Das Projekt "Short- and long-term effects of fire on soil organic matter along a toposequence on Mt. Etna, Sicily" wird vom Umweltbundesamt gefördert und von Universität Zürich, Geographisches Institut durchgeführt. In Mediterranean ecosystems, soil organic matter (SOM) can be directly affected by wildfires, both in terms of quantity and quality. The combustion is often incomplete, leading to the formation of pyrogenic organic matter (PyOM), a highly heterogeneous material with prevailing aromatic nature and often long residence time in soil. Focusing our attention on PyOM, we investigate a soil toposequence on the north-eastern side of Mount Etna, Italy, with six sites ranging from 500 m to 1800 m asl. A previous study on the same sites based on the radiocarbon dating of charcoal fragments and the most refractory fraction of SOM, supported the hypothesis that fire frequency is historically higher at lower elevations due to a warmer and drier climate regime. In this work, we evaluate the long-term effect of fire on the chemical and physical characteristics of SOM and, to a lesser extent also shorter-term effects using two sites having a different recent fire history. Chemical oxidation of SOM using acid dichromate are performed to evaluate the contribution of pyrogenic organic carbon (PyOC) to total SOC. Furthermore, SOM density fractions are separated and characterised for principal composition, spectroscopic properties (DRIFT and NMR), and particle morphology (SEM).
Das Projekt "Physical, molecular and microbial evidence of char degradation" wird vom Umweltbundesamt gefördert und von Universität Zürich, Geographisches Institut durchgeführt. Understanding soil organic matter (SOM) dynamics is critical to meeting many environmental, agricultural, and forestry challenges relating to productivity and sustainability, including the potential of soils to sequester atmospheric CO2. The amount of C as stored as SOM represents twothirds of the terrestrial C pool and is the primary energy source driving several critical biogeochemical processes. The mechanisms of C stabilization in soils remain poorly understood. A critical knowledge gap in soil organic C (SOC) cycling concerns the SOC portion known as pyrogenic C (PyC), which is a chemically heterogeneous class of highly reduced compounds produced by the incomplete combustion. In terrestrial ecosystems, C and N dynamics are closely linked due to the activity of organisms. During the last few decades, atmospheric nitrogen deposition in soils has increased as a result of climate changes and human activities. At present, however, it is not clear whether increased nitrogen deposition will accelerate or decelerate soilorganic-matter turnover. Also, because of these global changes, future summers in temperate regions will be warmer and drier than today, and wildfires will be more frequent, producing more fire-derived (pyrogenic) carbon (PyC), a relatively recalcitrant soil component. . In this proposed long-term experiment, cylindrical mesocosms (10 x 15 cm) will be installed in the soil and filled with (1) 13C/15N labelled pyrolyzed wood, (2) 13C/15N labelled wood and (3) a no litter control, either treated with nitrogen or not, resulting in a two-factor, two-treatment experiment. We propose a post-doc project to identify underlying processes of char and wood degradation under high and low nitrogen -by directly identifying micro-organisms decomposing PyC through the double label (13C, 15N), by describing microorganism community structures, by determining the alteration of the PyC chemical structure of the remaining char (CPMAS 13C and 15N NMR, molecular markers) in the dissolved fraction and in the bulk soil and by using the isotopes to trace the degradation products within the soil fractions and within the intact soil matrix using soil fractionation methods and NanoSIMS technology. This project will be novel and cutting edge for several reasons: For the first time, the proposed project will (1) directly identify PyC decomposers, (2) directly quantify PyC degradation in vivo in a long-term field study, and (3) test the effect of nitrogen on decomposition of PyC and its wood precursor. The project will help to clarify our fundamental understanding of the fate of pyrogenic carbon in forest soil under present and future atmospheric nitrogen deposition, and will improve urgently needed field-based and global turnover models.