Transpiration of a 64-year-old maritime pine stand in Portugal

Alpine plant species have been shown to exhibit a more pronounced increase in leaf photosynthesis under elevated CO₂ than lowland plants. In order to test whether this higher carbon fixation efficiency will translate into increased biomass production under CO₂ enrichment we exposed plots of narrow alpine grassland (Swiss Central Alps, 2470 m) to ambient (355 l l^-1) and elevated (680 l l^-1) CO₂ concentration using open top chambers. Part of the plost received moderate mineral nutrient additions (40 kg ha^-1 year^-1 of nitrogen in a complete fertilizer mix). Under natural nutrient supply CO₂ enrichment had no effect on biomass production per unit land area during any of the three seasons studied so far. Correspondingly, the dominant species Carex curvula and Leontodon helveticus as well as Trifolium alpinum did not show a growth response either at the population level or at the shoot level. However, the subdominant generalistic species Poa alpina strongly increased shoot growth (+47%). Annual root production (in ingrowth cores) was significantly enhanced in C. curvula in the 2nd and 3rd year of investigation (+43%) but was not altered in the bulk samples for all species. Fertilizer addition generally stimulated above-ground (+48%) and below-ground (+26%) biomass production right from the beginning. Annual variations in weather conditions during summer also strongly influenced above-ground biomass production (19–27% more biomass in warm seasons compared to cool seasons). However, neither nutrient availability nor climate had a significant effect on the CO₂ response of the plants. Our results do not support the hypothesis that alpine plants, due to their higher carbon uptake efficiency, will increase biomass production under future atmospheric CO₂ enrichment, at least not in such late successional communities. However, as indicated by the response of P. alpina, species-specific responses occur which may lead to altered community structure and perhaps ecosystem functioning in the long-term. Our findings further suggest that possible climatic changes are likely to have a greater impact on plant growth in alpine environments than the direct stimulation of photosynthesis by CO₂. Counter-intuitively, our results suggest that even under moderate climate warming or enhanced atmospheric nitrogen deposition positive biomass responses to CO₂ enrichment of the currently dominating species are unlikely.     

Transpiration of a 64-year old maritime pine stand in Portugal

Alpine plant species have been shown to exhibit a more pronounced increase in leaf photosynthesis under elevated CO₂ than lowland plants. In order to test whether this higher carbon fixation efficiency will translate into increased biomass production under CO₂ enrichment we exposed plots of narrow alpine grassland (Swiss Central Alps, 2470 m) to ambient (355 μl l^-1) and elevated (680 μl l^-1) CO₂ concentration using open top chambers. Part of the plost received moderate mineral nutrient additions (40 kg ha^-1 year^-1 of nitrogen in a complete fertilizer mix). Under natural nutrient supply CO₂ enrichment had no effect on biomass production per unit land area during any of the three seasons studied so far. Correspondingly, the dominant species Carex curvula and Leontodon helveticus as well as Trifolium alpinum did not show a growth response either at the population level or at the shoot level. However, the subdominant generalistic species Poa alpina strongly increased shoot growth (+47%). Annual root production (in ingrowth cores) was significantly enhanced in C. curvula in the 2nd and 3rd year of investigation (+43%) but was not altered in the bulk samples for all species. Fertilizer addition generally stimulated above-ground (+48%) and below-ground (+26%) biomass production right from the beginning. Annual variations in weather conditions during summer also strongly influenced above-ground biomass production (19–27% more biomass in warm seasons compared to cool seasons). However, neither nutrient availability nor climate had a significant effect on the CO₂ response of the plants. Our results do not support the hypothesis that alpine plants, due to their higher carbon uptake efficiency, will increase biomass production under future atmospheric CO₂ enrichment, at least not in such late successional communities. However, as indicated by the response of P. alpina, species-specific responses occur which may lead to altered community structure and perhaps ecosystem functioning in the long-term. Our findings further suggest that possible climatic changes are likely to have a greater impact on plant growth in alpine environments than the direct stimulation of photosynthesis by CO₂. Counter-intuitively, our results suggest that even under moderate climate warming or enhanced atmospheric nitrogen deposition positive biomass responses to CO₂ enrichment of the currently dominating species are unlikely.     

