Wet season cyanobacterial N enrichment highly correlated with species richness and <i>Nostoc</i> in the northern Australian savannah

Abstract

Abstract. The Boodjamulla National Park research station is situated in the north-western Queensland dry savannah, where the climate is dominated by summer monsoons and virtually dry winters. Under shrub canopies and in between the tussock grasses cyanobacterial crusts almost entirely cover the flood plain soil surfaces. Seasonality drives N fixation, and in the savannah this has a large impact on both plant and soil function. Many cyanobacteria fix dinitrogen that is liberated into the soil in both inorganic and organic N forms. We examined cyanobacterial species richness and bioavailable N spanning 7 months of a typical wet season. Over the wet season cyanobacterial richness ranged from 6 to 19 species. N-fixing Scytonema accounted for seasonal averages between 51 and 93 % of the biocrust. Cyanobacterial richness was highly correlated with N fixation and bioavailable N in 0–1 cm. Key N-fixing species such as Nostoc, Symploca and Gloeocapsa significantly enriched soil N although Nostoc was the most influential. Total seasonal N fixation by cyanobacteria demonstrated the variability in productivity according to the number of wet days as well as the follow-on days where the soil retained adequate moisture. Based on total active days per month we estimated that N soil enrichment via cyanobacteria would be ∼ 5.2 kg ha−1 annually which is comparable to global averages. This is a substantial contribution to the nutrient-deficient savannah soils that are almost entirely reliant on the wet season for microbial turnover of organic matter. Such well-defined seasonal trends and synchronisation in cyanobacterial species richness, N fixation, bioavailable N and C fixation (Büdel et al., 2018) provide important contributions to multifunctional microprocesses and soil fertility.

Strategies for restoring the structure and function of lichen‐moss biocrust communities

“…Soil water availability subsequently influences rates of soil C and N transformations, through its influence on soil microbial activity (e.g., Xiang et al 2008). Over longer time spans, naturally reestablishing biocrusts are known to increase the availability of soil C and N (20+ years, Liu et al 2014;10+ years, Jia et al 2017), but few studies have considered the effects of natural or assisted biocrust recovery on soil C and N in the short term or related these biogeochemical effects to soil water availability (Chiquoine et al 2016;Williams et al 2018). When natural biocrust reestablishment was evaluated two years after disturbance across four disparate European sites, total soil C and N was unchanged (Williams et al 2018).…”

“…Over longer time spans, naturally reestablishing biocrusts are known to increase the availability of soil C and N (20+ years, Liu et al 2014;10+ years, Jia et al 2017), but few studies have considered the effects of natural or assisted biocrust recovery on soil C and N in the short term or related these biogeochemical effects to soil water availability (Chiquoine et al 2016;Williams et al 2018). When natural biocrust reestablishment was evaluated two years after disturbance across four disparate European sites, total soil C and N was unchanged (Williams et al 2018). In contrast, in the Mojave Desert, USA, assisted biocrust restoration increased soil inorganic N availability after only 18 months (Chiquoine et al 2016).…”

Microbial biobanking – cyanobacteria-rich topsoil facilitates mine rehabilitation

“…The greatest determination of species richness occurred at quite shallow depths with highly significant decreases in richness beyond 6 cm of depth, even in the 9-month-old stockpile. Nonetheless, the resilience of the individual cyanobacterial species to burial in topsoil stockpiles appeared good; however, in an arid environment recolonisation and community diversity could be impeded by drought (Williams and Büdel, 2012).…”

“…Barger et al, 2016;Belnap and Eldridge, 2001;Bowker et al, 2014;Büdel et al, 2009;Chilton et al, 2017;Chiquoine et al, 2016;Weber et al, 2016). Similarly, in south-western Queensland and northern Australia cyanobacterial species richness was strongly linked to increased bioavailable nitrogen and carbon uptake Williams et al, 2018;Williams and Eldridge, 2011). Environmentally induced strategies, which have developed over a long evolutionary history, reflect their habitat.…”

Resting Subtropical Grasslands from Grazing in the Wet Season Boosts Biocrust Hotspots to Improve Soil Health

“…These biocrusts are dominated by photosynthesizing cyanobacteria that exude sticky polysaccharides to bind soil particles and protect from erosion. Cyanobacteria and other diazotrophic bacteria improve soil fertility with nitrogen fixation generating bioavailable nitrogen for pasture plants [16,17]. We investigated the drivers of soil function that influence the key principles for grazing management in northern Australia [18] including: (1) manage stocking rates to meet goals for livestock production and land condition, (2) periodically rest pastures to maintain a good condition, and (3) restore pastures from poor condition to increase productivity.…”