title: Autoclaving soil samples affects algal-available phosphorus.
abstract: Unwanted microbial interference in samples used for biological assays of P availability has routinely been eliminated by autoclaving samples before inoculation with algae. Twenty-three soils were selected to evaluate the relationship between algal growth in P-deficient solutions containing small quantities of soil and the level of P determined by a variety of tests used to evaluate P availability in soils and sediments. Soils were either autoclaved or not before addition to flasks containing P-starved algae in a nutrient solution without P. Compared to non-autoclaved samples, autoclaving soil resulted in approximately 60% more available P as estimated by increased algal growth. However, algal growth in the presence of autoclaved soil was highly correlated with growth in the presence of non-autoclaved samples. There was no consistent change in the correlations (r) between autoclaving or non-autoclaving samples in the relationships of algal numbers with P extracted by a number of soil tests. The effect of autoclaving soil on soluble P was also evaluated for a subset of six soils. Autoclaved soils had significantly greater concentrations of soluble P than non-autoclaved soils, with 78% more orthophosphate monoesters, 60% more orthophosphate diesters, and 54% more soluble inorganic P. Inhibition of algal growth may have occurred with two high-Zn soils that produced relatively low numbers of algae despite being very high in estimated available P by all extraction methods. Removing those samples from the calculations dramatically improved correlations between soil P measured by various methods and algal growth. With these two soils removed from calculations, algal growth with autoclaved soil was most highly correlated with Olsen P (r = 0.95), with other correlations as follows: Fe-oxide strip (r = 0.80), Mehlich 3 (r = 0.75,), modified Morgan (r = 0.61), and Bray-Kurtz 1 (r = 0.57).
authors.affiliation: Department of Plant and Soil Science, University of Vermont, Burlington, 05405, USA.
authors.forename: Brandon H
authors.initials: BH
authors.lastname: Anderson
authors.forename: Frederick R
authors.initials: FR
authors.lastname: Magdoff
mesh_terms: D001682:Biological Availability; D056890:Eukaryota / Q000254:growth & development / Q000378:metabolism*; D006358:Hot Temperature; D010758:Phosphorus / Q000032:analysis / Q000378:metabolism / Q000493:pharmacokinetics*; D012987:Soil; D013242:Sterilization / Q000379:methods*
chemical_list: D012987:Soil; D010758:Phosphorus