Biocrust Soil Research Articles

Reference for different sensitivities of greenhouse gases effluxes to warming climate among types of desert biological soil crust

There is much uncertainty about how climate warming will impact greenhouse gases (GHG) budget in dry environments due to the lack of available data for desert biocrust soil. We implemented a 2.5-year field measurement of CO2, CH4 and N2O effluxes in cyanobacteria-dominated, moss-dominated and mixed (cyanobacteria, moss and lichen) biocrust soils using open-top-chambers to simulate climate warming (1.2 °C on average). Desert biocrust soils generally acted as a weak sink of atmospheric CH4 and N2O. Although warming effects on daily CO2, CH4, and N2O effluxes varied depending on sampling date and biocrust soil, there was no significant difference in daily, monthly and seasonal average CO2, CH4 and N2O effluxes between warming and control in most cases for three biocrust soils. However, warming caused a marginal (p = 0.06) decrease (14.2%) in annual accumulative CO2 efflux in moss-dominated biocrust soil due to the drought effects caused by warming indirectly and OTC sheltering of precipitation directly, while there was no significant difference between warming and control for cyanobacteria-dominated and mixed biocrust soils, implying a neutral response of GHG effluxes to climate warming. These results suggest that the GHG budget in arid desert biocrust soil would not be significantly changed in the warmer future when the direct negative effects of drought on CO2 effluxes were excluded. Therefore, a marginal decrease of accumulative CO2 effluxes in response to warming coupled with drought for moss-dominated biocrust soil might offer a weak negative feedback to warming and drier climate change pattern.

Biological soil crusts structure the subsurface microbiome in a sandy agroecosystem

Biological soil crusts (biocrusts) are commonly found in semi-arid ecosystems and complete biological nitrogen (N) fixation, build soil carbon (C) stocks, and increase soil moisture. Biocrusts were recently identified in Florida agroecosystems, and based on traits of semi-arid biocrusts, could contribute to crop growth and soil health. This study determined the influence of biocrusts in a Florida citrus orchard on microbial diversity and composition of surface and crop root zone soil as related to soil C, N, and moisture. Soil samples were collected from areas with biocrust and proximate bare soil (control) in a Florida, USA, citrus orchard. Cores were divided into three soil depths, and soil bacterial and fungal communities were characterized using the 16S rRNA gene and ITS region sequences, respectively. Biocrust presence and sampling depth significantly impacted microbial community composition. Cyanobacteria and heterotrophic diazotrophs had low relative abundances compared to copiotrophic bacteria in the biocrust soil. Soil below biocrusts had increased moisture, nutrient concentrations, and relative abundances of nitrifying bacteria compared to the root zone below bare soil. Copiotrophic bacteria were enriched under biocrusts, indicating potential for nutrient competition between roots and microorganisms. Biocrust subsoil had elevated relative abundances of Ascomycota and Basidiomycota which contributed to higher fungal community richness and evenness in the rooting zone. Biocrust subsoil had increased relative abundances of microbiota compared to bare soil without biocrusts, potentially influencing nutrient cycling, crop nutrient uptake and growth, and soil health.

Spatial segregation of the biological soil crust microbiome around its foundational cyanobacterium, Microcoleus vaginatus, and the formation of a nitrogen-fixing cyanosphere

BackgroundBiological soil crusts (biocrusts) are a key component of arid land ecosystems, where they render critical services such as soil surface stabilization and nutrient fertilization. The bundle-forming, filamentous, non-nitrogen-fixing cyanobacterium Microcoleus vaginatus is a pioneer primary producer, often the dominant member of the biocrust microbiome, and the main source of leaked organic carbon. We hypothesized that, by analogy to the rhizosphere of plant roots, M. vaginatus may shape the microbial populations of heterotrophs around it, forming a specialized cyanosphere.ResultsBy physically isolating bundles of M. vaginatus from biocrusts, we were able to study the composition of the microbial populations attached to it, in comparison to the bulk soil crust microbiome by means of high-throughput 16S rRNA sequencing. We did this in two M. vaginatus-dominated biocrust from distinct desert biomes. We found that a small, selected subset of OTUs was significantly enriched in close proximity to M. vaginatus. Furthermore, we also found that a majority of bacteria (corresponding to some two thirds of the reads) were significantly more abundant away from this cyanobacterium. Phylogenetic placements suggest that all typical members of the cyanosphere were copiotrophs and that many were diazotrophs (Additional file 1: Tables S2 and S3). Nitrogen fixation genes were in fact orders of magnitude more abundant in this cyanosphere than in the bulk biocrust soil as assessed by qPCR. By contrary, competition for light, CO2, and low organic carbon concentrations defined at least a part of the OTUs segregating from the cyanobacterium.ConclusionsWe showed that M. vaginatus acts as a significant spatial organizer of the biocrust microbiome. On the one hand, it possesses a compositionally differentiated cyanosphere that concentrates the nitrogen-fixing function. We propose that a mutualism based on C for N exchange between M. vaginatus and copiotrophic diazotrophs helps sustains this cyanosphere and that this consortium constitutes the true pioneer community enabling the colonization of nitrogen-poor soils. On the other hand, a large number of biocrust community members segregate away from the vicinity of M. vaginatus, potentially through competition for light or CO2, or because of a preference for oligotrophy.

Biocrust ecology: unifying micro- and macro-scales to confront global change.

Biocrust ecology: unifying micro- and macro-scales to confront global change.