Search

The physiological effects of high CO2 concentrations, i.e., [CO2], on plant stomatal responses may be of major importance in understanding the consequences of climate change, by causing increases in runoff through suppression of plant transpiration. Radiative forcing by high [CO2] has been the main consideration in models of global change to the exclusion of plant physiological forcing, but this potentially underestimates the effects on the hydrological cycle, and the consequences for ecosystems. We tested the physiological responses of fossil plants from the Triassic--Jurassic boundary transition (Tr--J) succession of East Greenland. This interval marks a major high CO2-driven environmental upheaval, with faunal mass extinctions and significant floral turnover. Our results show that both stomatal size (expressed in fossil material as SL, the length of the stomatal complex opening) and stomatal density (SD, the number of stomata per mm²) decreased significantly during the Tr--J. We estimate, using a leaf gas-exchange model, that the decreases in SD and SL resulted in a 50%--60% drop in stomatal and canopy transpiration at the Tr--J. We also present new field evidence indicating simultaneous increases in runoff and erosion rates. We propose that the consequences of stomatal responses to elevated [CO2] may lead to locally increased runoff and erosion, and may link terrestrial and marine biodiversity loss via the hydrological cycle. [ABSTRACT FROM AUTHOR]

An introduction to the journal is presented in which the editor discusses an article on the impact of natural drought in Amazon, the quality of various global circulation models (GCMs) climate situations which are employed to drive dynamic global vegetation models (DGVMs), and the mechanisms involve in DGVM processes.

We model plant species diversity globally by country to show that future plant diversity capacity has a strong dependence on changing climate and carbon dioxide concentration. CO2 increase, through its impact on net primary production and warming is predicted to increase regional diversity capacity, while warming with constant CO2 leads to decreases in diversity capacity. Increased CO2 concentrations are unlikely to counter projected extinctions of endemic species, shown in earlier studies to be more strongly dependent on changing land use patterns than climate per se. Model predictions were tested against (1) contemporary observations of tree species diversity in different biomes, (2) an independent global map of contemporary species diversity and (3) time sequences of plant naturalisation for different locations. Good agreements between model, observations and naturalisation patterns support the suggestion that future diversity capacity increases are likely to be filled from a ‘cosmopolitan weed pool’ for which migration appears to be an insignificant barrier. [ABSTRACT FROM AUTHOR]

• The observation that stomatal density (number mm−2) on herbarium leaves had decreased over the last century represents clear evidence that plants have responded to anthropogenic increases in CO2 concentration. The mechanism of the response has proved elusive but here it is shown that density responses to both CO2 concentration and humidity are correlated with changes in whole-plant transpiration and leaf abscisic acid (ABA) concentration. • The transpiration rate of a range of accessions of Arabidopsis thaliana was manipulated by changing CO2 concentration, humidity and by exogenous application of ABA. Stomatal density increased with transpiration and leaf ABA concentration. • A common property of signal transduction systems is that they rapidly lose their ability to respond to the co-associated stimulus. Pathways of water movement within the plant are connected and so variations in supply and demand can be signalled throughout the plant directly, modifying stomatal aperture of mature leaves and stomatal density of developing leaves. Furthermore, the system identified here does not conform to the loss of ability to respond. • A putative mechanism is proposed for the control of stomatal density by transpiration rate and leaf ABA concentration. [ABSTRACT FROM AUTHOR]

Early experiments investigating the effects of CO2 enrichment on plants frequently showed photosynthetic stimulation and reduced stomatal aperture over short time periods. Work on the effects of elevated CO2 has advanced in two major areas: by the extension of long-term and field experiments, and through investigations on the wide range of negative feedbacks affecting plant responses to CO2. Downward photosynthetic acclimation in response to CO2 enrichment is frequently observed over the short and long term, and indicates the activity of diverse feedback mechanisms. CO2 is generally viewed as a limiting photosynthetic resource. However, recent work on stomatal development has shown that this view is simplistic: long- and short-distance signalling of CO2 concentration are necessary components of normal plant development. [ABSTRACT FROM AUTHOR]

Summary • Stomatal density responses by 48 accessions of Arabidopsis , to CO2 enrichment, broadly parallel interspecific observations. • Accessions differing in the degree of stomatal response to both CO2 and drought differed in flower production. Under well watered conditions flowering benefits from a small reduction in stomatal density with CO2 enrichment, but benefits from a large reduction under drought. • Stomatal density increases with altitude in Vaccinium myrtillus but is also strongly influenced by exposure. Exposed plants had higher stomatal densities than plants at the same altitude but in a community of individuals. This difference might be explained by systemic signalling within the plant as mature leaves detect both irradiance and [CO2 ], subsequently controlling the response of stomatal development in developing leaves. • Plants with the highest stomatal densities also had the highest stomatal conductances and photosynthetic rates. This suggests that signalling from mature to developing leaves predetermines the potential of the developing leaf to maximize its photosynthetic potential, including associated features such as nitrogen allocation, during early stages of development in the enclosed bud. [ABSTRACT FROM AUTHOR]

