Effects of ectomycorrhizas and vesicular–arbuscular mycorrhizas, alone or in competition, on root colonization and growth of Eucalyptus globulus and E. urophylla

Abstract

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.

Seedling mycorrhizal type and soil chemistry are related to canopy condition of Eucalyptus gomphocephala

“…For this reason, we harvested the plants after 7 months to allow adequate time for ECM colonization to occur. This succession in containerized seedlings has been described previously (Chen et al 2000a;Santos et al 2001;Egerton-Warburton and Allen, 2001). The lack of ECM in seedlings grown in cores taken from under trees with declining canopies may result from a lack of suitable ECM fungi inoculum at these sites.…”

“…In particular, mycorrhizal fungi may be important in the health of E. gomphocephala. Although eucalypts can form both arbuscular mycorrhiza (AM) and ectomycorrhiza (ECM) (Lapeyrie and Chilvers 1985;Brundrett et al 1996;Chen et al 2000a), the latter generally dominate in Australian eucalypt forests. The importance of mycorrhizal fungi for tree physiology and ecosystem function is well established (Read and Perez-Moreno 2003;Smith and Read 2008;Plassard and Dell 2010).…”

New isolates of ectomycorrhizal fungi and the growth of eucalypt

“…Eucalyptus dunnii seeds were disinfected by immersion in ethanol 70% for 1 min, washed in sterile distilled water, and germinated under constant agitation in a sterilized nutrient solution containing boric acid (3 µM), glucose (2 g L -1 ) and calcium sulphate (500 µM), pH 5.7, for three days at room temperature (Chen et al, 2000).…”

The mycorrhizal‐associated nutrient economy: a new framework for predicting carbon–nutrient couplings in temperate forests

“…There has been a paucity of work conducted on trees which can associate with both AM and ECM fungi (Chen et al, 2000;Egerton-Warburton & Allen, 2001), particularly for field-grown trees (Querejeta et al, 2009). Many of the species which can associate with both AM and ECM (e.g.…”