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Biological soil crusts (BSCs) consist of cyanobacteria, algae, fungi, lichens, and mosses, which live within the uppermost millimeters of the soil’s surface where they influence soil stability, nitrogen, and carbon cycles. BSCs are only a few millimeters thick but cover large expanses of ground allowing for possibly significant contributions to the carbon cycle in arid environments. Remote sensing of these organisms has been used to study BCS in a non-destructive manner over the last 36 years. In this project, we aimed to quantify the abundance and distribution of BSCs and to estimate their annual carbon fixation rate at different community stages in two unique research sites (T-East and T-West) in the Chihuahuan desert of southern New Mexico, USA. We first investigated the utility of an unoccupied aircraft system (UAS)-mounted hyperspectral camera to measure the spatial cover of two BSCs functional groups (light and dark BSC) in a shrub-dominated vs. predominantly grassland site. Using a spectral angle mapper (SAM) algorithm we classified the hyperspectral imagery into five cover classes (light BSC, dark BSC, bare soil, grasses, and shrubs). With observations collected utilizing a line point intercept (LPI) method, we quantified the percent cover of BSCs and vegetation within the transects to validate the SAM estimates. Lastly, we incorporated C-fixation rates from local BSC communities to estimate the mean annual C-fixation rates for both BSCs within our research plots. The SAM algorithm overestimated light biocrust (LBC) in T-East by 17.7% when compared with the LPI estimates. Inversely, the SAM underestimated dark biocrust (DBC) for T-East by 9.3% as well as underestimating both Light and DBCs for T-west (23.9% and 6.7% respectively) when compared to the LPI estimates. This produced a higher annual fixed CO2 value for T-East’s LBC of 36.4% and a lower rate for DBC of 37.2% in comparison with the LPI’s observations. The T-West annual fixed CO2 was underestimated by the SAM algorithm by 66.1% for LBC and 42.9% for DBC when compared to the LPI observations. The results indicate the heavily shrub-encroached T-East site had a better accuracy rate than the T-West grassland site for the accurate classification of the five cover classes. It was believed that the vegetation's close proximity to the soil surface and sample timing negatively interfered with the detection rates of light and dark BSCs.
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Biological Soil Crust Bacterial Communities Vary Along Climatic and Shrub Cover Gradients Within a Sagebrush Steppe Ecosystem
Numerous studies have examined bacterial communities in biological soil crusts (BSCs) associated with warm arid to semiarid ecosystems. Few, however, have examined bacterial communities in BSCs associated with cold steppe ecosystems, which often span a wide range of climate conditions and are sensitive to trends predicted by relevant climate models. Here, we utilized Illumina sequencing to examine BSC bacterial communities with respect to climatic gradients (elevation), land management practices (grazing vs. non-grazing), and shrub/intershrub patches in a cold sagebrush steppe ecosystem in southwestern Idaho, United States. Particular attention was paid to shifts in bacterial community structure and composition. BSC bacterial communities, including keystone N-fixing taxa, shifted dramatically with both elevation and shrub-canopy microclimates within elevational zones. BSC cover and BSC cyanobacteria abundance were much higher at lower elevation (warmer and drier) sites and in intershrub areas. Shrub-understory BSCs were significantly associated with several non-cyanobacteria diazotrophic genera, including Mesorhizobium and Allorhizobium - Neorhizobium - Pararhizobium - Rhizobium . High elevation (wetter and colder) sites had distinct, highly diverse, but low-cover BSC communities that were significantly indicated by non-cyanobacterial diazotrophic taxa including families in the order Rhizobiales and the family Frankiaceae. Abiotic soil characteristics, especially pH and ammonium, varied with both elevation and shrub/intershrub level, and were strongly associated with BSC community composition. Functional inference using the PICRUSt pipeline identified shifts in putative N-fixing taxa with respect to both the elevational gradient and the presence/absence of shrub canopy cover. These results add to current understanding of biocrust microbial ecology in cold steppe, serving as a baseline for future mechanistic research.
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- Award ID(s):
- 2012878
- PAR ID:
- 10233356
- Date Published:
- Journal Name:
- Frontiers in Microbiology
- Volume:
- 12
- ISSN:
- 1664-302X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fmicb.2021.569791