A survey of 100 species and 122 observations has shown an average reduction in stomatal density of 143% (SE ± 2.2%) with CO2 enrichment, with 74% of the cases exhibiting a reduction in stomatal density. A sign test demonstrated that stomata! density decreases, in response to CO2, significantly more often than expected by chance. Repeated observations on the same species indicated a significant repeatability in the direction of the stomatal response. Analyses which removed the potential effect of taxonomy on this data set showed no significant patterns in the dependency of the degree of stomatal change on growth form (woodiness vs. non-woodiness; trees vs. shrubs), habitat (cool VS. warm) or stomatal distribution on the leaf (amphi- vs. hypostomatous). Forty-three of the observations had been made in controlled environments and under a typical range in CO2 enrichment of 350-700 μmol mol-1. For these cases the average stomata! density declined by 9% (SE ± 3.3%) and 60% of the cases showed reductions in stomatal density. When analyses were restricted to these 43 observations, amphistomatous samples more frequently had greater changes in stomatal density than did hypostomatous samples. The degree of reduction in stomatal density with increasing CO2 increases with initial stomatal density, after the influence of taxonomy is removed using analyses of independent contrasts. When the data were examined for patterns that might be due explicitly to the effects of relatedness, the subclasses of the Hamamelidae and the Rosidae showed highly significant reductions in stomatal density with CO2 (87% of the specks studied in the Hamamelidae and 80% of the species in the Rosidae showed reduction with CO2 enrichment) and correlations between initial stomatal density and degree of reduction in stomatal density. [ABSTRACT FROM AUTHOR]

Rising levels of atmospheric CO2, climate change, and fertilizer pollution provide the ecological imperative for investigating the interaction between plant responses to atmospheric CO2 concentration, temperature and nutrient supply. In this study spring wheat (Triticum aestivum L, cv. Wemhley) was grown at 40, 50, 60 and 70 Pa atmospheric CO2 pressure and three experiments were conducted to investigate interactions between growth responses to the CO2 treatment and: (i) temperature (24/16 °C vs. 18/10 °C day/night), (ii) nutrient solution nitrate concentration (2.5, 5, 10 and 15 mM Ca(NO3,)2. 4H2O). and (iii) phosphate concentration (0.025 and 0.5 mM KH2PO4. Dry mass and root/shoot ratio increased with CO2, level at the higher temperature. These responses were reversed at the lower temperature. The increase in yield with CO2 enhancement was limited by low rates of nutrient supply in both absolute and relative terms. In the elevated CO2 treatments, the shoot nitrogen concentration was reduced, as was the proportional allocation to the uppermost leaves. These results are discussed with respect to possible physiological mechanisms and physiological for improved crop performance in a future, elevated CO2 World. [ABSTRACT FROM AUTHOR]

Predicting the future responses of plants and ecosystems to further changes in the CO2 concentration of the atmosphere and to the possibility of global warming are important current concerns. Predictions have been most frequently attempted using short-term, single-factor experiments in controlled environments. However, these experiments have failed to indicate the outcome of field experiments at larger spatial and temporal scales. Some of this failure is due to ignorance of environmental conditions and interactions while some is due to the use of inappropriate short-cuts, such as the addition of fertilizers for simulating enhanced mineralization, and some is due to ignorance of the processes involved in scaling-up from individual plants to populations. Long-term observations on plants in ecosystems nevertheless indicate that community-scale experiments may provide a useful but imperfect capacity to predict ecosystem responses. Although difficult to implement in practice, it is concluded that catchment-scale experiments offer the best opportunity to predict plant, community and ecosystem responses to environmental change. [ABSTRACT FROM AUTHOR]

Rising levels of atmospheric CO2 will have profound, direct effects on plant carbon metabolism. In this study we used gas exchange measurements, models describing the instantaneous response of leaf net CO2 assimilation rate (A) to intercellular CO2 partial pressure (Ci), in vitro enzyme activity assay, and carbohydrate assay in order to investigate the photosynthetic responses of wheat (Triticum aestivum L., cv. Wembley) to growth under elevated partial pressures of atmospheric CO2 (Ca). At flag leaf ligule emergence, the modelled, in vivo, maximum carboxylation velocity for RuBisCO was significantly lower in plants grown at elevated Ca than in plants grown at ambient Ca (70 Pa compared with 40 Pa). By 12 d after ligule emergence, no significant difference in this parameter was detectable. At ligule emergence, plants grown at elevated Ca exhibited reduced in vitro initial activities and activation states of RuBisCO. At their respective growth Ci values, the photosynthesis of 40-Pa-grown plants was sensitive to p(O2) and top(CO2), whereas that of 70-Pagrown plants was insensitive. Both sucrose and starch accumulated more rapidly in the leaves of plants grown at 70 Pa. At flag leaf ligule emergence, modelled non-photorespiratory respiration in the light (Rd) was significantly higher in 70-Pa-grown plants than in 40-Pa-grown plants. By 12 d after ligule emergence no significant differences in Rd were detectable. [ABSTRACT FROM AUTHOR]

