Response of Mycorrhizal Switchgrass to Phosphorus Fractions in Acidic Soil

Abstract

In acidic soils, acquisition of phosphorus (P) by plants is limited because of low P availability and slight solubility. Arbuscular mycorrhial fungi (AMF) have the ability to access much of soil P and make it more available to plants. Therefore, pools of available P to mycorrhizal (AM) plants grown in acidic soil are usually higher than in nonmycorrhizal (nonAM) plants. Switchgrass (Panicum virgatum L.) was grown in five acidic soils (Lily, Porters, Tatum, Rayne, and Pacolet) containing various amounts of original P with four different isolates of AMF in a glasshouse. The different fractions of P in each soil were determined to assess their importance to plant acquisition by AM and non‐AM plants. Total and organic P fractions in soil were relatively high compared with other extractable P fractions that are considered available to plants (extractable fractions), but differences among soils in total and organic P were relatively narrow compared with extractable fractions. With the exception of G. intraradices, each of the AMF isolates used (Glomus clarum, Glomus etunicatum, Glomus intraradices, and Acaulospora mellea) enhanced growth to some extent when grown in each of the soils. However, the highest dry matter (DM) for each of the AM plants was soil dependent. Shoot concentrations of mineral nutrients generally increased in AM plants that enhanced growth. None of the AMF isolates was best for these acidic soils, nor for each P fraction or other soil characteristic measured. Extractable P fractions appeared to be more readily available to AM plants than nonextractable fractions. †R. B. Clark is now retired.