Will rising atmospheric CO2 affect leaf litter quality and in situ decomposition rates in native plant communities?

Though field data for naturally senesced leaf litter are rare, it is commonly assumed that rising atmospheric CO₂ concentrations will reduce leaf litter quality and decomposition rates in terrestrial ecosystems and that this will lead to decreased rates of nutrient cycling and increased carbon sequestration in native ecosystems. We generally found that the quality of␣naturally senesced leaf litter (i.e. concentrations of C, N and lignin; C:N, lignin:N) of a variety of native plant species produced in alpine, temperate and tropical communities maintained at elevated CO₂ (600–680 μl l⁻¹) was not significantly different from that produced in similar communities maintained at current ambient CO₂ concentrations (340–355 μl l⁻¹). When this litter was allowed to decompose in situ in a humid tropical forest in Panama (Cecropia peltata, Elettaria cardamomum, and Ficus benjamina, 130 days exposure) and in a lowland temperate calcareous grassland in Switzerland (Carex flacca and a graminoid species mixture; 261 days exposure), decomposition rates of litter produced under ambient and elevated CO₂ did not differ significantly. The one exception to this pattern occurred in the high alpine sedge, Carex curvula, growing in the Swiss Alps. Decomposition of litter produced in situ under elevated CO₂ was significantly slower than that of litter produced under ambient CO₂ (14% vs. 21% of the initial litter mass had decomposed over a 61-day exposure period, respectively). Overall, our results indicate that relatively little or no change in leaf litter quality can be expected in plant communities growing under soil fertilities common in many native ecosystems as atmospheric CO₂ concentrations continue to rise. Even in situations where small reductions in litter quality do occur, these may not necessarily lead to significantly slower rates of decomposition. Hence in many native species in situ litter decomposition rates, and the time course of decomposition, may remain relatively unaffected by rising CO₂. Received: 12 September 1996 / Accepted: 30 November 1996     

Mid-season gas exchange of an alpine grassland under elevated CO2

Ecosystem net CO₂ uptake, evapotranspiration (ET) and night-time CO₂ efflux were measured in an alpine grassland dominated by Carex curvula, treated with doubled ambient partial pressure of CO₂ via open-top chambers. One quarter of the plots were treated with mineral nutrients to simulate the effect of lowland nitrogen deposition rates. Depending upon fertilizer supply, ecosystem net CO₂ uptake per ground area in full sunlight (NCE_max) was 41–81% higher in open-top chambers supplied with doubled ambient partial pressure (p _a) of CO₂ than in plots receiving ambient CO₂. Short-term reversals of the CO₂ level suggest that the extent of downward adjustment of canopy photosynthesis under elevated CO₂ was 30–40%. ET tended to decline, while water use efficiency (WUE), expressed as the NCE_max:ET ratio, increased more than twofold under elevated CO₂. Night-time ecosystem CO₂ efflux did not respond to changes in CO₂ p _a. NCE_max and night-time CO₂ efflux were more responsive to mineral fertilizer than the doubling of CO₂. This suggests that in these alpine plant communities, atmospheric nutrient input may induce equal or greater effects on gas exchange than increased CO₂.     

Long-term photosynthetic response in single leaves of A C3 and C4 salt marsh species grown at elevated atmospheric CO2 in situ

Summary Mono-specific communities of the C₃ sedge, Scirpus olneyi and the C₄ grass, Spartina patens, were exposed to normal ambient or elevated CO₂, (ca. 680 l l^–1) throughout the 1987 and 1988 growing seasons in open-top field chambers located on a tidal marsh. Single stems of C₃ plants grown in ambient or elevated CO₂ showed an increased photosynthetic rate when tested at elevated CO₂ for both seasons. This increase in photosynthetic response in the C₃ species was maintained throughout the 1987 and 1988 growing season. The stimulation of photosynthesis with elevated CO₂ appeared to increase as temperature increased and decreased as photosynthetic photon flux (PPF) increased. Analysis of the photosynthetic response of the C₃ species during the 1988 season indicated that significant differences in light-saturated photosynthetic rate between ambient and elevated CO₂ conditions continued until October. In contrast to the C₃ sedge, the C₄ grass showed no significant photosynthetic increase to elevated CO₂ except at the beginning of the 1988 season.     

