Growth and physiological responses of creeping bentgrass (Agrostis stolonifera) to elevated carbon dioxide concentrations.

Corn, with C4 photosynthetic metabolism, often has no photosynthetic or yield response to elevated carbon dioxide concentrations. In C3 species, the yield stimulation at elevated carbon dioxide concentrations often decreases with nitrogen limitation. I tested whether such a nitrogen interaction occurred in corn, by growing sweet corn in field plots in open top chambers at ambient and elevated (ambient + 180 mmol·mol-1) carbon dioxide concentrations for four seasons, with six nitrogen application rates, ranging from half to twice the locally recommended rate. At the recommended rate of nitrogen application, no carbon dioxide effect on production occurred. However, both ear and leaf plus stem biomass were lower for the elevated carbon dioxide treatment than for the ambient treatment at less than the recommended rate of nitrogen application, and higher at the highest rates of nitrogen application. There were no significant responses of mid-day leaf gas exchange rates to nitrogen application rate for either carbon dioxide treatment, and elevated carbon dioxide did not significantly increase leaf carbon dioxide assimilation rates at any nitrogen level. Leaf area index during vegetative growth increased more with nitrogen application rate at elevated than at ambient carbon dioxide. It is concluded that elevated carbon dioxide increased the responsiveness of corn growth to nitrogen application by increasing the response of leaf area to nitrogen application rate, and that elevated carbon dioxide increased the amount of nitrogen required to achieve maximum yields.

Increasing levels of atmospheric carbon dioxide leads to ocean acidification, causing significant reductions in the growth of crustose coralline algae. Owing to anthropogenic emissions, atmospheric concentrations of carbon dioxide could almost double between 2006 and 2100 according to business-as-usual carbon dioxide emission scenarios1. Because the ocean absorbs carbon dioxide from the atmosphere2,3,4, increasing atmospheric carbon dioxide concentrations will lead to increasing dissolved inorganic carbon and carbon dioxide in surface ocean waters, and hence acidification and lower carbonate saturation states2,5. As a consequence, it has been suggested that marine calcifying organisms, for example corals, coralline algae, molluscs and foraminifera, will have difficulties producing their skeletons and shells at current rates6,7, with potentially severe implications for marine ecosystems, including coral reefs6,8,9,10,11. Here we report a seven-week experiment exploring the effects of ocean acidification on crustose coralline algae, a cosmopolitan group of calcifying algae that is ecologically important in most shallow-water habitats12,13,14. Six outdoor mesocosms were continuously supplied with sea water from the adjacent reef and manipulated to simulate conditions of either ambient or elevated seawater carbon dioxide concentrations. The recruitment rate and growth of crustose coralline algae were severely inhibited in the elevated carbon dioxide mesocosms. Our findings suggest that ocean acidification due to human activities could cause significant change to benthic community structure in shallow-warm-water carbonate ecosystems.

The promotion and application of transgenic Bt crops provides an approach for the prevention and control of target lepidopteran pests and effectively relieves the environmental pressure caused by the massive usage of chemical pesticides in fields. However, studies have shown that Bt crops will face a new risk due to a decrease in exogenous toxin content under elevated carbon dioxide (CO2) concentration, thus negatively affecting the ecological sustainability of Bt crops. Arbuscular mycorrhizal fungi (AMF) are important beneficial microorganisms that can effectively improve the nutrient status of host plants and are expected to relieve the ecological risk of Bt crops under increasing CO2 due to global climate change. In this study, the Bt maize and its parental line of non-transgenic Bt maize were selected and inoculated with a species of AMF (Funneliformis caledonium, synonyms: Glomus caledonium), in order to study the secondary defensive chemicals and yield of maize, and to explore the effects of F. caledonium inoculation on the growth, development, and reproduction of the pest Mythimna separata fed on Bt maize and non-Bt maize under ambient carbon dioxide concentration (aCO2) and elevated carbon dioxide concentration (eCO2). The results showed that eCO2 increased the AM fungal colonization, maize yield, and foliar contents of jasmonic acid (JA) and salicylic acid (SA), but decreased foliar Bt toxin content and Bt gene expression in Bt maize leaves. F. caledonium inoculation increased maize yield, foliar JA, SA contents, Bt toxin contents, and Bt gene expression in Bt maize leaves, and positively improved the growth, development, reproduction, and food utilization of the M. separata fed on non-Bt maize. However, F. caledonium inoculation was unfavorable for the fitness of M. separata fed on Bt maize, and the effect was intensified when combined with eCO2. It is indicated that F. caledonium inoculation had adverse effects on the production of non-Bt maize due to the high potential risk of population occurrence of M. separata, while it was just the opposite for Bt maize. Therefore, this study confirms that the AMF can increase the yield and promote the expression levels of its endogenous (JA, SA) and exogenous (Bt toxin) secondary defense substances of Bt maize under eCO2, and finally can enhance the insect resistance capacity of Bt crops, which will help ensure the sustainable utilization and safety of Bt crops under climate change.

