Effects Of Atmospheric CO2 Concentration Research Articles

Less negative impacts of climate change on crop yields in West Africa in the new CMIP6 climate simulations ensemble

Food insecurity is among one of the greatest risks posed by climate change in Africa, where 90 to 95% of African food production is rainfed and a large proportion of the population already faces chronic hunger and malnutrition. Although, several studies have found robust evidence of future crop yield losses under climate change scenarios, there is wide variation among crops and regions as well as large modeling uncertainties. A large part of this uncertainty stems from climate projections, as climate models may differ in simulating future changes in precipitation and temperature, which could lead to different future crop production scenarios. This work examines the impacts of climate change on crop yields of maize, millet and sorghum in West Africa using climate change projections from the Coupled Model Intercomparison Project 5th Phase (CMIP5) and from the new generation of climate models from the Coupled Model Intercomparison Project 6th Phase (CMIP6). We use the SIMPLACE crop modeling framework to simulate historical and future crop yields, and bootstrap techniques to evaluate projected changes in crop productivity between the CMIP5 and CMIP6 ensembles. Using the new generation of climate models CMIP6, we find that the negative crop yield projections shown by CMIP5 simulations are largely reduced, with even large increases in crop yields when the effect of atmospheric CO2 concentration is considered in the crop model. These differences in crop yield impacts between the CMIP5 and CMIP6 simulations are mainly due to different climate projections of temperature and precipitation in West Africa; CMIP6 projections being significantly wetter and cooler by mid-century and to a lesser extent by the end of the century. Such results highlight the large uncertainties that remain in assessing the impacts of climate change in the region and the consequent difficulty for end-users to anticipate adaptation strategies.

Interactive effects of atmospheric CO2 concentration and water stress on the phenology and physiology of faba bean (Vicia faba L.)

Crop modelling is a critical tool for assessing the impact of climate change and for evaluating adaptation strategies to ensure the sustainability of agricultural systems. In addition to increased temperature and reduced precipitation, studying the effects of increased atmospheric CO2 concentration ([CO2]) and water stress on water efficiency of crops is highly relevant for identifying and evaluating impacts and new adaptation measures. We carried out 12 experiments with 4 faba bean cultivars under controlled conditions of [CO2], temperature and water supply. An increase of [CO2] from 430 to 650 ppm caused a 20% reduction in stomatal conductance under optimal irrigation supply but had almost zero effect under water stress conditions. Our study shows that the beneficial effect of a higher atmospheric [CO2] on faba bean growth is counteracted by water stress, with the beneficial effect only detected when proper water management is applied. Thus, stomatal conductance appeared to be more sensitive to water stress than to elevated [CO2], indicating that the beneficial effects of elevated [CO2] on faba bean are largely dependent on the plant water status. This is particularly relevant in Mediterranean agricultural systems, where water shortage associated with droughts will become more frequent, even in areas of irrigation. Although differences in the response between cultivars were observed in our study when the water status was intermediate between optimal and severe drought, no single genotype among those studied will be sufficient to improve or fully guarantee yield under conditions of increasing [CO2] and water shortage. Therefore, the introduction of irrigation and/or sowing date strategies currently represent the only adaptation measures. The gaps in knowledge of the response of faba bean to climate change, and the limited number of adaptation measures available highlight the need for continued research, with breeding of drought-tolerant and high-yielding faba bean genotypes as one of the most promising alternatives.

Growth and biochemical changes of sorghum genotypes in response to carbon dioxide and salinity interactions

In this study, the interactive effects of atmospheric CO2 concentration and salinity were evaluated on the growth of four sorghum genotypes (SG1, SG3, SG14, and SG28). For this purpose, sorghum plants were exposed to ambient (380 ± 50 µmol mol−1) and elevated (700 ± 50 µmol mol−1) CO2 concentrations under two salinity levels (1.55 and 10.55 dS m−1). Elevated CO2 increased shoot (10–25%) and root (9–26%) dry weights, the concentrations of chlorophyll a, chlorophyll b, carotenoids, and K+, and the activities of catalase, ascorbate peroxides, and superoxide dismutase but decreased those of Na+ and water-soluble carbohydrate. Increases of 14.9 and 8.6% in shoot dry weights, 14.4 and 9.6% in root dry weights were observed under the non-saline and saline conditions, respectively. While all genotypes showed increased biomass production in response to elevated CO2 under non-saline treatment, only two genotypes were positively affected by the elevated CO2 under saline condition. Moreover, the scales of increases in plant biomass were greater under the non-saline treatment. The results of this experiment showed that the response of sorghum to elevated CO2 depended on both salinity level and genotype.

