Michael Tausz

Increasing CO2 threatens human nutrition

Dietary deficiencies of zinc and iron are a substantial global public health problem. An estimated two billion people suffer these deficiencies, causing a loss of 63 million life-years annually. Most of these people depend on C3 grains and legumes as their primary dietary source of zinc and iron. Here we report that C3 grains and legumes have lower concentrations of zinc and iron when grown under field conditions at the elevated atmospheric CO2 concentration predicted for the middle of this century. C3 crops other than legumes also have lower concentrations of protein, whereas C4 crops seem to be less affected. Differences between cultivars of a single crop suggest that breeding for decreased sensitivity to atmospheric CO2 concentration could partly address these new challenges to global health.

Extraordinary drought of 2003 overrules ozone impact on adult beech trees (Fagus sylvatica)

The extraordinary drought during the summer of 2003 in Central Europe allowed to examine responses of adult beech trees (Fagus sylvatica) to co-occurring stress by soil moisture deficit and elevated O3 levels under forest conditions in southern Germany. The study comprised tree exposure to the ambient O3 regime at the site and to a twice-ambient O3 regime as released into the canopy through a free-air O3 fumigation system. Annual courses of photosynthesis (Amax), stomatal conductance (gs), electron transport rate (ETR) and chlorophyll levels were compared between 2003 and 2004, the latter year representing the humid long-term climate at the site. ETR, Amax and gs were lowered during 2003 by drought rather than ozone, whereas chlorophyll levels did not differ between the years. Radial stem increment was reduced in 2003 by drought but fully recovered during the subsequent, humid year. Comparison of AOT40, an O3 exposure-based risk index of O3 stress, and cumulative ozone uptake (COU) yielded a linear relationship throughout humid growth conditions, but a changing slope during 2003. Our findings support the hypothesis that drought protects plants from O3 injury by stomatal closure, which restricts O3 influx into leaves and decouples COU from high external ozone levels. High AOT40 erroneously suggested high O3 risk under drought. Enhanced ozone levels did not aggravate drought effects in leaves and stem.

Summer-time distribution of air pollutants in Sequoia National Park, California.

Concentrations of air pollutants were monitored during the May November 1999 period on a network of forested sites in Sequoia National Park, California. Measurements were conducted with: (1) active monitors for nitric oxide (NO), nitrogen dioxide (NO2) and ozone (O3); (2) honeycomb denuder/filter pack systems for nitric acid vapor (HNO3), nitrous acid vapor (HNO2), ammonia (NH3), sulfur dioxide (SO2), particulate nitrate (NO3-), ammonium (NH4+), and sulfate (SO4(2-)); and (3) passive samplers for O3, HNO3 and NO2. Elevated concentrations of O3 (seasonal means 41-71 ppb), HNO3 (seasonal means 0.4-2.9 microg/m3), NH3 (seasonal means 1.6-4.5 microg/m3), NO3 (1.1-2.0 microg/m3) and NH4+ (1.0-1.9 microg/m3) were determined. Concentrations of other pollutants were low. With increasing elevation and distance from the pollution source area of O3, NH3 and HNO3 concentrations decreased. Ammonia and NH4+ were dominant N pollutants indicating strong influence of agricultural emissions on forests and other ecosystems of the Sequoia National Park.

Significance of Glutathione to Plant Adaptation to the Environment

Preface. 1. Glutathione - An ancient metabolite with modern tasks H. Rennenberg. 2. Chemistry of glutathione W. Wonisch, R.-J. Schaur. 3. The molecular biology and metabolism of glutathione C.H. Foyer, G. Noctor. 4. The role of glutathione in the uptake and metabolism of sulfur and selenium J.W. Anderson, P.J. McMahon. 5. The role of glutathione in plant response and adaptation to natural stress M. Tausz. 6. The role of glutathione in plant reaction and adaptation to excess metals W.E. Rauser. 7. The role of glutathione and glutathione S-transferases in plant reaction and adaptation to xenobiotics P. Schroder. 8. The role of glutathione in plant reaction and adaptation to air pollutants L.J. De Kok, M. Tausz. 9. The role of glutathione and glutathione-related enzymes in plant-pathogen interactions G. Gullner, T. Komives. 10. Aspects of glutathione in the interaction between plants and animals E. Schnug, C. Sator. Index.

