Carbon isotope fractionation in metabolic processes following carboxylation of ribulose-1,5-bisphosphate (RuBP) is not as well described as the discrimination during photosynthetic CO2 fixation. However, post-carboxylation fractionation can influence the diel variation of d

Summary• The effects of drought on European beech ( Fagus sylvatica ) were assessed in a pot experiment under controlled conditions.• Plants from 11 autochthonous provenances originating from regions in Germany, which differed in annual precipitation, were exposed to a 3-wk drought period in a glasshouse after the first stage of shoot growth had been completed.• Drought reduced the water content to 97% of control in leaves and axes and to 92% in the roots. A strong reduction of predawn water potential in roots and shoots, as well as on transpiration rate, was found. In the roots, the effect on water potential was the same for all provenances, but differences were observed in the shoot water potential. Leaf concentrations of abscisic acid (ABA), proline and sucrose increased in the drought-treated plants compared with the controls.• Two extreme clusters from opposite climatic sites were identified by cluster analysis. A drought-sensitive cluster, originating from regions with high annual precipitation, had low water potential and transpiration rates, as well as high concentrations of fructose, ABA and proline after drought. Water potential and transpiration rates were less affected by drought in the other cluster, which comprised two provenances of relatively dry habitats, and concentrations of hexose, ABA and proline were low.

Summary• Competitive interactions between European beech ( Fagus sylvatica L.) seedlings and the early successional species Rubus fruticosus , and the role of water availability, are reported and discussed in relation to management practices and climatic changes in beech ecosystems of Central Europe.• Responses of growth, water status, gas exchange and carbon isotope composition ( δ 13 C) to two competition and three irrigation treatments were examined in a factorial-design glasshouse study.• Under regular irrigation, coexistence with R. fruticosus did not significantly affect growth, water potential and gas exchange of beech seedlings. However, moderate water shortage caused a twofold reduction in beech biomass and changes in root : shoot ratios. Drought lowered transpiration rates and predawn water potentials (below the xylem embolism threshold) for F. sylvatica ; δ 13 C of leaves and fine roots increased (discrimination was reduced). By contrast, significantly lower δ 13 C of R. fruticosus foliage indicated an improved water status. Competitive interference intensified the effects of reduced irrigation.• Water availability regulates the competitive interactions between beech seedlings and R. fruticosus . Natural regeneration of beech seedlings may be inhibited by interference from a species such as R. fruticosus , especially during summer drought, as predicted by actual climate models.

overall process of solute transport than do changes in mass flow. Due to transport behaviour, the chemical composition of leaves varied during the day only with regard to starch and soluble carbohydrates.

No abstract

No abstract

Phloem is a central conduit for the distribution of photoassimilate, nutrients, and signals among plant organs. A revised technique was used to collect phloem sap from small woody plants in order to assess changes in composition induced by water deficit and flooding. Bled phloem sap δ13C and sugar concentrations were compared to δ13C of bulk material, soluble carbon extracts, and the neutral sugar fraction from leaves. Amino acid composition and inorganic ions of the phloem sap was also analysed. Quantitative, systematic changes were detected in phloem sap composition and δ13C in response to altered water availability. Phloem sap δ13C was more sensitive to changes of water availability than the δ13C of bulk leaf, the soluble carbon fraction, and the neutral soluble fraction of leaves. Changes in water availability also resulted in significant changes in phloem sugar (sucrose and raffinose), inorganic nutrient (potassium), and amino acid (phenylalanine) concentrations with important implications for the maintenance of phloem function and biomass partitioning. The differences in carbohydrate and amino acid composition as well as the δ13C in the phloem, along with a new model system for phloem research, offer an improved understanding of the phloem-mediated signal, nutrient, and photoassimilate transduction in relation to water availability.

Beech seedlings from 11 German climatic provenances were exposed to a realistically timed drought treatment in a greenhouse experiment. The stable isotope composition of carbon (C) and nitrogen (N) was analysed in pooled bulk material of roots, stems and leaves, as well as in the aqueous extracts and starch fractions. The δ δ δ δ 13 C values increased in bulk samples (BS) of roots, stems and leaves by drought, although no leaf growth occurred during the experimental period. A clear drought effect on δ δ δ δ 13 C in aqueous extracts was detected in leaves. In aqueous extracts of stems and roots as well as in starch fractions of all organs, abundance of δ δ δ δ 13 C also tended to be increased by drought, but this effect was not statistically significant. For both δ δ δ δ 13 C and δ δ δ δ 15 N, enrichment was observed from the site of uptake/ source to the site of use/sink. A gradient for δ δ δ