Atmospheric CO2 and VPD alter the diel oscillation of leaf elongation in perennial ryegrass: compensation of hydraulic limitation by stored-growth.

We explored the effects of atmospheric CO2 concentration (Ca ) and vapor pressure deficit (VPD) on putative mechanisms controlling leaf elongation in perennial ryegrass. Plants were grown in stands at a Ca of 200, 400 or 800μmolmol-1 combined with high (1.17kPa) or low (0.59kPa) VPD during the 16h-day in well-watered conditions with reduced nitrogen supply. We measured day:night-variation of leaf elongation rate (LERday :LERnight ), final leaf length and width, epidermal cell number and length, stomatal conductance, transpiration, leaf water potential and water-soluble carbohydrates and osmotic potential in the leaf growth-and-differentiation zone (LGDZ). Daily mean LER or morphometric parameters did not differ between treatments, but LERnight strongly exceeded LERday , particularly at low Ca and high VPD. Across treatments LERday was negatively related to transpiration (R2 =0.75) and leaf water potential (R2 =0.81), while LERnight was independent of leaf water potential or turgor. Enhancement of LERnight over LERday was proportional to the turgor-change between day and night (R2 =0.93). LGDZ sugar concentration was high throughout diel cycles, providing no evidence of source limitation in any treatment. Our data indicate a mechanism of diel cycling between daytime hydraulic and night-time stored-growth controls of LER, buffering Ca and daytime VPD effects on leaf elongation.

Coupled effects of atmospheric CO2 concentration and nutrients on plant-induced soil suction

Some studies have shown that an increasing atmospheric CO2 concentration reduces plant transpiration while others have demonstrated that it interacts with nutrients in soil to enhance plant transpiration and plant growth including an increase in leaf area. However, none of these studies has focused on plant-induced suction in vegetated soils. The objective of this study is to quantify transpiration induced soil suction by Schefflera heptaphylla in NPK (Nitrogen, Phosphorus, Potassium) nutrient supplied, heavily compacted silty sand under two different atmospheric CO2 concentrations (400 ppm and 1000 ppm). Three replicates of the plant were grown in NPK nutrient supplied silty sand and their plant characteristics and soil matric suction were measured under 400 and 1000 ppm atmospheric CO2 for three months. Due to the supply of nitrogen-rich nutrient in silty sand, leaf area index (LAI) of plant increased by 22% under 1000 ppm CO2 compared to 400 ppm CO2. Thus, the larger LAI induced higher soil suction substantially since no significant difference in soil suction was found between current and elevated atmospheric CO2. LAI of Schefflera heptaphylla could be a reliable parameter to understand and predict soil suction as verified by strong correlation coefficient (R2 = 0.85–0.98; P value < 0.1) of peak induced suction and atmospheric CO2 concentration. This study reveals that the use of vegetation in soil structures needs proper management with additional supply of nutrients to thrive under future atmospheric condition and to induce suction hence improve shear strength in vegetated soil structures.

Carbon isotope fractionation including photosynthetic and post-photosynthetic processes in C3 plants: Low [CO2] matters

