SUMMARYMaize {Zea mays L.) was grown in fertilized calcareous soil in pots which were separated by 30 fim nylon nets into three compartments, the central one for root growth and the two outer ones for hyphal growth. The size of each compartment was 40 x 25 x 3 cm. The treatments comprised of sterilized soil, either inoculated witb rhizosphere microorganisms (other than VA mycorrhizal fungi), with rhizosphere microorganisms together witb a VA mycorrbizal fungus [Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe] or remained non-inoculated (sterile control). As inoculum for rbizospbere microorganisms the roots with adhering rhizospbere soil of nonmycorrhizal maize plants was used.Compared to the non-inoculated (sterile) control, inoculation with rhizosphere microorganisms did not affect shoot dry weight and morphology, but increased total root length (17 %) and root length per unit root dry weight (35%). The additional inoculation with VA mycorrhizal fungi had no influence on tbe shoot dry weight but increased area and dry weight of the leaf blades by about 30% and the ratio leaf blade:leaf sheath + stem (w/w) by 41 %. Tbe most profound effect of VA mycorrhizal fungi inoculation was on root growth and morphology. Compared to the non-inoculated control, root dry weight was decreased by 16%, root length by 31 % and root hair density and length by 41 and 43 %, respectively.In mycorrhizal plants the transpiration rates per plant were about 30 % higher than in the other treatments and this is attributed to tbe larger leaf area. Water uptake rate per unit root length and per unit time was about twice as high in mycorrhizal plants. For several reasons a substantial hyphal water transport seems unlikely. The results stress the necessity of detailed studies on root morphology for interpretation of effects of mycorrhizal fungi on mineral nutrient uptake and water relations in plants.

An investigation was carried out to test whether the mechanism of increased zinc (Zn) uptake by mycorrhizal plants is similar to that of increased phosphorus (P) acquisition. Maize (Zea mays L.) was grown in pots containing sterilised calcareous soil either inoculated with a mycorrhizal fungus Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe or with a mixture of mycorrhizal fungi, or remaining non-inoculated as non-mycorrhizal control. The pots had three compartments, a central one for root growth and two outer ones for hyphal growth. The compartmentalization was done using a 30-/xm nylon net. The root compartment received low or high levels of P (50 or 100 mg kg -1 soil) in combination with low or high levels of P and micronutrients (2 or 10mgkg -1 Fe, Zn and Cu) in the hyphal compartments.Mycorrhizal fungus inoculation did not influence shoot dry weight, but reduced root dry weight when low P levels were supplied to the root compartment. Irrespective of the P levels in the root compartment, shoots and roots of mycorrhizal plants had on average 95 and 115% higher P concentrations, and 164 and 22% higher Zn concentrations, respectively, compared to non-mycorrhizal plants. These higher concentrations could be attributed to a substantial translocation of P and Zn from hyphal compartments to the plant via the mycorrhizal hyphae. Mycorrhizal inoculation also enhanced copper concentration in roots (135%) but not in shoots. In contrast, manganese (Mn) concentrations in shoots and roots of mycorrhizal plants were distinctly lower, especially in plants inoculated with the mixture of mycorrhizal fungi.The results demonstrate that VA mycorrhizal hyphae uptake and translocation to the host is an important component of increased acquisition of P and Zn by mycorrhizal plants. The minimal hyphae contribution (delivery by the hyphae from the outer compartments) to the total plant acquisition ranged from 13 to 20% for P and from 16 to 25% for Zn.

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.