We set out to understand biologically available pools of phosphorus (P) in a cyanobacteria-dominated biological soil crust (biocrust). Current biogeochemical research has focused on nitrogen and carbon studies to understand these desert systems, as biocrusts are important drivers of dryland productivity and nutrient cycling. Although P has been characterized in drylands using extraction analyses, such as Hedley fractionation and Olsen-P, newly developed extraction methods incorporate more biologically relevant P fractions. Our hypothesis was that biocrust cover would increase P immobilization in comparison to areas with disturbed soils (no biocrust cover), and that the overall relative abundances of P, specifically in more easily accessible fractions, would be less than in mesic systems. To address this, we adopted a extraction method that incorporates four extractions using CaCl2, citric acid, a phosphatase enzyme, and HCl in parallel to emulate different bioavailable P fractions. We collected soils (10cm depth) from the Jornada Long-term Experimental Range in Las Cruces, NM from the interspaces of a Bouteloua eripoda dominated grassland, ranging in full cyanobacteria biocrust coverage to disturbed areas with no visible biocrust cover. Fresh soils were processed with each extractant and analyzed colormetrically for phosphate concentration using a microplate reader.
Results/Conclusions
We found that the soils collected from areas with cyanobacteria biocrust cover were significantly different from the soils collected in more disturbed interspace areas with no cyanobacteria dominance in three of the four P fractions. The concentration of P available via the CaCl2, citric acid and phosphatase enzyme extractant were significantly lower in all fractions, while the HCl extractant showed no significant difference between the biocrust covered versus the disturbed areas. Comparing this dryland system to mesic systems more commonly reported in the literature, we found that the more easily accessed P pools were comparatively low. This suggests that P is more tightly bound to the more dominant mineral surfaces in dryland soils, possibility due to higher temperatures, low precipitation, and lack of soil organic matter. The observed difference between collection types (biocrust coverage vs disturbed areas) suggests that biocrusts may immobilize P, supporting P storage vs. occlusion. Overall, this study provides evidence that cyanobacteria-dominated biocrusts affect P availability that may contribute to P accessibility in dryland ecosystems.