Search

Rising levels of atmospheric CO2 can alter plant growth and partitioning to secondary metabolites. The protein competition model (PCM) and the extended growth/differentiation balance model (GDBe) are similar but alternative models that address ontogenetic and environmental effects on whole-plant carbon partitioning to the phenylpropanoid biosynthetic pathway, making many divergent predictions. To test the validity of the models, we compare plant responses to one key prediction: if CO2 enrichment simultaneously stimulates both photosynthesis and growth, then PCM predicts that partitioning to phenolic compounds will decline, whereas GDBe generally predicts the opposite. Elevated CO2 (at 548 ppm) increased the biomass growth (ca 23%) as well as the net photosynthesis (ca 13%) of 1-year-old potted paper birch, Betula papyrifera Marsh., in a free air carbon dioxide enrichment study (FACE) in northern Wisconsin. Concomitantly, elevated CO2 increased carbon partitioning to all measured classes of phenolics (Folin-Denis phenolics, HPLC low molecular weight phenolics (i.e. cinnamic acid derivatives, flavonol glycosides, and flavon-3-ols), condensed tannins, and acid-detergent lignin) in leaves. In stem tissues, tannins and lignin increased, but F-D phenolics did not. In root tissues, F-D phenolics, and tannins increased, but lignin did not. The data suggest that CO2 enrichment stimulated pathway-wide increase in carbon partitioning to phenylpropanoids. High CO2 plants had 11.8% more F-D phenolics, 19.3% more tannin, and 10% more lignin than ambient plants after adjusting for plant mass via analysis of covariance. In general, the results unequivocally support the predictions of the GDBe model. By way of contrast, results from many parallel studies on FACE trembling aspen, Populus tremuloides Michx., suggest that although CO2 enrichment has consistently stimulated both photosynthesis and growth, it apparently did not generally stimulate pathway-wide increases, or decreases, in carbon partitioning to phenylpropanoids in leaves and wood, but rather has specifically, though not consistently, increased partitioning to foliar phenolic glycosides. Likewise, in this case, GDBe's predictions better accord with the FACE aspen data than PCM's. If further tests of the two models also support GDB rather than PCM, then PCM's main assumption (whole-plant N rather than C is limiting partitioning to phenolic synthesis) may be incorrect. [ABSTRACT FROM AUTHOR]

Elevated CO2 could alter the productivity of heterotrophic aquatic ecosystems through effects on allochthonous litter inputs. We examined the effects of atmospheric CO2 concentration, light availability to trees, and tree species, on leaf detritus quality as a food resource for eastern treehole mosquitoes (Aedes triseriatus). Larvae were reared in laboratory microcosms (simulated treeholes) with naturally senesced, abscised foliage from seedlings of red oak, Quercus rubra, and paper birch, Betula papyrifera, grown in ambient and elevated atmospheric CO2 environments. Elevated CO2 did not have significant effects on any measure of mosquito performance. In contrast, host species and light availability had dramatic effects on mosquito development time and survival; light availability had additional effects on adult size. Mosquito reproductive potential (1SE) averaged 8.4 1 1.5 females female-1 generation-1 when litter input was from birch-sun leaves, but was 19.6 1 1.8 when the litter was birch-shade leaves and 13.0 1 1.8 when the litter was oak-sun leaves. Mosquito development time was nearly halved when the litter input was oak-sun leaves vs birch-sun leaves, suggesting the potential for even greater demographic effects (e.g., two generations per year instead of one could yield a 20-fold increase in annual growth rate). Trophic transfer rates (mg insect detritivore g litter-1 d-1) were 3-fold greater on birch-shade leaves than birch-sun leaves. Changes in solar insolation and tree species composition can have important consequences for forestecosystems because of effects on litter quality that impact microbial saprobes and, ultimately, invertebrate detritivores. [ABSTRACT FROM AUTHOR]

