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Increasing soil salinity is a major threat to crop production in many agricultural areas throughout the world. Although sodium chloride (NaCl) is one of the most abundant salts in soils, others viz. sulfate salts may also be present in high concentrations in some soil types. Sulfate salts, e.g. Na2SO4, are still widely under-represented amongst salt stress studies and the mechanism of its toxicity is poorly understood. Exposure of Chinese cabbage to Na2SO4 already reduced growth at levels ≥20 mM, accompanied by an increase in the total sulfur content of both roots and shoots, which in the shoot for a greater part could be ascribed to an accumulation of sulfate. Moreover, there was an increase in the total water-soluble non-protein thiol content (glutathione) in roots and shoots. Enhanced sulfur metabolite levels (sulfate, glutathione) would down-regulate the expression and activity of the sulfate transporters and APS reductase (glutathione). Indeed, Na2SO4 exposure resulted in a down-regulation of the sulfate uptake capacity of the roots at ≥5 mM, whereas the transcript level of the sulfate transporters Sultr1;2 and Sultr4;1 and APS reductase in the roots was reduced at ≥20 mM. Apparently in the shoot this regulatory signal transduction pathway was overruled by the toxic effects of Na2SO4, since in contrast to the roots, the transcript levels of Sultr4;1 and APS reductase were enhanced in the shoot at ≥30 mM and ≥5 mM Na2SO4, respectively.

The competitiveness of young beech (Fagus sylvatica) and spruce plants (Picea abies) was analysed using cost/benefit ratios (efficiency ratios) related to (1) the efficiency of space sequestration (i.e. occupied aboveground space per unit of resource investment, e.g. biomass), (2) efficiency of resource gain (i.e. resource acquisition per unit of resource investment or occupied above or belowground space) and, (3) efficiency of “running costs” in terms of respiration and transpiration per unit of sequestered above and belowground space for sustaining the structural functionality related to competition. In 1998, two and three-year-old beech and spruce individuals, respectively, were planted in mixed and monocultures in containers that were filled with forest soil. Although each container was harboured with 20 trees, and measurements were concentrated on the six central plants. In 1999 and 2000, the containers were placed into the phytotrons at ambient and elevated CO2 concentrations in combination with ambient (1xO3) and twice-ambient (2xO3) ozone levels, resulting in four CO2/O3 gaseous regimes. Elevated levels of CO2 and O3 were used as disturbants to provoke changes in growth and resource allocation in order to more readily distinguish and derive underlying mechanisms of relevance for competitiveness from plant response. Four hypotheses were tested: (1) the competitiveness of beech rather than spruce is affected by the elevated O3 regime, whereas (2) spruce profits from the increase in resource availability (CO2) in mixed culture. However, (3) tree responses to CO2 and O3 depend on the type of competition (i.e. intra or interspecific). (4) The competitive ability of plants can be characterized and quantified in terms of the introduced efficiency ratios of competitiveness. In the studied plant systems, spruce was a better competitor than beech. After two growing seasons in the phytotrons, beech plants in mixed plantation showed significant reduction in above- and b, In der vorliegenden Arbeit wurde das Konkurrenzverhalten junger Buchen- und Fichtenindividuen durch Kosten/Nutzen-Bilanzen bezüglich der Effizienz (1) der Raumbesetzung (d.h. besetzter oberirdischer Raum pro Ressourceninvestition, z.B. von Biomasse), (2) des Ressourcengewinns (d.h. Ressourcenaufnahmen pro Ressourceninvestition oder pro besetztem ober- oder unterirdischem Raum) und (3) der laufenden Kosten (im Sinne von Atmung und Transpiration, die zum Strukturunterhalt aufgewendet werden pro besetztem ober- oder unterirdischem Raum) analysiert. Im Jahr 1998 wurden zwei- bzw. dreijährige Buchen- und Fichtenindividuen in Mono- und Mischkultur in Container mit Waldboden gepflanzt. In jeden Container (insgesamt 32) wurden 20 Bäume eingebracht, die Messungen aber auf die sechs zentralen Pflanzen konzentriert. In 1999 und 2000 wurden die Pflanzen im Phytotron unter ambientem und