A 3-year exposure to CO2 and O3 induced minor changes in soil N cycling in a meadow ecosystem

We investigated the individual and interactive effects of moderately elevated CO₂ (ambient air + 100 ppm) and/or O₃ (40–50 ppb) on soil N cycling and microbial biomass N in a 3-year open-top chamber experiment conducted in meadow mesocosms. The results show that elevated O₃ decreased the concentrations of mineral N and NH₄⁺-N in the mesocosm soil in the last growing season (2004). Total N, NO₃⁻-N, microbial biomass N, decomposition rate, potential nitrification and denitrification were not affected by elevated O₃ and/or CO₂. It is thus concluded that the proposed future ambient O₃ and CO₂ levels, such as used in this experiment, may not induce major changes in the below-ground N processes in N-poor northern European hay meadow ecosystems.     

Stimulated N2O flux from intact grassland monoliths after two growing seasons under elevated atmospheric CO2

Long-term exposure of native vegetation to elevated atmospheric CO₂ concentrations is expected to increase C inputs to the soil and, in ecosystems with seasonally dry periods, to increase soil moisture. We tested the hypothesis that these indirect effects of elevated CO₂ (600 μl l⁻¹ vs 350 μl l⁻¹) would improve conditions for microbial activity and stimulate emissions of nitrous oxide (N₂O), a very potent and long-lived greenhouse gas. After two growing seasons, the mean N₂O efflux from monoliths of calcareous grassland maintained at elevated CO₂ was twice as high as that measured from monoliths maintained at current ambient CO₂ (70 ± 9 vs 37 ± 4 μg N₂O m⁻² h⁻¹ in October, 27 ± 5 vs 13 ± 3 μg N₂O m⁻² h⁻¹ in November after aboveground harvest). The higher N₂O emission rates at elevated CO₂ were associated with increases in soil moisture, soil heterotrophic respiration, and plant biomass production, but appear to be mainly attributable to higher soil moisture. Our results suggest that rising atmospheric CO₂ may contribute more to the total greenhouse effect than is currently estimated because of its plant-mediated effects on soil processes which may ultimately lead to increased N₂O emissions from native grasslands. Received: 11 September 1997 / Accepted: 20 March 1998     

Growth responses of yellow-poplar(Liriodendron tulipifera L.) exposed to 5 years of O3 aloneor combined with elevated CO2

Field‐grown yellow‐poplar (Liriodendron tulipifera L.) werefumigated from May to October in 1992–96 within open‐topchambers to determine the impact of ozone (O₃) aloneor combined with elevated carbon dioxide (CO₂) on saplinggrowth. Treatments were replicated three times and included: charcoal‐filteredair (CF); 1 × ambient ozone (1 × O₃);1·5 × ambient ozone (1·5 × O₃);1·5 × ambient ozone plus 350 p.p.m.carbon dioxide (1·5 × O₃ + CO₂)(target of 700 p.p.m. CO₂); and open‐air chamberlessplot (OA). After five seasons, the total cumulative O₃ exposure (SUM₀₀ = sumof hourly O₃ concentrations during the study) rangedfrom 145 (CF) to 861 (1·5 × O₃) p.p.m. × h (partsper million hour). Ozone had no statistically significant effecton yellow‐poplar growth or biomass, even though total root biomasswas reduced by 13% in the 1·5 × O₃‐exposedsaplings relative to CF controls. Although exposure to 1·5 × O₃ + CO₂ hada stimulatory effect on yearly basal area growth increment aftertwo seasons, significant increases in shoot and root biomass (～ 60% increaserelative to all others) were not detected until the fifth season.After five seasons, the yearly basal area growth increment of saplingsexposed to 1·5 × O₃ + CO₂‐air increasedby 41% relative to all others. Based on this multi‐yearstudy, it appears that chronic O₃ effects on yellow‐poplargrowth are limited and slow to manifest, and are consistent withprevious studies that show yellow‐poplar growth is not highly responsiveto O₃ exposure. In addition, these results show thatenriched CO₂ may ameliorate the negative effects of elevatedO₃ on yellow‐poplar shoot growth and root biomass underfield conditions.     

Effects of elevated CO2 and nitrogen on growth ofPoa pratensis (L.)

