Growth of Corn Roots and Associated Arbuscular Mycorrhizae Are Affected by Long‐Term Tillage and Phosphorus Fertilization

Published in Agron. J. 104:1672–1678 (2012) Posted online 13 Sept. 2012. doi:10.2134/agronj2012.0153 Copyright © 2012 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. C one of the most important grain crops worldwide, is highly responsive to early P absorption (Miller, 2000) and P deficiency is a major constraint for its production in many low-input agro-ecosystems (Bayuelo-Jiménez et al., 2011). Phosphorus is an essential macronutrient that often limits plant growth due to its low bioavailability in soils. Enhanced P absorption depends on the extent to which roots are able to increase soil available P interception or to mobilize P from less soluble sources. Plant attributes determining the mobilization and absorption of P include root attributes, mycorrhizal associations, and rhizosphere conditions (Lambers et al., 2006). Most of these attributes can be modified by cropping practices, such as P fertilization and tillage (Hu et al., 2009; Jing et al., 2010; Miller, 2000). Repeated mineral P applications to soil increase soil P saturation level and general P fertility (Deubel et al., 2011), and this higher soil P fertility inhibits AM fungal development (Lekberg et al., 2008; Mathimaran et al., 2007; Treseder and Allen, 2002). In addition, P fertilization has been found to increase corn root length and mass (Ibrikci et al., 2009), stimulate root branching (Jing et al., 2010), and induce fine root proliferation in the fertilized soil zone (Jing et al., 2010). Beauregard et al. (2010) pointed out that tillage could modify the physical, chemical, and biological properties of a soil. Especially, the modifications in soil penetration resistance and air capacity may change soil functionality and P fertilizer requirement (Acton and Gregorich, 1995; Deubel et al., 2011). Normally, compared to no till, tillage tended to decrease AM fungal colonization in roots (Alguacil et al., 2008; Duan et al., 2010; Jasper et al., 1989; Kabir et al., 1997; McGonigle and Miller, 1996; Roldan et al., 2007) since tillage could destroy AM fungal propagules (Schalamuk and Cabello, 2010). Jansa et al. (2002, 2003) pointed out that tillage could cause a shift in AM fungal diversity. Reduced soil disturbance could favor AM fungal species richness (Boddington and Dodd, 2000), and the abundance of non-Glomus AM fungi (Jansa et al., 2002), such as Scutellospora spp. (Jansa et al., 2006). With regard to the influence of tillage on corn roots, the results are sometimes conflicting, perhaps as a result of differing conditions of the soil environment. Specifically, tillage can reduce (Hilfiker and Lowery, 1988), increase (Mosaddeghi et al., 2009; Qin et al., 2005), or have no effect (Raczkowski, 1989) on corn root length density. In addition, Qin et al. (2006) found that tillage could decrease average root diameter in corn. It was reported that corn P absorption could be modified by tillage or by P fertilization (Amusan et al., 2011; Chassot and Richner, 2002). Some studies conducted under controlled conditions indicated that the tillage-induced decrease in corn P absorption was due, at least in part, to the negative effects of tillage on the effectiveness of mycorrhizal symbiosis (Gavito and Miller, 1998; Miller, 2000). However, under field conditions, the reasons why tillage modifies corn P absorption remain unclear. Therefore, our study was performed in a long-term experiment site, which was established at an Agriculture and ABSTRACT Phosphorus deficiency is a major constraint for corn (Zea mays L.) production. Cropping practices, such as tillage, modify corn P absorption, but the underlying mechanism must be assessed. A study was conducted at a long-term (18-yr) experimental site in Quebec, Canada, to evaluate the effects of tillage and P fertilization on arbuscular mycorrhizal (AM) fungi, soil properties, root attributes, corn growth, and corn P concentration. Soil (0–10 cm) and plant samples were collected at the 8 to 10 leaf stage from plots under moldboard plow (MP) and no till (NT) fertilized with 0, 17.5, or 35 kg P ha–1. Tillage increased soil bulk density, vesicular colonization, shoot and root biomass, root surface area, average diameter, volume, total root length density, and the percentage of medium-sized roots; it decreased total soil C and N concentrations, specific root length, percentage of fine roots, and arbuscular and total AM fungal colonization. Phosphorus fertilization reduced total AM fungal colonization, enhanced soil Mehlich-3 P level, total root length density, and the percentage of fine roots. Corn shoot and root P concentrations, reduced by tillage, were positively correlated with the percentage of fine roots and arbuscular colonization, but negatively correlated with vesicular colonization and the percentage of medium-sized roots. Overall, P fertilization reduced total AM fungal colonization and increased root length density, and tillage decreased arbuscular development in roots and fine root growth in soil resulting in the low corn P concentration.