Growth and reproduction of the alpine grasshopper <Emphasis Type="Italic">Miramella alpina</Emphasis> feeding on CO<Subscript>2</Subscript>-enriched dwarf shrubs at treeline

The consequences for plant-insect interactions of atmospheric changes in alpine ecosystems are not well understood. Here, we tested the effects of elevated CO₂ on leaf quality in two dwarf shrub species (Vaccinium myrtillus and V. uliginosum) and the response of the alpine grasshopper (Miramella alpina) feeding on these plants in a field experiment at the alpine treeline (2,180 m a.s.l.) in Davos, Switzerland. Relative growth rates (RGR) of M. alpina nymphs were lower when they were feeding on V. myrtillus compared to V. uliginosum, and were affected by elevated CO₂ depending on plant species and nymph developmental stage. Changes in RGR correlated with CO₂-induced changes in leaf water, nitrogen, and starch concentrations. Elevated CO₂ resulted in reduced female adult weight irrespective of plant species, and prolonged development time on V. uliginosum only, but there were no significant differences in nymphal mortality. Newly molted adults of M. alpina produced lighter eggs and less secretion (serving as egg protection) under elevated CO₂. When grasshoppers had a choice among four different plant species grown either under ambient or elevated CO₂, V. myrtillus and V. uliginosum consumption increased under elevated CO₂ in females while it decreased in males compared to ambient CO₂-grown leaves. Our findings suggest that rising atmospheric CO₂ distinctly affects leaf chemistry in two important dwarf shrub species at the alpine treeline, leading to changes in feeding behavior, growth, and reproduction of the most important insect herbivore in this system. Changes in plant-grasshopper interactions might have significant long-term impacts on herbivore pressure, community dynamics and ecosystem stability in the alpine treeline ecotone.     

Post‐fire resprouting responses of native and exotic grasses from Cumberland Plain Woodland (Sydney,Australia) under elevated carbon dioxide

This study investigated the effect of elevated CO₂ on the post‐fire resprouting response of a grassland system of perennial grass species of Cumberland Plain Woodland. Plants were grown in mixtures in natural soil in mesocosms, each containing three exotic grasses (Nassella neesiana, Chloris gayana, Eragrostis curvula) and three native grasses (Themeda australis, Microlaena stipoides, Chloris ventricosa) under elevated (700 ppm) and ambient (385 ppm) CO₂ conditions. Resprouting response after fire at the community‐ and species‐level was assessed. There was no difference in community‐level biomass between CO₂ treatments; however, exotic species made up a larger proportion of the community biomass under all treatments. There were species‐level responses to elevated CO₂ but no significant interactions found between CO₂ and burning or plant status. Two exotic grasses (N. neesiana and E. curvula, a C₃ and a C₄ species respectively), and one native grass (M. stipoides, a C₃ species) significantly increased in biomass, and a native C₄ grass (C. ventricosa) significantly decreased in biomass under elevated CO₂. These results suggest that although overall productivity of this community may not change with increases in CO₂ and fire frequency, the community composition may alter due to differential species responses.     

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 l 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.     