The growth responses of a grass,Poa pratensis, to elevated CO₂ and nitrogen were investigated. Light-saturated photosynthetic rate per unit leaf area increased with exposure to elevated CO₂, while dry weight did not respond to increased CO₂. Patterns of biomass allocation within plants, including leaf area, leaf area ratio, specific leaf area, and root to shoot ratios, were not altered by elevated CO₂, but changed considerably with N treatment Shoot and whole-plant tissue N concentrations were significantly diluted by elevated CO₂ (Tukey test, P < 0.05). Total N content did not differ significantly among CO₂ treatments. The absence of a concomitant increase in N uptake under elevated CO₂ may have caused a dilution in plant tissue [N], probably negating the positive effects of increased photosynthesis on biomass accumulation.     

Decomposition and nitrogen release from leaves of three hardwood species grown under elevated O3 and/or CO2

Elevated concentrations of O₃ and CO₂ have both been shown to affect structure, nutrient status, and deposition of secondary metabolites in leaves of forest trees. While such studies have produced robust models of the effects of such air pollutants on tree ecophysiology and growth, few have considered the potential for broader, ecosystem-level effects after these chemically and structurally altered leaves fall as leaf litter and decay. To determine the effects of elevated O₃ and/or CO₂ on the subsequent decomposition and nutrient release from the leaves grown in such altered atmospheres, we grew seedlings of three widespread North American forest trees, black cherry (Prunus serotina) (BC), sugar maple (Acer saccharum) (SM), and yellow-poplar (Liriodendron tulipifera) (YP) for two growing seasons in charcoal-filtered air (CF-air=approximately 25% ambient O₃), ambient O₃ (1X) or twice-ambient O₃ (2X) in outdoor open-top chambers. We then assayed the loss of mass and N from the litter derived from those seedlings through one year litterbag incubations in the forest floor of a neighboring forest stand. Mass loss followed linear functions and was not affected by the O₃ regime in which the leaves were grown. Instantaneous decay rates (i.e. k values) averaged SM:–0.707 y^-1, BC:–0.613 y^-1, and YP:–0.859 y^-1. N loss from ambient (1X) O₃-grown SM leaves was significantly greater than from CF-air leaves: N loss from BC leaves did not differ among treatments. Significantly less N was released from CF-air-grown YP leaves than from 1X or 2X O₃-treated leaves. YP leaves from plants grown in pots at 2X O₃ and 350 ppm supplemental CO₂ in indoor pollutant fumigation chambers (CSTRs or Continuously Stirred Tank Reactors) loss 40% as much mass and 27% as much N over one year as did leaves from YP grown in CF-air or 2X O₃. Thus, for leaves from plants grown in pots in controlled environment fumigation chambers, the concentrations of both O₃ and CO₂ can affect N release from litter incubated in the field whereas mass loss rate was affected only by CO₂. Because both mass loss and N release from leaves grown at elevated CO₂ were reduced significantly (at least for yellow-poplar), forests exposed to elevated CO₂ may have significantly reduced N turnover rates, thereby resulting in increased N limitation of tree growth, especially in forests which are already N-limited.     

Seasonal response of photosynthesis to elevated CO2 in loblolly pine (Pinus taeda L.) over two growing seasons

Trees growing in natural systems undergo seasonal changes in environmental factors that generate seasonal differences in net photosynthetic rates. To examine how seasonal changes in the environment affect the response of net photosynthetic rates to elevated CO₂, we grew Pinus taeda L. seedlings for three growing seasons in open-top chambers continuously maintained at either ambient or ambient + 30 Pa CO₂. Seedlings were grown in the ground, under natural conditions of light, temperature nd nutrient and water availability. Photosynthetic capacity was measured bimonthly using net photosynthetic rate vs. intercellular CO₂ partial pressure (A-C_i) curves. Maximum Rubisco activity (Vc_max) and ribulose 1,5-bisphosphate regeneration capacity mediated by electron transport (J_max) and phosphate regeneration (PiRC) were calculated from A-C_i curves using a biochemically based model. Rubisco activity, activation state and content, and leaf carbohydrate, chlorophyll and nitrogen concentrations were measured concurrently with photosynthesis measurements. This paper presents results from the second and third years of treatment. Mean leaf nitrogen concentrations ranged from 13.7 to 23.8 mg g^?1, indicating that seedlings were not nitrogen deficient. Relative to ambient CO₂ seedlings, elevated CO₂ increased light-saturated net photosynthetic rates 60–110% during the summer, but < 30% during the winter. A relatively strong correlation between leaf temperature and the relative response of net photosynthetic rates to elevated CO₂ suggests a strong effect of leaf temperature. During the third growing season, elevated CO₂ reduced Rubisco activity 30% relative to ambient CO₂ seedlings, nearly completely balancing Rubisco and RuBP-regeneration regulation of photosynthesis. However, reductions in Rubisco activity did not eliminate the seasonal pattern in the relative response of net photosynthetic rates to elevated CO₂. These results indicate that seasonal differences in the relative response of net photosynthetic rates to elevated CO₂ are likely to occur in natural systems.     

