Abstract
The health of Eucalyptus gomphocephala is declining within its natural range in south-western Australia. In a pilot study to assess whether changes in mycorrhizal fungi and soil chemistry might be associated with E. gomphocephala decline, we set up a containerized bioassay experiment with E. gomphocephala as the trap plant using intact soil cores collected from 12 sites with E. gomphocephala canopy condition ranging from healthy to declining. Adjacent soil samples were collected for chemical analysis. The type of mycorrhiza (arbuscular or ectomycorrhizal) formed in containerized seedlings predicted the canopy condition of E. gomphocephala at the sites where the cores were taken. Ectomycorrhizal fungi colonization was higher in seedling roots in soil taken from sites with healthy canopies, whereas colonization by arbuscular mycorrhizal fungi dominated in roots in soil taken from sites with declining canopies. Furthermore, several soil chemical properties predicted canopy condition and the type of mycorrhizal fungi colonizing roots. These preliminary findings suggest that large-scale studies should be undertaken in the field to quantify those ectomycorrhiza (ECM) fungi sensitive to E. gomphocephala canopy decline and whether particular ECM fungi are bioindicators of ecosystem health.
Highlights
The health of many forest and woodlands is in decline
Root tips was positively related to TCHI (F(1, 46) = 14.975, β = 0.784, P < 0.0001), but negatively related to arbuscular mycorrhiza (AM) colonization (F(1, 46) = 7.357, β = −0.237, P < 0.009) (Fig. 3). This pilot study found that the gross type of mycorrhiza formed on tuart seedlings grown in soil cores taken from the field predicted the canopy condition of E. gomphocephala at the sites where the cores were taken
ECM dominated seedling roots produced in soils taken from under healthy canopies whereas AM dominated seedling roots in soils taken from under trees with declining canopies
Summary
The health of many forest and woodlands is in decline. The causes of some of these declines are understood, for example, soil acidification leading to depletion of soil calcium is associated with Acer saccharum (sugar maple) decline in the USA and Canada Other declines are manifested without known causes including many eucalypt declines in Australia (Jurkis 2005; Robinson 2008), most of which are poorly understood. One of these is Eucalyptus gomphocephala (tuart), a woodland tree endemic to the Swan Coastal Plain of Western Australia (Elridge et al 1994), that has experienced a marked reduction in health and vitality (known as tuart decline) (Archibald et al 2010; Cai et al 2010) locally reaching up to 90 % mortality across all age classes (Tuart Response Group 2002). 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)
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