A branch bag and CO2 control system for long-term CO2 enrichment of mature Sitka spruce [Picea sitchensis (Bong.) Carr.]

This paper describes the construction and performance of branch bags and a CO₂ control system used to fumigate branches of mature Sitka spruce trees with air enriched in CO₂ (700 μmolmol^-1). It contains some examples of results obtained using the system over the course of the first two growing seasons. The branch bags have run continuously for 2 years with very few problems. CO₂ concentrations were within 20 μmol mol^-1 of the target concentration for more than 90% of the time. Temperatures within the bags were slightly higher than ambient (1–2 °C) and this had some effect on phenology. Attenuation of quantum flux density (photosynthetically active radiation) was 10–15%. The branch bag system has enabled investigation into the effects of elevated CO₂ on mature tissue without the problems and expense of fumigating whole trees. Growth in elevated CO₂ resulted in an increase in starch and a decrease in soluble protein content of needles. Stomatal conductance was higher in elevated CO₂ grown needles, and there was some evidence of an increase in photosynthetic capacity.     

Competition increasingly dominates the responsiveness of juvenile beech and spruce to elevated CO2 and/or O3 concentrations throughout two subsequent growing seasons

Saplings of Fagus sylvatica and Picea abies were grown in mono‐ and mixed cultures in a 2‐year phytotron study under all four combinations of ambient and elevated ozone (O₃) and carbon dioxide (CO₂) concentrations. The hypotheses tested were (1) that the competitiveness of beech rather than spruce is negatively affected by the exposure to enhanced O₃ concentrations, (2) spruce benefits from the increase of resource availability (elevated CO₂) in the mixed culture and (3) that the responsiveness of plants to CO₂ and O₃ depends on the type of competition (i.e. intra vs. interspecific). Beech displayed a competitive disadvantage when growing in mixture with spruce: after two growing seasons under interspecific competition, beech showed significant reductions in leaf gas exchange, biomass development and crown volume as compared with beech plants growing in monoculture. In competition with spruce, beech appeared to be nitrogen (N)‐limited, whereas spruce tended to benefit in terms of its plant N status. The responsiveness of the juvenile trees to the atmospheric treatments differed between species and was dominated by the type of competition: spruce growth benefited from elevated CO₂ concentrations, while beech growth suffered from the enhanced O₃ regime. In general, interspecific competition enhanced these atmospheric treatment effects, supporting our hypotheses. Significant differences in root : shoot biomass ratio between the type of competition under both elevated O₃ and CO₂ were not caused by readjustments of biomass partitioning, but were dependent on tree size. Our study stresses that competition is an important factor driving plant development, and suggests that the knowledge about responses of plants to elevated CO₂ and/or O₃, acquired from plants growing in monoculture, may not be transferred to plants grown under interspecific competition as typically found in the field.     

Effect of low temperatures on the activity of oxygen-scavenging enzymes in two populations of the C4 grass Echinochloa crus-galli

To discriminate among possible mechanisms responsible for the differential response to cold temperatures among ecotypes of the C₄ grass weed species Echinochloa crus-galli (L.) Beauv., the specific activities of five oxygen-scavenging enzymes responsible for the elimination or reduction of free radicals and hydrogen peroxide during cold-induced photoinhibition were determined in 5-week-old plants of two populations of the species collected from sites of contrasting climates, Québec (QUE) and Mississippi (MISS). Enzyme activities were measured at temperatures ranging from 5 to 30°C. The specific activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase were significantly higher in cold-adapted QUE plants at low assay temperatures than in warm-adapted MISS plants at the same temperature. The specific activities of superoxide dismutase assayed at 5 and 25°C were similar among plants of the two E. crus-galli populations. Ascorbate concentrations were not different among plants of the two populations, suggesting that the observed differences in the specific activities of ascorbate peroxidase assayed at 5°C, truly reflect a better capacity of the QUE enzyme to reduce H₂O₂ to water at temperature conditions associated with the photoinhibitory process. The enhanced specific activity of four of the five oxygen-scavenging enzymes measured in the cold-adapted QUE population at low assay temperatures correlates with the syndrome of cold-adapted features reported for plants of this population in earlier studies.     