The interactive effects of elevated CO2 and O3 concentration on photosynthesis in spring wheat

This study investigated the interacting effects of carbon dioxide and ozone on photosynthetic physiology in the flag leaves of spring wheat (Triticum aestivum L. cv. Wembley), at three stages of development. Plants were exposed throughout their development to reciprocal combinations of two carbon dioxide and two ozone treatments: [CO₂] at 350 or 700 mol mol^–1, [O₃] at < 5 or 60 nmol mol^–1. Gas exchange analysis, coupled spectrophotometric assay for RuBisCO activity, and SDS-PAGE, were used to examine the relative importance of pollutant effects on i) stomatal conductance, ii) quantum yield, and iii) RuBisCO activity, activation, and concentration. Independently, both elevated [CO₂] and elevated [O₃] caused a loss of RuBisCO protein and V_cmax. In combination, elevated [CO₂] partially protected against the deleterious effects of ozone. It did this partly by reducing stomatal conductance, and thereby reducing the effective ozone dose. Elevated [O₃] caused stomatal closure largely via its effect on photoassimilation.     

Fungal community composition and function after long‐term exposure of northern forests to elevated atmospheric CO2 and tropospheric O3

The long‐term effects of rising atmospheric carbon dioxide (CO₂) and tropospheric O₃ concentrations on fungal communities in soil are not well understood. Here, we examine fungal community composition and the activities of cellobiohydrolase and N‐acetylglucosaminidase (NAG) after 10 years of exposure to 1.5 times ambient levels of CO₂ and O₃ in aspen and aspen–birch forest ecosystems, and compare these results to earlier studies in the same long‐term experiment. The forest floor community was dominated by saprotrophic fungi, and differed slightly between plant community types, as did NAG activity. Elevated CO₂ and O₃ had small but significant effects on the distribution of fungal genotypes in this horizon, and elevated CO₂ also lead to an increase in the proportion of Sistotrema spp. within the community. Yet, although cellobiohydrolase activity was lower in the forest floor under elevated O₃, it was not affected by elevated CO₂. NAG was also unaffected. The soil community was dominated by ectomycorrhizal species. Both CO₂ and O₃ had a minor effect on the distribution of genotypes; however, phylogenetic analysis indicated that under elevated O₃Cortinarius and Inocybe spp. increased in abundance and Laccaria and Tomentella spp. declined. Although cellobiohydrolase activity in soil was unaffected by either CO₂ or O₃, NAG was higher (～29%) under CO₂ in aspen–birch, but lower (～18%) under aspen. Time series analysis indicated that CO₂ increased cellulolytic enzyme activity during the first 5 years of the experiment, but that the magnitude of this effect diminished over time. NAG activity also showed strong early stimulation by elevated CO₂, but after 10 years this effect is no longer evident. Elevated O₃ appears to have variable stimulatory and repressive effects depending on the soil horizon and time point examined.     

Effect of elevated carbon-dioxide on plant growth,physiology, yield and seed quality of chickpea (Cicer arietinum L.) in Indo-Gangetic plains

In the present scenario of climate change with constantly increasing CO₂ concentration, there is a risk of altered crop performance in terms of growth, yield, grain nutritional value and seed quality. Therefore, an experiment was conducted in open top chamber (OTCs) during 2017–18 and 2018–19 to assess the effect of elevated atmospheric carbondioxide (e[CO₂]) (600 ppm) on chickpea (cv. JG 14) crop growth, biomass accumulation, physiological function, seed yield and its quality in terms of germination and vigour. The e[CO₂] treatment increased the plant height, leaf and stem biomass over ambient CO₂ (a[CO₂]) treatment. The e[CO₂] increased seed yield by 11–18% which was attributed to an increase in the number of pods (6–10%) and seeds plant⁻¹ (8–9%) over a[CO₂]. However, e[CO₂] reduced the seed protein (7%), total phenol (13%) and thiobarbituric acid reactive substances (12%) and increased the starch (21%) and water uptake rate as compared to seeds harvested from a[CO₂] environment. Exposing chickpea plant to e[CO₂] treatment had no impact on germination and vigour of the harvested seeds. Also, the physical attributes, total soluble sugar and antioxidant enzymes activities of harvested seeds were comparable in a[CO₂] and e[CO₂] treatment. Hence, the experimental findings depict that e[CO₂] upto 600 ppm could add to the growth and productivity of chickpea in a sub-tropical climate with an implication on its nutritional quality of the produce.     

