The role of mycorrhizal fungi in acquisition of mineral nutrients by host plants is examined for three groups of mycorrhizas. These are; the ectomycorrhizas (ECM), the ericoid mycorrhizas (EM), and the vesicular-arbuscular mycorrhizas (VAM). Mycorrhizal infection may affect the mineral nutrition of the host plant directly by enhancing plant growth through nutrient acquisition by the fungus, or indirectly by modifying transpiration rates and the composition of rhizosphere microflora.A capacity for the external hyphae to take up and deliver nutrients to the plant has been demonstrated for the following nutrients and mycorrhizas; P (VAM, EM, ECM), NH4 ÷ (VAM, EM, ECM), N0 3-(ECM), K (VAM, ECM), Ca (VAM, EM), S042-(VAM), Cu (VAM), Zn (VAM) and Fe (EM). In experimental chambers, the external hyphae of VAM can deliver up to 80% of plant P, 25% of plant N, 10% of plant K, 25% of plant Zn and 60% of plant Cu. Knowledge of the role of mycorrhiza in the uptake of nutrients other than P and N is limited because definitive studies are few, especially for the ECM. Although further quantification is required, it is feasible that the external hyphae may provide a significant delivery system for N, K, Cu and Zn in addition to P in many soils. Proposals that ECM and VAM fungi contribute substantially to the Mg, B and Fe nutrition of the host plant have not been substantiated.ECM and EM fungi produce ectoenzymes which provide host plants with the potential to access organic N and P forms that are normally unavailable to VAM fungi or to non mycorrhizal roots. The relative contribution of these nutrient sources requires quantification in the field.Further basic research, including the quantification of nutrient uptake and transport by fungal hyphae in soil and regulation at the fungal-plant interface, is essential to support the selection and utilization of mycorrhizal fungi on a commercial scale.

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Drought and heat-induced forest dieback and mortality are emerging global concerns.Although Mediterranean-type forest (MTF) ecosystems are considered to be resilient to drought and other disturbances, we observed a sudden and unprecedented forest collapse in a MTF in Western Australia corresponding with record dry and heat conditions in 2010/2011.An aerial survey and subsequent field investigation were undertaken to examine: the incidence and severity of canopy dieback and stem mortality, associations between canopy health and stand-related factors as well as tree species response. Canopy mortality was found to be concentrated in distinct patches, representing 1.5% of the aerial sample (1,350 ha).Within these patches, 74% of all measured stems (> 1cm DBHOB) had dying or recently killed crowns, leading to 26% stem mortality six months following the collapse. Patches of canopy collapse were more densely stocked with the dominant species, Eucalyptus marginata, and lacked the prominent midstorey species Banksia grandis, compared to the surrounding forest. A differential response to the disturbance was observed among cooccurring tree species, which suggests contrasting strategies for coping with extreme water stress. These results suggest that MTFs, once thought to be resilient to climate change, are susceptible to sudden and severe forest collapse when key thresholds have been reached.

Summary• The fungal genus Pisolithus is cosmopolitan in warm temperate regions and forms ectomycorrhizal associations with a wide range of woody plants. To delimit phylogenetic Pisolithus species and identify their geographical distribution, 102 collections were made worldwide and their rDNA internal transcribed spacer (ITS) was sequenced.• Phylogenetic analyses of these sequences, together with 46 additional GenBank accessions, identified 11 species.• A strong phylogeographical pattern was observed related to the native geographical origin of the host plants. In the Holarctic, P. tinctorius was widely distributed, associated with Pinus and Quercus . It has been co-introduced with pines to other biogeographical regions. Several Pisolithus lineages, including P. aurantioscabrosus , occurred in restricted biogeographical regions associated with endemic plants, such as Afzelia in eastern Africa. Pisolithus albus , P. marmoratus and P. microcarpus were associated with Australasian hosts ( Eucalyptus , Acacia ) and were distributed with their hosts worldwide. By contrast, two additional unnamed species were restricted to Australia.• The present study shows that evolutionary lineages within Pisolithus are related to the biogeographical origin of the hosts. In addition, regional floras and endemic plants could act as hosts of endemic species of Pisolithus .

Globally, phosphorus (P) limits productivity of trees in many forests and plantations especially in highly weathered, acidic or calcareous profiles. Most trees form mycorrhizal associations which are prevalent in the organic and mineral soil horizons. This review critically examines mechanisms that enhance the acquisition of P by tree roots. Mycorrhizal roots have a greater capacity to take up phosphate (Pi) from the soil solution than non-mycorrhizal root tips. Factors that contribute to this include the extent of extraradical hyphal penetration of soil and the physiology and biochemistry of the fungal/soil and fungal/plant interfaces. Ectomycorrhizal (ECM) trees are likely to benefit from association with basidiomycetes that possess several high-affinity Pi transporters that are expressed in extraradical hyphae and whose expression is enhanced by P deficiency. To understand fully the role of these putative transporters in the symbiosis, data regarding their localization, Pi transport capacities and regulation are required. Some ECM fungi are able to effect release of Pi from insoluble mineral P through excretion of low-molecular-weight organic anions such as oxalate, but the relative contribution of insoluble P dissolution in situ remains to be quantified. How the production of oxalate is regulated by nitrogen remains a key question to be answered. Lastly, phosphatase release from mycorrhizas is likely to play a significant role in the acquisition of Pi from labile organic forms of P (Po). As labile forms of Po can constitute the major fraction of the total P in some tropical and temperate soils, a greater understanding of the forms of Po available to the phosphatases is warranted.

