Direct Effects Of Elevated CO2 Research Articles

Seasonal interactive effects of pCO2 and irradiance on the ecophysiology of brown macroalga Fucus vesiculosus L.

ABSTRACT Stochastic upwelling of seawater in the Baltic Sea from the deep, anoxic bottoms may bring low-pH water rich in CO2 close to the surface. Such events may become more frequent with climate change and ongoing ocean acidification (OA). Photoautotrophs, such as macroalgae, which are important foundation species, have been proposed to benefit from increased carbon availability due to reduced energetic cost in carbon acquisition. However, the exact effects of CO2 fertilization may depend on the ambient light environment, as photosynthesis rates depend on available irradiance. In this experimental study, interacting effects of CO2 addition and irradiance on the habitat-forming macroalga Fucus vesiculosus were investigated during two seasons – winter and summer – in the northern Baltic Sea. Growth rates remained unaffected by CO2 or irradiance during both seasons, suggesting that direct effects of elevated CO2 on mature F. vesiculosus are small. Increases in CO2 affected algal elemental ratios by increasing carbon and decreasing nitrogen content, with resulting changes in the C:N ratio, but only in winter. In summer, chlorophyll a content increased under low irradiance. Increases in CO2 caused a decline in light-harvesting efficiency (decrease in Fv/Fm and α) under high irradiance in summer, and conversely increased α under low irradiance. High irradiance caused increases in the maximum relative electron transport rate (rETRmax) in summer, but not in winter. Differences between winter and summer indicate that F. vesiculosus responses to CO2 and irradiance are season-specific. Increases in carbon content during winter could indicate slightly positive effects of CO2 addition in the long run if the extra carbon gained may be capitalized in growth. The results of this study suggest that increases in CO2, either through upwelling or OA, may have positive effects on F. vesiculosus, but these effects are probably small.

Impacts of elevated atmospheric CO2 concentration on terrestrial-aquatic carbon transfer and a downstream aquatic microbial community

Under higher atmospheric CO2 concentrations, increases in soil moisture and, hence in terrestrial-aquatic carbon transfer are probable. In a coupled terrestrial-aquatic experiment we examined the direct (e.g. through changes in the CO2 water concentration) and indirect (e.g. through changes in the quality and quantity of soil leachates) effects of elevated CO2 on a lake microbial community. The incubation of soils under elevated CO2 resulted in an increase in the volume of leachates and in both chromophoric dissolved organic matter (CDOM) absorption and fluorescence in leachate. When this leachate was added to lake water during a 3-day aquatic incubation, we observed negative direct effects of elevated CO2 on photosynthetic microorganism abundance and a positive, indirect effect on heterotrophic microbial community cell abundances. We also observed a strong, indirect impact on the functional structure of the community with higher metabolic capacities under elevated CO2 along with a significant direct effect on CDOM absorption. All of these changes point to a shift towards heterotrophic processes in the aquatic compartment under higher atmospheric CO2 concentrations.

Past and future drought in Mongolia.

The severity of recent droughts in semiarid regions is increasingly attributed to anthropogenic climate change, but it is unclear whether these moisture anomalies exceed those of the past and how past variability compares to future projections. On the Mongolian Plateau, a recent decade-long drought that exceeded the variability in the instrumental record was associated with economic, social, and environmental change. We evaluate this drought using an annual reconstruction of the Palmer Drought Severity Index (PDSI) spanning the last 2060 years in concert with simulations of past and future drought through the year 2100 CE. We show that although the most recent drought and pluvial were highly unusual in the last 2000 years, exceeding the 900-year return interval in both cases, these events were not unprecedented in the 2060-year reconstruction, and events of similar duration and severity occur in paleoclimate, historical, and future climate simulations. The Community Earth System Model (CESM) ensemble suggests a drying trend until at least the middle of the 21st century, when this trend reverses as a consequence of elevated precipitation. Although the potential direct effects of elevated CO2 on plant water use efficiency exacerbate uncertainties about future hydroclimate trends, these results suggest that future drought projections for Mongolia are unlikely to exceed those of the last two millennia, despite projected warming.

