Depth profiles of stable water isotopes in the soil provide important information on flow and transport processes in the subsurface. We sampled depth profiles of stable water isotopes (2H and 18O) in the pore waters on two occasions at 46 sites in the Attert catchment, Luxembourg and are partly located in mixed deciduous forest and partly on grassland. These sites correspond to the sensor cluster sites of the DFG research unit CAOS. Sampling took place once between February 2012 and October 2013 and once in June 2014. Sampling procedure: We took 1-3 soil cores of 8 cm diameter in close proximity with a percussion drill (Atlas Copco Cobra, Stockholm, Sweden) at each study site within a radius of 5 m from the soil moisture sensor profiles. We drilled as deep as possible and divided the extracted soil cores into subsamples of 5 to 10 cm length and sealed the material in air tight bags (Weber Packaging, Güglingen, Germany). The soil sample depths were corrected for compaction during the drilling pro-cess and are provided as the mean depth of 5 or 10 cm soil core subsamples.
For isotope analyses of the pore water, we used the direct equilibration method (Wassenaar et al., 2008). Analyses were carried out at the Chair of Hydrology, University of Freiburg. We provide detailed information about the laboratory analyses in Sprenger et al. (2015) and Sprenger et al. (2016) and the data description associated with the data.
The effects of climate and topography on soil physico-chemical and microbial parameters were studied along an extensive latitudinal climate gradient in the Coastal Cordillera of Chile (26° - 38°S). The study sites encompass arid (Pan de Azúcar), semiarid (Santa Gracia), mediterranean (La Campana) and humid (Nahuelbuta) climates and vegetation, ranging from arid desert, dominated by biological soil crusts (biocrusts), semiarid shrubland and mediterranean sclerophyllous forest, where biocrusts are present but do have a seasonal pattern to temperate-mixed forest, where biocrusts only occur as an early pioneering development stage after disturbance. All soils originate from granitic parent materials and show very strong differences in pedogenesis intensity and soil depth.
Most of the investigated physical, chemical and microbiological soil properties showed distinct trends along the climate gradient. Further, abrupt changes between the arid northernmost study site and the other semi-arid to humid sites can be shown, which indicate non-linearity and thresholds along the climate gradient. Clay and total organic carbon contents (TOC) as well as Ah horizons and solum depths increased from arid to humid climates, whereas bulk density (BD), pH values and base saturation (BS) decreased. These properties demonstrate the accumulation of organic matter, clay formation and element leaching as key-pedogenic processes with increasing humidity. However, the soils in the northern arid climate do not follow this overall latitudinal trend, because texture and BD are largely controlled by aeolian input of dust and sea salts spray followed by the formation of secondary evaporate minerals. Total soil DNA concentrations and TOC increased from arid to humid sites, while areal coverage by biocrusts exhibited an opposite trend. Relative bacterial and archaeal abundances were lower in the arid site, but for the other sites the local variability exceeds the variability along the climate gradient. Differences in soil properties between topographic positions were most pronounced at the study sites with the mediterranean and humid climate, whereas microbial abundances were independent on topography across all study sites.
In general, the regional climate is the strongest controlling factor for pedogenesis and microbial parameters in soils developed from the same parent material. Topographic position along individual slopes of limited length augmented this effect only under humid conditions, where water erosion likely relocated particles and elements downward. The change from alkaline to neutral soil pH between the arid and the semi-arid site coincided with qualitative differences in soil formation as well as microbial habitats. This also reflects non-linear relationships of pedogenic and microbial processes in soils depending on climate with a sharp threshold between arid and semi-arid conditions. Therefore, the soils on the transition between arid and semi-arid conditions are especially sensitive and may be well used as indicators of long and medium-term climate changes. Concluding, the unique latitudinal precipitation gradient in the Coastal Cordillera of Chile is predestined to investigate the effects of the main soil forming factor – climate – on pedogenic processes.
The data presented here is part of the German-Chilean Priority Program “EarthShape” (Earth Surface Shaping by Biota), funded by the German Research Foundation (DFG). We provide the basic background data, which includes investigations into the influence of climate, vegetation and topography on pedogenesis and microbial abundances. The data are supplementary material to Bernhard et al. (2018).
All tables are available as one Excel file, as individual tables in .csv format in a zipped archive and as PDF file. The samples are assigned with International Geo Sample Numbers (IGSN) and linked to a comprehensive sample description in the internet.
The content of the five data tables is:
Table S1: Soil profile field description for the EarthShape study sites
Table S2: Soil physico-chemical properties for the depth increment samples in the four study sites
Table S3: Soil physico-chemical properties for the horizon samples in the four study sites
Table S4: Relative microbial abundances in the four study sites
Table S5: Plant species and abundance (% cover) in the four study sites