Combined Effects of CO2 and O3 on Antioxidative and Photoprotective Defense Systems in Needles of Ponderosa Pine

Ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings were exposed to near ambient or elevated CO₂ (average concentrations during the last growing season 446 versus 699 mol mol^–1), combined with low or elevated O₃ for three seasons. Ozone exposure during the last growing season (accumulated dose above threshold 0.06 mol mol^–1) was 0.05 versus 26.13 mol mol^–1 h. Needles of the youngest age class were harvested after the dormancy period. Ozone exposure decreased needle contents of chlorophyll a, chlorophyll b, and ascorbate, and resulted in a more oxidized total ascorbate and a more de-epoxidized xanthophyll cycle pool irrespective of the CO₂ level. Trees under elevated CO₂ had a more oxidized glutathione pool and lower chlorophyll a content. Contents of glutathione, tocopherol, and carotenoids were not affected by the CO₂ or O₃ treatments. There were no interactive effects between elevated CO₂ and elevated O₃ on any of the parameters measured. The results suggest that elevated atmospheric CO₂ concentration does not compensate for ozone stress by increasing antioxidative capacity in ponderosa pine.     

Leaf and canopy responses to elevated CO2 in a pine forest under free-air CO2 enrichment

Physiological responses to elevated CO₂ at the leaf and canopy-level were studied in an intact pine (Pinus taeda) forest ecosystem exposed to elevated CO₂ using a free-air CO₂ enrichment (FACE) technique. Normalized canopy water-use of trees exposed to elevated CO₂ over an 8-day exposure period was similar to that of trees exposed to current ambient CO₂ under sunny conditions. During a portion of the exposure period when sky conditions were cloudy, CO₂-exposed trees showed minor (7%) but significant reductions in relative sap flux density compared to trees under ambient CO₂ conditions. Short-term (minutes) direct stomatal responses to elevated CO₂ were also relatively weak (5% reduction in stomatal aperture in response to high CO₂ concentrations). We observed no evidence of adjustment in stomatal conductance in foliage grown under elevated CO₂ for nearly 80 days compared to foliage grown under current ambient CO₂, so intrinsic leaf water-use efficiency at elevated CO₂ was enhanced primarily by direct responses of photosynthesis to CO₂. We did not detect statistical differences in parameters from photosynthetic responses to intercellular CO₂ (A _net-C _i curves) for Pinus taeda foliage grown under elevated CO₂ (550 mol mol^–1) for 50–80 days compared to those for foliage grown under current ambient CO₂ from similar-sized reference trees nearby. In both cases, leaf net photosynthetic rate at 550 mol mol^–1 CO₂ was enhanced by approximately 65% compared to the rate at ambient CO₂ (350 mol mol^–1). A similar level of enhancement under elevated CO₂ was observed for daily photosynthesis under field conditions on a sunny day. While enhancement of photosynthesis by elevated CO₂ during the study period appears to be primarily attributable to direct photosynthetic responses to CO₂ in the pine forest, longer-term CO₂ responses and feedbacks remain to be evaluated.     

CO2 exchange in the alpine sedge Carex curvula as influenced by canopy structure,light and temperature

Summary The temperature and light responses of CO₂ uptake (F_n) in the sedge Carex curvula were investigated in situ by IRGA technic in the Austrian Central Alps at an altitude of 2,310 m. F_n in Carex leaves reaches a maximum of 15.6 mg CO₂ dm^-2 h^-1 at a leaf temperature of 22.5°C and a quantum flux density larger than 1.0 mmol photons m^-2 s^-1 (400–700 nm). A model based on a polynomal regression analysis of the F_n responses and informations about the microclimate and the canopy structure was used to simulate F _n for individual days and for a whole season. It turned out that the major rate limiting factor is the availability of light in the canopy: The calculated photosynthetic yield for a hypothetical optimum season of clear days with fully illuminated leaves and optimum temperature as well as for a typical season with the actual light and temperature conditions in the canopy, shows that insufficient illumination of the leaves accounts for almost 40% reduction of the possible CO₂ uptake while suboptimal temperatures cause only a loss of 8%. Half of the light deficit is caused by mutual shading of the leaves. The minor importance of temperature for the annual CO₂ uptake results from the fact that temperature adaptation of F _n in this sedge allows optimal utilization of short periods with high light intensity and hence high photosynthetic yield. The weaker the quantum supply the more becomes temperature limiting. This indicates that the length of the growing season is probably less important for the success of this prominent alpine plant than the sum of hours with high radiation.List of Symbols I _o quantum flux density in a horizontal plane above the plant canopy (mol photons m^-2 s^-1, 400–700 nm) - I _z as I _o, but at level z in the leaf canopy - I ₁ quantum flux density received by a leaf at level z and with leaf inclination (for diffuse light I _z=I ₁) - solar elevation angle (°) - leaf angle to the vertical (°) - extinction coefficient - LAI leaf area index - T ₁ leaf temperature (°C) - F _n rate of net photosynthesis (CO₂ uptake; mg CO₂ g dry weight^-1 h^-1, or mg CO₂ dm^-2 h^-1, projected leaf area) - R _d rate of dark respiration (mg CO₂ g^-1 h^-1)     