The article focuses on the benefits of the increasing concentrations of carbon dioxide to plant growth. Carbon dioxide increases photosynthesis and reduces water loss, which helps in the development of plants. The effect of the pollutant tropospheric ozone on plant productivity can be reduced by carbon dioxide enrichment, which results in unique changes in gene expression that can be seen when plants are exposed jointly to tropospheric ozone and carbon dioxide.

Stomatal functioning regulates the fluxes of CO2 and water vapor between vegetation and atmosphere and thereby influences plant adaptation to their habitats. Stomatal traits are controlled by external environmental and internal cellular signaling. The objective of this study was to quantify the effects of CO2 enrichment (CE) on stomatal density (SD)-related properties, guard cell length (GCL) and carbon isotope ratio (δ13C) of a range of Arabidopsis thaliana ecotypes originating from a wide altitudinal range [50-1260 m above sea level (asl)], and grown at 400 and 800 ppm [ CO2], and thereby elucidate the possible adaptation and acclimation responses controlling stomatal traits and water use efficiency (WUE). There was a highly significant variation among ecotypes in the magnitude and direction of response of stomatal traits namely, SD and stomatal index (SI) and GCL, and δ13C to CE, which represented a short-term acclimation response. A majority of ecotypes showed increased SD and SI with CE with the response not depending on the altitude of origin. Significant ecotypic variation was shown in all stomatal traits and δ13C at each [ CO2]. At 400 ppm, means of SD, SI and GCL for broad altitudinal ranges, i.e. low (<100 m), mid (100-400 m) and high (>400 m), increased with increasing altitude, which represented an adaptation response to decreased availability of CO2 with altitude. δ13C was negatively correlated to SD and SI at 800 ppm but not at 400 ppm. Our results highlight the diversity in the response of key stomatal characters to CE and altitude within the germplasm of A. thaliana and the need to consider this diversity when using A. thaliana as a model plant. [ABSTRACT FROM AUTHOR]

Abstract The distribution and abundance of trees can be strongly affected by disturbance such as fire. In mixed tree/grass ecosystems, recurrent grass-fuelled fires can strongly suppress tree saplings and therefore control tree dominance. We propose that changes in atmospheric [CO2 ] could influence tree cover in such metastable ecosystems by altering their postburn recovery rates relative to flammable herbaceous growth forms such as grasses. Slow sapling recovery rates at low [CO2 ] would favour the spread of grasses and a reduction of tree cover. To test the possible importance of [CO2 ]/fire interactions, we first used a Dynamic Global Vegetation Model (DGVM) to simulate biomass in grassy ecosystems in South Africa with and without fire. The results indicate that fire has a major effect under higher rainfall conditions suggesting an important role for fire/[CO2 ] interactions. We then used a demographic model of the effects of fire on mesic savanna trees to test the importance of grass/tree differences in postburn recovery rates. We adjusted grass and tree growth in the model according to the DGVM output of net primary production at different [CO2 ] relative to current conditions. The simulations predicted elimination of trees at [CO2 ] typical of the last glacial period (180 ppm) because tree growth rate is too slow (15 years) to grow to a fire-proof size of ca. 3 m. Simulated grass growth would produce an adequate fuel load for a burn in only 2 years. Simulations of preindustrial [CO2 ] (270 ppm) predict occurrence of trees but at low densities. The greatest increase in trees occurs from preindustrial to current [CO2 ] (360 ppm). The simulations are consistent with palaeo-records which indicate that trees disappeared from sites that are currently savannas in South Africa in the last glacial. Savanna trees reappeared in the Holocene. There has also been a large increase... [ABSTRACT FROM AUTHOR]

It is sometimes assumed that because increases in atmospheric CO2 concentration usually enhance water use efficiency per unit leaf area, there will be a tendency for plants to show greater drought tolerance as well as increased biomass in the future. A critical examination of the responses to elevated CO2 in three temperate tree species shows that this assumption might be incorrect in the case of two of them. Both beech (Fagus sylvatica L.) and birch (Betula pubescens Ehrh.) display minimal stomatal closing responses to elevated CO2, and in the case of F. sylvatica the stomatal control of transpiration per unit leaf area appears to be unable to compensate for the greater development of leaf area. By contrast, the stomata of oak (Quercus robur L.) close appreciably in elevated CO2, to an extent which might be sufficient to compensate for an increase in total leaf area. A simple model for the controls on water supply and consumption for the whole tree suggests that in F. sylvatica the potential height attainment for a given sapwood area might decrease as the atmospheric CO2 concentration rises. The conclusions drawn from experimental data and from modelling are supported by field observations made in the UK in 1995, when the three species responded very differently to severe drought. We suggest that the progressive increase in the concentration of atmospheric CO2 over the past 200 yr might have accentuated differences in drought sensitivity between these species. [ABSTRACT FROM AUTHOR]