erhöhtem CO2 in Kombination mit ambientem und doppelt-ambientem Ozon behandelt. Das Wachstum und die Ressourcenallokation der Pflanzen sollten durch die eingebrachten CO2/O3-Regime gestört werden, um Änderungen hervorzurufen, die das Studium der zugrundeliegenden Mechanismen der Konkurrenz erleichtern. Insgesamt wurden vier Hypothesen geprüft: (1) Die Konkurrenzstärke der Buche im Gegensatz zur Fichte wird von erhöhtem O3 beeinflusst, während (2) die Fichte von der Zunahme der Ressourcenverfügbarkeit (CO2) in der Mischkultur profitiert. (3) Die Antworten der Bäume auf CO2 und O3 hängen von der Art der Konkurrenz (d.h. intra- oder interspezifisch) ab. (4) Das Konkurrenzverhalten der Pflanzen kann mit Hilfe der vorgestellten Effizienzen sinnvoll charakterisiert und quantifiziert werden. Fichte zeigt sich als der bessere Konkurrent gegenüber der Buche. Nach zwei Vegetationsperioden zeigte letztere in Mischpflanzung niedrigere ober- und unterirdische Biomasse, jährlichen Biomassenzuwachs und Kronenvolumen im Vergleich zur Monokultur. Im Gegensatz hierzu zeigte die Fichte bei interspezifischer Konkurr

The effects of local climate and silvicultural treatment on the inorganic N availability, net N uptake capacity of mycorrhizal beech roots and microbial N conversion were assessed in order to characterise changes in the partitioning of inorganic N between adult beech and soil microorganisms. Fine root dynamics, inorganic N in the soil solution and in soil extracts, nitrate and ammonium uptake kinetics of beech as well as gross ammonification, nitrification and denitrification rates were determined in a beech stand consisting of paired sites that mainly differed in aspect (SW vs. NE) and stand density (controls and thinning treatments). Nitrate was the only inorganic N form detectable in the soil water. Its concentration was high in control plots of the NE aspect, but only in canopy gaps and not influenced by thinning. Neither thinning nor aspect affected the abundance of root tips in the soil. Maximum nitrate net uptake by mycorrhizal fine roots of beech, however, differed with aspect, showing significantly lower values at the SW aspect with warm–dry local climate. There were no clear-cut significant effects of local climate or thinning on microbial N conversion, but a tendency towards higher ammonification and nitrification and lower denitrification rates on the untreated controls of the SW as compared to the NE aspect. Apparently, the observed sensitivity of beech towards reduced soil water availability is at least partially due to impaired N acquisition. This seems to be mainly a consequence of reduced N uptake capacity rather than of limited microbial re-supply of inorganic N or of changed patterns of inorganic N partitioning between soil bacteria and roots.

The competitiveness of young beech (Fagus sylvatica) and spruce plants (Picea abies) was analysed using cost/benefit ratios (efficiency ratios) related to (1) the efficiency of space sequestration (i.e. occupied aboveground space per unit of resource investment, e.g. biomass), (2) efficiency of resource gain (i.e. resource acquisition per unit of resource investment or occupied above or belowground space) and, (3) efficiency of “running costs” in terms of respiration and transpiration per unit of sequestered above and belowground space for sustaining the structural functionality related to competition. In 1998, two and three-year-old beech and spruce individuals, respectively, were planted in mixed and monocultures in containers that were filled with forest soil. Although each container was harboured with 20 trees, and measurements were concentrated on the six central plants. In 1999 and 2000, the containers were placed into the phytotrons at ambient and elevated CO2 concentrations in combination with ambient (1xO3) and twice-ambient (2xO3) ozone levels, resulting in four CO2/O3 gaseous regimes. Elevated levels of CO2 and O3 were used as disturbants to provoke changes in growth and resource allocation in order to more readily distinguish and derive underlying mechanisms of relevance for competitiveness from plant response. Four hypotheses were tested: (1) the competitiveness of beech rather than spruce is affected by the elevated O3 regime, whereas (2) spruce profits from the increase in resource availability (CO2) in mixed culture. However, (3) tree responses to CO2 and