Interactive effects of elevated CO2 and nitrogen deposition accelerate litter decomposition cycles of invasive tree (Triadica sebifera)

Litter decomposition is an important component of forest nutrient recycling potentially impacted by elevated CO2, nitrogen (N) deposition, and biological invasions. Each can affect decomposition indirectly via changes in litter quantity, litter quality, and soils, which may increase or offset direct effects of elevated CO2 on decomposition. To date, no study has examined how elevated CO2 and N deposition interact to determine exotic plant litter cycling or the importance of variation among native and invasive populations of exotic plants for these effects.In this study, we examine elevated CO2 and N deposition effects on litter production and decomposition of native (China) and invasive (USA) populations of tallow tree (Triadica sebifera). First, we investigated litter production in greenhouse chambers. Then, we conducted three additional experiments using experimentally created litter and soils to examine CO2 and N effects on litter decomposition via changes in litter quality, soils, and atmospheric environment.Elevated CO2 and N deposition increased litter production with their combined effects more than additive. Nitrogen deposition increased litter production of native populations more than that of invasive populations. Litter produced in elevated CO2 had higher C:N and decomposed more slowly than litter produced in ambient CO2 but N deposition weakened these effects. Decomposition was slower in soils with histories of N deposition or plant association. Elevated CO2 had no direct effects on litter decomposition.The net effect of elevated CO2 alone on litter decomposition throughputs was negative for invasive populations due to strong reductions in litter decomposability. The net effect of elevated CO2 and N deposition together on litter throughputs was positive, especially for native populations due to strong litter production increases.Results suggest that elevated CO2 and N deposition impact litter cycling primarily through changes in litter quantity and quality with smaller effects via soils. Elevated CO2 and N deposition had strong positive effects on litter throughputs together due to synergistic positive effects on litter production and offsetting effects on decomposability. Although elevated CO2 and N deposition had consistent effects on native and invasive populations, the relative magnitudes of their effects on litter quantity and quality impacted litter cycling, suggesting the importance of considering plant trait variation in an overall estimation of global change effects on nutrient dynamics in forests and other ecosystems.

In vitro CO2 enrichment of CAM orchid plantlets

SummaryIncreased growth of an in vitro-propagated CAM orchid hybrid Mokara ‘White’ was obtained using a novel method of CO2 enrichment in an optimized photoautotrophic open system compared with the conventional closed system of culture. The optimization process for the open system involved the manipulation of external CO2 concentrations (0.03%, 1% and 10%), sucrose requirements, light intensities (80 and 200 µmol m–2 s–1) and the venting of headspace ethylene from the culture vessels. The physiological basis for increased growth in these CAM orchid plantlets after three months was attributed to the direct effects of elevated CO2 resulting in higher CAM activity for the plantlets and to the elevated CO2 present in the system which might interact with the ethylene present thereby reducing the inhibition of growth of plantlets due to ethylene.