Carbon isotope ratios of plants are highly informative for the reconstruction of ancient environments and for the interpretation of plant physiological processes to climate, but their responses to changing atmospheric CO2 concentration are currently debated. Moreover, plants in the geological past have experienced long-term low CO2 concentration (LC). However, the effects of LC on the plant C isotope ratios are still elusive.To investigate effects of atmospheric CO2 concentration ([CO2]) and drought on isotope ratios of plant metabolites we grew winter wheat (Triticum aestivum) in climate-controlled chambers under different [CO2] covering glacial, pre-industrial, and present concentrations (170, 280, and 400 ppm) and water regimes (well-watered and drought).First, we quantified total C isotope discrimination between plant and atmosphere (Δ) using 13C on-line measurements of plant gas exchange and 13C values of plant metabolites, i.e., cellulose, n-alkane, and phospholipid fatty acids (PLFA). We found that LC yielded a higher Δ regardless of water regime, i.e. more 13C-depleted values were found under LC; the effect was stronger for n-C29 alkane (1.5‰/100 ppm) and C16:0 PLFA (1.1‰/100 ppm) than that for cellulose (0.6‰/100 ppm). We then calculated post-photosynthetic C isotope shift (ɛ) between specific metabolites and plant bulk isotope values. δ13Cn-C29 alkane and δ13CPLFA were 8.3‰ and 7.3‰ lighter than the δ13Cbulk under 400 ppm; these depletions became higher (9.8‰ and 8.2‰ lighter than the δ13Cbulk for n-C29 alkane and PLFA, respectively) under 170 ppm. In contrast, δ13Ccellulose was 1.2‰ heavier than the δ13Cbulk under 400 ppm while this enrichment became higher (1.6‰) under 170 ppm.Changes in atmospheric [CO2] affected C fractionation not only via photosynthetic but also post-photosynthetic processes and thus must be taken into account when interpreting C isotopes for paleoclimate reconstruction and future global C cycle prediction.

Yield of canola (Brassica napus L.) benefits more from elevated CO2 when access to deeper soil water is improved

This study investigated the interactive effects of atmospheric CO2 concentration ([CO2]) and water availability on yield, root growth and water use of two canola cultivars with contrasting growth and vigour (vigorous hybrid cv. Hyola 50 and non-hybrid cv. Thumper). Plants were grown under ambient [CO2] (a[CO2], ∼400 μmol mol−1) or elevated [CO2] (e[CO2], ∼700 μmol mol−1) in a glasshouse. Two water treatments (well-watered and drought) were established in each [CO2] treatment. During the growing season leaf gas exchange parameters were measured. Leaf area was measured at 80 days after sowing. Aboveground biomass, seed yield, yield components and root biomass in four different soil layers (Layer 1: 0–20 cm, Layer 2: 21–40 cm, Layer 3: 41–60 cm and Layer 4: 61–80 cm depth) were measured at maturity. Weekly water use was determined gravimetrically.Elevated [CO2] stimulated seed yield (38%), aboveground biomass (34%), root biomass (42%), leaf area (42%) and leaf biomass (41%). Whilst e[CO2] stimulated root biomass in all soil layers, this stimulation was greater in the deeper than upper soil layers, and was associated with greater extraction of deeper soil water under e[CO2]. The cultivar with greater stimulation of deeper root biomass under e[CO2] showed greater yield benefit from the ‘CO2 fertilisation effect’. Under well-watered conditions, e[CO2]-induced reductions of stomatal conductance (gs) balanced the effect of increased leaf area on water use, resulting in similar water use compared to a[CO2]. In contrast, under drought conditions, water use was greater under e[CO2] than a[CO2]. The ‘CO2 fertilisation effect’ depended on cultivar and water treatment. Under well-watered conditions, aboveground biomass of the hybrid cultivar benefitted more from the ‘CO2 fertilisation effect’. However, under drought both aboveground biomass and seed yield of the non-hybrid cultivar benefitted more from the ‘CO2 fertilisation effect’. These findings show that interactions between environmental conditions (here experimental water treatments) and expression of genotypic traits (here differences between cultivars) play a decisive role in determining potential yield and growth benefits from rising [CO2].

Effects of atmospheric CO2 concentration on soil-water retention and induced suction in vegetated soil

Current atmospheric CO2 (400 ppm) is increasing 2 ppm annually and might reach up-to 1000 ppm by year 2100 due to global climate change. Different plant growth was observed under elevated CO2 in the previous studies. However, plant induced soil suction besides plants growth due to increasing atmospheric CO2 concentration in heavily compacted soil remain elusive. The objective of this study is to quantify transpiration and evapo-transpiration induced soil suction by Schefflera heptaphylla in heavily compacted soil under different atmospheric CO2 concentration. Three replicates of the plant were grown, and their characteristics were measured under 400 ppm and 1000 ppm CO2 concentration for three months. Leaf area index of plants decreased by 35% under 1000 ppm CO2 concentration due to soil nitrogen scarcity which impedes the plants ability to metabolize increased atmospheric CO2 concentration. Despite having LAI of 0.5–0.7, plant induced suction decreased by 10–25 kPa during transpiration and evapo-transpiration test under 1000 ppm CO2 concentration. Although a strong positive linear correlation (R2 = 0.8–0.9; P-value < 0.1) of LAI and root-shoot biomass ratio with induced peak soil suction under 400 ppm CO2 concentration, a weak linear correlation (R2 = 0.6–0.8; P-value > 0.1) of the same plant traits under 1000 ppm CO2 concentration was observed. This is because leaves cannot open stomata wide enough to transpire more water when they absorb more CO2 from the atmosphere resulting in soil suction reduction. This implies that the effects of atmospheric CO2 concentration on plant induced soil suction must be considered in vegetated soils.

