Inhaltszusammenfassung

Enrichment of C-13 in SOM with soil depth is related to interacting processes influenced by temperature and precipitation. Our objectives were to derive climate effects on patterns of vertical delta C-13 values of soil organic matter (SOM) while minimizing the effect of confounding variables. We investigated vertical changes in delta C-13 values of SOM in 1-cm depth intervals in silvicultural mature beech (Fagus sylvatica L.) forest ecosystems in northern Rhineland-Palatinate across gradie...Enrichment of C-13 in SOM with soil depth is related to interacting processes influenced by temperature and precipitation. Our objectives were to derive climate effects on patterns of vertical delta C-13 values of soil organic matter (SOM) while minimizing the effect of confounding variables. We investigated vertical changes in delta C-13 values of SOM in 1-cm depth intervals in silvicultural mature beech (Fagus sylvatica L.) forest ecosystems in northern Rhineland-Palatinate across gradients of MAT (7.9 to 9.7 degrees C mean annual temperature) and MAP (607 to 1085 mm mean annual precipitation) in winter 2011. Forest stands (n = 10) were chosen based on data sets provided by the Rhineland-Palatinate Forest Administration so that variations in these gradients occurred while other environmental factors like physico-chemical soil properties, tree species, stand age, exposition and precipitation (for the temperature gradient) or temperature (for the precipitation gradient) did not differ among study sites. From litter down to the mineral soil at 10 cm depth, soil organic carbon (SOC) content decreased (47.5 +/- SE 0.1% to 2.5 +/- 0.1%) while the delta C-13 values increased (-29.4 +/- 0.1 parts per thousand to -26.1 +/- 0.1 parts per thousand). Litter of sites under higher MAP/lower MAT had lower 813C values which was in line with literature data on climate driven plant physiological process. To compare the dimension of the vertical C-13 enrichment, delta C-13 values were regressed linearly against log-transformed carbon contents yielding absolute values of these slopes (beta). Beta values ranged between 0.6 and 4.5 (range of r from -0.7 to -1.0; p < 0.01). Due to an assumed decay continuum and similar variations of delta C-13 values in litter and in 10 cm depth, we conclude that effects on isotope composition in the Oi layer continue vertically and therefore, delta C-13 values in litter do not solely control beta values. Beta values decreased with increasing MAT (r = -0.83; p < 0.05). Reduced soil moisture and therefore both, reduced microbial activity and reduced downward transport of microbial cycled DOM (=C-13 enriched) might be responsible for less pronounced delta C-13 depth profiles in case of high temperatures. Greater C:N ratios (lower degradability) of the litter under higher temperatures likely contributed to these depth trends. Beta values increased with increasing MAP (r = 0.73; p < 0.05). We found decreasing C:N ratios in the mineral soil that possibly indicates higher decomposition under higher precipitation. Exclusion of the organic layers from linear regressions indicated a stronger impact of MAP on the development of delta C-13 depth profiles. Our results confirm temperature and precipitation effects on delta C-13 depth profiles and indicate stronger C-13 enrichment under lower MAT/higher MAP. Therefore, time series of vertical delta C-13 depth profiles might provide insights into climate change effects. (C) 2014 Elsevier B.V. All rights reserved.» weiterlesen» einklappen

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DDC Sachgruppe:
Naturwissenschaften