O3 depend on the type of competition (i.e. intra or interspecific). (4) The competitive ability of plants can be characterized and quantified in terms of the introduced efficiency ratios of competitiveness. In the studied plant systems, spruce was a better competitor than beech. After two growing seasons in the phytotrons, beech plants in mixed plantation showed significant reduction in above- and b, In der vorliegenden Arbeit wurde das Konkurrenzverhalten junger Buchen- und Fichtenindividuen durch Kosten/Nutzen-Bilanzen bezüglich der Effizienz (1) der Raumbesetzung (d.h. besetzter oberirdischer Raum pro Ressourceninvestition, z.B. von Biomasse), (2) des Ressourcengewinns (d.h. Ressourcenaufnahmen pro Ressourceninvestition oder pro besetztem ober- oder unterirdischem Raum) und (3) der laufenden Kosten (im Sinne von Atmung und Transpiration, die zum Strukturunterhalt aufgewendet werden pro besetztem ober- oder unterirdischem Raum) analysiert. Im Jahr 1998 wurden zwei- bzw. dreijährige Buchen- und Fichtenindividuen in Mono- und Mischkultur in Container mit Waldboden gepflanzt. In jeden Container (insgesamt 32) wurden 20 Bäume eingebracht, die Messungen aber auf die sechs zentralen Pflanzen konzentriert. In 1999 und 2000 wurden die Pflanzen im Phytotron unter ambientem und erhöhtem CO2 in Kombination mit ambientem und doppelt-ambientem Ozon behandelt. Das Wachstum und die Ressourcenallokation der Pflanzen sollten durch die eingebrachten CO2/O3-Regime gestört werden, um Änderungen hervorzurufen, die das Studium der zugrundeliegenden Mechanismen der Konkurrenz erleichtern. Insgesamt wurden vier Hypothesen geprüft: (1) Die Konkurrenzstärke der Buche im Gegensatz zur Fichte wird von erhöhtem O3 beeinflusst, während (2) die Fichte von der Zunahme der Ressourcenverfügbarkeit (CO2) in der Mischkultur profitiert. (3) Die Antworten der Bäume auf CO2 und O3 hängen von der Art der Konkurrenz (d.h. intra- oder interspezifisch) ab. (4) Das Konkurrenzverhalten der Pflanzen kann mit Hilfe der vorgestellten Effizienzen sinnvoll charakterisiert und quantifiziert werden. Fichte zeigt sich als der bessere Konkurrent gegenüber der Buche. Nach zwei Vegetationsperioden zeigte letztere in Mischpflanzung niedrigere ober- und unterirdische Biomasse, jährlichen Biomassenzuwachs und Kronenvolumen im Vergleich zur Monokultur. Im Gegensatz hierzu zeigte die Fichte bei interspezifischer Konkurr

Sulphate leaching losses may reduce the long-term possibility of maintaining the S supply of crops in low input farming systems. In order to maintain a sufficient S supply in the future when further reductions in the atmospheric deposition are expected, it is important to reduce leaching losses of sulphate. As leaching primarily occurs during autumn and winter, a plant cover in this period must be expected to affect the quantity of S leached. It has been demonstrated that a catch crop succeeding the main crop can absorb nitrate from the root zone during autumn and winter and thereby reduce nitrate leaching (Thorup-Kristensen and Nielsen 1998). Similar beneficial effects of catch crops on sulphate leaching may be expected. The ability of catch crops (Italian ryegrass [Lolium multiflorum Lam], winter rape [Brassica napus L.] and fodder radish [Raphanus sativus L.]) to reduce soil sulphate concentrations in autumn and make it available to a succeeding crop was investigated in a field experiment on sandy loam soil, as described by Eriksen and Thorup-Kristensen (2002). All catch crops reduced soil sulphate concentrations in the autumn compared to bare soil (Fig. 1). Especially the cruciferous catch crops had the ability to deplete efficiently soil sulphate levels and thus, reduce the sulphate leaching potential. The S uptake in aboveground catch crop was 8, 22 and 36 kg S ha-1 for ryegrass, winter rape and fodder radish, respectively. In the following spring, sulphate levels of the autumn bare soil were low in the top 0.5 m and a peak of sulphate was found at 0.75-1 m depth (Fig. 1). In contrast, where a fodder radish catch crop had been grown, high sulphate levels were present in the top 0.5 m but only small amounts of sulphate were found at 0.5-1.5 m depth. The release of S to barley (Hordeum vulgare L.) were investigated in pot experiments (setup described by Eriksen et al. 1995) after incorporation of the catch crops Cichorium intybus L., Medicago lupulina L., Anthyl