Leaf quality and insect herbivory in model tropical plant communities after long-term exposure to elevated atmospheric CO2

Results from laboratory feeding experiments have shown that elevated atmospheric carbon dioxide can affect interactions between plants and insect herbivores, primarily through changes in leaf nutritional quality occurring at elevated CO₂. Very few data are available on insect herbivory in plant communities where insects can choose among species and positions in the canopy in which to feed. Our objectives were to determine the extent to which CO₂-induced changes in plant communities and leaf nutritional quality may affect herbivory at the level of the entire canopy. We introduced equivalent populations of fourth instar Spodoptera eridania, a lepidopteran generalist, to complex model ecosystems containing seven species of moist tropical plants maintained under low mineral nutrient supply. Larvae were allowed to feed freely for 14 days, by which time they had reached the seventh instar. Prior to larval introductions, plant communities had been continuously exposed to either 340 l CO₂ l^–1 or to 610 l CO₂ l^–1 for 1.5 years. No major shifts in leaf nutritional quality [concentrations of N, total non-structural carbohydrates (TNC), sugar, and starch; ratios of: C/N, TNC/N, sugar/N, starch/N; leaf toughness] were observed between CO₂ treatments for any of the species. Furthermore, no correlations were observed between these measures of leaf quality and leaf biomass consumption. Total leaf area and biomass of all plant communities were similar when caterpillars were introduced. However, leaf biomass of some species was slightly greater-and for other species slightly less (e.g. Cecropia peltata)-in communities exposed to elevated CO₂. Larvae showed the strongest preference for C. peltata leaves, the plant species that was least abundant in all communites, and fed relatively little on plants species which were more abundant. Thus, our results indicate that leaf tissue quality, as described by these parameters, is not necessarily affected by elevated CO₂ under relatively low nutrient conditions. Hence, the potential importance of CO₂-induced shifts in leaf nutritional quality, as determinants of herbivory, may be overestimated for many plant communities growing on nutrient-poor sites if estimates are based on traditional laboratory feeding studies. Finally, slight shifts in the abundance of leaf tissue of various species occurring under elevated CO₂ will probably not significantly affect herbivory by generalist insects. However, generalist insect herbivores appear to become more dependent on less-preferred plant species in cases where elevated CO₂ results in reduced availability of leaves of a favoured plant species, and this greater dependency may eventually affect insect populations adversely.     

Effect of changes in water content on photosynthesis,transpiration and discrimination against 13CO2 and C18O16O in Pleurozium and Sphagnum

