Development of cyanobacterial application methods for soil protection and restoration: case studies in Australian drylands

Land degradation, as a result of increased soil erosion and loss of fertility among other factors, is currently one of the most serious environmental problems. In recent years, the role of cyanobacteria from soil biocrusts in re-establishing soil function of degraded areas is gaining interest due to the potential of these organisms for soil stabilization and increase of soil fertility. In order to fully exploit the use of cyanobacteria in large-scale restoration of degraded lands, new approaches that facilitate their application must be explored in order to face with the harsh abiotic conditions of these environments. In this presentation, we showcase two different methods for the inoculation of cyanobacteria from soil biocrust in degraded soils of Australian dryland ecosystems: i) direct inoculation of cyanobacteria cultures and ii) incorporation of cyanobacteria within extruded pellets. Three soil native cyanobacterial strains from two representative N-fixing genera (Nostoc and Scytonema) and a non-heterocystous filamentous genus (Leptolyngbya) previously collected from the Pilbara region (north-west Western Australia), were used as inoculum. Then, in a multifactorial microcosm experiment under laboratory conditions, we evaluated the survival and establishment of the cyanobacteria for both methods. For the direct inoculation, cultures of isolated cyanobacteria and a mixture of them were applied as a liquid inoculum directly into a degraded soil from the Pilbara. In the case of application using extruded pellets, fresh cultures of each strain alone and an equal mixed of them were added into a substrate composed of commercial bentonite powder and sand (1:10 weight ratio). The composed solution was extruded through a jerky gun with an extruder nozzle into pellets (1 cm diameter x 2 cm length) and dried at 30^oC for 24h. Pellets were then placed on the surface of three different degraded soils representative of Australian drylands: a mine waste from an active mine site in the Pilbara, a degraded soil from the Cobar Peneplain (New South Wales), and a soil from the Simpson Strzelecki Dunefields (South Australia). In both experiments, cyanobacteria growth and establishment were monitored. Our results showed that in both treatments cyanobacteria colonize almost the entire Petri dish surface in all treatments. Furthermore, the levels of chlorophyll a (a proxy for cyanobacterial biomass) remained constant on inoculated samples during the study period, suggesting that cyanobacteria survived the pelleting process. In the case of direct inoculation, a decrease of chlorophyll a was observed in the beginning but then it stabilized and started to increase at the final stage of the experiment. This process may be due to the adaptation period of the cyanobacteria in the new environment, which is most progressive in the case of pellets application. Overall, our results showed that cyanobacteria can be successfully applied as a liquid inoculum and incorporated into extruded pellets, quickly colonizing degraded soi substrates. These technologies are ready for further testing and refining through field trials, opening a wide range of opportunities to face with large scale restoration programs.