Biogeochemical Proxies of Anthropic Impact in Mediterranean Forest Soils

Abstract

Quantitative changes in soil organic matter (SOM) from undisturbed Mediterranean forests and neighbouring deforested sites were assessed by analysing soil lipids and humic acids (HAs), in total studying 80 variables. Changes in the composition of free lipids reflected vegetation types, whereas HAs analysed by visible and 13 C NMR spectroscopy, sodium perborate degradation and Curie-point pyrolysis indicated the extent of structural alteration of lignin in soil. The molecular fractions released by degradation techniques applied to HAs showed that demethoxylation and oxidation were associated with the removal of forest vegetation, and the aromatic compounds consisted mainly of methoxyphenols and benzenecarboxylic acids. Decreased concentration of alkanes and increased amounts of alcohols were observed after removal of forests. The chain lengths of alkyl compounds also tended to decrease. In forest soil, there was a series of diterpene resin acids, whereas in pasture soil steroids from animal origin and a root-derived triterpenoids with friedelan structure were found. In relation to the total quantity and quality of soil C, the overall chemical descriptors indicated that clearing and cultivation (semiarid cereal fields) lead to intense mineralization of SOM (mainly particulate, free organic matter) but the residual humic substances have enhanced maturity in terms of structural condensation and potential resilience. Conversely, the cleared forest soil under pasture had a comparatively higher potential for C sequestration, but the HA characteristics suggested selective preservation of plant biomacromolecules directly incorporated as underground biomass.

Effects of Soil Quality on the Microbial Community Structure of Poorly Evolved Mediterranean Soils

“…The main objective of this study was to establish to what extent soil conditions altered by some human activities influence the patterns of microbial diversity of Mediterranean ecosystems, where the decrease in soil quality is understood as a loss of potential vegetation linked to a gradual decrease in SOM associated with human activity [66,67]. The results of Table 3 coincide with those reported by Boluda et al [15,39], who found wide variations of soil properties due to changes in the soil formation factors, particularly vegetation, climate, and soil uses in this area, which relates soil biology with soil quality.…”

Land use legacy footprint in Mediterranean forest soils: An infrared spectroscopy approach

“…Among the few studies related to the effect of land-use history on Mediterranean forest soils, it was shown that (i) quantitative changes in soil organic matter (lipids and humic acid fractions) between undisturbed Mediterranean forests and neighbouring deforested sites (Tinoco et al, 2010), (ii) vegetation thinning treatments, more frequent in Mediterranean forests, modified physical and microbiological properties in comparison with soil quality of unmanaged and undisturbed forest areas (Andrés-Abellán et al, 2019;Lull et al, 2020;Wic Baena et al, 2013), (iii) different land uses and agricultural practices were discriminated by the aromatic and carbonate compounds in the soils (Delcourt et al, 2019;Du et al, 2008;Mendham et al, 2002), (iv) soils keep, at different depths, the marks of past uses in their chemical composition and their spectral signature appears like an "historical footprint" of their natural or anthropogenic conversion over time (Ertlen et al, 2015;Vysloužilová et al, 2015), (v) different chemical signatures of forest soils were observed under different bioclimatic stages (Delcourt et al, 2019).…”