The Influence of Root Zone Temperature on Photosynthetic Acclimation to Elevated Carbon Dioxide Concentrations

The study compared the effects of water stress under ambient (350 μmol mol−1) and elevated (700 μmol mol−1) carbon dioxide concentrations on canopy carbon assimilation rates, soil water use, and water use efficiency (WUE) of cotton plants on a daily basis. This research was carried out in four sun-lit SPAR (Soil Plant Atmosphere Research) units with soil bins located at Beltsville, Maryland, USA. Whole canopy net photosynthetic rates were recorded at 5-min intervals, and soil water content was measured hourly using time-domain reflectometry. Pre-dawn and mid-day leaf water potentials were measured during the water stress and the recovery periods. The soil water use rates of plants grown under elevated CO2 were significantly lower than those grown under ambient levels for both water-stressed and well-watered plants. The WUE of the ambient treatment did not begin to increase until most of the available water was depleted from the soil. The elevated CO2 non-irrigated treatment was able to maintain carbon assimilation rates similar to that of the well-watered treatment while decreasing water uptake during the first 10 days of the drying period. Both water use and carbon assimilation rates decreased in the ambient non-irrigated treatment, shortly after withholding water. Plants grown at 350 μmol mol−1 CO2 concentration depleted more water from the deepest part of the profile (0.35–0.85 m) than did the plants from the elevated CO2 treatment.

Assessment of photosynthetic efficiency of greater yam and white yam subjected to elevated carbon dioxide

BackgroundChanges in aboveground plant species diversity as well as variations of environmental conditions such as exposure of ecosystems to elevated concentrations of atmospheric carbon dioxide may lead to changes in metabolic activity, composition and diversity of belowground microbial communities, both bacterial and fungal.ResultsWe examined soil samples taken from a biodiversity × CO2 grassland experiment where replicate plots harboring 5, 12, or 31 different plant species had been exposed to ambient or elevated (600 ppm) levels of carbon dioxide for 5 years. Analysis of soil bacterial communities in these plots by temporal temperature gradient gel electrophoresis (TTGE) showed that dominant soil bacterial populations varied only very little between different experimental treatments. These populations seem to be ubiquitous. Likewise, screening of samples on a high-resolution level by terminal restriction fragment length polymorphism (T-RFLP) showed that increased levels of carbon dioxide had no significant influence on both soil bacterial community composition (appearance and frequency of operational taxonomic units, OTUs) and on bacterial richness (total number of different OTUs). In contrast, differences in plant diversity levels had a significant effect on bacterial composition but no influence on bacterial richness. Regarding species level, several bacterial species were found only in specific plots and were related to elevated carbon dioxide or varying plant diversity levels. For example, analysis of T-RFLP showed that the occurrence of Salmonella typhimurium was significantly increased in plots exposed to elevated CO2 (P < 0.05).ConclusionPlant diversity levels are affecting bacterial composition (bacterial types and their frequency of occurrence). Elevated carbon dioxide does not lead to quantitative alteration (bacterial richness), whereas plant diversity is responsible for qualitative changes (bacterial diversity).

Although climate change is expected to affect the ecology of many weed species, the nature and scale of these responses is presently not well defined. This presages a suite of potential problems for the agricultural industries. Consequently, we investigated the effects of anticipated climate change on biomass and seed production, for two varieties of wild sage, Salvia verbenaca L. var. verbenaca and Salvia verbenaca var. vernalis Bioss. For the investigation, ambient (400 ppm) and elevated (700 ppm) carbon dioxide conditions, in combination with well-watered (100% field capacity) and drought conditions (60% field capacity), were selected to represent alternative climate scenarios. The alteration in biomass production was represented by a combined measurement of nine variables; plant height, stem diameter, number of leaves, number of branches, leaf area, leaf thickness, shoot biomass, root biomass and dry leaf weight, and fecundity was measured via two variables; 100 seed weight and number of seeds per plant. All biomass measurements were reduced in a drought situation compared with well-watered conditions in ambient carbon dioxide (400 ppm), and each corresponding measurement was greater under elevated carbon dioxide (700 ppm) regardless of water treatment. In contrast, this was not observed for 100 seed weight or number of seeds per plant. Although a similar profile of a reduction in fecundity parameters was observed under drought conditions compared with well-watered conditions in ambient carbon dioxide, there was an increase in seed mass only for var. verbenaca under elevated carbon dioxide in both water treatments. In addition, there was a very small increase in the number of seeds in this species under drought conditions in elevated carbon dioxide, with neither increase in seed mass or seed number being observed in var. vernalis. These results suggest that although future climate change may result in increased competition of both these varieties with desirable plants, their management strategies will need to focus on effects of increased size of the weeds, rather than only attempting to reduce the seed bank holdings.