Interactions of elevated CO2, NH3 and O3 on mycorrhizal infection,gas exchange and N metabolism in saplings of Scots pine

Four-year-old saplings of Scots pine (Pinus sylvestris) (L.) were exposed for 11 weeks in controlled-environment chambers to charcoad-filtered air, or to charcoal-filtered air supplemented with NH₃ (40 g m^–3), O₃ (110 g m^–3 during day/ 40 g m^–3 during night) or NH₃+O₃. All treatments were carried out at ambient (259 L L^–1) and at elevated CO₂ concentration (700 L L^–1). Total tree biomass, mycorrhizal infection, net CO₂ assimilation (P_n), stomatal conductance (g_s), transpiration of the shoots and NH₃ metabolization of the needles were measured. In ambient CO₂ (1) gaseous NH₃ decreased mycorrhizal infection, without significantly affecting tree biomass or N concentration and it enhanced the activity of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in one-year-old needles; (2) ozone decreased mycorrhizal infection and the acitivity of GS in the needles, while it increased the activity og GDH; (3) exposure to NH₃+O₃ lessened the effects of single exposures to NH₃ and O₃ on reduction of mycorrhizal infection and on increase in GDH activity. Similar lessing effects on mycorrhizal infection as observed in trees exposed to NH₃+O₃ at ambient CO₂, were measured in trees exposed to NH₃+O₃ at elevated CO₂. Exposure to elevated CO₂ without pollutants did not significantly affect any of the parameters studied, except for a decrease in the concentration of soluble proteins in the needles. Elevated CO₂ _NH₃ strongly decreased root branching and mycorrhizal infection and temporarily stimulated P_n and g_s. The exposure to elevated CO₂+NH₃+O₃ also transiently stimulated P_n. The possible mechanisms underlying and integrating these effects are discussed. Elevated CO₂ clearly did not alleviate the negative effects of NH₃ and O₃ mycoorhiral infection. The significant reduction of mycorrhizal infection after exposure to NH₃ or O₃, observed before significant changes in gas exchange or growth occurred, suggest the use of mycorrhizal infection as an early indicator for NH₃ and O₃ induced stress.Abbreviations DW dry weight - FA filtered air - FA_a filtered air at ambient CO₂ - FA_e filtered air at elevated CO₂ - FW fresh weight - GDH glutamate dehydrogenase - GS glutamine synthetase - g_s stomatal conductance - P_n net CO₂ assimilation - RWR root weight ratio - SRL specific root length     

Fine-root respiration in a loblolly pine (Pinus taeda L.) forest exposed to elevated CO2 and N fertilization

Forest ecosystems release large amounts of carbon to the atmosphere from fine-root respiration (R(r)), but the control of this flux and its temperature sensitivity (Q(10)) are poorly understood. We attempted to: (1) identify the factors limiting this flux using additions of glucose and an electron transport uncoupler (carbonyl cyanide m-chlorophenylhydrazone); and (2) improve yearly estimates of R(r) by directly measuring its Q(10)in situ using temperature-controlled cuvettes buried around intact, attached roots. The proximal limits of R(r) of loblolly pine (Pinus taeda L.) trees exposed to free-air CO(2) enrichment (FACE) and N fertilization were seasonally variable; enzyme capacity limited R(r) in the winter, and a combination of substrate supply and adenylate availability limited R(r) in summer months. The limiting factors of R(r) were not affected by elevated CO(2) or N fertilization. Elevated CO(2 )increased annual stand-level R(r) by 34% whereas the combination of elevated CO(2) and N fertilization reduced R(r) by 40%. Measurements of in situ R(r) with high temporal resolution detected diel patterns that were correlated with canopy photosynthesis with a lag of 1 d or less as measured by eddy covariance, indicating a dynamic link between canopy photosynthesis and root respiration. These results suggest that R(r) is coupled to daily canopy photosynthesis and increases with carbon allocation below ground.     