Temperature and CO2 Level Influence Potato leafroll virus Infection in Solanum tuberosum.

We determined the effects of atmospheric temperature (10–30 ± 2°C in 5°C increments) and carbon dioxide (CO2) levels (400 ± 50 ppm, 540 ± 50 ppm, and 940 ± 50 ppm) on the infection of Solanum tuberosum cv. Chubaek by Potato leafroll virus (PLRV). Below CO2 levels of 400 ± 50 ppm, the PLRV infection rate and RNA content in plant tissues increased as the temperature increased to 20 ± 2°C, but declined at higher temperatures. At high CO2 levels (940 ± 50 ppm), more plants were infected by PLRV at 30 ± 2°C than at 20 or 25 ± 2°C, whereas PLRV RNA content was unchanged in the 20–30 ± 2°C temperature range. The effects of atmospheric CO2 concentration on the acquisition of PLRV by Myzus persicae and accumulation of PLRV RNA in plant tissues were investigated using a growth chamber at 20 ± 2°C. The M. persicae PLRV RNA content slightly increased at elevated CO2 levels (940 ± 50 ppm), but this increase was not statistically significant. Transmission rates of PLRV by Physalis floridana increased as CO2 concentration increased. More PLRV RNA accumulated in potato plants maintained at 540 or 940 ± 50 ppm CO2, than in plants maintained at 400 ± 50 ppm. This is the first evidence of greater PLRV RNA accumulation and larger numbers of S. tuberosum plants infected by PLRV under conditions of combined high CO2 levels (940 ± 50 ppm) and high temperature (30 ± 2°C).

Interactive effects of waterlogging and atmospheric CO2 concentration on gas exchange, growth and functional traits of Australian riparian tree seedlings

AbstractThe ability to survive and thrive in repeatedly waterlogged soils is characteristic of plants adapted to riparian habitats. Rising atmospheric CO2 has the potential to fundamentally alter plant responses to waterlogging by altering gas exchange rates and stoichiometry, modifying growth, and shifting resource‐economic trade‐offs to favor different ecological strategies. While plant responses to waterlogging and elevated CO2 individually are relatively well characterized, few studies have asked how the effects of waterlogging might be mediated by atmospheric CO2 concentration.We investigated interactive effects of elevated (550 ppm) atmospheric CO2 and waterlogging on gas exchange, biomass accumulation and allocation, and functional traits for juveniles of three woody riparian tree species. In particular, we were interested in whether elevated CO2 mitigated growth reduction under waterlogging, and whether this response was sustained following a refractory “recovery” period during which soils were re‐aerated.We found species‐specific effects of atmospheric CO2 concentration and waterlogging status on growth, gas exchange, and functional traits between species, and no evidence for a general effect of elevated CO2 in mediating plant responses to flooding. For one specie, Casuarina cunninghamiana, elevated CO2 substantially increased growth, but this effect was entirely removed by waterlogging, and there was no recovery following a refractory period.Differential responses to combined waterlogging and elevated CO2 among species may result in compositional changes to riparian plant communities and associated changes in ecosystem functioning.

