Integrating effects of leaf nitrogen,age, rank,and growth temperature into the photosynthesis-stomatal conductance model LEAFC3-N parameterised for barley (Hordeum vulgare L.)

A crucial challenge for including biophysical photosynthesis–transpiration models into complex crop growth models is to integrate the plasticity of photosynthetic processes that is related to factors like nitrogen (N) content, age, and rank of leaves, or to the adaptation of plants to growth temperature (T_g). Here we present a new version of the combined photosynthesis-stomatal conductance model LEAFC3-N [Müller, J., Wernecke, P., Diepenbrock, W., 2005. LEAFC3-N: a nitrogen sensitive extension of the CO₂ and H₂O gas exchange model LEAFC3 parameterised and tested for winter wheat (Triticum aestivum L.). Ecological Modelling 183, 183–210.] that was revised, extended and completely re-parameterised for barley (Hordeum vulgare L.) with special regard for these factors to facilitate the use of the model in ecophysiological studies and in crop modelling. The analysis is based on novel comprehensive data on photosynthetic CO₂ and light response curves measured at two oxygen concentrations and different temperatures on leaves of barley (H. vulgare L.) differing in leaf N and chlorophyll content. Plants were grown in climatic chambers or in the field at different N and T_g.We thoroughly revised the existing and introduced new nitrogen relations for key model parameters that account for a linear increase with leaf N of V_max, J_max, T_p, and R_dmax (maximum rates of carboxylation, electron transport, triose phosphate export, and mitochondrial respiration), a saturation-type increase of φ (quantum yield of electron transport), and a non-linear decrease of θ and m (curvature of the light dependence of electron transport rate, scaling factor of the stomata model). The adaptation of photosynthetic characteristics to T_g was included into the model by linear relations that were observed between T_g and the activation energy ΔH_a of the temperature response characteristics of V_max, J_max, and T_p as well as of the nitrogen dependency of these characteristics. Based on an analysis of diurnal time courses of gas exchange rates it was found necessary including not only the relation between leaf water potential (Ψ) and stomatal conductance as used originally in LEAFC3, but additional effects on V_max and J_max. With the above-listed extensions, the model was capable to reproduce the observed plasticity and the recorded diurnal time courses of gas exchange rates fairly well. Thus, we conclude that the new model version can be used under a broad range of conditions, both for ecophysiological studies and as a submodel of crop growth models. The results presented here for barley will facilitate adapting photosynthesis models like LEAFC3-N to other C₃-species as well. The modelling of the effects of drought stress should be further elaborated in future based on more specific experiments.     

Risk assessment of an old landfill regarding the potential of gaseous emissions – A case study based on bioindication,FT-IR spectroscopy and thermal analysis

Risk assessment of two sections (I and II) of an old landfill (ALH) in Styria (Austria) in terms of reactivity of waste organic matter and the related potential of gaseous emissions was performed using conventional parameters and innovative tools to verify their effectiveness in practice. The ecological survey of the established vegetation at the landfill surface (plant sociological relevés) indicated no relevant emissions over a longer period of time. Statistical evaluation of conventional parameters reveals that dissolved organic carbon (DOC), respiration activity (RA₄), loss of ignition (LOI) and total inorganic carbon (TIC) mostly influence the variability of the gas generation sum (GS₂₁). According to Fourier Transform Infrared (FT-IR) spectral data and the results of the classification model the reactivity potential of the investigated sections is very low which is in accordance with the results of plant sociological relevés and biological tests. The interpretation of specific regions in the FT-IR spectra was changed and adapted to material characteristics. Contrary to mechanically–biologically treated (MBT) materials, where strong aliphatic methylene bands indicate reactivity, they are rather assigned to the CH vibrations of plastics in old landfill materials. This assumption was confirmed by thermal analysis and the characteristic heat flow profile of plastics containing landfill samples. Therefore organic carbon contents are relatively high compared to other stable landfills as shown by a prediction model for TOC contents based on heat flow profiles and partial least squares regression (PLS-R). The stability of the landfill samples, expressed by the relation of CO₂ release and enthalpies, was compared to unreactive landfills, archeological samples, earthlike materials and hardly degradable organic matter. Due to the material composition and the aging process the landfill samples are located between hardly degradable, but easily combustible materials and thermally resistant materials with acquired stability.     

Formation of chlorinated and brominated dioxins and other organohalogen compounds at the pilot incineration plant VERONA

Experiments were conducted at the VERONA pilot plant, an incineration plant with stationary grate and separate post-combustion chamber, using wood and propane as basic combustible materials and with controlled dosage of various bromine-, chlorine- and copper-containing compounds. The behaviour of the following compounds was studied in the combustion chamber, after the post-combustion chamber and after the heat exchanger: polychlorinated phenols (PCPh), polybrominated phenols (PBrPh), polychlorinated benzenes (PCBz), polybrominated benzenes (PBrBz), polychlorinated dioxins and furans (PCDD/F) and polybrominated dioxins and furans (PBDD/F). The bromine co-incineration leaded to very high bromophenol concentrations after the post-combustion chamber. The formation of brominated and mixed-halogenated phenols and the further reaction to halogenated dioxins is apparently a relevant reaction mechanism for dioxin formation in processes involving bromine. This assumption is supported by the high formation rates of PBDD/F found in the heat exchanger, which were 4-20 times higher than those of PCDD/F. Moreover, the strong correlations found between the formation rates of PCPh, PCBz and PCDD/F in the heat exchanger indicate that in addition considerable new formation of dioxins takes place through de novo synthesis. Experiments involving the variation of primary operational parameters and fuel properties have shown that the quality of post-combustion plays a much greater role than the other parameters. Furthermore, it became apparent that the congeners of the chlorophenols and of the chlorobenzenes, measured in various incineration stages, do not correlate closely with the dioxin concentrations after the heat exchanger.