Mycorrhizal Mediated Partitioning of Phosphorus: Ectomycorrhizal (Populus x canescens x Paxillus involutus) Potential to Exploit Simultaneously Organic and Mineral Phosphorus Sources

Many natural and anthropogenic soils are phosphorus (P) limited often due to larger Pstocks sequestered in forms of low bioavailability. One of the strategies to overcome thisshortage lies in the symbiosis of plants with mycorrhizal fungi, increasing the plant Puptake of these hardly accessible sources. However, little is known about mycorrhizalfungal mediated partitioning of differently available P forms, which could contributeto more efficient use of P by plants and, thereby, reduce competition for soil P. Thisstudy aimed to investigate the uptake of P from differently bioavailable P sources byectomycorrhiza. For that, we conducted a rhizotrone study using Populus x canescensand its compatible ectomycorrhizal fungus Paxillus involutus. Four different P sources[ortho-phosphate (oP), adenosine monophosphate (AMP), hydroxyapatite (HAP), andoP bound to goethite (gP)] or only HAP as 1P control were supplied in separatecompartments, where only the fungal partner had access to the P sources. The amountof the specific P sources was increased according to their decreasing bioavailability. Inorder to distinguish between the P sources, we applied 33P to track its incorporation inplants by a non-destructive analysis via digital autoradiography. Our results show that anectomycorrhizal plant is able to utilize all provided P sources via its mycorrhizal fungalassociate. The acquisition timing was determined by the most bioavailable P sources,with oP and AMP over HAP and gP, and a mixed P pool over a single P source. Incontrast, the magnitude was defined by the by the amount of supplied P source provisionof additional nitrogen, hence AMP over oP and gP, as well as by P source complexity,with gP as the least favorable P form. Nevertheless, the results of the present studyprovide evidence that an ectomycorrhiza has the potential to occupy fundamental nichesof various P sources differing in their bioavailability, indicating that being a generalist in Pnutrition can facilitate adaptation to various nutritional settings in soil