Effect of a vesicular–arbuscular mycorrhizal fungus and rhizosphere micro‐organisms on manganese reduction in the rhizosphere and manganese concentrations in maize (Zea mays L.)

Abstract

SUMMARYMaize {Zea mays L. cv. Tau) plants were grown in a calcareous soil for six weeks in pots having separate compartments for growth of roots and vesicular-arbuscular (VA) mycorrhizal fungal hyphae. Soil was sterilized and either left non-inoculated (sterile treatment), or was inoculated with rhizosphere micro-organisms only (MO -VA) or with rhizosphere micro-organisms together with a VA mycorrhizal fungus [Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe (MO-I-VA)]. Concentrations of Mn in roots and shoots, as well as exchangeable Mn in rhizosphere soil, decreased in the order MO -VA > MO-t-V.-^ > sterile treatment. In all treatments, the concentration of exchangeable Mn was lower in the rhizosphere soil (0-5 mm distance from the root surface) thati in the bulk soil (5-15 or 15-25 mm distance from the root surface). In the rhizosphere soil, the total microbial population was sitnilar in mycorrhizal (MO-l-VA) and non-mycorrhizal (MO -VA) treatments, but the proportion of Fe-or Mti-reducers was 20-to 30-fold higher in the non-mycorrhizal treatment, suggesting substantial qualitative changes in rhizosphere microbiai populations upon root infection with the mycorrhizal fungi. The Mn^'''-reducing potential (net balance between reduction and oxidation) in the rhizosphere soil was also distinctly lower in mycorrhizal treattnent compared to non-mycorrhizal tt-eatment.In the sterile treatment, low Mn*'^ -reducing potential and correspondingly low concentration of exchangeable Mn in soil, compared to the other treatments, indicates the importance of micro-organisms in Mn reduction in soil and acquisition of Mn by plants. Therefore, the lower Mn concentrations in mycorrhizal plants are most probably caused by a shift in composition and activity of rhizosphere micro-organisms. As a side effect of the treatments, improved soil aggregation, as indicated by soil adhering to the nylon net (facing hyphal compartments) after platit harvest, occurred in non-mycorrhizal and sterile treatments but not in the mycorrhizal treatment.

Effects of ectomycorrhizal inoculation and the type of substrate on mycorrhization, growth and nutrition of containerised Pinus pinea L. seedlings produced in a commercial nursery

“…Different authors [2,20] have demonstrated a lower Mn uptake in plants mycorrhizal with arbuscular fungi compared with non-mycorrhizal ones. The availability of Mn for the plants is dependent on oxidation/reduction processes often driven by soil microorganisms capable to reduce Mn [22].…”

Root colonization of mycorrhizal and non‐mycorrhizal pepper (Capsicum annuum) by Pseudomonas fluorescens 2–79RL

“…It has been speculated that high carbon demand of the fungus decreases root exudation, thus reducing substrate availahility for micro-organisms in the rhizosphere (Dixon et al, 1989;Pauhtz & Linderman, 1989). It has also been suggested that mycorrhizal infection could alter the composition of the root exudates (Kothari et al, 1991;Waschkies et al, 1994). However, it cannot be ruled out that the observed effect of mycorrhizal infection on the population density and physiological status of P. fluorescens 2-79RL was only indirect by favouring certain bacterial groups that are antagonistic to P. fluorescens 2-79RL.…”

“…tritium incorporation (Chnstenseii & Jakobseii, In most instances, arbuscular mycorrhizal (AM) 1993), and might influence the species composition infection increases the total number of aerobic of the soil microbial community by stimulating some bacteria m the rhizosphere (Bagyaraj & Menge, groups and decreasing others (Ames et al. 1984;1978;Mever & Linderman, 1986;Krishnaraj & Secilia & Bagyaraj,, 1987;Kothari et al, 1991;Sreenivasa' 1992;Posta, Marschner & Romheld, Christensen & Jakobsen, 1993;Posta et al, 1994). 1994), although no effect (Kothari, Marschner & 1986; Paulitz & Linderman, 1989;Klyuchnikov & Kozhevm, 1990 ;Posta et al, 1994;Waschkies et al, 1994).…”

Absorção e translocação de manganês por plantas de soja micorrizadas, sob doses crescentes deste nutriente

“…A atenuação da toxidez de Mn pode se dar tanto por efeitos indiretos da micorrização, como pela alteração da composição da comunidade microbiana da micorrizosfera (Kothari et al, 1991), ou, ainda, pelo aumento da absorção de P, principalmente em solos com alta capacidade de fixação de fosfatos (Li et al, 1991). Para limitar as interferências de outros microrganismos do solo e da fixação de P, este trabalho foi realizado em substrato arenoso autoclavado.…”