DOI: 10.5061/dryad.4j0zpc87g
title: Mycorrhizal phosphorus efficiencies and microbial competition drive root P uptake

description: Phosphorus (P) availability shows large differences among different soil
 types, affecting P nutrition of forest trees. Chemical binding of P to
 soil moieties affects partitioning of P between soil particles and
 solution, affecting soluble P concentrations upon which plants, their
 associated mycorrhizal symbionts, and microbes feed. The goal of this
 study was to characterize root P uptake by mycorrhizal and non-mycorrhizal
 root tips in competition with microbes in situ in the organic and mineral
 layer of a P-rich and a P-poor forest. We used intact soil cores (0.2m
 depth) from beech (Fagus sylvatica) forests to tracing the fate of 33P in
 soil, plant and microbial fractions. We used the dilution of 33P in the
 rhizosphere of each soil layer to estimate the enrichment with new P in
 mycorrhizal and non-mycorrhizal root tips and root P uptake. In soil cores
 from P-rich conditions, 25% and 75% of root P uptake occurred in the
 organic and mineral layer, respectively, whereas in the P-poor forest, 60%
 occurred in the organic and 40% in the mineral layer. Mycorrhizal P
 efficiency, determined as enrichment of new P in mycorrhizal root tips,
 differed between soil layers. Root P uptake was correlated with
 mycorrhizal P efficiency and root tip abundance but not with root tip
 abundance as a single factor. This finding underpins the importance of the
 regulation of mycorrhizal P acquisition for root P supply. The composition
 of mycorrhizal assemblages differed between forests but not between soil
 layers. Therefore, differences in P efficiencies resulted from
 physiological adjustments of the symbionts. Non-mycorrhizal root tips were
 rare and exhibited lower enrichment with new P than mycorrhizal root tips.
 Their contribution to root P supply was negligible. Microbes were strong
 competitors for P in P-poor but not in P-rich soil. Understory roots were
 present in the P-rich soil but did not compete for P. Our results uncover
 regulation of mycorrhizal P efficiencies and highlight the complexity of
 biotic and abiotic factors that govern P supply to trees in forest
 ecosystems.
description: <b>Collection of
 forest soil cores</b> We collected ten intact soil
 cores in the HP (27.6.2017) and the LP (19.6.2017) forest, respectively,
 using PVC pipes of 120 mm diameter and a length of 200mm. <b>Radioactive labeling and
 harvest</b> We labelled five soil cores per
 forest by addition of 1850 kBq of
 H<sub>3</sub><sup>33</sup>PO<sub>4</sub> (Hartmann Analytic GmbH, Braunschweig, Germany) in 40 ml of tap water to each soil core. <b>Analyses of root tips and mycorrhizal species </b> Fresh beech roots (10 fragments) were weighed and used to count the number of root tips under a stereomicroscope (Leica M205 FA, Wetzlar, Germany). <b>Determination</b> <b>of total and soluble phosphorus in roots and soil</b> Dry soil and root samples were milled in a ball mill (Retsch MN 400, Haan, Germany) to a fine powder. <b>Determination of <sup>33</sup>P by scintillation counting </b> The extracts of all soil, plant and root tip samples were used to measure <sup>33</sup>P.
description: Table
 1_Masses_P_33P Read_me1 contains
 information for Table 1 Table2_Morphotypes Read_me2 contains information for Table 2