The Incomplete Filling of the N‐dimensional Hypervolume

Starting as an undergraduate in the early 1980's, and going on to graduate school later in the decade, I immersed myself in the classic papers of evolutionary ecology, especially Hutchinson's 1957 niche paper and its embellishments by MacArthur, Horn, Levins, and Whittaker through the 1960's and 1970's. Working in Fakhri Bazzaz's lab, we saw the world as a kaleidoscope of environmental gradients, with responses to biotic and abiotic factors intimately interwoven and always dependent on environmental context. Hutchinson's N-dimensional hypervolume was realized in multi-factorial niche experiments, capturing spatial heterogeneity in forests and fields, or the interplay of spatial and temporal variation that emerges in disturbance regimes. Lab meetings were consumed by long discussions of how to interpret 2nd, 3rd, and even 4th order interactions in analysis of variance. Starting in the mid-1980's, greenhouse experiments increasingly focused on direct effects of elevated CO2, and interactions with temperature, water, and nutrient availability. The conceptual foundations provided by niche theory provided the critical tools to address the emerging questions related to global warming and directional environmental change. Over the next 10 years, my own work expanded in temporal scope, thinking about trait evolution across phylogenetic lineages, and the consequences for the assembly of communities in a biogeographic and evolutionary context. Somewhere in this process, I read Jackson and Overpeck's 2000 paper in Paleobiology: “Responses of plant populations and communities to environmental changes of the Late Quaternary” (JO2000). I wish now I could remember who suggested I read it, or how I may have stumbled across it, as I don't routinely scan the pages of Paleobiology. For me, though, this was the right paper at the right time; it had an immediate impact on the direction of my work, and I can trace the thread of its continuing importance through to my current research in climate change and conservation biology. JO2000 covers a lot of ground, and as with all papers, each reader will find a different idea, theme, or thread of information that intersects with their own work. For me, the key idea that I took away from this paper is that not all environments exist at a given point in time, whether considered regionally or at a global scale. JO2000 highlighted the importance of looking at large-scale climate patterns in climate space, the analog to Hutchinson's niche space from more than 40 years before. In climate space, where each factor is plotted on a separate axis, it becomes clear that not all combinations of conditions actually exist. Here in the Bay Area where I work, there are coastal locations where winter minimum temperatures average 6°C, and interior locations where summer maxima average 30°C and above. But there is nowhere that experiences this combination of winter and summer. Under future climate scenarios, however, this combination is projected to occur as warming winters and summers create new combinations. Over the past decade these new combinations have come to be called “novel climates,” and conversely conditions that appear today and may vanish may be called “disappearing climates” (Williams et al. 2007). Linking back to niche theory, the fact that not all conditions exist has profound implications for our understanding of biological distributions. Hutchinson's key formalization was the idea of the fundamental vs. realized niche, i.e., the roles of abiotic and biotic factors as limits to niche breadth and hence spatial distributions. By definition, the observations of where species live in field environments only informs us of the dimensions and breadth of the realized niche. But JO2000's observation that not all conditions exist means that we actually can't know the climatic limits of the realized or fundamental niche in certain portions of climate space, creating a fundamental limitation in our ability to extrapolate from modern distributions into potential distributions under past or future climates. JO2000 is where I first encountered these basic ideas, and it led me down a path of thinking about the geographic distribution of climate and climate space, how that will change in the future, and the implications for biological impacts of climate change. Published in the first year of the 21st century, it is a foundational paper that is shaping the new century of biology and the synthesis of climate science, ecology, and evolution with profound implications for our ability to project our future path, and perhaps intervene to stave off some of the potential impacts of climate change on biodiversity and our own well-being.

Laser-induced breakdown spectroscopy (LIBS) of a high-pressure CO2-water mixture: application to carbon sequestration.

Geologic carbon storage in deep saline aquifers is considered a feasible and possible approach of mitigating the problem of increasing greenhouse gas emissions. However, there are latent risks in which carbon dioxide (CO2) could migrate from the deep saline formations to shallower aquifers. In the event of a significant CO2 leakage to an underground source of drinking water, CO2 will dissolve in the water, thereby increasing its acidity, which could potentially enhance the solubility of various aquifer constituents, including hazardous compounds, subsequently compromising groundwater quality due to increased concentration of aqueous metals. In this paper we explore the possibility of detecting such leakage by the use of laser-induced breakdown spectroscopy (LIBS). The experiments were conducted in calcium chloride solution at three pressures of 10, 50, and 120 bar. To evaluate the direct effect of elevated CO2 on the intensity of calcium emission lines (422.67 and 393.37 nm), we also performed experiments with pure nitrogen (N2) gas, offering large water solubility contrast. We found that when performed in presence of CO2, LIBS showed only a modest decrease in Ca emission intensity from 10 to 120 bar compared to N2. These results indicate that LIBS is a viable tool for measuring brine/water contents in high-pressure CO2 environment and can be applied for monitoring CO2 leakage and displaced brine migration.

Marine bacterial communities are resistant to elevated carbon dioxide levels.