This paper reports on seasonal cycles of physical and chemical factors, over a period of two years, which were expected to affect the size and seasonal variation of phytoplankton production in the eutrophic, dimictic Lake Esrom, Denmark. Insolation, transparency, temperature, oxygen, total carbon dioxide, free carbon dioxide, pH, alkalinity, silicate, nitrate, ammonia, orthophosphate and total phosphate, were measured to describe the lake hydrography. They are presented as isopleths. After the spring maximum of phytoplankton, nitrogen and silica rapidly declined to insignificant and limiting concentrations while phosphate- phosphorus declined to 50% (150 μg litre-1) of the winter value. Light can limit phytoplankton production at all seasons. A phosphorus balance showed that there was about 80 t of phosphorus in the lake. Phoshorus recycled in the lake ecosystem was 20 t, 10 t from tributaries and 10 t annually being added to the sediment. The evidence for enrichment includes a discussion on the history of the lake, coring, ground water analyses, changes in hypolimnetic dissolved oxygen, and changes in transparency. The possible influence of pollution from sewage is discussed in relation to the estimated nutrient budget of nitrogen and phosphorus. Increase in nutrients failed to increase phytoplankton production during 17 years. [ABSTRACT FROM AUTHOR]

Understanding the responses of soil nitrous oxide (N2O) emissions from terrestrial ecosystems to future CO2 enrichment and warming is critical for the development of mitigation and adaptation policies. The effects of continuous increase in elevated CO2 (EC) and elevated temperature (ET) on N2O emissions are not fully known. We synthesized 209 measurements from 70 published studies and carried out a meta‐analysis to examine individual and interactive effects of EC and ET on N2O emissions from grasslands, croplands and forests. On average, a significant increase of 23% in N2O emissions was observed under EC across all case studies. EC did not affect N2O emissions from grasslands or forests, but significantly increased N2O emissions in croplands by 38%. The extent of ET effects on N2O emissions was nonsignificant and there was no significant difference in N2O emission responses among these three terrestrial systems. ET only promoted N2O emissions in forest by about 32% when ET was less than 2°C. The interactive effect of EC and ET on N2O emissions was significantly synergistic, showing a greater increase than the sum of the effects caused by EC and ET alone. Our findings indicated that the combination of EC and ET substantially promoted soil N2O and highlighted the urgent need to explore its mechanisms to better understand N2O responses under future climate change. [ABSTRACT FROM AUTHOR]

Direct and interactive effects of CO2 and light on tree phytochemistry and insect fitness parameters were examined through experimental manipulations of plant growth conditions and performance ofinsect bioassays. Three species of deciduous trees (quaking aspen, Populus tremuloides; paper birch, Betula papyrifera; sugar maple, Acersaccharum) were grown under ambient (387 8 mu L/L) and elevated (696 2 mu L/L) levels of atmospheric CO2, with low and high light availability (375 and 855 mu mol ? m-2 ? s-1 at solar noon). Effects on the population and individual performance of a generalist phytophagous insect, the white-marked tussock moth (Orgyia leucostigma) were evaluated. Caterpillars were reared on experimental trees for the duration of the larval stage, and complementary short-term (fourth-instar) feeding trials were conducted with insects fed detached leaves. Phytochemical analyses demonstrated strong effects of both CO2 and light on all foliar nutritional variables (water, starch and nitrogen). For all species, enriched CO2 decreased water content and increased starch content, especially under high light conditions. High CO2 availability reduced levels of foliar nitrogen, but effects were species specific and most pronounced for high light aspen and birch. Analyses of secondary plant compounds revealed that levels of phenolic glycosides (salicortin and tremulacin) in aspen and condensed tannins in birch and maple were positively influenced by levels of both CO2 and light. In contrast, levels of condensed tannins in aspen were primarily affected by light, whereas levels of ellagitannins and gallotanninsin maple responded to light and CO2, respectively. [ABSTRACT FROM AUTHOR]

