Elevated atmospheric humidity shapes the carbon cycle of a silver birch forest ecosystem: A FAHM study.

Processes determining the carbon (C) balance of a forest ecosystem are influenced by a number of climatic and environmental factors. In Northern Europe, a rise in atmospheric humidity and precipitation is predicted. The study aims to ascertain the effect of elevated atmospheric humidity on the components of the C budget and on the C-sequestration capacity of a young birch forest. Biomass production, soil respiration, and other C fluxes were measured in young silver birch (Betula pendula Roth) stands growing on the Free Air Humidity Manipulation (FAHM) experimental site, located in South-East Estonia. The C input fluxes: C sequestration in trees and understory, litter input into soil, and methane oxidation, as well as C output fluxes: soil heterotrophic respiration and C leaching were estimated. Humidified birch stands stored C from the atmosphere, but control stands can be considered as C neutral. Two years of elevated air humidity increased C sequestration in the understory but decreased it in trees. Humidification treatment increased remarkably the C input to the soil. The main reason for such an increase was the higher root litter input into the soil, brought about by the more than two-fold increase of belowground biomass production of the understory in the humidification treatment. Elevated atmospheric humidity increased C sequestration in young silver birch stands, mitigating increasing CO2 concentration in the atmosphere. However, the effect of elevated atmospheric humidity is expected to decrease over time, as plants and soil organisms acclimate, and new communities emerge.

New exposure-based metric approach for evaluating O(3) risk to North American aspen forests.

The United States and Canada currently use exposure-based metrics to protect vegetation from O(3). Using 5 years (1999-2003) of co-measured O(3), meteorology and growth response, we have developed exposure-based regression models that predict Populus tremuloides growth change within the North American ambient air quality context. The models comprised growing season fourth-highest daily maximum 8-h average O(3) concentration, growing degree days, and wind speed. They had high statistical significance, high goodness of fit, include 95% confidence intervals for tree growth change, and are simple to use. Averaged across a wide range of clonal sensitivity, historical 2001-2003 growth change over most of the 26 Mha P. tremuloides distribution was estimated to have ranged from no impact (0%) to strong negative impacts (-31%). With four aspen clones responding negatively (one responded positively) to O(3), the growing season fourth-highest daily maximum 8-h average O(3) concentration performed much better than growing season SUM06, AOT40 or maximum 1h average O(3) concentration metrics as a single indicator of aspen stem cross-sectional area growth.

Ozone-induced H2 O2 accumulation in field-grown aspen and birch is linked to foliar ultrastructure and peroxisomal activity.

• Saplings of three aspen (Populus tremuloides) genotypes and seedlings of paper birch (Betula papyrifera) were exposed to elevated ozone (1.5× ambient) and 560 p.p.m. CO2 , singly and in combination, from 1998 at the Aspen-FACE (free-air CO2 enrichment) site (Rhinelander, USA). • The plants were studied for H2 O2 accumulation within the leaf mesophyll, number of peroxisomes, level of gene expression for catalase (Cat), and changes in ultrastructure. • In tolerant clones, ozone-elicited excess H2 O2 production was restricted to the apoplast, without any ultrastructural injuries. This was associated with ozone-induced proliferation of peroxisomes and increased transcript levels of Cat. In sensitive plants, ozone-induced H2 O2 accumulation continued from the cell wall to the plasma membrane, cytosol and chloroplasts, particularly in older leaves. However, chloroplastic precipitation was absent in the presence of elevated CO2 . In the most sensitive aspen clone, H2 O2 accumulation was found in conjunction with chloroplast injuries, low number of peroxisomes and low cell wall volume, whereas in birch a simultaneous increase in cell wall thickness indicated defence activation. • Our results indicate that oxidative stress manifests as H2 O2 effects on leaf ultrastructure in sensitive trees exposed to elevated ozone. However, CO2 enrichment appears to alleviate chloroplastic oxidative stress.

Growth responses of Populus tremuloides clones to interacting elevated carbon dioxide and tropospheric ozone.