It is well established that the release of anthropogenic-derived CO2 into the atmosphere will be mainly absorbed by the oceans, with a concomitant drop in pH, a process termed ocean acidification. As such, there is considerable interest in how changes in increased CO2 and lower pH will affect marine biota, such as bacteria, which play central roles in oceanic biogeochemical processes. Set within an ecological framework, we investigated the direct effects of elevated CO2, contrasted with ambient conditions on the resistance and resilience of marine bacterial communities in a replicated temporal seawater mesocosm experiment. The results of the study strongly indicate that marine bacterial communities are highly resistant to the elevated CO2 and lower pH conditions imposed, as demonstrated from measures of turnover using taxa–time relationships and distance–decay relationships. In addition, no significant differences in community abundance, structure or composition were observed. Our results suggest that there are no direct effects on marine bacterial communities and that the bacterial fraction of microbial plankton holds enough flexibility and evolutionary capacity to withstand predicted future changes from elevated CO2 and subsequent ocean acidification.

A simulation study for assessing yield optimization and potential for water reduction for summer-sown maize under different climate change scenarios

SUMMARYThe objective of the present paper was to study the impact of climate change on grain yield, water balance, crop water productivity (CWP) and water requirements for the summer-sown maize in Faisalabad, Pakistan. Climate-change scenarios (Special Report on Emission Scenarios (SRES) A1B, A2 and B1) were derived from the general circulation model ECHAM 5 and the crop model CERES-Maize was used to simulate impacts of the applied climate scenarios. Calibration and validation of the crop models were carried out for the summer-sown maize in 2007 and for the spring-sown maize in 2008. Three predefined reduced irrigation scenarios were compared to traditional irrigation practices for the summer-sown maize. Under the current conditions, scenario S1 (one irrigation event skipped at the vegetative stage) showed a higher simulated yield than scenario S2 (one irrigation event skipped at the grain-filling stage) due to higher water drainage and nitrogen (N) leaching rates in scenario S2. Scenario S3 (irrigation events skipped at both crop establishment and the grain-filling stage) showed significantly higher grain yield because it had the lowest drainage and N leaching rates. In this irrigation scenario, 60 mm of water were saved compared to the other two scenarios, and much more water was saved compared to the traditional local regime.In the predicted climatic scenarios and with reduced irrigation, the simulated maize yields and crop water productivities were affected differently. For the period from 2036 to 2065, a more significant yield decrease was shown in all emission and irrigation scenarios. A yield decrease was simulated by both, including and not including the direct effect of elevated atmospheric CO2 concentrations on photosynthesis. However, the simulated direct effect of elevated CO2 was to produce higher yield and CWP in all scenarios. The highest grain yields and crop water productivities were achieved in the reduced irrigation scenario S3 for all emission scenarios and climatic periods for the same reason as under the current conditions (N leaching). However, the yield differences between the climate scenarios were mainly due to the shortening of the simulated growing period. This was caused by increased temperatures compared to current conditions. A shortened growing cycle reduced the potential time for biomass accumulation and in the present case it was not balanced by the CO2 fertilizing effect (without a potential change in maize cultivars).By simulating optimum yields (where automatic irrigation is determined by the model to receive optimum yield), under the current conditions it was found that 285 mm of irrigation would ensure the highest grain yield and CWP (30 mm more than under irrigation scenario S3). In this case, actual evapotranspiration reached 373 mm and less deep drainage and N leaching occurred. In the future climate scenarios, optimum yields and irrigation demands diminished depending on the emission scenario, but CWP increased slightly.The present simulation study shows a clear decreasing yield trend for autumn maize under a warm climate for each type of (unchanged) irrigation management due to the shortening of the growing period. However, in the current climate, as well as in the future climate scenarios, maize yield levels could be improved by optimized (and reduced) irrigation compared to traditional irrigation due to reduced N leaching. Even in the scenario with the highest warming trend (A1B emission scenario for the period 2036–65), the current yield levels could be kept or even improved.

Soil Fungi Respond More Strongly than Fine Roots to Elevated CO2 in a Model Regenerating Longleaf Pine-Wiregrass Ecosystem

Rising atmospheric CO2 concentration will affect belowground processes and forest function. However, the direction and magnitude of change for many soil processes are unknown. We used minirhizotrons to observe fine root and fungal dynamics in response to elevated CO2 in a model regenerating longleaf pine community in open-top chambers. The model community consisted of five plant species common to xeric sandhills longleaf pine stands: Pinus palustris, Quercus margaretta, Aristida stricta, Crotalaria rotundifolia, and Asclepias tuberosa. Elevated CO2 significantly increased both fine root and mycorrhizal tip standing crop by more than 50% in the deeper soil horizon (17–34 cm). Rhizomorph standing crop was nearly doubled in both deep and shallow soil (P = 0.04). Survivorship results for fine roots and rhizomorphs varied between soil depths. Fine root survivorship was likely influenced more by changes in community composition and species interactions driven by elevated CO2 rather than by direct effects of elevated CO2 on the fine roots of individual species. In this system, it appears that elevated CO2 led to a greater reliance on fungal symbionts to meet additional nutrient requirements rather than substantially increased root growth.