Basmati rice (&lt;I&gt;Oryza sativa&lt;/I&gt; L.) cultivars viz. PRH-10 (pusa rice hybrid-10) and PS-2 (Pusa Sugandh-2) were grown under two different day/night temperatures (31/24°C, 35/28°C) at ambient (370 &amp;mu;mol/mol) and elevated (550 &amp;mu;mol/mol) carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) concentration, respectively, to characterize how an increase in CO&lt;sub&gt;2&lt;/sub&gt; and temperature affects rice photosynthesis and carbohydrate metabolism. At elevated CO&lt;sub&gt;2&lt;/sub&gt;, the photosynthetic rates increased under both the temperature regimes, compared with plants grown at ambient CO&lt;sub&gt;2&lt;/sub&gt;. The photosynthetic rate, sucrose-P synthase (SPS) activity and accumulation of soluble sugars and starch were higher in PRH-10 (pusa rice hybrid-10), compared to PS-2 (Pusa Sugandh-2). Elevated temperature decreased the photosynthetic rates both under ambient and elevated CO&lt;sub&gt;2&lt;/sub&gt; conditions. The SPS (sucrose-P synthase) activity and the accumulation of soluble sugars and starch were enhanced at elevated CO&lt;sub&gt;2&lt;/sub&gt; under both temperature regimes compared with plants grown at ambient CO&lt;sub&gt;2&lt;/sub&gt;. The up-regulation of SPS (sucrose-P synthase) under elevated CO&lt;sub&gt;2&lt;/sub&gt; and temperature would be beneficial for growth and productivity of rice plants for the future climatic conditions.

Previous work indicated that long-term exposure to ele- vated carbon dioxide levels can reduce hydraulic conduc- tance in some species, but the basis of the response was not determined. In this study, hydraulic conductance was measured at concentrations of both 350 and 700 cm 3 nT 3 carbon dioxide for plants grown at both concentrations, to determine the reversibility of the response. In Zea mays and Amaranthus hypochondriacus, exposure to the higher carbon dioxide concentration for several hours reduced whole-plant transpiration rate by 22-40%, without any consistent change in leaf water potential, indicating reversible reductions in hydraulic conductance at elevated carbon dioxide levels. Hydraulic conductance in these species grown at both carbon dioxide concentrations responded similarly to measurement concentration of carbon dioxide, indicating that the response was reversible. In Glycine max, which in earlier work had shown a long-term decrease in hydraulic conductance at elevated carbon dioxide levels, and in Abutilon theophrasti, no short-term changes in hydraulic conductance with measurement con- centration of carbon dioxide were found, despite lower transpiration rates at elevated carbon dioxide. In G. max and Medicago sativa, growth at high dew-point tempera- ture reduced transpiration rate and decreased hydraulic conductance. The results indicate that both reversible and irreversible decreases in hydraulic conductance can occur at elevated carbon dioxide concentrations, and that both could be responses to reduced transpiration rate, rather than to carbon dioxide concentration itself.

Perennial ryegrass (Lolium perenne L. cv. Parcour) grown at eight levels of nitrogen (N) fertilization (0–765 mg/pot) was exposed to ambient (390 ppm) and elevated (690 ppm) carbon dioxide (CO2) concentrations for 83 days. Plants were cut three times and dry matter yields determined for each harvest. At final harvest, dry weight of root and stubble biomass was determined, as N concentrations of all plant fractions were determined. Carbon dioxide enrichment effects on yield and total plant biomass increased with increasing N fertilization. The weaker CO2‐related yield enhancement at low N supply was due to the plants inability to increase tiller number. Root fraction of total plant biomass at final harvest was increased by high CO2 and decreased by N supply. Root biomass was significantly increased by CO2 enrichment and for both CO2 treatments the N supply for maximum root mass coincided with the N supply for reaching maximum total plant biomass. A significant correlation between root fraction of total plant dry matter and N concentration of total plant biomass, which was not changed by CO2 enrichment, indicates that biomass partitioning between shoot and root is controlled by the internal N status of the plant.