Changes in antioxidant and pigment pool dimensions in UV-B irradiated maize seedlings

Abstract Ultraviolet-B (UV-B) radiation (280–320 nm) is an environmental challenge affecting a number of metabolic functions through the generation of reactive oxygen species (ROS). Plants protect themselves from this harmful radiation by synthesizing flavonoids, which act as a screen inside the epidermal cell layer, and by making adjustments to the antioxidant systems at both cell and whole organism level. This study describes the flavonoid content, the photosynthetic pigment composition and the proline, tocopherol and ascorbate content in UV-B exposed maize plants. Following exposure, the tocopherol content was slightly, but significantly lower, pointing to the membrane environment as a primary target for UV-B radiation. The water-soluble antioxidant content was largely unaffected, but an enhanced turnover in the ascorbate–glutathione cycle might be needed for tocopherol regeneration.

Effects of drought on needle anatomy of Pinus canariensis

Summary The needles of Pinus canariensis exhibit morphological drought adaptations, such as special stomata morphology or rigid sclerenchymatic hypodermis. In the present paper the hypothesis that drought exposure during needle elongation triggers formation of xeromorphic traits was tested. With onset of the elongation growth of the new flush, 5-year old P. canariensis seedlings were exposed to 53 days of reduced water supply under controlled climate chamber conditions. The treatment resulted in a decrease of needle water potentials from –1.5 MPa to −4 MPa in drought stressed plants, whereas no change was observed in water potentials of control needles. Needles of drought exposed trees remained shorter and thinner. Cross-sections of elongating needles taken at 1 cm distance from the needle base were taken repeatedly during the experiment. Cross-section areas of different needle tissues were measured in an image analysis system. In needles of drought stressed trees sclerenchymatic tissues in the hypodermis and adjacent to the vascular bundles increased due to large increases in the number – not the size – of sclerenchymatic cells. The ratio of assimilation parenchyma to the vascular bundle (supplied versus supplying tissue) decreased. We conclude that these changes, which adapt needles to drought conditions, are triggered by drought stress experienced while needles are growing.

Responses of foliar antioxidative and photoprotective defence systems of trees to drought: a meta-analysis

Current climate change predictions hint to more frequent extreme weather events, including extended droughts, making better understanding of the impacts of water stress on trees even more important. At the individual plant level, stomatal closure as a result of water deficit leads to reduced CO2 availability in the leaf, which can lead to photo-oxidative stress. Photorespiration and the Mehler reaction can maintain electron transport rates under low internal CO2, but result in production of reactive oxygen species (ROS). If electron consumption is decreased, upstream photochemical processes can be affected and light energy is absorbed in excess of photochemical requirements. Trees evolved to cope with excess energy and elevated concentration of ROS by activating photoprotective and antioxidative defence systems. The meta-analysis we present here assessed responses of these defence systems reported in 50 studies. We found responses to vary depending on stress intensity, foliage type and habitat, and on whether experiments were done in the field or in controlled environments. In general, drought increased concentrations of antioxidants and photoprotective pigments. However, severe stress caused degradation of antioxidant concentrations and oxidation of antioxidant pools. Evergreen trees seemed to preferentially reinforce membrane-bound protection systems zeaxanthin and tocopherol, whereas deciduous species showed greater responses in water-soluble antioxidants ascorbic acid and glutathione. Trees and shrubs from arid versus humid habitats vary in their antioxidative and photoprotective defence responses. In field experiments, drought had greater effects on some defence compounds than under controlled conditions.