Effects of elevated CO2 associated with maize on multiple generations of the cotton bollworm, Helicoverpa armigera

AbstractUnder elevated environmental carbon dioxide (CO2), leaf chewers tend to compensate for decreased leaf nutritional quality with increased consumption; mortality and development times also increase and cause a reduction in the fitness of leaf chewers. However, the effect of elevated CO2 on multiple successive generations of these and other insects is not well understood. Furthermore, information about the direct effects of increased environmental CO2 on developmental time and consumption of herbivores is lacking. In this paper, we tested the hypothesis that cascade effects of elevated CO2 through plants, rather than the direct effects of elevated CO2, are the main factors decreasing the fitness of cotton bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae). We used two series of experiments to quantify the growth, development, and consumption of H. armigera fed on an artificial diet or C4 plants (maize) grown under two CO2 levels (ambient vs. double ambient). In the first series of experiments, elevated CO2 had no effect on the population abundance or individual consumption for three successive generations of cotton bollworms fed on an artificial diet. In the second series of experiments, elevated CO2 reduced population abundance of cotton bollworm larvae for two successive generations when they were fed maize milky grains. The specific effects were longer larval duration, lower fecundity, and decreased rm of cotton bollworms. Furthermore, elevated CO2 increased individual consumption when cotton bollworm was fed maize milky grains for two successive generations and decreased the population’s total consumption in the first generation but increased it in the second generation. The results from this study indicate that: (1) The effects of elevated CO2 on three successive generations of cotton bollworm fed on artificial diet were weak, or even non‐existent, and (2) elevated CO2 increased the consumption when cotton bollworm were fed maize. Our study also suggests that the damage inflicted by cotton bollworm on maize (a C4 plant) will be seriously affected by the increases in atmospheric CO2, which is unlike our previous results for spring wheat (a C3 plant).

Living in a high CO2 world: impacts of global climate change on marine phytoplankton

The planet is currently going through a period of global climate change, the pace of which is unprecedented in geological history. Marine phytoplankton contribute approximately 50% of the total global primary productivity and play a vital role in global carbon cycling. Consequently it is extremely important to understand the impact that global climate change will have on the ecological performance of these organisms. In this review we summarise current understanding of the influence that global climate change has on the physiological properties, productivity and assemblage composition of marine phytoplankton. While most phytoplankton are likely to show little direct effect of elevated CO2 on photosynthetic rates, some, including the ecologically important coccolithophorids, are likely to show significant stimulation of growth. The rise in temperature consequent upon the elevated atmospheric levels of CO2 and other greenhouse gases will stimulate growth of some species and increase ocean temperatures in some areas beyond their current optima. However, more importantly, increasing global temperatures will stimulate stratification of the water column which, in tropical and mid-latitudes will exacerbate nutrient limitation in surface waters. This in turn will lead to changes in phytoplankton assemblage composition, primary productivity and sensitivity to UVB radiation.

Microbial Community Responses to Atmospheric Carbon Dioxide Enrichment in a Warm-Temperate Forest