Photosynthetic gas exchange characteristics of two common boreal forest mosses, Sphagnum (section acutifolia) and Pleurozium schreberi, were measured continuously during the time required for the moss to dry out from full hydration. Similar patterns of change in CO₂ assimilation with variation in water content occurred for both species. The maximum rates of CO₂ assimilation for Sphagnum (approx. 7 mol m^–2 s^–1) occurred at a water content of approximately 7 (fresh weight/dry weight) while for Pleurozium the maximum rate (approx. 2 mol m^–2 s^–1) occurred at a water content of approximately 6 (fresh weight/dry weight). Above and below these water contents CO₂ assimilation declined. In both species total conductance to water vapour (expressed as a percentage of the maximum rates) remained nearly constant at a water content above 9 (fresh weight/dry weight), but below this level declined in a strong linear manner. Short-term, on-line ¹³CO₂ and C¹⁸O¹⁶O discrimination varied substantially with changes in moss water content and associated changes in the ratio of chloroplast CO₂ to ambient CO₂ partial pressure. At full hydration (maximum water content) both Sphagnum and Pleurozium had similar values of ¹³CO₂ discrimination (approx. 15). Discrimination against ¹³CO₂ increased continuously with reductions in water content to a maximum of 27 in Sphagnum and 22 in Pleurozium. In a similar manner C¹⁸C¹⁶O discrimination increased from approximately 30 at full hydration in both species to a maximum of 150 in Sphagnum and 90 in Pleurozium, at low water content. The observed changes in C¹⁸O¹⁶O were strongly correlated to predictions of a mechanistic model of discrimination processes. Field measurements of moss water content suggested that photosynthetic gas exchange by moss in the understory of a black spruce forest was regularly limited by low water content.     

Inter- and intra-generic differences in growth,reproduction, and fitness of nine herbaceous annual species grown in elevated CO2 environments

In assessing the capacity of plants to adapt to rapidly changing global climate, we must elucidate the impacts of elevated carbon dioxide on reproduction, fitness and evolution. We investigated how elevated CO₂ influenced reproduction and growth of plants exhibiting a range of floral morphologies, the implications of shifts in allocation for fitness in these species, and whether related taxa would show similar patterns of response. Three herbaceous, annual species each of the genera Polygonum, Ipomoea, and Cassia were grown under 350 or 700 ppm CO₂. Vegetative growth and reproductive output were measured non-destructively throughout the full life span, and vegetative biomass was quantified for a subsample of plants in a harvest at first flowering. Viability and germination studies of seed progeny were conducted to characterize fitness precisely. Early vegetative growth was often enhanced in high-CO₂ grown plants of Polygonum and Cassia (but not Ipomoea). However, early vegetative growth was not a strong predictor of subsequent reproduction. Phenology and production of floral buds, flowers, unripe and abscised fruits differed between CO₂ treatments, and genera differed in their reproductive and fitness responses to elevated CO₂. Polygonum and Cassia species showed accelerated, enhanced reproduction, while Ipomoea species generally declined in reproductive output in elevated CO₂. Seed quality and fitness (in terms of viability and percentage germination) were not always directly correlated with quantity produced, indicating that output alone may not reliably indicate fitness or evolutionary potential. Species within genera typically responded more consistently to CO₂ than unrelated species. Cluster analyses were performed separately on suites of vegetative and reproductive characters. Some species assorted within genera when these reproductive responses were considered, but vegetative responses did not reflect taxonomic affinity in these plants. Congeners may respond similarly in terms of reproductive output under global change, but fitness and prognoses of population persistence and evolutionary performance can be inferred only rarely from examination of vegetative characters alone.     

CO2 is the first species formed upon CO oxidation by CO dehydrogenase from Pseudomonas carboxydovorans

The active species of CO₂, i.e. CO₂ or HCO ₃ ^- , formed in the CO dehydrogenase reaction was determined using the pure enzyme from the carboxydotrophic bacterium Pseudomonas carboxydovorans. Employing an assay system similar to that used to test for carbonic anhydrase, data were obtained which are quite compatible with those expected if CO₂ is the first species formed. In addition, carbonic anhydrase activity was not detected in P. carboxydovorans.     

The active species of “CO2” utilized in ferredoxin-linked carboxylation reactions

The active species of CO₂ , i.e. CO₂ or HCO ₃ ^– –(H₂CO₃) utilized by enzymes catalyzing ferredoxin-linked carboxylation reactions was determined. The enzyme investigated was pyruvate synthase from Clostridium pasteurianum (EC 1.2.7.1; Pyruvate: ferredoxin oxidoreductase). Data were obtained which were compatible with those expected if CO₂ is the active species.The dissociation constant (K _S) of the enzyme-CO₂ complex was measured. At pH 7.2 K _Sfor CO₂ of pyruvate synthase was found to be approximately 5 mM.Abbreviations Fd ferredoxin No distinctions are made between CO₂, H₂CO₃, HCO ₃ ^– and CO ₃ ⁼ when the symbol CO₂ is used.     

