The effects of oxalates produced by Salsola tragus on the phosphorus nutrition of Stipa pulchra.

Oxalic acid is produced by some species of plants and mycorrhizal fungi and it may solubilize unavailable soil phosphorus (P) bound by cations (Ca++, Al++, Fe+++). Field and greenhouse experiments were conducted to show whether oxalate produced by the annual Salsola tragus or added oxalic acid would solubilize P from the inorganic-bound soil P pool, making it available for uptake by Stipa pulchra. Oxalate could be leached in the laboratory from the senescent canopy of Salsola, and leaching by rainfall was hypothesized to be a source of potential increased soil P under the Salsola canopy. Both oxalate leached from the canopy of Salsola and added oxalic acid increased the availability of soil P in greenhouse experiments. The source of the increase in available soil P in the greenhouse experiment was shown to be the inorganic-bound P pool, as the total P concentration of the soil decreased with increasing oxalate. There were significant increases in Stipa shoot P in response to Salsola leachates and in response to added oxalate in the greenhouse studies. These results suggest an important role for oxalate in P cycling. On disturbed sites where Salsola invades it may act to facilitate the establishment of later seral species like Stipa by creating a nutrient island of available P.