Forest productivity depends on nutrient supply, and sustained increases in forest productivity under elevated carbon dioxide (CO2) may ultimately depend on the response of microbial communities to changes in the quantity and chemistry of plant-derived substrates, We investigated microbial responses to elevated CO2 in a warm-temperate forest under free-air CO2 enrichment for 5 years (1997–2001). The experiment was conducted on three 30 m diameter plots under ambient CO2 and three plots under elevated CO2 (200 ppm above ambient). To understand how microbial processes changed under elevated CO2, we assayed the activity of nine extracellular enzymes responsible for the decomposition of labile and recalcitrant carbon (C) substrates and the release of nitrogen (N) and phosphorus (P) from soil organic matter. Enzyme activities were measured three times per year in a surface organic horizon and in the top 15 cm of mineral soil. Initially, we found significant increases in the decomposition of labile C substrates in the mineral soil horizon under elevated CO2; this overall pattern was present but much weaker in the O horizon. Beginning in the 4th year of this study, enzyme activities in the O horizon declined under elevated CO2, whereas they continued to be stimulated in the mineral soil horizon. By year 5, the degradation of recalcitrant C substrates in mineral soils was significantly higher under elevated CO2. Although there was little direct effect of elevated CO2 on the activity of N- and P-releasing enzymes, the activity of nutrient-releasing enzymes relative to those responsible for C metabolism suggest that nutrient limitation is increasingly regulating microbial activity in the O horizon. Our results show that the metabolism of microbial communities is significantly altered by the response of primary producers to elevated CO2. We hypothesize that ecosystem responses to elevated CO2 are shifting from primary production to decomposition as a result of increasing nutrient limitation.

Monoterpene and herbivore-induced emissions from cabbage plants grown at elevated atmospheric CO2 concentration

Abstract The warming of the lower atmosphere due to elevating CO2 concentration may increase volatile organic compound (VOC) emissions from plants. Also, direct effects of elevated CO2 on plant secondary metabolism are expected to lead to increased VOC emissions due to allocation of excess carbon on secondary metabolites, of which many are volatile. We investigated how growing at doubled ambient CO2 concentration affects emissions from cabbage plants (Brassica oleracea subsp. capitata) damaged by either the leaf-chewing larvae of crucifer specialist diamondback moth (Plutella xylostella L.) or generalist Egyptian cotton leafworm (Spodoptera littoralis (Boisduval)). The emission from cabbage cv. Lennox grown in both CO2 concentrations, consisted mainly of monoterpenes (sabinene, limonene, α-thujene, 1,8-cineole, β-pinene, myrcene, α-pinene and γ-terpinene). (Z)-3-Hexenyl acetate, sesquiterpene (E,E)-α-farnesene and homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) were emitted mainly from herbivore-damaged plants. Plants grown at 720 μmol mol −1 of CO2 had significantly lower total monoterpene emissions per shoot dry weight than plants grown at 360 μmol mol −1 of CO2, while damage by both herbivores significantly increased the total monoterpene emissions compared to intact plants. (Z)-3-Hexenyl acetate, (E,E)-α-farnesene and DMNT emissions per shoot dry weight were not affected by the growth at elevated CO2. The emission of DMNT was significantly enhanced from plants damaged by the specialist P. xylostella compared to the plants damaged by the generalist S. littoralis. The relative proportions of total monoterpenes and total herbivore-induced compounds of total VOCs did not change due to the growth at elevated CO2, while insect damage increased significantly the proportion of induced compounds. The results suggest that VOC emissions that are induced by the leaf-chewing herbivores will not be influenced by elevated CO2 concentration.

Species control variation in litter decomposition in a pine forest exposed to elevated CO2

AbstractNet primary production and the flux of dry matter and nutrients from vegetation to soils has increased following four years of exposure to elevated CO2 in a southern pine forest in NC, USA. This has increased the demand for nutrients to support enhanced rates of NPP and altered the conditions for litter decomposition on the forest floor. We quantified the chemistry and decomposition dynamics of leaf litter produced by five of the most abundant tree species in this ecosystem during the third and fourth growing seasons under elevated CO2. The objectives of this study were to determine (i) if there were systemic or species‐specific changes in leaf litter chemistry associated with a sustained enhancement of plant growth under elevated CO2; and (ii) whether the process of litter decomposition was altered by increased inputs of energy and nutrients to the forest floor in the plots under elevated CO2. Leaf litter chemistry, including various C fractions and N concentration, was virtually unchanged by elevated CO2. With few exceptions, plant litter produced under elevated CO2 lost mass or N at the same relative rate as that produced under ambient CO2. The relationship between initial litter chemistry and decomposition was not altered by elevated CO2. The greater forest floor mass and nutrient content in the plots under elevated CO2 had no consistent or long‐term effect on litter decomposition. Thus, we found no evidence that plant and microbial processes under elevated CO2 resulted in systemic changes in mass loss or N dynamics during decomposition. In contrast to the limited effects of elevated CO2 on litter chemistry and decomposition, there were large differences among species in initial litter chemistry, mass loss and N dynamics during decomposition. If the species composition of this forest community is altered by elevated CO2, the indirect effect of a change in species composition will exert greater control over the long‐term rate of nutrient cycling than the direct effect of elevated CO2 on litter chemistry and decomposition dynamics alone.