Genetic variation in plant below-ground response to elevated CO2 and two herbivore species

It is unclear how changing atmospheric conditions, including rising carbon dioxide concentration, influence interactions between above and below-ground systems and if intraspecific variation exists in this response. We assessed interactive effects of atmospheric CO2 concentration, above-ground herbivory, and plant genotype on root traits and mycorrhizal associations. Plants from five families of Asclepias syriaca, a perennial forb, were grown under ambient and elevated atmospheric CO2 concentrations. Foliar herbivory by either lepidopteran caterpillars or phloem-feeding aphids was imposed. Mycorrhizal colonization, below-ground biomass, root biomass, and secondary defensive chemistry in roots were quantified. We observed substantial genetic variation among A. syriaca families in their mycorrhizal colonization levels in response to elevated CO2 and herbivory treatments. Elevated CO2 treatment increased root biomass in all genetic families, whereas foliar herbivory tended to decrease root biomass. Root cardenolide concentration and composition varied greatly among plant families, and elevated CO2 treatment increased root cardenolides in two of the five plant families. Moreover, herbivores differentially affected the composition of cardenolides expressed below ground. Increased atmospheric CO2 has the potential to influence interactions among plants, herbivores and mycorrhizal fungi and intraspecific variation suggests that such interactions can evolve.

The effect of atmospheric CO2 concentration on carbon isotope fractionation in C3 land plants

Because atmospheric carbon dioxide is the ultimate source of all land-plant carbon, workers have suggested that pCO2 level may exert control over the amount of 13C incorporated into plant tissues. However, experiments growing plants under elevated pCO2 in both chamber and field settings, as well as meta-analyses of ecological and agricultural data, have yielded a wide range of estimates for the effect of pCO2 on the net isotopic discrimination (Δδ13Cp) between plant tissue (δ13Cp) and atmospheric CO2 (δ13CCO2). Because plant stomata respond sensitively to plant water status and simultaneously alter the concentration of pCO2 inside the plant (ci) relative to outside the plant (ca), any experiment that lacks environmental control over water availability across treatments could result in additional isotopic variation sufficient to mask or cancel the direct influence of pCO2 on Δδ13Cp. We present new data from plant growth chambers featuring enhanced dynamic stabilization of moisture availability and relative humidity, in addition to providing constant light, nutrient, δ13CCO2, and pCO2 level for up to four weeks of plant growth. Within these chambers, we grew a total of 191 C3 plants (128 Raphanus sativus plants and 63 Arabidopsis thaliana) across fifteen levels of pCO2 ranging from 370 to 4200ppm. Three types of plant tissue were harvested and analyzed for carbon isotope value: above-ground tissues, below-ground tissues, and leaf-extracted nC31-alkanes. We observed strong hyperbolic correlations (R≥0.94) between the pCO2 level and Δδ13Cp for each type of plant tissue analyzed; furthermore the linear relationships previously suggested by experiments across small (10–350ppm) changes in pCO2 (e.g., 300–310ppm or 350–700ppm) closely agree with the amount of fractionation per ppm increase in pCO2 calculated from our hyperbolic relationship. In this way, our work is consistent with, and provides a unifying relationship for, previous work on carbon isotopes in C3 plants at elevated pCO2. The values for Δδ13Cp we determined in our ambient pCO2 chambers are consistent with the Δδ13Cp values measured in large modern datasets of plants growing within the Earth’s wettest environments, suggesting that it may be possible to reconstruct changes in paleo-pCO2 level from plants that grew in consistently wet environments, if δ13CCO2 value and initial pCO2 level can be independently quantified. Several implications arise for the reconstruction of water availability and water-use efficiency in both ancient and recent plant Δδ13Cp values across periods of changing pCO2 level. For example, the change in Δδ13Cp implied by our relationship for the rise in pCO2 concentration observed since 1980 is of the same magnitude (= ∼0.7‰) as the isotopic correction for changes in δ13CCO2 required by the input of 13C-depleted carbon to the atmosphere. For these reasons, only the portion of the terrestrial isotopic excursion that persists after accounting for changes in pCO2 concentration should be used for the interpretation of a change in paleo-environmental conditions.

