Tephra is an effective P diffusion barrier in root exclusion experiments

Background and Aims To understand the bioavailability of phosphorus (P) under different conditions, it is important to consider the P uptake by plant roots and arbuscular mycorrhizal fungi (AMF) hyphae separately. This can be done with root study containers that separate soil into root– and hyphal–zone by a layer of nylon <30 μm mesh, which impedes root access to parts of the soil while enabling exploration by AMF (termed the hyphal zone). However, diffusion of P from the hyphal zone to the root zone can complicate the analysis of such experiments when a concentration gradient is created by a P–rich patch in the hyphal zone. This study tested whether a layer of tephra with high P sorption characteristics can be arranged to prevent P diffusion between the root zone and the hyphal zone.