Maternal and direct effects of elevated CO2 on seed provisioning, germination and seedling growth in Bromus erectus.

Elevated CO2 can affect plant fitness not only through its effects on seed production but also by altering the quality of seeds and therefore germination and seedling performance. We collected seeds from mother plants of Bromus erectus grown in field plots at ambient and elevated CO2 (m-CO2, maternal CO2) and germinated them in the greenhouse in a reciprocal design under ambient and elevated CO2 (o-CO2, offspring CO2). This design allowed us to examine both the direct effects of elevated CO2 on germination and seedling growth and the indirect (maternal) effects via altered seed quality. Elevated m-CO2 significantly increased seed mass and increased the C:N ratio of seeds from field-grown plants. Percentage and rate of germination were not affected by the m-CO2 or o-CO2 treatments. Similarly, elevated m-CO2 had no significant effect on seedling size as estimated by the total leaf length. When differences in seed mass were adjusted by using seed mass as a covariate in ANOVA, a negative effect of m-CO2 on seedling size appeared which increased with increasing seed mass (significant covariate×m-CO2 interaction). This may indicate that the advantage of increased seed mass at elevated m-CO2 was offset by the reduced concentration of nitrogen (and possibly other nutrients) in these seeds. In contrast to m-CO2, elevated o-CO2 greatly increased seedling size, and this stimulatory effect of elevated o-CO2 was found to increase with increasing seed mass (significant covariate×o-CO2 interaction). Taken together, these results suggest that in B. erectus transgenerational effects of elevated CO2 are relatively small. However, other factors (genetic and environmental) that contribute to variation in seed provisioning can critically influence the responsiveness of seedlings to elevated CO2.

Effect at the ecosystem level of elevated atmospheric CO2in an aquatic microcosm

We studied the responses of an aquatic microcosm in two different eutrophic conditions to elevated atmospheric CO2concentration. We used microcosms, consisting of Escherichia coli(bacteria), Tetrahymena thermophila(protozoa) and Euglena gracilis(algae), in salt solution with 50 and 500 mg l−1of proteose peptone (eutrophic and hypereutrophic conditions, respectively) under ambient and elevated CO2(1550±100 μl l−1) conditions. The density of E. gracilisincreased significantly under elevated CO2in both eutrophic and hypereutrophic microcosms. In the eutrophic microcosm, the other elements were not affected by elevated CO2. In the hypereutrophic microcosm, however, the concentrations of ammonium and phosphate decreased significantly under elevated CO2. Furthermore, the density of T. thermophilawas maintained in higher level than that in the microcosm with ambient CO2and the density of E. coliwas decreased by CO2enrichment. Calculating the carbon biomasses of T. thermophilaand E. colifrom their densities, the changes in their biomasses by CO2enrichment were little as compared with large increase of E. graciliscarbon biomass converted from chlorophyll a. From the responses to elevated CO2in the subsystems of the hypereutrophic microcosm consisting of either one or two species, the increase of E. graciliswas a direct effect of elevated CO2, whereas the changes in the density of E. coliand T. thermophilaand the decreases in the concentration of ammonium and phosphate are considered to be indirect effects rather than direct effects of elevated CO2. The indirect effects of elevated CO2were prominent in the hypereutrophic microcosm.

Direct effect of elevated CO(2) on nocturnal in situ leaf respiration in nine temperate deciduous tree species is small.

