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The impacts of oil pollution, unlike other disturbances, on the structure and activity of microorganisms in biological soil crusts have never been investigated. We exposed crust pieces from Wadi Al-Khoud, Sultanate of Oman to different oil concentrations and studied changes in their chlorophyll a (Chl a ) content, bacterial communities and photosynthetic and respiration activities. Chl a concentrations did not change in dry oil-polluted crusts but increased in the crusts exposed to oil in the presence of water. Nevertheless, extended incubation with oil for ≥3 weeks or in the presence of higher concentrations resulted in a considerable decline in Chl a in the wet polluted crusts. A remarkable shift in the bacterial community composition of oil-polluted crusts was detected, with the replacement of Cyanobacteria by Firmicutes . Sequences affiliated to Firmicutes constituted 86% of total sequences after 96 days of incubation with oil. This community shift was concomitant with alkanes degradation, as assessed by gas chromatography-mass spectrometry (GC–MS) analysis. Using oxygen microsensors, addition of oil to crusts was shown to result in an instantaneous decline in oxygen production but a quick recovery within hours of incubation. The net oxygen production and net photosynthesis decreased whereas the recovery time increased with increasing concentrations of oil. Recovery was not possible when crusts were exposed to ≥2000 mg oil g −1 crust. Incubation of crust pieces at different oil concentrations in air-tight bottles in the dark showed an increase in CO 2 evolution with increasing oil concentration. We conclude that oil pollution has drastic effects on crust microorganisms, and these effects depend on oil pollution levels, hydration conditions and duration of exposure. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biological soil crusts significantly increased soil enzyme activities. [•] Moss crusts had greater soil enzyme activities than cyanobacteria–lichen crusts. [•] The elapsed time since sand dune stabilization correlated positively with soil enzyme activity. [•] Soil enzyme activities under crusts varied with soil depth and season. [Copyright &y& Elsevier]

Abstract: Biological soil crusts (BSCs) play an important role in the dune fixation and maintaining soil biota in arid desert systems. Free-living soil nematode communities could be used as significant bioindicators to reflect soil recover regime after sand burial. However, the relationship between BSCs and nematodes is rarely known. To examine the effects of BSCs on soil nematodes, 72 soil samples under cyanobacteria–lichen and moss crusts were collected to analyse nematode communities in the different aged vegetated areas at the southeastern edge of the Tengger Desert. Our results showed the colonization and development of BSCs significantly enhanced nematode diversity. Nematode abundances, generic richness, H′, MI, EI and SI were greater under crusts than those under noncrust. In particular, nematode abundances, generic richness, H′, MI, EI and SI were positively correlated with crust ages. The differences in nematode communities were also dependent upon crust types. Nematode abundances and generic richness under moss crusts were higher than those under cyanobacteria–lichen crusts. This can be contributed to the present and succession of BSCs that increased thickness of topsoil after dunes have been stabilized, namely, creating suitable habitats and providing an essential food source for nematodes. [Copyright &y& Elsevier]

Abstract: Biological soil crusts are important cover in arid desert landscapes, yet their importance as habitats to secondary producers such as ants is relatively unknown. This study was conducted to determine if the presence and development of biological soil crusts on dune surfaces stabilized by revegetation facilitates ant establishment and survival. We measured topsoil properties and crustal features during different successional stages, which were characterized by cyanobacteria and algae, lichens, and mosses, respectively. The species richness and abundance (nest density) of ants were closely associated with silt content, soil organic matter, nitrogen and soil moisture, as well as topsoil temperature. However, ant nest distribution was largely dependent on the biomass and thickness of crusts and topsoil. These findings provide evidence that the recovery or development of biological soil crusts on dune surfaces in the Tengger Desert could favor and maintain higher ant species diversity. Therefore, the disturbance of crusts would result in a reduction of ant species richness and abundance in desert systems. [ABSTRACT FROM AUTHOR]

Frequent low-intensity fires are a natural component of the ecology of the Palouse prairies of northwestern North America. To study the effects of fire upon biological soil crusts (BSCs) occurring in these grasslands, we sampled three burned (in 2000) sites and three unburned sites in the Hell’s Canyon area (OR, USA) ∼1 year post-fire. We measured vascular plant and BSC cover, soil microbe pigmentation, texture and chemistry, and soil surface physical properties (stability and rugosity). Festuca idahoensis was two times more abundant in unburned plots (P=0.0006), and vascular plant and litter cover were generally higher in unburned plots. At the community scale, there was no difference in the lichen and moss species composition, suggesting much less drastic effects of fire on BSCs than reported in other systems. Soil surface stability (measured using slake value) was significantly lower in burned sites than unburned sites (median value=5 versus 6, P=0.008), a result which is likely due to the greater density of lichens and mosses encountered in the unburned plots. Soil microbe pigmentation was lower in burned plots (P=0.03), suggesting that the biomass of photosynthetic microbes had decreased; however, the presence of intra- and extracellular pigments in burned soils indicates that microorganisms were not eradicated. Pigments most strongly associated with cyanobacteria were more abundant in unburned sites, suggesting that cyanobacteria may have been more strongly impacted by the fire than other BSC components. Composition of nutrients and surface rugosity did not differ significantly between treatments. We hypothesize that Palouse prairie soil crusts are relatively resistant to wildfire because of low fire intensity and their occupation of space away from the vascular plant fuel load. [Copyright &y& Elsevier]