Effects of genotype,elevated CO2 and elevated O3 on aspen phytochemistry and aspen leaf beetle Chrysomela crotchi performance

• 1 Trembling aspen Populus tremuloides Michaux is an important forest species in the Great Lakes region and displays tremendous genetic variation in foliar chemistry. Elevated carbon dioxide (CO₂) and ozone (O₃) may also influence phytochemistry and thereby alter the performance of insect herbivores such as the aspen leaf beetle Chrysomela crotchi Brown.
• 2 The present study aimed to relate genetic‐ and atmospheric‐based variation in aspen phytochemistry to C. crotchi performance (larval development time, adult mass, survivorship). The experiment was conducted at the Aspen Free‐Air CO₂ Enrichment (FACE) site in northern Wisconsin. Beetles were reared on three aspen genotypes under elevated CO₂ and/or O₃. Leaves were collected to determine chemical characteristics.
• 3 The foliage exhibited significant variation in nitrogen, condensed tannins and phenolic glycosides among genotypes. CO₂ and O₃, however, had little effect on phytochemistry. Nonetheless, elevated CO₂ decreased beetle performance on one aspen genotype and had inconsistent effects on beetles reared on two other genotypes. Elevated O₃ decreased beetle performance, especially for beetles reared on an O₃‐sensitive genotype. Regression analyses indicated that phenolic glycosides and nitrogen explain a substantial amount (27–45%) of the variation in herbivore performance.
• 4 By contrast to the negative effects that are typically observed with generalist herbivores, aspen leaf beetles appear to benefit from phenolic glycosides, chemical components that are largely genetically‐determined in aspen. The results obtained in the present study indicate that host genetic variation and atmospheric concentrations of greenhouse gases will be important factors in the performance of specialist herbivores, such as C. crotchi, in future climates.

     

Influence of elevated CO2 and O3 on Betula pendula Roth crown structure

Elevated CO(2) and ozone effects were studied singly and in combination on the crown structure of two Betula pendula clones. Measurements were made at the end of the second fumigation period in an open-top-chamber experiment with 9-year-old trees. Shoot ramification (number of long and short daughter shoots), shoot length, and number of metamers, leaves and buds were measured at four positions in every tree. As a result of increased temperature, trees in chambers had longer shoots and more frequent shoot ramification than control trees not enclosed in chambers. Ozone treatment decreased shoot ramification significantly. Additionally, ozone treatment resulted in an increased number of metamers in one clone. There was no statistically significant interaction between ozone effect and crown position; however, there was a slight tendency for the lower crown to be more affected by ozone. Elevated CO(2) caused a significant increase in the number of long-shoot metamers. Therefore, 2x ambient CO(2) concentration partly ameliorated the negative effect of ozone because the increased number of leaves per shoot counteracted the decreased branching. Although the main effects of elevated ozone and CO(2) were similar in the two clones, slight, statistically insignificant, differences appeared in their responses when interactions with crown position were considered.     

Intra- specific variation in response of Jatropha (Jatropha curcas L.) to elevated CO2 conditions

Twenty genotypes of Jatropha collected from diverse eco-geographic regions from the states of Chhattisgarh (3), Andhra Pradesh (12), Rajasthan (4) and Uttarakhand (1) of India were subjected to elevated CO₂ conditions. All the genotypes showed significant difference (p < 0.05 and 0.01) in the phenotypic traits in both the environments (elevated and ambient) and genotype x environment interaction. Among the physiological traits recorded, maximum photosynthetic rate was observed in IC565048 (48.8 μmol m⁻² s⁻¹) under ambient controlled conditions while under elevated conditions maximum photosynthetic rate was observed in IC544678 (41.3 μmol m⁻² s⁻¹), and there was no significant difference in the genotype x environment interaction. Stomatal conductance (Gs) emerged as the key factor as it recorded significant difference among the genotypes, between the environments and also genotype x environment interaction. The Gs and transpiration (E) recorded a significant decline in the genotypes under the elevated CO₂ condition over the ambient control. Under elevated CO₂ conditions, the minimum values recorded for Gs and E were 0.03 mmol m⁻² s⁻¹ and 0.59 mmol m⁻² s⁻¹ respectively in accession IC565039, while the maximum values for Gs and E were 1.8 mmol m⁻² s⁻¹ and 11.5 mmol m⁻² s⁻¹ as recorded in accession IC544678. The study resulted in the identification of potential climate ready genotypes viz. IC471314, IC544654, IC541634, IC544313, and IC471333 for future use.