Mycorrhizas and Other Specialized Nutrient-Acquisition Strategies: Their Occurrence in Woodland Plants From Kakadu and Their Role in Rehabilitation of Waste Rock Dumps at a Local Uranium Mine

Abstract

The presence of mycorrhizas, proteoid roots and leguminous nodules was determined in a range of woodland species (from a variety of habitats in soils formed on different parent materials) in the Kakadu area in the monsoonal tropics of northern Australia. In addition, the chemical fertility and the occurrence of mycorrhizal fungi and rhizobia in rudimentary soils ('minesoils') forming in situ on waste rock dumps at a mine site in the region were compared with stockpiled topsoils from the mine area and undisturbed topsoils collected from the surrounding native woodland. A major aim of these investigations was to assess the feasibility of rehabilitating the waste rock dumps without spreading topsoils. More than 90% of the woodland flora examined had one or more specialised nutrient-gathering mechanism. Mycorrhizas were found on 82% of the species, with some 16% of species having both ecto and VA mycorrhizas, often on the same individual plant. Many of these observations are the first records of mycorrhizal infection in the particular genera and species involved. Soil baiting and dilution experiments showed that rhizobia and mycorrhizal fungi were ubiquitous components of the soil biota in all undisturbed woodland soils. However, they were absent or poorly represented in the stockpiled topsoils and in some of the rudimentary soils formed in waste rock at the mine site. The diversity of spore types and/or numbers of infective propagules of VAM fungi was lower in stockpiled topsoils and in minesoils than in the undisturbed woodland soils. Nutrient omission experiments identified that acute deficiency of P, and to a lesser extent N, was a limitation to growth of seedlings on all soils. Zn deficiency was detected in the only soil for which this was examined. A glasshouse experiment, using a young minesoil and application of basal nutrients, demonstrated that inoculation of Acacia holosericea seedlings with rhizobium could completely alleviate the effects of N deficiency. Under conditions of both N and P deficiency, dual inoculation of A. holosericea with rhizobium and spores of the VAM fungus, Glomus, only partly overcame the limitations of P deficiency on seedling growth. Induction of deficiencies of P and Zn in a second minesoil (through application of basal nutrients), demonstrated that inoculation of seedlings of Eucalyptus pellita with spores of the ectomycorrhizal fungus, Scleroderma, partly alleviated the effects of both deficiencies. Rehabilitation strategies implemented at the mine site using either soils forming in situ on the waste rock dumps, or by spreading stockpiled topsoils, will need to ensure deficiencies of P and other nutrients are alleviated and that viable populations of mycorrhizal fungi and rhizobia are introduced and maintained during early phases of vegetation establishment.

Temporal and spatial dynamics of vesicular-arbuscular mycorrhizal fungi under the canopy of Zygophyllum dumosum Boiss. in the Negev Desert

“…When soil conditions are suitable for spore germination, mycorrhizal colonization increases and spore abundance decreases (Mason et al, 1992;Ragupathy & Mahadevan, 1993). Our results, similar to other studies in Mexico and Australia (Reddell & Milnes, 1992;Allen et al, 1998), suggest that the root distribution pattern of the tested plant and nutrient availability under the plant may have an effect on the abundance and colonization of VAM fungi on a tempo-spatial basis. Spore density and percentage of colonization of VAM structure groups, especially vesicular and arbuscular colonization, are an important component in the rhizosphere because of their contribution to water and nutrient absorption, especially in stressful environments.…”

Mixed-species plantations of Eucalyptus with nitrogen-fixing trees: A review

“…(Gardina and Malajczuk, 1988;Bellei et al, 1992;Adjoud-Sadadou and Halli-Hargas, 2000) and Acacia spp. (McGee, 1986;Bellgard, 1991;Brundrett and Abbott, 1991;Reddell and Milnes, 1992) can both form symbioses with arbuscular mycorrhizal fungi, Eucalyptus also form ectomycorrhizal associations as they age (Gardina and Malajczuk, 1988;Bellei et al, 1992). Therefore chemical stratification may occur in mixed plantations of Eucalyptus and N 2 -fixing species at certain stages of stand development when different mycorrhizal associations are formed.…”

On the success and failure of mixed-species tree plantations: lessons learned from a model system of Eucalyptus globulus and Acacia mearnsii

“…(Gardina and Malajczuk, 1988;Bellei et al, 1992;Adjoud-Sadadou and Halli-Hargas, 2000) and Acacia spp. (McGee, 1986;Bellgard, 1991;Brundret and Abbott, 1991;Reddell and Milnes, 1992) can both form symbioses with arbuscular mycorrhizal fungi. However, there is no evidence for this process to occur in mixtures of eucalypts and acacias; (3) because N-fixing plants often rely heavily on fixed N, which may be 10% to nearly 100% of the N used by the N-fixing plant (Binkley, 1992;Binkley and Giardina, 1997;Khanna, 1998;Fisher and Binkley, 2000;May and Attiwill, 2003) more soil N may be available to E. globulus plants before the fixed N is cycled and transferred to the E. globulus trees.…”