The effects of SO2 and O3 on the foliar nutrition of Scots pine, Norway spruce and Sitka spruce in the Liphook open-air fumigation experiment

Foliar elements were analysed in Scots pine, Sitka spruce and Norway spruce over a 6 year period before and during continuous exposure to SO₂ and O₃ in an open-air fumigation experiment. Sulphur dioxide treatment elevated foliar sulphur concentration in all species, and there were increases in foliar nitrogen in the two spruce species but not in pine. The concentrations of cations were frequently increased by SO₂ treatment, but there was no correlation between the sulphur concentration of needles and their total cation charge. SO₂-related elevations of foliar magnesium were correlated with the concentration of this element in soil solution, but the mechanism by which other cations were enhanced remains unclear. The only consistent effects on nutrient ratios were for SO₂ treatments to increase sulphur/cation ratios.     

Responses of antioxidative enzymes to elevated CO2 in leaves of beech (Fagus sylvatica L.) seedlings grown under a range of nutrient regimes

To study whether responses of antioxidative enzymes to enhanced atmospheric CO₂ concentrations are affected by plant nutrition, the activities of superoxide dismutase, catalase and peroxidase were investigated in leaves of 3-year-old beech trees grown with low (0.1 × optimum), intermediate (0.5 × optimum) and high (2 × optimum) nutrient supply rates in open-top chambers at either ambient (～ 355 μmol mol^?1) or elevated (700 μmol mol^?1) CO₂ concentrations. These treatments resulted in foliar C/N ratios of about 20 in the presence of high and > 30 in the presence of low nutrient supply rates. Pigment and malon-dialdehyde contents were determined to assess plant stress levels. Low nutrient supply rates caused pigment loss, whereas elevated CO₂ had no effect on pigmentation. Guaiacol peroxidase activities did not respond to either CO₂ or nutrient treatment. Catalase activity decreased with decreasing nutrient supply rate and also in response to elevated CO₂. Superoxidase dismutase activity was affected by both nutrient supply and CO₂ concentration. In leaves from trees grown with the high-nutrient treatment, superoxide dismutase activity was low irrespective of CO₂ concentration. In chlorotic leaves, superoxide dismutase activity was increased, suggesting an enhanced need for detoxification of reactive oxygen species. Leaves from plants grown under elevated CO₂ with medium nutrient supply rates showed decreased malondialdehyde contents and superoxide dismutase activities. This suggests that the intrinsic oxidative stress of leaves was decreased under these conditions. These results imply that intrinsic oxidative stress is modulated by the balance between N and C assimilation.     

Seasonal Changes of the Antioxidative Systems in Foliar Buds and Leaves of Field-grown Beech Trees (Fagus sylvatica,L.) in a Stressful Climate

The activities of superoxide dismutase, ascorbate peroxidase, monodehydroascorbate radical reductase, and dehydroascorbate reductase and the contents of ascorbate, chlorophyll and soluble protein were determined in beech (Fagus sylvatica, L.) foliage over two or three seasons. Four important stages of leaf development were distinguished: resting buds, emerging, mature and senescent leaves. Foliar buds in spring, prior to the emergence of new leaves, contained a lower chlorophyll content but a higher protein content and higher activities of ascorbate peroxidase and monodehydroascorbate radical reductase than mature leaves in summer. By contrast, superoxide dismutase and glutathione reductase activities and ascorbate contents were higher in mature leaves than in swollen foliar buds. Dehydroascorbate reductase activity was low in all developmental stages. Resting buds in winter contained activities of superoxide dismutase, ascorbate peroxidase and monodehydroascorbate radical reductase that were similar to those found in mature leaves in summer, whereas the contents of total and reduced ascorbate were 6- and 20-times lower, respectively, in buds than in mature leaves. The low foliar concentration of reduced ascorbate in resting buds, despite high monodehydroascorbate radical reductase activity, suggests that the regeneration of ascorbate might be limited by the availability of reductant. High antioxidative capacity was conferred by mature beech leaves and may be an important protection measure for coping with the large fluctuations in temperature and exposure to elevated ozone concentrations in summer.     

