Characterisation of soil organic matter under intensively used grassland along an alpine elevation gradient in South Tyrol, Italy

Alpines Grasland speichert hohe Mengen an organischer Bodensubstanz (SOM) und alpine Graslandböden stellen damit eine wichtige und aktive Kohlenstoffsenke dar. Es ist noch unbekannt, wie sich die verändernden klimatischen Bedingungen auf den gespeicherten organischen Bodenkohlenstoff (SOC) in den alpinen Böden auswirken werden. In der vorliegenden Studie werden vier intensiv genutzte Grünlandflächen der Südtiroler Alpen untersucht um Änderungen in Menge und Eigenschaften der organischen Substanz im Boden zu können. Die Standorte befinden sich entlang eines Höhengradienten von 1.000 bis 2.000 m über dem Meeresspiegel und weisen ähnliche bodenbildende Faktoren (z.B. Geologie, Bodentyp, Vegetation) auf. Die Analysen reichen von der Elementaranalyse und Simultane Thermoanalyse der entnommenen Bodenproben (0 40 cm Bodentiefe) bis zur Fourier-Transform Infrarot-Spektroskopie der extrahierten Huminsäuren (1M NaOH). Es stellte sich heraus, dass die Böden inAlpine grasslands are known to accumulate large amounts of soil organic matter (SOM) and present an important and active terrestrial carbon pool. Alpine ecosystems are also known to be especially vulnerable to climate changes. It is still unknown however, how the changing climatic condition will impact the stored soil organic carbon (SOC) in alpine grasslands. In this study four intensively used grassland sites in the South Tyrolean Alps along an elevation gradient from 1000 to 2000 m asl, having similar soil forming factors (i.e. geology, soil type, vegetation), were characterised in order to determine the quantity and properties of the SOM. Besides elemental analysis (i.e. organic C and total N content) we applied Simultaneous Thermal Analysis on bulk soil and Fourier Transform Infrared Spectrometry on extracted humic acids (1 M NaOH), taken from soils at depths down to 0 40 cm. We found that the soils in the 0 15 cm soil depth accumulated 0.48 kg/m2 SOC per 100 m altitude in the sites. The highest SOM amount was observed in the upper layer (0 5 cm) and that the tendency decreased with increasing soil depth. Within the profile we could observe a decrease in labile organic compounds and an increase in more stabile pool with soil depth. However, the SOM was dominated (63 - 77%) by thermal labile compounds, resulting from high annual inputs of manure and low decomposition/mineralization rates of the organic matter in the study area. Labile aliphatic bounds and N-related compounds in the humic acids showed altitudinal variations at all soil depths whereas most other bands did not change with the elevation. The amount and composition of SOM was mainly controlled by the prevailing climatic conditions, soil properties (i.e. pH and C:N ratio ) and land management practices.Cecilie Birgitte FoldalZsfassung in dt. SpracheWien, Univ. für Bodenkultur, Masterarb., 2012(VLID)108308