Environmental factors controlling soil organic carbon stability in French forest soils

The soil organic carbon content was analyzed in more than 7 000 soil samples under different land uses, climates and lithologies from northern Spain (Galicia, Asturias, Cantábria y País Vasco). GIS maps (1:50 000) were made of the % SOC and SOC stocks. The % SOC varies according to land use (higher in forest and scrub soils and lower in agricultural soils) and climate, and there is a highly significant correlation between SOC content and mean annual precipitation. There are significant differences between the soils of Galicia/Western Asturias (GAw) and those of the rest of the study area (Central and Eastern Asturias, Cantabria and País Vasco) (AceCV), although these are neighbouring regions. In forest and/or scrub soils with a udic soil moisture regime, in GAw, the SOC is usually > 7% and the average stocks 260 t ha -1 (0-30 cm), and >340 t ha-1 (0-50 cm) in soils with thick organic matter rich horizons (> 40 cm); these values greatly exceed the average contents observed in forest soils from temperate zones. Under similar conditions of vegetation and climate in soils of AceCV the SOC average is 3% and the mean stocks 90-100 t ha-1 (0-30 cm). The andic character of acid forest soils in GAw and the formation of C-Al,Fe complexes are pointed out as the SOC stabilization mechanism, in contrast to the neutral and calcareous soils that predominate in AceCV, where the main species of OC are easily biodegradable.

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Pedogenic Threshold in Acidity Explains Context-Dependent Tree Species Effects on Soil Carbon

Frontiers in Forests and Global Change ◽

10.3389/ffgc.2021.679813 ◽

2021 ◽

Vol 4 ◽

Author(s):

Ellen Desie ◽

Bart Muys ◽

Boris Jansen ◽

Lars Vesterdal ◽

Karen Vancampenhout

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Forest Soils ◽

Tree Species ◽

Litter Quality ◽

Species Selection ◽

Species Effects ◽

Tree Species Effects ◽

Soc Stocks ◽

The Way

Despite the general agreement that maximizing carbon storage and its persistence in forest soils are top priorities in the context of climate change mitigation, our knowledge on how to steer soil organic carbon (SOC) through forest management remains limited. For some soils, tree species selection based on litter quality has been shown a powerful measure to boost SOC stocks and stability, whereas on other locations similar efforts result in insignificant or even opposite effects. A better understanding of which mechanisms underpin such context-dependency is needed in order to focus and prioritize management efforts for carbon sequestration. Here we discuss the key role of acid buffering mechanisms in belowground ecosystem functioning and how threshold behavior in soil pH mediates tree species effects on carbon cycling. For most forests around the world, the threshold between the exchange buffer and the aluminum buffer around a pH-H2O of 4.5 is of particular relevance. When a shift between these buffer domains occurs, it triggers changes in multiple compartments in the soil, ultimately altering the way carbon is incorporated and transformed. Moreover, the impact of such a shift can be amplified by feedback loops between tree species, soil biota and cation exchange capacity (CEC). Hence, taking into account non-linearities related to acidity will allow more accurate predictions on the size and direction of the effect of litter quality changes on the way soil organic carbon is stored in forest soils. Consequently, this will allow developing more efficient, context-explicit management strategies to optimize SOC stocks and their stability.

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