Within the global carbon cycle the world's ecosystenls are most sensitive to environmental change. We present a global model for calculating the seasonal pattern of uptake and release of CO, by vegetation and soil in a steady-state climate simulation as well as the long-term development in a changing environment. Within the terrestrial ecosystems 32 vegetation types are distinguished and combined with 7 distinct soil types with respect to their water-holding capacities. Within each vegetation type the llving b~omass is divided into 2 compartments, one with a short (seasonal) turnover containing the photosynthesizing tissue, feeder roots, and assinl~late store, and the other with a long turnover mainly consisting of structural plant material. The mathematical description is based on 2 hypotheses: (1) vegetation tends to maximize photosynthesizing tissue; and (2) a minimum amount of structural tissue is needed to support and maintain the product~ve parts, described by an allometric relation. The fluxes are modeled using standard equations for gross photosynthesis of the canopy, autotrophic respiration, and decomposition of dead organic matter depending on surface temperature, soil moisture, and irradiation. Within the system of differential equations the free parameters for each vegetation type are calibrated on the basis of a characteristic seasonal climate. In this paper the results of steady-state chmate experiments for the 2 vegetation types 'cold deciduous forest' and 'boreal forest' are compared with ecological measurements It was shown that the model yields satisfactory results with respect to phenology, gradients in net primary production, and standing b~omass and thus holds the promise to also yield good global results. KEY WORDS: Carbon balance. Terrestrial ecosystems. Global simulation model. Allocation and phenology. Primary production. CO2 exchange fluxes The metamorphosis of plants calls to our attention a dual law: (I) the law of the ~nternal nature by which plants are constituted; (2) the law of the external circumstances b y which plants are moddied.

A method to refine organic crystal structures from powder diffraction data with incorrect lattice parameters has been developed. The method is based on the similarity measure developed by de Gelder et al. [J. Comput. Chem. (2001), 22, 273-289], using the cross- and auto-correlation functions of a simulated and an experimental powder pattern. The lattice parameters, molecular position, molecular orientation and selected intramolecular degrees of freedom are optimized until the similarity measure reaches a maximum; subsequently, a Rietveld refinement is carried out. The program FIDEL (FIt with DEviating Lattice parameters) implements this method. The procedure is also suitable for unindexed powder data, powder diagrams of very low quality and powder diagrams of non-phase-pure samples. Various applications are shown, including structure determinations from powder data using crystal structure predictions by standard force-field methods. Other useful applications include the automatic structure determination from powder data starting from the crystal structures of isostructural compounds (e.g. a solvate, hydrate or chemical derivative), or from crystal data measured at a different temperature or pressure.

A method for the ab initio crystal structure determination of organic compounds by a fit to the pair distribution function (PDF), without prior knowledge of lattice parameters and space group, has been developed. The method is called `PDF-Global-Fit' and is implemented by extension of the program FIDEL (fit with deviating lattice parameters). The structure solution is based on a global optimization approach starting from random structural models in selected space groups. No prior indexing of the powder data is needed. The new method requires only the molecular geometry and a carefully determined PDF. The generated random structures are compared with the experimental PDF and ranked by a similarity measure based on cross-correlation functions. The most promising structure candidates are fitted to the experimental PDF data using a restricted simulated annealing structure solution approach within the program TOPAS, followed by a structure refinement against the PDF to identify the correct crystal structure. With the PDF-Global-Fit it is possible to determine the local structure of crystalline and disordered organic materials, as well as to determine the local structure of unindexable powder patterns, such as nanocrystalline samples, by a fit to the PDF. The success of the method is demonstrated using barbituric acid as an example. The crystal structure of barbituric acid form IV solved and refined by the PDF-Global-Fit is in excellent agreement with the published crystal structure data.

Four different structural models, which all fit the same X-ray powder pattern, were obtained in the structure determination of 4,11-difluoroquinacridone (C20H10N2O2F2) from unindexed X-ray powder data by a global fit. The models differ in their lattice parameters, space groups, Z, Z′, molecular packing and hydrogen bond patterns. The molecules form a criss-cross pattern in models A and B, a layer structure built from chains in model C and a criss-cross arrangement of dimers in model D. Nevertheless, all models give a good Rietveld fit to the experimental powder pattern with acceptable R-values. All molecular geometries are reliable, except for model D, which is slightly distorted. All structures are crystallochemically plausible, concerning density, hydrogen bonds, intermolecular distances etc. All models passed the checkCIF test without major problems; only in model A a missed symmetry was detected. All structures could have probably been published, although 3 of the 4 structures were wrong. The investigation, which of the four structures is actually the correct one, was challenging. Six methods were used: (1) Rietveld refinements, (2) fit of the crystal structures to the pair distribution function (PDF) including the refinement of lattice parameters and atomic coordinates, (3) evaluation of the colour, (4) lattice-energy minimizations with force fields, (5) lattice-energy minimizations by two dispersion-corrected density functional theory methods, and (6) multinuclear CPMAS solid-state NMR spectroscopy (1H, 13C, 19F) including the comparison of calculated and experimental chemical shifts. All in all, model B (perhaps with some disorder) can probably be considered to be the correct one. This work shows that a structure determination from limited-quality powder data may result in totally different structural models, which all may be correct or wrong, even if they are chemically sensible and give a good Rietveld refinement. Additionally, the work is an excellent example that the refinement of an organic crystal structure can be successfully performed by a fit to the PDF, and the combination of computed and experimental solid-state NMR chemical shifts can provide further information for the selection of the most reliable structure among several possibilities.

Regional variability and seasonal courses of atmospheric CO, provide important clues to the understanding of the carbon exchange fluxes which determine the global carbon budget. We apply the Frankfurt Biosphere Model (FBM) to all 32 vegetation types of a modified global Matthews' vegetation map, simulating seasonal carbon exchange fluxes of the terrestrial ecosystems and their geographical variability on a global scale. For each 0.5" by 0.5" grid element the model calculates gross photosynthesis of the canopy and autotrophic respiration on an hourly time step, and heterotrophic respiration as well as the model-compartment sizes and LA1 (leaf area index) on a daily time step. The driving variables temperature, irradiation, and soil moisture are derived from the Cramer and Leemans database. Soil moisture is calculated by an improved bucket model in which the soil properties given by the FAO soil map are combined with the rooting depth of different vegetation types to deduce the available water capacity and the permanent wilting point. Based on mean estimates of ecological variables [e.g. net primary production (NPP), biomass and soil carbon] and a characteristic seasonal c11-mate, the free parameters of each vegetation type are calibrated. With these parameters, taking the climate variation within the vegetation types into account, the seasonal courses of NPP are calculated, summing up to a global annual integral of 50.3 Gt C yr-' The results are presented in the form of a world map showing the annual NPP and a table with monthly values of NPP averaged over 5Olatitude belts. The latter results are graphically displayed not only for NPP but also for heterotrophic respiration and the resulting seasonal net ecosystem production. Since the FBM keeps track of the seasonal development of leaf biomass, the corresponding seasonal LA1 is examined for each grid element. The calculated leaf emergence dates are in good agreement with observations from phenological gardens as well as with NDVI (normalized difference vegitation index) derived phenology.