Under elevated levels of atmospheric CO2, leaf N concentration usually decreases due to dilution of N by excess carbon. Thus, the larger the growth response to elevated CO2, the larger the decrease in leaf N concentration should be. This should, in turn, lead to a proportional decline in litter N concentration and litter decomposition rate. Thus, we hypothesize a trade-off between a plant's growth response to elevated CO2 and subsequent litter decomposability. We tested this hypothesis by measuring the growth response, green leaf and leaf litter chemistry and litter respiration of six plant species grown under ambient and elevated atmospheric CO2 concentrations in the greenhouse. Growth response increased in the order Calluna vulgaris2 and litter decomposability. This implies that the productivity response of plant species to elevated CO2 is, in general, uncoupled from the decomposition response. [ABSTRACT FROM AUTHOR]

Examines the effects of species richness and elevated carbon dioxide on community productivity under altered nutrient levels. Increased community biomass at medium and high species richness; Link between productivity and species diversity; Impact of harvest time on the results of diversity-productivity experiments.

Rising atmospheric carbon dioxide has the potential to alter leaf litter chemistry, potentially affecting decomposition and rates of carbon and nitrogen cycling in forest ecosystems. This study was conducted to determine whether growth under elevated atmospheric CO2 altered the quality and microbial decomposition of leaf litter of a widely distributed northern hardwood species at sites of low and high soil nitrogen availability. In addition, we assessed whether the carbon–nutrient balance (CNB) and growth differentiation balance (GDB) hypotheses could be extended to predict changes in litter quality in response to resource availability. Sugar maple (Acer saccharum ) was grown in the field in open-top chambers at 36 and 55 Pa partial pressure CO2 , and initial soil mineralization rates of 45 and 348 μg N g-1 d-1 . Naturally senesced leaf litter was assessed for chemical composition and incubated in the laboratory for 111 d. Microbial respiration and the production of dissolved organic carbon (DOC) were quantified as estimates of decomposition. Elevated CO2 and low soil nitrogen resulted in higher litter concentrations of nonstructural carbohydrates and condensed tannins, higher C/N ratios and lower N concentrations. Soil N availability appears to have had a greater effect on litter quality than did atmospheric CO2 , although the treatments were additive, with highest concentrations of nonstructural carbohydrates and condensed tannins occurring under elevated CO2 –low soil N. Rates of microbial respiration and the production of DOC were insensitive to differences in litter quality. In general, concentrations of litter constituents, except for starch, were highly correlated to those in live foliage, and the CNB/GDB hypotheses proved useful in predicting changes in litter quality. We conclude the chemical composition of sugar maple litter will change in the future in response to rising atmospheric CO2 , and that soil N availability will exert a major control. It appears that microbial metabolism will not be directly affected by changes in litter quality, although conclusions regarding decomposition as a whole must consider the entire soil food web. [ABSTRACT FROM AUTHOR]

Young beech (Fagus sylvatica ) and spruce (Picea abies ) trees from different provenances or genotypes were grown in competition in large model ecosystems and were exposed to two concentrations of atmospheric CO2 (370 vs 570 μmol mol-1 ), two levels of wet nitrogen deposition (7 vs 70 kg N ha-1 yr-1 ), and two native forest soils (acidic vs calcareous) for four years in open-top chambers. The 2×2×2 factorial experimental design was fully replicated (n =4) with each CO2 ×N combination applied to each soil type. Exposure to atmospheric CO2 enrichment stimulated daytime net ecosystem CO2 flux (NEC) as measured during sunny days in the middle of the third growing season. Nevertheless, we observed substantial down-regulation of NEC, with larger adjustments on acidic than on calcareous soil. NEC adjustment was associated with slightly reduced leaf area index (LAI) on the acidic soil (no response on calcareous soil), enhanced soil CO2 efflux from both substrate types, and, most importantly, with down-regulation of CO2 uptake at the leaf scale. Downward adjustment of light-saturated single-leaf photosynthesis (A ) and of Rubisco was more pronounced in beech than in spruce and these species-specific differences increased over time. By year four, A adjustment (except in one specific treatment combination in each species) had become complete in beech but had disappeared in spruce. At no time did we observe a genotype or provenance effect on the downward adjustment of carbon fluxes, and nitrogen deposition rate generally had little effect as well. Overall, our results suggest that tree species and soil quality will have profound effects on ecosystem CO2 fluxes under continued atmospheric CO2 enrichment. [ABSTRACT FROM AUTHOR]

