Soil macroaggregate dynamics in a mountain spatial climate gradient

Abstract

We investigated the response of soil macroaggregate dynamics to soil temperature modification along a spatial gradient located on a forested north-facing slope in the southern French Alps, simulating long-term adjustment of soil-plant interactions to absence or occurrence of soil frost. Soil macroaggregate (> 250 µm) content of Ah horizons was strongly depleted (72%) in colder plots affected by freeze-thaw events, compared to 96% in warmer and frost-free plots (p < 0.05). A visual assessment of soil macroaggregation showed that physical processes were the main drivers of soil macroaggregation in colder plots, with 66% of the 5-12.5 mm fraction and the whole 3.15-5 mm fraction. Conversely, we found a balanced contribution of biological and physical aggregation pathways in warmer plots. All identified macroaggregate types could be classified, depending on their organic matter (OM) quality, using principal component analyses of their near infrared spectra. Such spectral classifications indicated temporal changes in OM quality of macroaggregates, from formation to colonization by fine roots, suggesting ecosystem-specific ontogenic trajectories for soil macroaggregation. Further physico-chemical characterizations of soil macroaggregates and Ah horizons showed that soil organic carbon content in the Ah horizon was constant along the gradient, whereas soil erodibility was reduced in warmer soils, which prevented the occurrence of fragile macroaggregates formed by freeze-thaw events. Our study thus suggests changes in the erodibility of mountain forest soils under changing climate. Soil erodibility could be affected either positively under warmer conditions, or negatively, under increased soil frost.

The human impact on the transformation of juniper forest landscape in the western part of the Pamir-Alay range (Tajikistan)

“…Other researchers (e.g. Cécillion et al 2010) attribute important roles in soil development mainly to dynamic geomorphological processes and arid climate changeability at different altitude levels, ignoring the human role in the status of these sensitive mountain ecosystems. The latter, in turn, contributes to the formation of soil mosaic typical of mountain areas on which plant islands are created, along with the phytogenic fields under their canopies.…”

Ecohydrology and Climate Change in the Mountains of the Western USA – A Review of Research and Opportunities

“…Direct effects of increased temperature may be reinforced by changes in snow cover, although effects are complex. The presence of snow is not only linked to cooler temperature, but snow also acts to insulate underlying soil and reduce frost effects (Cécillon et al. 2010).…”

“…Direct effects of increased temperature may be reinforced by changes in snow cover, although effects are complex. The presence of snow is not only linked to cooler temperature, but snow also acts to insulate underlying soil and reduce frost effects (Cécillon et al 2010). In colder environments, warming soil temperatures typically increase rates of soil biogeochemical cycling and ultimately may increase forest productivity when nutrients are limiting.…”

Impacts of more frequent droughts on a relict low-altitude Pinus uncinata stand in the French Alps

“…(Rolland and Schueller, 1995), but seven stands have been reported to grow at abnormally low elevations within a mountain belt of the Rhone Alpes and at altitudes comprised between 1100 and 1500 m a.s.l. The existence of these exceptional stands in the Devoluy (Combe Obscure; Bertinelli et al, 1993; Bois du Sappey; Cécillon et al, 2010) and Grande Chartreuse (La Plagne cirque; Cassagne et al, 2008) massifs was associated with the circulation of cold air in scree slopes, which may locally create periglacial pedoclimatic conditions (Cécillon et al, 2010). The microclimate of cold scree slopes allows for exceptional microhabitats to develop with very thick and raw humus (Cassagne et al, 2008), forming ideal niches for various cold living plants (Bertinelli et al, 1993) and periglacial relict species of non-vascular plants (Asta et al, 2001), beetles (Molenda, 1996), spiders and mites (Zacharda et al, 2005).…”