Development of gypsy moth larvae feeding on red maple saplings at elevated CO<Subscript>2</Subscript> and temperature

Predicted increases in atmospheric CO₂ and global mean temperature may alter important plant-insect associations due to the direct effects of temperature on insect development and the indirect effects of elevated temperature and CO₂ enrichment on phytochemicals important for insect success. We investigated the effects of CO₂ and temperature on the interaction between gypsy moth (Lymantria dispar L.) larvae and red maple (Acer rubrum L.) saplings by bagging first instar larvae within open-top chambers at four CO₂/temperature treatments: (1) ambient temperature, ambient CO₂, (2) ambient temperature, elevated CO₂ (+300 l l^-1 CO₂), (3) elevated temperature (+3.5°C), ambient CO₂, and (4) elevated temperature, elevated CO₂. Larvae were reared to pupation and leaf samples taken biweekly to determine levels of total N, water, non-structural carbohydrates, and an estimate of defensive phenolic compounds in three age classes of foliage: (1) immature, (2) mid-mature and (3) mature. Elevated growth temperature marginally reduced (P <0.1) leaf N and significantly reduced (P <0.05) leaf water across CO₂ treatments in mature leaves, whereas leaves grown at elevated CO₂ concentration had a significant decrease in leaf N and a significant increase in the ratio of starch:N and total non-structural carbohydrates:N. Leaf N and water decreased and starch:N and total non-structural carbohydrates:N ratios increased as leaves aged. Phenolics were unaffected by CO₂ or temperature treatment. There were no interactive effects of CO₂ and temperature on any phytochemical measure. Gypsy moth larvae reached pupation earlier at the elevated temperature (female =8 days, P <0.07; male =7.5 days, P <0.03), whereas mortality and pupal fresh weight of insects were unrelated to either CO₂, temperature or their interaction. Our data show that CO₂ or temperature-induced alterations in leaf constituents had no effect on insect performance; instead, the long-term exposure to a 3.5°C increase in temperature shortened insect development but had no effect on pupal weight. It appears that in some tree-herbivorous insect systems the direct effects of an increased global mean temperature may have greater consequences for altering plant-insect interactions than the indirect effects of an increased temperature or CO₂ concentration on leaf constituents.     

Effects of elevated CO2 and increased nitrogen deposition on photosynthesis and growth of understory plants in spruce model ecosystems

We studied the effects of atmospheric CO₂ enrichment (280, 420 and 560 l CO₂ l^–1) and increased N deposition (0,30 and 90 kg ha^–1 year^–1) on the spruce-forest understory species Oxalis acetosella, Homogyne alpina and Rubus hirtus. Clones of these species formed the ground cover in nine 0.7 m² model ecosystems with 5-year-old Picea abies trees (leaf area index of approx 2.2). Communities grew on natural forest soil in a simulated montane climate. Independently of N deposition, the rate of light-saturated net photosynthesis of leaves grown and measured at 420 l CO₂ l^–1 was higher in Oxalis and in Homogyne, but was not significantly different in Rubus compared to leaves grown and measured at the pre-industrial CO₂ concentration of 280 l l^–1. Remarkably, further CO₂ enrichment to 560 l l^–1 caused no additional increase of CO₂ uptake. With increasing CO₂ supply concentrations of non-structural carbohydrates in leaves increased and N concentrations decreased in all species, whereas N deposition had no significant effect on these traits. Above-ground biomass and leaf area production were not significantly affected by elevated CO₂ in the more vigorously growing species O. acetosella and R. hirtus, but the slow growing H. alpina produced almost twice as much biomass and 50% more leaf area per plant under 420 l CO₂ l^–1 compared to 280 l l^–1 (again no further stimulation at 560 l l^–1). In contrast, increased N addition stimulated growth in Oxalis and Rubus but had no effect on Homogyne. In Oxalis (only) biomass per plant was positively correlated with microhabitat quantum flux density at low CO₂, but not at high CO₂ indicating carbon saturation. On the other hand, the less shade-tolerant Homogyne profited from CO₂ enrichment at all understory light levels facilitating its spread into more shady micro-habitats under elevated CO₂. These species-specific responses to CO₂ and N deposition will affect community structure. The non-linear responses to elevated CO₂ of several of the traits studied here suggest that the largest responses to rising atmospheric CO₂ are under way now or have already occurred and possible future responses to further increases in CO₂ concentration are likely to be much smaller in these understory species.     