Will intra-specific differences in transpiration efficiency in wheat be maintained in a high CO2 world? A FACE study

This study evaluates whether the target breeding trait of superior leaf level transpiration efficiency is still appropriate under increasing carbon dioxide levels of a future climate using a semi-arid cropping system as a model. Specifically, we investigated whether physiological traits governing leaf level transpiration efficiency, such as net assimilation rates (A(net)), stomatal conductance (g(s)) or stomatal sensitivity were affected differently between two Triticum aestivum L. cultivars differing in transpiration efficiency (cv. Drysdale, superior; cv. Hartog, low). Plants were grown under Free Air Carbon dioxide Enrichment (FACE, approximately 550 µmol mol⁻¹ or ambient CO₂ concentrations (approximately 390 µmol mol⁻¹). Mean A(net) (approximately 15% increase) and gs (approximately 25% decrease) were less affected by elevated [CO₂] than previously found in FACE-grown wheat (approximately 25% increase and approximately 32% decrease, respectively), potentially reflecting growth in a dry-land cropping system. In contrast to previous FACE studies, analyses of the Ball et al. model revealed an elevated [CO₂] effect on the slope of the linear regression by 12% indicating a decrease in stomatal sensitivity to the combination of [CO₂], photosynthesis rate and humidity. Differences between cultivars indicated greater transpiration efficiency for Drysdale with growth under elevated [CO₂] potentially increasing the response of this trait. This knowledge adds valuable information for crop germplasm improvement for future climates.

Photostress, photoprotection, and water soluble antioxidants in the canopies of five Canarian laurel forest tree species during a diurnal course in the field

Minimal relative water contents of more than 85% indicated that dehydration was not a stress factor. Stomatal conductances decreased from 150 to 200 mmol H 2 O m –2 s –1 in the morning to about 50 mmol H 2 O m –2 s –1 during the day in all species, but this did not limit CO 2 uptake. De-epoxidation of xanthophylls only occurred in sun leaves of I. canariensis (to more than 50%) and M. faya (more than 60%). Decreases in Fv/Fm were only found in sun leaves of P. indica (from ca. 0.80 in the morning to a minimum of 0.70) and, as a trend, also in L. azorica (from ca. 0.75 to ca. 0.65). I. perado showed neither of those responses. P. indica and L. azorica exhibited the highest photosynthesis rates of about 10 µmol CO2 m –2 s –1 compared to 8 in the other species. The photoprotection strategy of P. indica and L. azorica admitted slow recovery from photoinhibition, did not activate protective energy dissipation through xanthophylls, and allowed highest production under these typical conditions.

Photosynthetic capacity of Eucalyptus globulus is higher when grown in mixture with Acacia mearnsii

Mixed species plantations of Eucalyptus and N2-fixing species can be significantly more productive than monocultures. The aim of this study was to determine whether the improved growth resulted from increases in photosynthesis, light absorption and light-use efficiency, in addition to previously measured increases in leaf area, water-use efficiency and higher ratios of annual above-ground net primary production per unit of total annual below-ground carbon allocation in 1:1 mixtures near Cann River, Victoria, Australia. Light-saturated photosynthetic rate (Amax), electron transport (J), stomatal conductance (gs) and foliar nitrogen concentrations were higher for Eucalyptus globulus trees growing in mixtures than those in monocultures. Similar increases in maximum rates of carboxylation (Vcmax), Rubisco, chlorophyll, and phosphorus concentrations were not significant. In contrast, Amax, Vcmax and J did not vary between mixtures and monocultures for A. mearnsii, whose growth was negligible by age 15 years. Mixtures also absorbed 24 and 41% more light than E. globulus and A. mearnsii., respectively, and were 38 and 154% more light-use efficient in the mixtures compared to monocultures. The increased nutrient availability in mixtures appeared to increase productivity of E. globulus by increasing the photosynthetic capacity of the foliage, as well as the leaf area, light absorption and light-use efficiency of the canopy.