Direct (i.e., short-term) effects of elevated CO(2) on nocturnal in situ leaf respiration rate were measured in nine deciduous tree species (seven genera) in 20 3.5-4.0-h experiments. During the experiments, CO(2) concentration was alternated between 400 and 800 ppm (approximately 40 and 80 Pa of CO(2)). Data analysis accounted for effects on respiration rate of the normal decline in temperature with time after sunset. The median response to a 40-Pa increase in CO(2) was a 1.5% decrease in respiration rate, with responses ranging from a 5.6% inhibition to a 0.4% stimulation. Direct effects of elevated CO(2) on respiration were similar among the species. Thus, the response of nocturnal leaf respiration rate to a short-term CO(2) increase was small, and of little practical importance to the accuracy of measurements of respiration involving similar changes in CO(2) concentration during measurement. These direct respiratory responses of leaves to elevated CO(2) would translate into only slight, if any, effects on the carbon balance of temperate deciduous forests in a future atmosphere containing as much as 80 Pa CO(2).

Effect of enhanced atmospheric CO2 on mycorrhizal colonization and phosphorus inflow in 10 herbaceous species of contrasting growth strategies

1. Ten herbaceous species were grown over a 4‐month period under ambient (360 μmol mol–1) and elevated (610 μmol mol–1) atmospheric CO2 conditions. Plants were inoculated with the arbuscular mycorrhizal (AM) fungus Glomus mosseae and given a phosphorus (P) supply which was not immediately available to the plants. 2. Multiple harvests were taken in order to determine whether the effect of elevated CO2 on mycorrhizal colonization and phosphorus inflow was independent of its effect on plant growth. 3. All species grew faster under elevated CO2 and carbon partitioning was altered, generally in favour of the shoots. All species responded similarly to elevated CO2. 4. Elevated CO2 did not affect the percentage of root length colonized by AM fungi, but the total amount of colonized root length was increased, because the plants were bigger. 5. Elevated CO2 increased total P content, but had little or no effect on P concentration. At a given age, P inflow was stimulated by elevated CO2, but when root length was taken into account the CO2 effect disappeared. 6. In these host species there is no evidence for a direct effect of elevated CO2 on mycorrhizal functioning, because both internal mycorrhizal colonization and P inflow are unaffected. 7. Future research should concentrate on the potential for carbon flow to the soil via the external mycelial network.

Effect of elevated atmospheric CO2 on mycorrhizal colonization, external mycorrhizal hyphal production and phosphorus inflow in Plantago lanceolata and Trifolium repens in association with the arbuscular mycorrhizal fungus Glomus mosseae

Abstract Plantago lanceolata and Trifolium repens were grown under ambient (400 μmol mol–1) and elevated (650 μmol mol–1) atmospheric CO2 conditions. Plants were inoculated with the arbuscular mycorrhizal fungus Glomus mosseae and given a phosphorus supply in the form of bonemeal. Six sequential harvests were taken in order to determine whether the effect of elevated CO2 on internal mycorrhizal colonization and external hyphal production was independent of the stimulatory effect of elevated CO2 on plant growth. At a given time, elevated CO2 increased the percentage of root length colonized (RLC), the total length of colonized root and the external mycorrhizal hyphal (EMH) density and decreased the ratio of EMH to total length of colonized root. When plant size was taken into account, the CO2 effect on RLC and total length of colonized root was greatly reduced (and only apparent for early harvests in T. repens) and the effects on the EMH parameters disappeared. Root tissue P concentration was unchanged at elevated CO2, but there was a decrease in shoot P at the later harvests. There was no direct effect of elevated CO2 on P inflow for the earlier period (< 50 d) of the experiment. However, over the last period, there was a significant negative effect of elevated CO2 on P inflow for both species, independent of plant size. It is concluded that elevated CO2 had no direct effect on mycorrhizal colonization or external hyphal production, and that any observed effects on a time basis were due to faster growing plants at elevated CO2. However, for older plants, elevated CO2 had a direct negative effect on P inflow. This decrease in P inflow coincides with the observed decrease in shoot P concentration. This is discussed in terms of downregulation of photosynthesis often seen in elevated CO2 grown plants, and the potential for mycorrhizas (via external hyphal turnover) to alleviate the phenomenon. The direction for future research is highlighted, especially in relation to carbon flow to and storage in the soil.