Physiological and biochemical response of potato (Solanum tuberosum L. cv. Kara) to O3 and antioxidant chemicals: possible roles of antioxidant enzymes

An Egyptian cultivar of potato (Solanum tuberosum L. cv. Kara) was grown in the field at two locations in northern Egypt: a ‘rural’ and a ‘suburban’ site, from October 2000 and November 2002. The antiozonant ethylenediurea (EDU) and the fungicide chlorothalonil (1,3‐benzenedicarbonitrile‐2,4,5,6 tetrachloroisophthalnitrile) were applied as a foliar spray to plants at both sites. It was found that foliar injury symptoms were reduced greatly in plants treated with EDU and/or chlorothalonil, and the yield of treated plants was higher than that of the untreated ones, with the EDU having a greater protection than chlorothalonil. Antiozonant (EDU) and fungicide (chlorothalonil) combination sprays were even more effective in reducing O₃ injury. Moreover, the percentage of protection was higher in the rural area than in the suburban one, and this was associated with higher levels of O₃ recorded in the rural area. The response to O₃, EDU, and chlorothalonil of the leaf antioxidant scavenger system was examined. Antiozonant‐treated plants had the highest reduced glutathione/oxidised glutathione ratio. The results suggest that EDU and chlorothalonil do not act directly as antiozonant to inhibit O₃ injury but act through maintaining some antioxidant enzymes during O₃ exposure. To the best of knowledge, this is the first report demonstrating the marked enhancement of yield and plant oxidative enzymes by fungicides as a mechanism of protecting plants against noxious oxidative stress from the environment in the developing world.     

Antioxidant status of the potato tuber and Ca2+ deficiency as a physiological stress

The antioxidant status of potato ( Solanum tuberosum L.) tubers of two genotypes, cv. Désirée and clone 10337de40 was investigated in relation to susceptibility to internal rust spot (IRS), a Ca²⁺-related physiological disorder. Concentrations of total calcium within the perimedulla tissue of tubers, grown with a restricted (1 m M CaCl₂) Ca²⁺ supply, were similar in cv. Désirée (IRS resistant) and clone 10337de40 (IRS susceptible). A range of antioxidants was assayed in order to assess antioxidant status in both genotypes under the two Ca²⁺ treatments. Although no appreciable differences were detected between low Ca²⁺ and control treatments, certain antioxidants were present at significantly higher levels in the IRS resistant genotype, cv. Désirée. These included dehydroascorbate reductase (EC 1.8.5.1) activity (more than 100% higher), total glutathione content (ca 40% higher), glutathione reductase (EC 1.6.4.2) activity (almost 50% higher), peroxidase (EC 1.11.1.7) activity (ca 60% higher) and superoxide dismutase (EC 1.15.1.1) activity (almost 80% higher). There was no difference in ascorbate content, ascorbate free radical reductase activity (EC 1.6.5.4), α-tocopherol levels and catalase activity (EC 1.11.1.6) between the two genotypes. The possible relationship between resistance to IRS and a superior antioxidant status, found in cv. Désirée, is discussed.     

NO2‐induced nitrate reductase activity in needles of Norway spruce (Picea abies) under laboratory and field conditions

The induction of activity of the enzyme nitrate reductase (NR, EC 1.6.6.1, 1.6.6.2) in needles of Norway spruce ( Picea abies [L.] Karst.) by nitrogen dioxide (NO₂) was studied under laboratory and field conditions. In fumigation chambers an increase in nitrate reductase activity (NRA) was detected 4 h after the start of the NO₂ treatment. During the first 2 days with 100 µg NO₂ m⁻³, NRA reached a constant level and did not change during the following 4 days. At the same level of NO₂, NRA was lower in needles from trees grown on NPK‐fertilized soil than on non‐fertilized soil. After the transfer of spruce trees from fertilized soil to NPK‐rich nutrient solution, NRA was transiently increased. This effect was assigned to root injuries causing nitrate transport to the shoot and subsequent induction of NRA. Neither trees on fertilized soil nor trees transferred to NPK‐poor nutrient solution had increased NRA unless NO₂ was provided. The NO₂ gradient in the vicinity of a highway was used to test the long‐term effect of elevated levels of NO₂ on needle NRA of potted and field‐grown spruce trees. Compared with less polluted sites, permanently increased NRAs were detected when NO₂ concentrations were above 20 µg m⁻³. Controls of field measurements some 10 years after the introduction of catalytic converters in cars showed no significant change neither in NO₂ levels nor in the decreasing NRA of spruce needles with the distance from the highway.