The Intergovernmental Panel of Climate Change (IPCC) has concluded that the greenhouse gases carbon dioxide (CO2) and tropospheric ozone (O3) are increasing concomitantly globally. Little is known about the effect of these interacting gases on growth, survival, and productivity of forest ecosystems. In this study we assess the effects of three successive years of exposure to combinations of elevated CO2 and O3 on growth responses in a five trembling aspen (Populus tremuloides) clonal mixture in a regenerating stand. The experiment is located in Rhinelander, Wisconsin, USA (45 degrees N 89 degrees W) and employs free air carbon dioxide and ozone enrichment (FACE) technology. The aspen stand was exposed to a factorial combination of four treatments consisting of elevated CO2 (560 ppm), elevated O3 (episodic exposure-90 microl l(-1) hour(-1)), a combination of elevated CO2 and O3, and ambient control in 30 m treatment rings with three replications. Our overall results showed that our three growth parameters including height, diameter and volume were increased by elevated CO2, decreased by elevated O3, and were not significantly different from the ambient control under elevated CO2 + O3. However, there were significant clonal differences in the responses; all five clones exhibited increased growth with elevated CO2, one clone showed an increase with elevated O3, and two clones showed an increase over the control with elevated CO2 + O3, two clones showed a decrease, and one was not significantly different from the control. Notably. there was a significant increase in current terminal shoot dieback with elevated CO2 during the 1999-2000 dormant season. Dieback was especially prominent in two of the five clones, and was attributed to those clones growing longer into the autumnal season where they were subject to frost. Our results show that elevated O3 negates expected positive growth effects of elevated CO2 in Populus tremuloides in the field, and suggest that future climate model predictions should take into account the offsetting effects of elevated O3 on CO2 enrichment when estimating future growth of trembling aspen stands.

Consequences of elevated carbon dioxide and ozone for foliar chemical composition and dynamics in trembling aspen (Populus tremuloides) and paper birch (Betula papyrifera).

Atmospheric chemical composition affects foliar chemical composition, which in turn influences the dynamics of both herbivory and decomposition in ecosystems. We assessed the independent and interactive effects of CO2 and O3 fumigation on foliar chemistry of quaking aspen (Populus tremuloides) and paper birch (Betula papyrifera) at a Free-Air CO2 Enrichment (FACE) facility in northern Wisconsin. Leaf samples were collected at five time periods during a single growing season, and analyzed for nitrogen. starch and condensed tannin concentrations, nitrogen resorption efficiencies (NREs), and C:N ratios. Enriched CO2 reduced foliar nitrogen concentrations in aspen and birch; O3 only marginally reduced nitrogen concentrations. NREs were unaffected by pollution treatment in aspen, declined with 03 exposure in birch, and this decline was ameliorated by enriched CO2. C:N ratios of abscised leaves increased in response to enriched CO2 in both tree species. O3 did not significantly alter C:N ratios in aspen, although values tended to be higher in + CO2 + O3 leaves. For birch, O3 decreased C:N ratios under ambient CO2 and increased C:N ratios under elevated CO2. Thus, under the combined pollutants, the C:N ratios of both aspen and birch leaves were elevated above the averaged responses to the individual and independent trace gas treatments. Starch concentrations were largely unresponsive to CO2 and O3 treatments in aspen. but increased in response to elevated CO2 in birch. Levels of condensed tannins were negligibly affected by CO2 and O3 treatments in aspen, but increased in response to enriched CO2 in birch. Results from this work suggest that changes in foliar chemical composition elicited by enriched CO2 are likely to impact herbivory and decomposition, whereas the effects of O3 are likely to be minor, except in cases where they influence plant response to CO2.

Impacts of elevated CO2 and/or O3 on leaf ultrastructure of aspen (Populus tremuloides) and birch (Betula papyrifera) in the aspen FACE experiment.

Impacts of elevated atmospheric O3 and/or CO2 on three clones of aspen (Populus tremuloides Michx.) and birch (Betula papyrifera Marsh.) were studied to determine, whether or not elevated CO2 ameliorates O3-induced damage to leaf cells. The plants were exposed for 3 years at the Aspen FACE exposure site in Wisconsin (USA) prior to sampling for ultrastructural investigations on 19 June 1999. In the aspen clones, elevated CO2 increased chloroplast cover index, leaf and spongy mesophyll layer thickness, intercellular air space volume in mesophyll, amount of starch in chloroplasts and cytoplasmic lipids but decreased the number of plastoglobuli in chloroplasts. In contrast, elevated O3 decreased chloroplast cover index, starch content, and the proportion of cytoplasm and intercellular space in mesophyll, and increased the proportion of vacuoles, the amount of condensed vacuolar tannins and the number of plastoglobuli. Ozone also caused structural thylakoid injuries (dilation, distortion) and stromal condensation in chloroplasts, which was ameliorated by elevated CO2 by 5-66% in aspen clones and by 2-10% in birch. Birch ultrastructure was less affected by elevated CO2 or O3 stress compared to aspen. In the most O3-sensitive aspen clone, thinner leaves and cell walls, lower proportion of cell wall volume, and higher volume for vacuoles was found compared to more-tolerant clones.

