as arthropods, fungi and soil bacterial communities. Different land management
practices (e.g. various grazing pressures in pasturelands, timber removal in subalpine forests, etc.) is another source of variation that affects the C cycling and
storage. All these factors result in soils with a highly heterogeneous amount of
stored C, making difficult the prediction of current stocks and its response to the
expected climate and land-use changes.
9.3 Factors Controlling Soil Organic C Stocks
in Mountain Grasslands
The development of soil is a complex and continuous process, driven by parent
material, climate and soil biota. In the mountains, the topography also plays an
important role modifying the climate and creating different landforms for soil
development. All these factors determine the physical, chemical and biological
properties of soils and control their capacity to accumulate organic C.
9.3.1 Bedrock Type
Mountain areas are often geologically complex, as a result of past volcanism,
compression and tension faults, plate subduction and uplift. The parental material
from which a soil develops determines many hydrological, ecological and pedogenic processes, having implications for the capacity of soils to store C, the C
accumulation rates and its persistence in the soil. Differences in the lithology
determine the differences in the mineral composition of soils and influence their
texture, chemistry and weathering processes. Changes in plant composition and
structure are also frequently associated with changes in the bedrock type through its
effect on nutrient status and physical characteristics of the soil.
Soil texture is the most relevant characteristic that is determined by the bedrock
type. For instance, soils developed on sandstones or granites usually have coarser
textures than those developed on limestones or slates. Soil texture is particularly
relevant for organic matter accumulation in soils, as organic matter is stabilised in
soil through its interaction with the finest mineral particles. Indeed, organic matter
associated with the finest particles (i.e. fine silt and clay) is usually older
(Eusterhues et al. 2003) and has longer residence times (Balesdent 1996) than the
organic matter in the coarser fractions. In the Pyrenees, although C and N availability were more important explaining topsoil basal respiration, soils developed
on granites showed high rates of basal respiration (Garcia-Pausas et al. 2008),
suggesting that they may contain a higher proportion of non-stabilised organic
matter.
9 Are Soil Carbon Stocks in Mountain Grasslands …
211
practices (e.g. various grazing pressures in pasturelands, timber removal in subalpine forests, etc.) is another source of variation that affects the C cycling and
storage. All these factors result in soils with a highly heterogeneous amount of
stored C, making difficult the prediction of current stocks and its response to the
expected climate and land-use changes.
9.3 Factors Controlling Soil Organic C Stocks
in Mountain Grasslands
The development of soil is a complex and continuous process, driven by parent
material, climate and soil biota. In the mountains, the topography also plays an
important role modifying the climate and creating different landforms for soil
development. All these factors determine the physical, chemical and biological
properties of soils and control their capacity to accumulate organic C.
9.3.1 Bedrock Type
Mountain areas are often geologically complex, as a result of past volcanism,
compression and tension faults, plate subduction and uplift. The parental material
from which a soil develops determines many hydrological, ecological and pedogenic processes, having implications for the capacity of soils to store C, the C
accumulation rates and its persistence in the soil. Differences in the lithology
determine the differences in the mineral composition of soils and influence their
texture, chemistry and weathering processes. Changes in plant composition and
structure are also frequently associated with changes in the bedrock type through its
effect on nutrient status and physical characteristics of the soil.
Soil texture is the most relevant characteristic that is determined by the bedrock
type. For instance, soils developed on sandstones or granites usually have coarser
textures than those developed on limestones or slates. Soil texture is particularly
relevant for organic matter accumulation in soils, as organic matter is stabilised in
soil through its interaction with the finest mineral particles. Indeed, organic matter
associated with the finest particles (i.e. fine silt and clay) is usually older
(Eusterhues et al. 2003) and has longer residence times (Balesdent 1996) than the
organic matter in the coarser fractions. In the Pyrenees, although C and N availability were more important explaining topsoil basal respiration, soils developed
on granites showed high rates of basal respiration (Garcia-Pausas et al. 2008),
suggesting that they may contain a higher proportion of non-stabilised organic
matter.
9 Are Soil Carbon Stocks in Mountain Grasslands …
211