Eucalyptus species are considered to have ectomycorrhizas (ECM), but many also have vesicular–arbuscular mycorrhizas (VAM) and their relative importance is unclear. Interactions between ECM and VAM fungi colonizing roots of Eucalyptus species were examined in a glasshouse experiment. This experiment investigated competition between these two types of fungi and compared benefits provided to Eucalyptus globulus and E. urophylla. Eucalyptus seedlings were inoculated with spores of the ECM fungus Laccaria lateritia and/or pot‐ culture soil for a VAM fungus (species of Glomus, Acaulospora or Scutellospora). Initial inoculum levels were important, as VAM fungi became established much more rapidly than Laccaria. In plants with both types of mycorrhizas, Laccaria mycorrhizas substantially increased after 2 or 3 months and the proportion of roots with VAM declined. However, the proportion of roots with VAM also decreased significantly in plants without ECM after 2 months. Thus, the relative susceptibility of eucalypt roots to these mycorrhizal associations changed. Substantial growth responses to mycorrhizal inoculation occurred when a low concentration of phosphorus fertilization was used (5 mg kg−1), but not at a higher concentration (10 mg kg−1). Treatments where Laccaria was applied, alone or in combination with a VAM fungus, resulted in the largest growth increases relative to nonmycorrhizal plants. An Acaulospora isolate was the most effective VAM fungus for E. urophylla although other VAM fungi also increased growth relative to the control. VAM fungi alone had little effect on E. globulus growth, but plants inoculated with both ECM and VAM fungi were larger than plants only inoculated with Laccaria. ECM fungi had a major impact on root system form by reducing the proportion of fine roots (specific root length) relative to nonmycorrhizal plants or those with VAM. Changes in root colonization patterns over time must be considered in studies of ECM/VAM interactions, as there can be substantial changes in the relative importance of the two associations.

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SUMMARYTwenty isolates of Pisolithus, covering a range of hosts, basidiocarp types and geographic locations were corapared on their ability to form mycorrhiza in vitro with Eucalyptus grandis and to stimulate scedlmg growth in vivo. There was a large \ariation between isolates in the rate of mycorrhiza! development and this was used to categorize isolates into six types. Mycorrhiza of seediings inoculated with t\'pe I isolates were the most advanced with a duallayered mantle, a fuliy-developed Hartig net and radially elongated epidermal cells. Mycorrhiza of seedlings inoculated with types II-V isolates were progressively less advanced so that m\corrhiza of type V isolates had a thin single-lajered n:iantle, the Hartig net was onl\ partial!\ developed and the epidermal cells were not elongated. Root tipy of seedlings inoculated with type VI isolates were non-mycorrhizal. Inoculated seedlings were transplanted directly into undrained pots containing a yellow sand deficient in phosphorus. Growth stimulation of .E. grandis seedling.s in the glasshouse \aried greatly between Pisolithus isolates, with dry weight incrt-ases ranging from two to 45 times that of the non-inoculated t-ontrol seedlings. Extent of mycorrhiza] de\ elopment was positively correlated to growth stimulation in the glasshouse and it is proposed that this could be used as an indicator of isolate aggressiveness and consequently the potential of an isolate to promote tree growth. Key words; Aggressiveness, ectomycorrhiza. growth stimuiation. Eucalyptus grondis, Pisolithus. and subsequent seedling growth (Marx & Byran, INTRODUCTION j^^^. MaTx, 1981;Dixon, Garrett & Stelzer. 1987; Pisolithus tinctorius (Pers) Cocker & Couch is a Lamhamedi f/a/., 1*^90; Lei f/a/., 1990; Malajczuk, commercially important ectomycorrhizal fungus that Lapeyrie & Garbaye, 1990). has been used successfully to increase the growth of In Australia, Pisolithus is widely distributed in plantation eucalypts (Garbaye, Delwaulle & association with a range of host genera including Diangana, 1988; de la Cruz, Lorilla & Aggangan, Eucalyptus, Melaleuca, Acacia and AUocasuarina. 1990) and pines (Marx, Byran & Cordell. 1977; Little is know n about the variation among Australian Delwaulle, Garbaye & Okombi, 1982). P. tinctorius Pisolithus in their capacity to form ectomycorrhizal is considered to have a broad host range and is found associations and pron^ote the growth of eutalypts as world-wide associated with both angiosperms and previous studies have used only a limited number of gymnosperms (Molina, Massicotte & Trappe, 1992). isolates. Burgess, Malajczuk & Grove (1993) found However, the taxonomy of this genus is currently that Western Australian isolate H445, dramatically unclear and it may be composed of a number of increased the growth of E.|r/ofcu/w5 and £. ti/V^M^co/or species (Bronchart, Collange & Demoulin, 1975; under conditions of limiting phosphorus. Tonkin, Kope & Fortm, 1990; Burgess, Malajczuk & Deli, Malajczuk & McComb (1988) inoculated E. 1994. This observation h...