Effects of elevated CO2 and O3 on aspen clones varying in O3 sensitivity: can CO2 ameliorate the harmful effects of O3?

To determine whether elevated CO2 reduces or exacerbates the detrimental effects of O3 on aspen (Populus tremuloides Michx.). aspen clones 216 and 271 (O3 tolerant), and 259 (O3 sensitive) were exposed to ambient levels of CO2 and O3 or elevated levels of CO2, O3, or CO2 + O3 in the FACTS II (Aspen FACE) experiment, and physiological and molecular responses were measured and compared. Clone 259. the most O3-sensitive clone, showed the greatest amount of visible foliar symptoms as well as significant decreases in chlorophyll, carotenoid, starch, and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) concentrations and transcription levels for the Rubisco small subunit. Generally, the constitutive (basic) transcript levels for phenylalanine ammonialyase (PAL) and chalcone synthase (CHS) and the average antioxidant activities were lower for the ozone sensitive clone 259 as compared to the more tolerant 216 and 271 clones. A significant decrease in chlorophyll a, b and total (a + b) concentrations in CO2, O3, and CO2 + O3 plants was observed for all clones. Carotenoid concentrations were also significantly lower in all clones; however. CHS transcript levels were not significantly affected, suggesting a possible degradation of carotenoid pigments in O3-stressed plants. Antioxidant activities and PAL and 1-aminocyclopropane-l-carboxylic acid (ACC)-oxidase transcript levels showed a general increase in all O3 treated clones, while remaining low in CO2 and CO2 + O3 plants (although not all differences were significant). Our results suggest that the ascorbate-glutathione and phenylpropanoid pathways were activated under ozone stress and suppressed during exposure to elevated CO2. Although CO2 + O2 treatment resulted in a slight reduction of O3-induced leaf injury, it did not appear to ameliorate all of the harmful affects of O3 and, in fact. may have contributed to an increase in chloroplast damage in all three aspen clones.

Fine-root biomass and fluxes of soil carbon in young stands of paper birch and trembling aspen as affected by elevated atmospheric CO2 and tropospheric O3.

Rising atmospheric CO2 may stimulate future forest productivity, possibly increasing carbon storage in terrestrial ecosystems, but how tropospheric ozone will modify this response is unknown. Because of the importance of fine roots to the belowground C cycle, we monitored fine-root biomass and associated C fluxes in regenerating stands of trembling aspen, and mixed stands of trembling aspen and paper birch at FACTS-II, the Aspen FACE project in Rhinelander, Wisconsin. Free-air CO2 enrichment (FACE) was used to elevate concentrations of CO2 (average enrichment concentration 535 µl l-1) and O3 (53 nl l-1) in developing forest stands in 1998 and 1999. Soil respiration, soil pCO2, and dissolved organic carbon in soil solution (DOC) were monitored biweekly. Soil respiration was measured with a portable infrared gas analyzer. Soil pCO2 and DOC samples were collected from soil gas wells and tension lysimeters, respectively, at depths of 15, 30, and 125 cm. Fine-root biomass averaged 263 g m-2 in control plots and increased 96% under elevated CO2. The increased root biomass was accompanied by a 39% increase in soil respiration and a 27% increase in soil pCO2. Both soil respiration and pCO2 exhibited a strong seasonal signal, which was positively correlated with soil temperature. DOC concentrations in soil solution averaged ~12 mg l-1 in surface horizons, declined with depth, and were little affected by the treatments. A simplified belowground C budget for the site indicated that native soil organic matter still dominated the system, and that soil respiration was by far the largest flux. Ozone decreased the above responses to elevated CO2, but effects were rarely statistically significant. We conclude that regenerating stands of northern hardwoods have the potential for substantially greater C input to soil due to greater fine-root production under elevated CO2. Greater fine-root biomass will be accompanied by greater soil C efflux as soil respiration, but leaching losses of C will probably be unaffected.

Immunoaffinity purification of two major proteins of bovine leukemia virus (gp51 and p24) and their use for discrimination between vaccinated and infected animals.

The outer envelope glycoprotein gp51 and the core protein p24 of bovine leukemia virus (BLV), were purified from culture media of FLK-BLV cells by a single-step procedure, using immunoaffinity chromatography based on monoclonal antibodies to the respective proteins. About 90% of the envelope glycoprotein in the culture medium was recovered as a highly purified product. Both purified protein (gp51 and p24) preparations, were found to be highly specific antigens by ELISA, and did not cross-react with sera raised against the other antigen. The conformational epitopes on the purified gp51 were preserved as judged by their reactions with the corresponding monoclonal antibodies. The p24 ELISA reacted only with sera from naturally infected animals and not with sera from animals immunized with an experimental gp51-iscom vaccine. The p24 antigen is therefore useful for discriminating between BLV-infected animals and those immunized with a gp51 subunit vaccine.