In two experiments, winter wheat (Triticum aestivum cv. Cerco) was grown in 350 (ambient) and 700 μmol mol-1 (elevated) atmospheric CO2 concentrations, In the first experiment, plants were grown at five levels of nitrogen fertilization, and in the second experiment, plants were grown at three levels of water supply. All plants were infected with powdery mildew, caused by the fungus Erysiphe graminis. Plants grown in elevated atmospheric CO2 concentrations had significantly reduced % shoot nitrogen contents and significantly increased % shoot water contents. At elevated atmospheric CO2 concentrations, where plant nitrogen content was significantly reduced, the severity of mildew infection was significantly reduced, and where host water content was significantly increased, the severity of mildew infection was significantly increased. In a moderate water supply treatment, the plants grown in elevated atmospheric CO2 concentrations had significantly reduced nitrogen contents (9.9%) and significantly increased water content (4%), the amount of mildew infection was unchanged. The severity of mildew infection appeared to be more sensitive to host water content than to host nitrogen content. [ABSTRACT FROM AUTHOR]

1. Populations of an annual plant, Abutilon theophrasti, were grown at four densities (100. 500. 1500 and 4000m[Sup-2]) and two CO[Sub2] concentrations (350 and 700 μ11[Sup-1] to examine the influence of CO[Sub2] environment on density-dependent patterns of demography and reproduction. Variables measured included survivorship, proportion of plants flowering and fruiting, number of fruiting individuals, number of seeds per individual, total seed production per population, mean seed mass, and germination of seeds produced in each environment. 2. All variables, except the number of fruiting individuals, declined with increasing density, and at the highest density no individuals set seed. The number of fruiting individuals was highest at a density of 500m[Sup-2]. In the elevated CO[Sub2] environment, survivorship was significantly reduced but the proportion of plants flowering and fruiting and the number of fruiting individuals in each population all increased. Total population seed production was higher in the elevated CO[Sub2] environment at all densities. although the differences were not significant. Significant effects of CO[Sub2] concentration were observed only for population-level variables, but not for mean individual fecundity or seed size. Seed germination declined with increasing maternal density. and no germination was recorded For seeds produced at 1500 m[Sup-2]. 3. Simple models of population dynamics, utilizing difference equations, were constructed to examine potential population-level consequences of these density and CO[Sub2] effects. In the absence of a persistent Seed pool, the simulated populations exhibited damped or stable oscillations under low germination values, but displayed non-cyclic ('chaotic') oscillations or went extinct for higher germination due to the complete failure of seed-set at high density. [ABSTRACT FROM AUTHOR]

Elevated levels of Co2 in the atmosphere are expected to affect plant performance and may alter global temperature patterns. Changes in mean air temperatures that might be induced by rising levels of CO2 and other greenhouse gases could also be accompanied by increased variability in daily temperatures such that acute increases in air temperature may be more likely than at present. Consequently, we investigated whether plants grown in a CO2 enriched atmosphere would be differently affected by a heat shock than plants grown at ambient CO2 levels. Plants of a C3 annual (Abutilon theophrasti), a C3 annual crop (Sinapis alba) and a C4 annual (Amaranthus retroflexus) were grown from seed in growth chambers under either 400 or 700cm ³ m-3 CO2, and were fertilized with either a high or low nutrient regime. Young seedlings of S. alba, as well as plants of all species in either the vegetative or reproductive phase of growth were exposed to a 4-h heat chock in which the temperature was raised an additional 14-23°C (depending on plant age). Total biomass and reproductive biomass were examined to determine the effect of CO2, nutrient and heat shock treatments on plant performance heat shock, CO2, and nutrient treatments, all had sonic significant effects on plant performance, but plants from both CO2 treatments responded similarly to heat shocks. We also found, as expected, that plants grown under high CO2 had dramatically decreased tissue N concentrations relative to plants grown under ambient conditions. We predicted that high-CO2-grown plants would be more susceptible to a heat shock than ambient-CO2-grown plants, because the reduced N concentrations of high-CO2 grown plants could result in the reduced synthesis of heat shock proteins and reduced thermotolerance. Although we did not examine heat shock proteins, our results showed little relationship between plant nitrogen status and the ability of a plant to tolerate an acute increase in temperature. [ABSTRACT FROM AUTHOR]