root and shoot occur, the proportion of this extra assimilate made available for sink growth is not known. Root:shoot ratios tend to increase for CO2‐enriched herbaceous plants and decrease for CO2‐enriched trees. Root:shoot ratios for cereals tend to remain constant. In contrast, elevated temperatures decrease carbohydrate accumulation within source and sink regions of a plant and decrease root:shoot ratios. Allometric analysis of at least two species showing changes in root: shoot ratios due to elevated CO2show no alteration in the whole‐plant partitioning of biomass. Little information is available for interactions between temperature and CO2. Cold‐adapted plants show little response to elevated levels of CO2, with some species showing a decline in biomass accumulation. In general though, increasing temperature will increase sucrose synthesis, transport and utilization for CO2‐enriched plants and decrease carbohydrate accumulation within the leaf. Literature reports are discussed in relation to the hypothesis that sucrose is a major factor in the control of plant carbon partitioning. A model is presented i

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01445.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Climatic change as a result of the greenhouse effect is widely predicted to increase mean temperatures globally and, in turn, increase the frequency with which plants are exposed to heat shock conditions, particularly in the semi‐arid tropics. The consequences of extreme high‐temperature treatments on plants have been considered, particularly in relation to the synthesis of heat shock proteins (HSPs) and the capacity to acquire thermotolerance. The heat shock response is described using results obtained with seedlings of the tropical cereals, sorghum (Sorghum bicolor) and pearl millet (Pennisetum glaucum). A gradual temperature increase, as would occur in the field, is sufficient to induce thermotolerance. The synthesis of HSPs is a transient phenomenon and ceases once the stress is released. Despite the persistence of the HSPs themselves,de novosynthesis of HSPs is required for the induction of thermotolerance each time high temperatures are encountered. The effect of a repeated, diurnal heat shock was investigated and genotypic differences found in the ability to induce the heat shock response repeate

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01446.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Recent data concerning the impact of elevated atmospheric CO2upon water use efficiency (WUE) and the related measure, instantaneous transpiration efficiency (ITE), are reviewed. It is concluded from both short and long‐term studies that, at the scale of the individual leaf or plant, an increase in WUE or ITE is generally observed in response to increased atmospheric CO2levels. However, the magnitude of this increase may decline with time. The opinion that elevated CO2may substantially decrease transpiration at the regional scale is discussed. The mechanisms by which elevated CO2may cause a change in these measures are discussed in terms of stomatal conductance, assimilation and respiration responses to elevated CO2. Finally, recent experimental data and model outputs concerning the impact of the interaction of increased temperature with elevated CO2on WUE, ITE and yield are reviewed. It is concluded that substantially more data is required before reliable predictions about the regional scale response of WUE and catchment hydrology can be mad

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01447.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.There have been seven studies of canopy photosynthesis of plants grown in elevated atmospheric CO2: three of seed crops, two of forage crops and two of native plant ecosystems. Growth in elevated CO2increased canopy photosynthesis in all cases. The relative effect of CO2was correlated with increasing temperature: the least stimulation occurred in tundra vegetation grown at an average temperature near 10°C and the greatest in rice grown at 43°C. In soybean, effects of CO2were greater during leaf expansion and pod fill than at other stages of crop maturation. In the longest running experiment with elevated CO2treatment to date, monospecific stands of a C3sedge,Scirpus olneyi(Grey), and a C4grass,Spartina patens(Ait.) Muhl., have been exposed to twice normal ambient CO2concentrations for four growing seasons, in open top chambers on a Chesapeake Bay salt marsh. Net ecosystem CO2exchange per unit green biomass (NCEb) increased by an average of 48% throughout the growing season of 1988, the second year of treatment. Elevated CO2increased net ecosystem carbon assimilation by 88% in theScirpus olneyicommunity and 40% in theSpartina patenscommunit

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01448.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY