Direct and indirect effects of VA mycorrhizal fungi and rhizosphere microorganisms on acquisition of mineral nutrients by maize (Zea mays L.) in a calcareous soil

Abstract

SUMMARYMaize {Zea mays L.) was grown in a fertilized calcareous soil in pots which were separated by 30 /tm nylon nets into three compartments, a central one for root growth and two outer ones for hyphal growth. The treatments comprised of sterilised soil, either inoculated with rhizosphere microorganisms together with Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe, with rhizosphere microorganisms alone, or non-inoculated (sterile control).In the mycorrhizal treatment concentrations of P and Zn were increased in shoot and roots, as was uptake of P and Zn per unit root dry weight or per unit root length. Copper concentration in roots of mycorrhizal plants, and total uptake and uptake per unit root dry weight or per unit root length of Cu was also increased. The higher acquisition of P, Zn and Cu in the mycorrhizal plants is ascribed to VA mycorrhiza per se (hyphal uptake and translocation to the host). Besides these direct effects, VA mycorrhizal fungi and rhizosphere microorganisms affected the acquisition of other nutrients mostly through alteration of root morphology. In both mycorrhizal and sterile treatments, the decreased concentrations of Ca and Si in the shoot but increased concentrations in the roots seem to be related to restricted apoplasmic solute transport across the endodermal barrier due to decreased number of lateral roots.The concentration of K in both shoot and roots, and Fe in shoot were lower in mycorrhizal plants due to reduced root length. Manganese concentration was also distinctly lower in both shoot and roots in mycorrhizal and sterile treatments, an effect which is attributed to the decrease in Mn reduction in the rhizosphere. Irrespective of nutrient, the uptake per unit root length was higher in mycorrhizal plants, probably due to hyphal contribution and increased supply of nutrients to the root surface by mass flow. Soil analysis indicates hyphal translocation of K but not Mg.The results demonstrate that effects of VA mycorrhizal infection on root morphology and rhizosphere microorganisms have to be considered in interpretations of mycorrhizal efFects on mineral nutrient acquisition.

Effects of soil compaction on phosphorus uptake and growth of Trifolium subterraneum colonized by four species of vesicular–arbuscular mycorrhizal fungi

“…City Beach to increase the concentration of Zn in clover plants and Cu in clover roots, but not in the shoots, compared with G. etunicatum, and to some extent G. mosseae, might result from their greater formation of external hyphae in compacted soil. A similar increase in the concentration of Cu in the roots upon mycorrhizal colonization has been shown for Zea mays (Kothari, Marschner & Ro$ mheld, 1990). The reason for the increase being observed only in mycorrhizal roots is not clear, but might be due to sequestration of Cu in the fungus, for example, via a chemical reaction between Cu and fungal polyphosphate granules, as has been shown for Ca and Fe by White & Brown (1979).…”

The reduction in proline buildup in mycorrhizal plants affected by nematodes

“…Plants inoculated with AMF displayed good development and, hence, were more resistant to that stress because vascular cylinders are clogged and the root area decreases in plants infested by nematodes (Agrios, 1989). AMF provide benefits to the plant, likely through root hydration mechanisms strengthened or mediated by fungal hyphae (Hardie, 1985;Marulanda et al, 2003;Ruiz-Lozano and Azcón, 1995), facilitating mineral nutrient absorption (Varma, 1995) or through morphological changes in roots caused by AMF (Kothari et al, 1990). Such effects of mycorrhizae enable plants to maintain a better hydration and nutrition status at all times, even in the presence of the parasite (Augé, 2001).…”

Influence of Glomus etunicatum/Zea mays mycorrhiza on atrazine degradation, soil phosphatase and dehydrogenase activities, and soil microbial community structure

“…Studies have indicated that AM fungi can increase the activities of soil enzymes such as phosphatase and dehydrogenase (Dodd et al, 1987;Kothari et al, 1990;Vá zquez et al, 2000). Dehydrogenase, a soil oxidoreductase, is an intracellular enzyme catalyzing oxidoreduction reactions of organic compounds.…”