Stomatal control as a driver of plant evolution

Stomata are the pores on a leaf surface through which plants regulate the uptake of carbon dioxide (CO2) for photosynthesis against the loss of water via transpiration. Turgor changes in the guard cells determine the area of stomatal pore through which gaseous diffusion can occur, thus maintaining a constant internal environment within the leaf (Gregory et al., 1950). Stomata first occurred in the fossil record ;400 million years ago (Ma), and are largely identical in form to the stomatal complexes of many extant plants, illustrating their effectiveness and importance to terrestrial plants (Edwards et al., 1998). Stomatal control is critical to a plant’s adaptation to its environment; it is this fundamental importance that has led to a wealth of stomatal research ranging in scale from biomolecular analysis to landscape processes (e.g. Gedney et al., 2006; Hu et al., 2010). The first issue of Journal of Experimental Botany, published 60 years ago, contained four papers relating to stomatal function. These included an analysis by Heath of the effects of atmospheric CO2 concentration ([CO2]) on stomatal aperture and conductance; an area of research that is increasingly relevant to our understanding of the past and prediction of future vegetation responses to atmospheric composition. Heath (1950) was the first to observe that reductions in [CO2] below ambient levels induced stomatal opening, an ecophysiological response of great interest, and that the site of CO2 sensing was most probably in the substomatal cavity and not the guard cells. Stomatal research has become vastly important to crop production, biodiversity responses, and hydrology (particularly in terms of ‘run-off’) with respect to rising atmospheric [CO2], changing water regimes, and growing populations. As our understanding of stomatal physiology develops, the role of stomata in the evolution of terrestrial vegetation and development of the terrestrial landscape and atmospheric composition is becoming increasingly evident, alongside the use of fossil stomata as palaeo-proxies of past atmospheres (e.g. McElwain et al., 2004; Berry et al., 2010; Smith et al., 2010). The stomatal control responses of plants consist of ‘shortterm’ stomatal aperture changes in response to availability of water, light, temperature, wind speed, and carbon dioxide, and also ‘longer term’ changes in stomatal density that set the limits for maximum stomatal conductance in response to atmospheric [CO2], light intensity/quality, and root-to-shoot signals of water availability (Schoch et al., 1980, 1984; Davies et al., 2000; Casson et al., 2009). Stomatal control determines the water use efficiency (WUE) of a plant by optimizing water lost against carbon gained. Additionally, the stomatal control mechanisms employed by a plant species will determine: the risk of xylem embolism by reducing the probability of cavitation through stomatal closure during episodes of high transpirative demand (Brodribb and Jordan, 2008; Meinzer et al., 2009); leaf temperature and resistance to heat stress (Srivastava et al., 1995; Jones et al., 2002); tolerance of toxic atmospheric gases (Mansfield and Majernik, 1970); nutrient uptake via promotion of root mass flow (Van Vuuren et al., 1997); and the maximum rate of photosynthesis (Korner et al., 1979). Those plant species with more effective stomatal control will be expected to be more successful than those with less effective stomatal control. However, not all plant species, or individuals within a species, possess equally effective stomatal control, in the setting of either stomatal numbers or the regulation of stomatal aperture (i.e. speed and ‘tightness’ of closure). Given that any trait that confers a selective advantage is likely to become universal within a population (McNeilly, 1968), it may be reasonable to assume that stomatal control incurs certain ‘costs’, and that these costs have played a significant role in plant evolution over the last 400 million years. The origination of major plant groups, and morphological advances such as the development of planate leaves, coincide with periods of ‘low’ atmospheric [CO2] (Fig. 1) (Woodward, 1998; Beerling et al., 2001). The reduced availability of the substrate for photosynthesis is predicted to be compensated by increases in the carboxylation efficiency of RubisCO and enhanced stomatal conductance to maintain CO2 uptake during periods of low [CO2] (Woodward, 1998; Franks and Beerling, 2009). This elevated stomatal conductance incurs higher rates of water loss and associated risks of desiccation and xylem embolism, in addition to the metabolic costs of enhanced construction of stomatal complexes. It is these costs during periods of low [CO2] that may serve as evolutionary tipping points, where species with more efficient and effective stomata and hydraulic systems are favoured (Robinson, 1994; Brodribb

Forest productivity under climate change: a checklist for evaluating model studies

AbstractClimate change is highly likely to impact on forest productivity over the next century. The direction and magnitude of change are uncertain because many factors are changing simultaneously, such as atmospheric composition, temperature, rainfall, and land use. Simulation models have been widely used to estimate how these interacting factors might combine to alter forest productivity. Such studies have used many different types of models with different underlying assumptions. To evaluate predictions made by such studies, it is essential to understand the type of model and the assumptions used. In this article, we provide a checklist for use when evaluating modeled estimates of climate change impacts on forest productivity. The checklist highlights the assumptions that we believe are critical in determining model outcomes. Models are classified into different general types, and assumptions relating to effects of atmospheric CO2 concentration, temperature, water availability, nutrient cycling, and disturbance are discussed. Our main aim is to provide a guide to enable correct interpretation of model projections. The article also challenges modelers to improve the quality of information provided about their model assumptions. WIREs Clim Change 2011 2 332–355 DOI: 10.1002/wcc.108This article is categorized under: Assessing Impacts of Climate Change &gt; Evaluating Future Impacts of Climate Change