In the Northern Hemisphere, ozone levels in the troposphere have increased by 35 per cent over the past century, with detrimental impacts on forest and agricultural productivity, even when forest productivity has been stimulated by increased carbon dioxide levels. In addition to reducing productivity, increased tropospheric ozone levels could alter terrestrial carbon cycling by lowering the quantity and quality of carbon inputs to soils. However, the influence of elevated ozone levels on soil carbon formation and decomposition are unknown. Here we examine the effects of elevated ozone levels on the formation rates of total and decay-resistant acid-insoluble soil carbon under conditions of elevated carbon dioxide levels in experimental aspen (Populus tremuloides) stands and mixed aspen-birch (Betula papyrifera) stands. With ambient concentrations of ozone and carbon dioxide both raised by 50 per cent, we find that the formation rates of total and acid-insoluble soil carbon are reduced by 50 per cent relative to the amounts entering the soil when the forests were exposed to increased carbon dioxide alone. Our results suggest that, in a world with elevated atmospheric carbon dioxide concentrations, global-scale reductions in plant productivity due to elevated ozone levels will also lower soil carbon formation rates significantly.

Global atmospheric carbon dioxide concentration, presently at about 350 μl 1-1, is expected to continue to increase in the future (Lindzen, 1993) and may double by the end of the next century (Gates, 1983; Keeling et al., 1989; Houghton and Woodwell, 1989). Higher levels of carbon dioxide may increase the growth rate of trees and the productivity of forests (Teskey, 1995). At the present-day, ambient carbon dioxide concentration and under optimal conditions, the photosynthesis of plants is limited by the supply of carbon dioxide (Arp, 1991). Numerous studies have shown increased plant growth in elevated levels of carbon dioxide (Higginbotham et al., 1983, 1985; Stewart and Hoddinott, 1993; Gunderson et al., 1993), but these studies have used potted seedlings, optimum levels of resources (including water and nutrients), and short-term exposure to higher carbon dioxide concentrations. Because seedlings differ from older trees both physiologically and morphologically (Cregg et al., 1989), it is unknown how much carbon gain in trees will be affected by long-term exposures to elevated carbon dioxide levels under field conditions in which water and nutrient availability may limit growth.

Climate change necessitates research into interactions between elevated carbon dioxide (CO2) concentrations and drought on plant photosynthetic physiology. This study describes the physiological properties of Platycladus orientalis (Chinese thuja) and Quercus variabilis (Chinese cork oak) saplings cultivated through orthogonal treatments of four CO2 concentrations combined with five soil volumetric water contents (SWC). It highlights the differences between the interactive effects from the treatments. Water stress had little effect on photosynthetic traits until the soil volumetric water contents exceeded 70–80 or 100%. Similar variations in carbon-13 isotope abundance (δ13C) of water soluble compounds (δ13CWSC) extracted from leaves of two species have been observed. Whether soil volumetric water contents exceeded or fell below the water threshold values (70–80% of field capacity for P. orientalis and 100% of field capacity for Q. variabilis), instantaneous water use efficiency decreased. Elevated carbon dioxide could increase iWUE and enhance drought tolerance, depending on stimulating net photosynthetic rates and declining stomatal conductance and transpiration rates. Augmenting either drought, excess water, or ambient carbon dioxide could alleviate the physiological inhibition caused by the stresses described above.

Elevated concentrations of atmospheric carbon dioxide ([CO2]) and tropospheric ozone ([O3]) have the potential to affect tree physiology and structure and hence forest water use, which has implications for climate feedbacks. We investigated how a 40% increase above ambient values in [CO2] and [O3], alone and in combination, affect tree water use of pure aspen and mixed aspen-birch forests in the free air CO2-O3 enrichment experiment near Rhinelander, Wisconsin (Aspen FACE). Measurements of sap flux and canopy leaf area index (L) were made during two growing seasons, when steady-state L had been reached after more than 6 years of exposure to elevated [CO2] and [O3]. Maximum stand-level sap flux was not significantly affected by elevated [O3], but was increased by 18% by elevated [CO2] averaged across years, communities and O(3) regimes. Treatment effects were similar in pure aspen and mixed aspen-birch communities. Increased tree water use in response to elevated [CO2] was related to positive CO2 treatment effects on tree size and L (+40%). Tree water use was not reduced by elevated [O3] despite strong negative O3 treatment effects on tree size and L (-22%). Elevated [O3] predisposed pure aspen stands to drought-induced sap flux reductions, whereas increased tree water use in response to elevated [CO2] did not result in lower soil water content in the upper soil or decreasing sap flux relative to control values during dry periods. Maintenance of soil water content in the upper soil in the elevated [CO2] treatment was at least partly a function of enhanced soil water-holding capacity, probably a result of increased organic matter content from increased litter inputs. Our findings that larger trees growing in elevated [CO2] used more water and that tree size, but not maximal water use, was negatively affected by elevated [O3] suggest that the long-term cumulative effects on stand structure may be more important than the expected primary stomatal closure responses to elevated [CO2] and [O3] in determining stand-level water use under possible future atmospheric conditions.