Soil organic matter content and its aliphatic character define the hydrophobicity of biocrusts in different successional stages

Abstract

In humid areas, biocrusts cover topsoils of inland dunes and influence soil characteristics, which, in turn, may affect the hydrophobicity of soils. The hydrophobicity of topsoils typically increases with increasing organic matter content. In addition, the soil organic matter quality, for example, described by the ratio of its hydrophilic and hydrophobic functional groups, also influences hydrophobicity. Because biocrust development goes along with an increase in the organic matter content and a shift in microbial community composition, the chemical character of soil organic matter likely changes over time, which, in turn, affects the hydrophobicity of the crusts. We hypothesize that the hydrophobicity of biocrusts increases during succession because of increasing amounts and aliphatic character of organic matter. We compared organic matter contents and Fourier‐transform infrared spectra of cyanobacterial biocrusts and moss‐dominated biocrusts at two European inland dunes. The organic carbon content as well as the hydrophobicity increased during crust development at both sites. Older moss‐dominated biocrusts showed the highest hydrophobicity and the highest organic carbon content. Moreover, at one study site, the hydrophobicity of the biocrusts did increase with decreasing ratio between hydrophilic and hydrophobic (i.e., aliphatic) moieties of soil organic matter. At the second study site, this effect was only visible for the moss‐dominated biocrust. We conclude that biocrust development and organic matter accumulation go ahead with changes in the organic matter composition and induce increased hydrophobicity with a strong impact on water redistribution in inland dune ecosystems. This knowledge will help to improve nature protection strategies in rare ecosystems.

Water repellency decreases with increasing carbonate content and pH for different biocrust types on sand dunes

“…This trend is in line with earlier studies on WR of biocrusts. As biocrusts develop, their thickness and the amount of OM increase as well, and so does their WR (Drahorad et al, 2020;Gypser et al, 2016;Lichner et al, 2018). For both study sites, TOC and CA are highly correlated (r = 0.81 Sekule and r = 0.83 Negev).…”

“…In contrast to this, biocrusts from the humid Sekule site in Slovakia show strong WR on carbonate-free dunes with an acidic pH-value (Lichner et al, 2012). This effect increased with ongoing biocrust development and increasing amounts of OM (Drahorad et al, 2013b;Drahorad et al, 2020). Until now, studies comparing the WR and correlated soil properties of biocrusts in contrasting ecosystems are missing.…”

“…For the Negev samples, we included an OM characterization via FT-IR. For recording FT-IR spectra, we used 1 mg of ground, desiccated soil (< 0.5 mm) mixed with 80 mg of potassium bromide and dried over night over silicagel in an exsiccator (Ellerbrock et al, 1999). The mixture was pressed into a pellet by applying a pressure of 980.7 MPa for 10 min.…”

“…The spectra were smoothed (boxcar moving average algorithm, factor 45) and corrected for baseline shifts using WIN-IR Pro 3.4 software (Digilab, Massachusetts, USA). For a detailed description on FT-IR spectra of the Sekule samples see Drahorad et al (2020).…”

“…FT-IR was used to describe the OM of the biocrusts at the Negev site as already done in an earlier work for the biocrusts of Sekule (Drahorad et al, 2020). The FT-IR spectra are characterized by the same bands as the previously recorded for data on biocrusts in Sekule (Figure 2).…”