CO&lt;sub&gt;2&lt;/sub&gt;: Different interpretation of the same data

From the complex topic, fundamental and com-prehensible arguments are selected and pre-sented so that the effect of atmospheric CO2concentration on balance in troposphere can be clearly evaluated. Presentation of relative values as used in the last report of an accredited scien-tific authority, the Intergovernmental Panel on Climate Change (IPCC), leads to considerable overestimation of the real situation. We docu-ment that the outcomes from this report of IPCC are provably false. Using a simple calculation, it is possible to demonstrate that the elevating of CO2 concentration does not cause the global warming in a degree that is expected basing on the report.

Elevated CO2 effects on semi‐arid grassland plants in relation to water availability and competition

Summary 1. It has been suggested that much of the elevated CO2 effect on plant productivity and N cycling in semi‐arid grasslands is related to a CO2‐induced increase in soil moisture, but the relative importance of moisture‐mediated and direct effects of CO2 remain unclear. 2. We grew five grassland species common to the semi‐arid grasslands of northern Colorado, USA, as monocultures and as mixtures of all five species in pots. We examined the effects of atmospheric CO2 concentration (ambient vs. 780 p.p.m.) and soil moisture (15 vs. 20% m/m) on plant biomass and plant N uptake. Our objective was to separate CO2 effects not related to water from water‐mediated CO2 effects by frequently watering the pots, thereby eliminating most of the elevated CO2 effects on soil moisture, and including a water treatment similar in magnitude to the water‐savings effect of CO2. 3. Biomass of the C3 grasses Hesperostipa comata and Pascopyrum smithii increased under elevated CO2, biomass of the C4 grass Bouteloua gracilis increased with increased soil moisture, while biomass of the forbs Artemisia frigida and Linaria dalmatica had no or mixed responses. Increased plant N uptake contributed to the increase in plant biomass with increased soil moisture while the increase in plant biomass with CO2 enrichment was mostly a result of increased N use efficiency (NUE). Species‐specific responses to elevated CO2 and increased soil moisture differed between monocultures and mixtures. Both under elevated CO2 and with increased soil moisture, certain species gained N in mixtures at the expense of species that lost N, but elevated CO2 led to a different set of winners and losers than did increased water. 4. Elevated CO2 can directly increase plant productivity of semi‐arid grasslands through increased NUE, while a CO2‐induced increase in soil moisture stimulating net N mineralization could further enhance plant productivity through increased N uptake. Our results further indicate that the largest positive and negative effects of elevated CO2 and increased soil moisture on plant productivity occur with interspecific competition. Responses of this grassland community to elevated CO2 and water may be both contingent upon and accentuated by competition.

Effects of atmospheric CO2 concentration, irradiance, and soil nitrogen availability on leaf photosynthetic traits of Polygonum sachalinense around natural CO2 springs in northern Japan

Long-term exposure to elevated CO2 concentration will affect the traits of wild plants in association with other environmental factors. We investigated multiple effects of atmospheric CO2 concentration, irradiance, and soil N availability on the leaf photosynthetic traits of a herbaceous species, Polygonum sachalinense, growing around natural CO2 springs in northern Japan. Atmospheric CO2 concentration and its interaction with irradiance and soil N availability affected several leaf traits. Leaf mass per unit area increased and N per mass decreased with increasing CO2 and irradiance. Leaf N per area increased with increasing soil N availability at higher CO2 concentrations. The photosynthetic rate under growth CO2 conditions increased with increasing irradiance and CO2, and with increasing soil N at higher CO2 concentrations. The maximal velocity of ribulose 1,5-bisphosphate carboxylation (V (cmax)) was affected by the interaction of CO2 and soil N, suggesting that down-regulation of photosynthesis at elevated CO2 was more evident at lower soil N availability. The ratio of the maximum rate of electron transport to V (cmax) (J (max)/V (cmax)) increased with increasing CO2, suggesting that the plants used N efficiently for photosynthesis at high CO2 concentrations by changes in N partitioning. To what extent elevated CO2 influenced plant traits depended on other environmental factors. As wild plants are subject to a wide range of light and nutrient availability, our results highlight the importance of these environmental factors when the effects of elevated CO2 on plants are evaluated.