Differential response of CO2 uptake parameters of soil- and sand-grown phaseolus vulgaris (L.) plants to absorbed ozone flux.

Shoots of a soil- or sand-grown dwarf bean variety were exposed to O(3) concentrations in the range of 500 to 900 ppb for up to 5 h. The measured exchange rates of water vapor and CO(2) during exposures were used to calculate stomatal and mesophyll conductances averaged across all leaves. Changes in conductances were related to exposure duration and absorbed O(3) totals (AOT). Both conductances were more sensitive to AOT in sand-grown plants, which also had more visible injury under comparable AOT values. Measurements of the relationship between CO(2) exchange and internal CO(2) concentration of single leaflets of treated plants also showed greater sensitivity of CO(2)-saturated photosynthesis in sand-grown plants. Diffusional processes were not likely to have been the cause of dissimilar responses because the O(3) absorption rate was lower in sand-grown plants. A difference in the scaveninng capacities in cells is suggested to be the cause of the differences in sensitivity to acute O(3) exposure.

Characterization of purified gp 51 from bovine leukemia virus integrated into iscom. Physicochemical properties and serum antibody response to the integrated gp51.

It is proposed that the envelope glycoprotein, gp 51, is the protective antigen of bovine leukemia virus (BLV). An experimental iscom vaccine has been prepared from immunoaffinity purified gp 51. To overcome the problem of integrating a nonamphipathic protein, gp 51 was partially denatured at pH 2.4 before integration into the iscom. The recovery of gp 51 into the iscom was calculated to be 85%. The gp 51 incorporated into iscom retained its physicochemical properties and the neutralizing epitopes F, G and H were found to be intact. The iscom preparation was shown to induce a specific immune response to gp 51 after inoculation into mice and calves, as tested by ELISA and Western blotting. Sera from the immunized calves specifically inhibited the VSV-(BLV) pseudotypes. Thus the gp 51-iscom preparations appear to be highly immunogenic and to induce a gp 51 specific response.

Identification of an immunodominant region on the isolated bovine leukaemia virus (BLV) major envelope protein gp51 by monoclonal antibodies presumably not exposed during natural BLV infection.

A panel of newly isolated monoclonal antibodies (MoAbs) is described which are specific for bovine leukaemia virus (BLV) envelope protein gp51. Epitope mapping using competition antibody binding assays and binding studies with gp51-related fusion proteins and synthetic peptides show that they are directed against seven independent antigenic determinants. Four of them are unrelated to the epitopes described earlier (Bruck et al., 1982a). We define three binding regions for the MoAbs on the gp51 molecule. The region between amino acids 170 and 217 is highly immunogenic when the isolated protein is used for immunization, and seems to be inaccessible for immune recognition when gp51 is associated with the virus envelope as it occurs during natural BLV infection.

Growth rate-reserve content relationship as influenced by irradiance, CO2 concentration, and temperature.

The patterns of the CO2 exchange of single vegetative bean plants were monitored during steady state exchange and after lowering the irradiance, the CO2 concentration, or the temperature. The measured patterns were used to calculate the dynamics of the rate of synthesis of structural dry matter and of the amount of the reserve materials during the experiments. The rate of synthesis of structural dry matter was assumed to be proportional to growth respiration (total minus maintenance). The growth conversion efficiency was assumed to be independent of the treatments. The maintenance respiration coefficient was taken to be dependent only on the temperature. Change in the amounts of reserve materials was calculated as a difference between the net CO2 input and the amount converted into new structural dry matter.During the first day of a low CO2 uptake a substantial depletion of reserve materials took place also during light hours, since the rate of synthesis of structural dry matter lagged behind the decrease of photosynthesis. On the second day the rate of synthesis was adapted to the low CO2 input and there occurred little change in the amount of reserve materials. There was a rapid increase in the amount of reserve materials after the irradiance was increased again or after temperature was lowered.A saturating dependence of the specific growth rate on the content of reserve materials was found to exist irrespective of the mode of changing the content of reserve materials. A hysteresis-like retardation of the specific growth rate took place after the reserve had already been exhausted for some time. During retardation a replenishment of reserve materials took place.It is suggested that adaptation processes tend to keep the content of reserve materials within a certain (probably optimal) range.