Dioecious plant species and those occupying diverse habitats may present special analytical problems to researchers examining effects of climate change. Here we report the results from two complementary studies designed to determine the importance of sex and habitat on gas exchange and growth of male and female individuals of a dioecious, circumpolar willow, Salix arctica, in the Canadian High Arctic. In fieldstudies, male and female willows from dry and wet habitats were subjected to passively enhanced summer temperature (~1.3 deg. C) using small open-top chambers over three years. Peak season gas exchange varied significantly by willow sex and habitat. Overall net assimilation was higher in the dry habitat than in the wet, and higher in females than in males. In the dry habitat, net assimilation of females was enhanced by experimental warming, but decreased in males. In the wet habitat, net assimilation of females was substantially depressed by experimental warming, while males showed an inconsistent response. Development and growth of male and female catkins were enhanced by elevated temperature more than leaf fascicles, but leaf fascicle developmentand growth varied more between the two habitats, particularly in males. In a controlled environment study, male and female willows from these same wet and dry habitats were grown in a 2 x 2 factorial experiment including 1x or 2x ambient [CO2] and 5 or 12 deg. C. The sexes responded very differently to the experimental treatments, but we found no effect of original habitat. Net assimilation in maleswas affected by the interaction of temperature and CO2, but in females by CO2 only. Our results demonstrate (a) significant intraspecific and intersexual differences in arctic willow physiology and growth, (b) that these differences are affected by environmental conditions expected to accompany global climate change, and(c) that sex- and habitat-specific responses should be explicitly accoun [ABSTRACT FROM AUTHOR]

Interactions between insect herbivores and plants grown under conditions of ambient and elevated CO2 were investigated by analyzing data on 43 herbivores, representing 61 plant-herbivore interactions. Changes in herbivore performance in enhanced CO2 environments were correlated with changes in the quality of the host plants, measured as nitrogen content, water content, carbohydrate content and secondary plant compounds. The data were analysed to determine whether CO2 mediated effects on insect performance differed between feeding guilds (leaf-chewers, leaf miners, phloem-feeders (root and shoot), xylem-feeders, whole-cell-feeders and seed-eaters) or instar stage. Host-plant quality changed in elevated CO2; leaf nitrogen content decreased, on average, by 15% while carbohydrates increased by 47% and secondary plant compounds (phenolics) by 31%. Water content did not change. Of the variables measured, changes in nitrogen and carbohydrate levels only were found to be correlated with changes in food consumption. No differences were found in CO2 mediated herbivore responses on woody plant compared with non-woody plants. Insects from different feeding guilds respond CO2 mediated changes in host-plant quality in various ways. Leaf-chewers generally seem able to compensate for the decreased nitrogen levels in the plant tissues by increasing their food consumption (by 30%) and with no adverse effects on pupal weights. Leaf miners only slightly increase their food consumption. The negative effect on pupal weight suggests that their population dynamics may change over several generations. Limited data on seed-eaters suggests that enhanced CO2 conditions no effect on these insects. Phloem-feeders andwhole-cell-feeders are the only insects to show a positive CO2 response. Population sizes generally increased in elevated CO2 and development time of phloem-feeders was reduced by 17%.E [ABSTRACT FROM AUTHOR]

A system is described for measuring in situ CO2 evolution rates from forest soil. The apparatus incorporates an infrared gas analyzer with open air flow through 10 chambers which sequentially lower over the forest floor during measurements and raise after measurements are complete. Unlike methods using stationary chambers, this system allows litter and soil horizons to undergo a natural drying cycle. Litter moisture under stationary chambers was 76% of dry weight at the end of a 3-day sample period as compared to 40% under moving chambers and 39% in control plots. Carbon dioxide evolution rates from plots enclosed by stationary chambers ranged from 54 to 90% higher than those from moving chamber plots. Effects of such discrepancies in calculating the carbon balance of forest ecosystems are discussed. Application of the moving chamber apparatus in monitoring gaseous losses from biodegradable waste such as by-products of petroleum is also discussed. [ABSTRACT FROM AUTHOR]