Abstract
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.
Highlights
Drylands are characterized by low precipitation and limited vegetation (Belnap and Lange, 2003; Huang et al, 2016)
Blay et al (2017) examined variation in biological soil crusts (BSCs) bacterial phyla with respect to elevation at a single time point. These authors found that the abundance of Actinobacteria and Firmicutes increased whereas Cyanobacteria decreased at higher elevations with cooler, wetter climates. We significantly extend this prior work by quantifying variation of BSC bacterial communities, with respect to both structure and composition, over multiple seasons and with previously defined environmental factors, namely grazing disturbance, shrub/intershrub patches, and climatic shifts with elevation
Biological soil crusts are increasingly acknowledged as providing vital functions in drylands; the ecology of BSCs associated with colder, more mesic drylands in the Intermountain West is unknown
Summary
Drylands are characterized by low precipitation and limited vegetation (Belnap and Lange, 2003; Huang et al, 2016). BSC communities perform vital ecological functions (Belnap et al, 2016; Bowker et al, 2018), including reducing nutrient loss by runoff (Barger et al, 2006), decreasing erosion by wind (Belnap and Lange, 2003), fixing carbon (C) and nitrogen (N; Belnap, 2003; Belnap and Lange, 2003), facilitating vascular plant establishment (Belnap, 2003; Coe et al, 2014), and decreasing soil surface albedo (Belnap and Lange, 2003; Kuske et al, 2012) Despite their importance in the ecosystem structure and function in drylands, current understanding of how BSC communities respond to changing climatic conditions and environmental disturbances is still incomplete (Belnap, 2002; Belnap and Lange, 2003; Yeager et al, 2004; Kuske et al, 2012; Chen et al, 2020). Addressing these knowledge gaps may be important in environments whose winter precipitation is primarily snow, as these areas are likely to undergo pronounced climate changes, with declines in precipitation amount and shifts in precipitation phase (Nayak et al, 2010; Seyfried et al, 2011; Flerchinger et al, 2019)
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