M. Nahm

Seasonal courses of key parameters of nitrogen, carbon and water balance in European beech (Fagus sylvatica L.) grown on four different study sites along a European North–South climate gradient during the 2003 drought

During the growing season of the exceptionally dry and warm year 2003, we assessed seasonal changes in nitrogen, carbon and water balance related parameters of mature naturally grown European beech (Fagus sylvatica L.) along a North–South transect in Europe that included a beech forest stand in central Germany, two in southern Germany and one in southern France. Indicators for N balance assessed at all four sites were foliar N contents and total soluble non-protein nitrogen compounds (TSNN) in xylem sap, leaves and phloem exudates; C and water balance related parameters determined were foliar C contents, δ13C and δ18O signatures. Tissue sampling was performed in May, July and September. The N related parameters displayed seasonal courses with highest concentrations during N remobilization in May. Decreased total foliar N contents as well as higher C/N ratios in the stands in central Germany and southern France compared to the other study sites point to an impaired N nutrition status due to lower soil N contents and precipitation perception. TSNN concentrations in leaves and phloem exudates of all study sites were in ranges previously reported, but xylem sap content of amino compounds in July was lower at all study sites when compared to literature data (c. 1 μmol N mL−1). In September, TSNN concentrations increased again at the two study sites in southern Germany after a rain event, whereas they remained constant at sites in central Germany and southern France which hardly perceived precipitation during that time. Thus, TSNN concentrations in the xylem sap might be indicative for water balance related N supply in the beech trees. TSNN profiles at all study sites, however, did not indicate drought stress. Foliar δ13C, but not foliar C and δ18O followed a seasonal trend at all study sites with highest values in May. Differences in foliar δ13C and δ18O did not reflect climatic differences between the sites, and are attributed to differences in altitude, photosynthesis and δ18O signatures of the water sources. Except of low TSNN concentrations in the xylem sap, no physiological indications of drought stress were detected in the trees analysed. We suppose that the other parameters assessed might not have been sensitive to the drought events because of efficient regulation mechanisms that provide a suitable physiological setting even under conditions of prolonged water limitation. The uniform performance of the trees from southern France and central Germany under comparably dry climate conditions denotes that the metabolic plasticity of mature beech from the different sites studied might be similar.

Ecophysiology of selected tree species in different plant communities at the periphery of the Atlantic Forest of SE Brazil I. Performance of three different species of Clusia in an array of plant communities

Three species of Clusia, namely two CAM-species (C. hilariana Schlecht. and C. fluminensis Planch. et Triana) and a C3-species (C. parviflora Saldanha et Engl.) were studied in different plant communities at the periphery of the Atlantic Forest in the state of Rio de Janeiro, Brazil. The sites chosen were an inselberg (C. parviflora), a range of wet restinga – dry restinga – semideciduous dry forest (C. fluminensis), and a gradient from the sea shore inland with a first sand dune beach ridge – a dry forest – a second beach ridge (C. hilariana). Analyses comprised C and N contents, soluble carbohydrates, soluble nonprotein N compounds and carbon isotope ratios (δ13C) in leaves, roots, phloem and wood. Photosynthetic performance was assessed by chlorophyll fluorescence with measurements of instant photosynthetic yield as well as light dependence and potential quantum-use efficiency of photosystem II.The data allow, first, to discuss differences between the ecophysiological performance of C3- and CAM-species of Clusia. The C3-species, C. parvifolia, had an overall weaker performance than the two CAM-species, where, however, the effects of mode of photosynthesis may have been overlaid by site conditions. Second, it was studied whether ecophysiological performance relates to patterns of local abundance, which was confirmed by showing that the dominant Clusia species of the restingas, C. hilariana, showed the strongest performance overall.Finally, it was studied whether the ecophysiological performance varied in response to site-dependent gradients of environmental water relations, which was confirmed for functions such as photosynthetic capacity, photoinhibition and solute accumulation of C. hilariana and C. fluminensis in relation to moisture of sites.

In situ measurements of carbon and nitrogen distribution and composition, photochemical efficiency and stable isotope ratios in Araucaria angustifolia

Araucaria angustifolia (Bertol.) Kuntze is an indigenous conifer restricted to the southern region of South America. In this on-site field study, we provide a detailed description of the nitrogen compounds and sugars allocated to the different plant compartments in tall adult trees, young trees about 2–3 m tall and small seedlings at its northernmost occurrence in the mountains of Itatiaia (20°25′S; 44°50′W; 2,000 m a.s.l.), SE Brazil. We determined C and N contents, soluble sugars, soluble non-protein N-compounds and δ15 N-signatures in leaves, roots, wood of stems, xylem- and phloem- sap. We also measured chlorophyll a fluorescence of photosystem II and carbon isotope discrimination reflecting photosynthetic activity and water-use efficiency. The high C and N concentrations in fine roots suggest that they are important reservoirs of N and C. Most nitrogen taken up from the soil was metabolised in the roots. The only inorganic nitrogen form detectable in the xylem sap was a small amount of ammonium. Glutamine was the dominant transport form of nitrogen in the xylem, while glutamate and the amides glutamine and asparagine were the most abundant soluble N compounds in the phloem. Total soluble non-protein N and sugar concentrations were significantly higher in the phloem of adult trees. In this particular site, A. angustifolia was apparently not exposed to water stress, as indicated by the high values of carbon isotope discrimination. The three developmental stages were clearly separated in terms of photosynthetic performance. Indeed, effective quantum yield of photosystem II increased from seedlings to adult trees under ambient irradiance.