Bioavailability of phosphorus to loblolly pine and red maple in clay and saprolite from the southeastern Piedmont, USA

This is the authors' abstract. We don't add key points for this paper.

Soil P is present in multiple forms through the profile with plants potentially accessing different P pools at different depths through distinct pathways. Understanding P pool distribution and dynamics is necessary for sustainable forest management. Our research investigates soil P dynamics in clay (at 60–100 cm depth) and saprolite (at 450–500 cm depth) of the Calhoun Critical Zone Observatory (CCZO) in South Carolina through a 1‐yr greenhouse planting of loblolly pine ( Pinus taeda L.) and red maple ( Acer rubrum L.). We compared total plant P uptake to changes in soil P pools defined by Mehlich 3 (MIII) P, Hedley P, or total P fractions and to indices of potential iron (Fe) reduction and phosphatase activity as potential pathways of P release. We hypothesized that (a) the soil content of MIII P would be insufficient to meet plant demand; (b) ectomycorrhizal (EM) pine to differ from arbuscular mycorrhizal (AM) maple in accessing organic P pools; and (c) Fe reduction to correlate with declines in NaOH P (associated with Fe‐bound P) with greater decreases in the Fe‐oxide‐rich clay layer. Our results indicated MIII extractable P is plant available but present in insufficient quantities to meet total demand. In Hedley P pools, resin P i and NaOH P i supplied the most P for plant growth, and stable P pools (concentrated HCl P and residual P) buffered losses from these P pools. Plant‐available P in these soils seems sufficient to meet long‐term plant demand particularly if deeply rooted trees grow into the saprolite that had higher available soil P supply.