Long-term persistence in a changing climate: DNA analysis suggests very old ages of clones of alpine Carex curvula

Carex curvula is a very slow-growing rhizomatous sedge that forms extensive stands in the European an alpine belt. The recruitment of sexual progeny is extremely rare and propagation occurs predominantly through clonal growth. The randomly amplified polymorphic DNA (RAPD) technique was used to analyse clonal structure in a small patch (2.0x0.4 m sampling transect plus some additional samples) of a high-alpine population of the species. Amplification of the DNA of 116 tiller samples from the patch with eight ten-base primers yielded a total of 95 bands, of which 73 were polymorphic. Based on the RAPD amplification profiles a total of 15 multilocus genotypes (putative clones) were identified. Due to the high number of polymorphic loci the number of genetic markers delineating individual clones was high (range: 16–39 markers) which suggests that our estimates of clonal diversity are precise. More than half of the sampled tillers were identified as belonging to a single clone which formed a relatively homogeneous disc intermingling with other clones only at its margin. Based on the maximum diameter of this large clone of more than 7000 tillers and estimates of annual expansion growth of rhizomes (0.4 mm year^-1), the age of the clone was calculated to be around 2000 years. This demonstrates that clones of C. curvula may persist on a single spot over long periods with quite diverse alpine climates ranging from rather mild periods in the Middle Ages to cool periods during the so called little ice age in the last century. Our results suggest caution with plant migration scenarios based on shifting isotherms where late-successional clonal species, which dominate the alpine vegetation all over the world, are concerned.     

Loblolly pine grown under elevated CO2 affects early instar pine sawfly performance

Seedlings of loblolly pine Pinus taeda (L.), were grown in open-topped field chambers under three CO₂ regimes: ambient, 150 l l^–1 CO₂ above ambient, and 300 l l^–1 CO₂ above ambient. A fourth, non-chambered ambient treatment was included to assess chamber effects. Needles were used in 96 h feeding trials to determine the performance of young, second instar larvae of loblolly pine's principal leaf herbivore, red-headed pine sawfly, Neodiprion lecontei (Fitch). The relative consumption rate of larvae significantly increased on plants grown under elevated CO₂, and needles grown in the highest CO₂ regime were consumed 21% more rapidly than needles grown in ambient CO₂. Both the significant decline in leaf nitrogen content and the substantial increase in leaf starch content contributed to a significant increase in the starch:nitrogen ratio in plants grown in elevated CO₂. Insect consumption rate was negatively related to leaf nitrogen content and positively related to the starch:nitrogen ratio. Of the four volatile leaf monoterpenes measured, only -pinene exhibited a significant CO₂ effect and declined in plants grown in elevated CO₂. Although consumption changed, the relative growth rates of larvae were not different among CO₂ treatments. Despite lower nitrogen consumption rates by larvae feeding on the plants grown in elevated CO₂, nitrogen accumulation rates were the same for all treatments due to a significant increase in nitrogen utilization efficiency. The ability of this insect to respond at an early, potentially susceptible larval stage to poorer food quality and declining levels of a leaf monoterpene suggest that changes in needle quality within pines in future elevated-CO₂ atmospheres may not especially affect young insects and that tree-feeding sawflies may respond in a manner similar to herb-feeding lepidopterans.