European emissions of isoprene and monoterpenes from the Last Glacial Maximum to present

Abstract. Biogenic volatile organic compounds (BVOC), such as isoprene and monoterpenes, play an important role in atmospheric processes. BVOC species are oxidized in the atmosphere and influence levels of ozone. The less volatile amongst the BVOC and their oxidation products are important for the formation and growth of secondary biogenic aerosol. In this way, the Earth's radiation balance is affected. Geographic distribution and temporal changes in BVOC emissions are highly uncertain. Here we assessed changes in emission patterns across Europe since the Last Glacial Maximum (LGM) with a dynamic vegetation model. This model reproduces European tree species distribution and includes a process-based algorithm for terpenoid production. In a set of simulations the model was driven with paleoclimate anomalies and reconstructed CO2 concentrations. We quantified three main driving factors for the changes in emissions of isoprene and monoterpenes since the LGM: (1) the changes in climate, with temperature changes as the most important factor affecting plant physiology and terpenoid production in all plant species, (2) a change in species distribution related to the changes in climate, causing local shifts in emission characteristics of the vegetation, and (3) a change in CO2 concentration, causing opposing effects on the availability of different substrates for terpenoid production. The effect of atmospheric CO2 concentration is particularly uncertain, but sensitivity simulations showed an increase in European BVOC emissions in all sensitivity experiments irrespective of the use of a direct inhibition of terpenoid production by CO2. The effects of climate change on physiology and terpenoid production resulted in an overall relatively uniform increase of emissions in Europe over the simulation period, but regionally the effect of changes in species distribution and the related changes in emission capacities resulted in changes of emissions that can dominate over the physiology effects. This may have consequences for regional atmospheric chemistry simulations for the past, that have to rely on suitable geographic patterns of forest emissions.

Microbially mediated CH4 consumption and N2O emission is affected by elevated CO2, soil water content, and composition of semi-arid grassland species

Elevated CO2 affects plant productivity, but also water availability and plant species composition in semi-arid grasslands, thereby potentially causing complex effects on CH4 consumption and N2O emission. We studied the effects of atmospheric CO2 concentration (400 vs 780 μL L−1), water content (15 vs 20% gravimetric soil moisture), and composition of semi-arid grassland species (perennial grasses Bouteloua gracilis, Hesperostipa comata, and Pascopyrum smithii; sub-shrub Artemisia frigida; invasive forb Linaria dalmatica grown in monoculture and all five species together) on CH4 consumption and N2O emission in a full factorial greenhouse experiment. We used a unique method where we measured microbial effects on CH4 consumption and N2O emission in isolation from effects of gas diffusivity. Microbially mediated CH4 consumption was significantly higher under elevated CO2 (by 20%), but was not affected by soil water content or plant species composition. Microbially mediated N2O emission was not significantly affected by elevated CO2, but was significantly higher with high water content (by 67%) and differed significantly among species. Treatment effects on CH4 consumption and N2O emission often could not be explained simply by differences in soil moisture, suggesting that treatment-induced changes in other soil and microbial properties played a role in causing these effects.

Astronomically modulated late Pliocene equatorial Pacific climate transition and Northern Hemisphere ice sheet expansion

The equatorial Pacific underwent a significant climate transition during the late Pliocene, which is characterized by cooling of global sea surface temperatures (SSTs) and formation of a marked SST gradient between the eastern and western equatorial Pacific. Moreover, this transition was nearly synchronous with the late Pliocene Northern Hemisphere glaciation. Probing the relationship among solar insolation, low and high latitude processes is the key to unravel the mechanism of this climate transition. A series of statistical methods were used in this study to analyze the orbital components of the equatorial Pacific SST and global ice volume records for the past 5 Ma. We found that integrated solar insolation rather than the monthly mean insolation is the primary external forcing of the late Pliocene climate transition, and that on orbital time scale the SSTs of the eastern and western equatorial Pacific display consistent change rather than a “seesaw” pattern. Changes of Earth’s orbital configuration have been responsible for this climate transition whereas the positive feedback effects of atmospheric CO2 concentration have further cooled the global climate since the early Cenozoic.