Effect of north and south exposure on organic matter in high Alpine soils

Abstract

The present work focuses on the subalpine range of the Italian Alps to determine the influence of aspect and consequently climate on soil humus properties and chemistry. This was done by comparing soils developing in north-and south-facing sites on siliceous parent material. The soils were investigated with respect to the total organic C and N content, C and N contents of organic matter (OM) density fractions and of labile(oxidised by H2O2) and stable (H2O2-resistant) fractions. Further characterisation of OM and the different fractions was performed with Diffuse Reflection Infrared Fourier Transform (DRIFT), Scanning Electron Microscopy/Electron Diffuse Scattering (SEM/EDS) and radiocarbon dating. The soils at north-facing slopes had a higher OM content. Density measurements and the H2O2 fractionation proved that this higher content was primarily due to a more pronounced accumulation of weakly degraded, labile organic materials when compared to the south-facing slopes. Independent of the sites, a large part of OM (around 50% of OM) was fixed in the densest fraction (N2 g/cm3) which correlated well with the abundance of the H2O2-resistant fraction. The 14C ages of the latter were up to 17,000 years, reflecting the presence of stable, refractory OM and the effectiveness of organo-mineral interactions in protecting OM from decay. Podzolisation has been more intense at north-facing sites. Due to the accumulation of weakly degraded OM, eluviation of Fe and Al is strongly enhanced. High-mountain ecosystems like the Alps are very sensitive to changing environmental conditions such as global warming. Especially at cooler sites, the obtained results suggest that a warmer climate, and thus more favourable conditions for biological activity, will lead in the short-to mid-term to an increased loss of accumulated, weakly degraded OM . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 and thus more favourable conditions for biological activity, will lead in the short-to mid-term 21to an increased loss of accumulated, weakly degraded OM. 22 23

Chemical and microbiological changes in Norway spruce deadwood during the early stage of decomposition as a function of exposure in an alpine setting

“…In line with previous studies performed in the Trentino area (Egli et al 2006(Egli et al , 2009Fravolini et al 2016;Bardelli et al 2017), the soils located at the north-facing slope were moister and richer in total C and nitrogen contents compared to those at the south-facing slope. Along a climosequence, Fravolini et al (2016) observed faster decay rates of the P. abies wood blocks at the north-than at the south-facing slopes up to an elevation of 1,800 m a.s.l., probably because of the higher soil moisture and clay content along with a lower soil pH.…”

“…Mountain Alpine ecosystems have gained increasing attention during the past several years because they are particularly sensitive to ever-changing climatic conditions (Egli et al 2006(Egli et al , 2009. Indeed, an increase of about 2°C has been recorded in the annual minimum temperature in the European Alps during the twentieth century (Beniston, Diaz, and Bradley 1997).…”

(Pre-) historic changes in natural and anthropogenic heavy metals deposition inferred from two contrasting Swiss Alpine lakes

“…2A) (Hedenström and Possnert, 2001;Doner, 2003). Such an old carbon effect might originate from the input of stable and old refractory organic matter present in Alpine podzols Egli et al, 2009). A relatively old 14 C date of macrorests was found for the beginning of the record (ca 14315 BC at 119 cm), confirming the age of the earliest formation of Pleistocene/Holocene -age Alpine soils (Favilli et al, 2008).…”

Soil organic carbon variation in relation to land use changes: the case of Birr watershed, upper Blue Nile River Basin, Ethiopia

“…On the other hand, elevation and temperature differences are identified as the dominant controls on mountain SOC at regional scales (Djukic et al 2010;Van Miegroet et al 2007, 2005; Leifeld et al 2005), local topographic changes (e.g., slope curvature and aspect, Egli et al 2009;Tan et al 2004), soil properties (e.g., soil type, soil moisture, pH and clay-content; Djukic et al 2010;Leifeld et al 2005), and vegetation (e.g., type and stand age; Luyssaert et al 2008;Zhou et al 2006) may introduce a large variability of mountain SOC at local scales. Small-scale variability may even impose strong scatter at large-scales and conceal relationships between SOC, topography, and climate.…”