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BTU
Modified wick lysimeters for critical water use efficiency evaluation and yield crop modelling
(2011)
Als Pionierbaumart besiedelt die Robinie (Robinia pseudoacacia) schnell offene Flächen und gilt im Vergleich zu anderen mitteleuropäischen Baumarten als relativ gut angepasst an trockene Standorte mit lockeren Böden. Sie gehört zu den wenigen Baumarten Mitteleuropas, die zur biologischen Stickstoff-Fixierung (BNF) befähigt sind. In dieser Studie soll der jährliche Eintrag von Stickstoff (N) aus der biologischen N-Fixierung der Robinie in Kurzumtriebsplantagen und Agroforstsystemen abgeschätzt werden.
Ecosystems are characterized as complex systems with abiotic and biotic processes interacting between the various components that have evolved over long-term periods. Most ecosystem studies so far have been carried out in mature systems. Only limited knowledge exists on the very initial phase of ecosystem development. Concepts on the development of ecosystems are often based on assumptions and extrapolations with respect to structure–process interactions in the initial stage. To characterize the effect of this initial phase on structure and functioning of ecosystems in later stages, it is necessary to disentangle the close interaction of spatial and temporal patterns of ecosystem structural assemblages with processes of ecosystem development. The study of initial, less complex systems could help to better identify and characterize coupled patterns and processes. This paper gives an overview of concepts for the initial development of different ecosystem compartments and identifies open questions and research gaps. The artificial catchment site “Chicken Creek” is introduced as a new research approach to investigate these patterns and processes of initial ecosystem development under defined boundary conditions. This approach allows to integrate the relevant processes with related pattern and structure development over temporal and spatial scales and to derive thresholds and stages in state and functioning of ecosystems at the catchment level.
Normalized Difference Vegetation Indices (NDVIs) are typically determined using satellite or airborne remote sensing, or field portable spectrometers, which give an averaged signal on centimetre to metre scale plots. Biological soil crust (BSC) patches may have smaller sizes, and ecophysiological, hydrological as well as pedological processes may be heterogeneously distributed within this level of resolution. A ground-based NDVI imaging procedure using low-cost equipment (Olympus Camedia 5000z digital camera equipped with a Hoya R72 infrared filter) was developed in this study to fill this gap at the level of field research, where carrying costly and bulky equipment to remote locations is often the limiting factor for data collection. Method principle and field data are presented, and the field experiment was deepened comparing NDVI measurements and CO2 turnover of soil crust samples in the laboratory, backing the reliability of the approach.
A commercially available colour rendition chart with known red (600–700 nm) and NIR (800–900 nm) reflectances was placed into each scene and used for calibration purposes on a per-image basis. Generation of NDVI images involved (i) determination of red and NIR reflectances from the pixel values of the red and NIR channels, respectively, and (ii) calculation and imaging of the NDVI, where NDVI values of −1 to +1 were mapped to grey values of 0 to 255. The correlation between NDVI values retrieved from these images and NDVI values determined using field spectrometry was close (r2 = 0.91), the 95% confidence interval amounted to 0.10 NDVI units. The pixel resolution was 0.8 mm in the field and 0.2 mm in the laboratory, but can still be improved significantly with closer distance to the crust or with higher camera resolution. NDVI values obtained using the new method were related to the net CO2 uptake of BSCs, where both slope and correlation coefficient of the respective regression function conformed with literature data. Geostatistical analysis revealed that both spatial variability of net CO2 uptake as well as size of individual hot spots of this parameter increased with crust development. The latter never exceeded 4 mm in the investigated crusts, which points to the necessity of high resolution imaging for linking remote sensing with ecophysiology. Perspectively, the new method could be used for field monitoring of both biological soil crusts and vascular vegetation.