Abstract
Eucalyptus obliqua, the most widespread timber tree in Tasmania, is a pioneer after fire which can eliminate the organic layer of forest soil, exposing the underlying mineral soil. We compared seedling growth, mycorrhiza formation, and mineral nutrient limitation in organic layer vs. mineral soil. We grew E. obliqua seedlings separately in pots of organic layer and mineral soil in a glasshouse. Additional treatments of organic soil only, involved fully crossed methyl-bromide fumigation and fertilization. Fertilization comprised chelated iron for 121 days after transplant (DAT) followed by soluble phosphorus. At 357 DAT, whole plant dry weight was three times greater in ambient organic than in mineral soil. In organic soil, fumigation halved ectomycorrhiza abundance and reduced seedling growth at 149 DAT, but by 357 DAT when negative effects of fumigation on seedling growth had disappeared, neither fumigation nor fertilization affected mycorrhiza abundance. Iron fertilization diminished seedling growth, but subsequent phosphorus fertilization improved it. E. obliqua seedlings grow much better in organic layer soil than in mineral soil, although phosphorus remains limiting. The prevalent forestry practice of burning to mineral soil after timber harvest exposes a poor growth medium likely only partially compensated by fire-induced mineral soil alterations.
Highlights
Eucalyptus obliqua L’Hér. (Myrtaceae) is a tree species of broad ecological amplitude reflecting diverse ecotypes (Anderson and Ladiges, 1978; Wilkinson, 2008; Bloomfield et al, 2011) in southeastern Australia including Tasmania
Ectomycorrhizas have been demonstrated to enhance the growth of E. regnans seedlings (Ashton, 1976; Launonen et al, 1999, 2004), we found no reports of the effects of either ectomycorrhizas or arbuscular mycorrhizas on E. obliqua
After approximately 1300 cm3 of soil was dispensed to 20 plastic pots (120 mm diameter × 140 mm deep) for each treatment, one-half of the pots containing organic soil were treated with methyl bromide gas at a rate of 48 g m−3 for 24 h at 21◦C (Tasmanian Ports Quarantine Facility, Hobart)
Summary
Eucalyptus obliqua L’Hér. (Myrtaceae) is a tree species of broad ecological amplitude reflecting diverse ecotypes (Anderson and Ladiges, 1978; Wilkinson, 2008; Bloomfield et al, 2011) in southeastern Australia including Tasmania. Wet, mountainous areas it forms tall, open forests, sometimes mixed with other eucalypt species such as the closely-related E. regnans F. E. obliqua is capable of becoming a giant tree with a reported maximum height of 98.8 m (Tng et al, 2012). Like other giant eucalypts including E. regnans (Dignan et al, 1998; Van Der Meer et al, 1999) and the tropical E. grandis W. Rapid early growth is imperative for seedlings to avoid being overtopped by competing vegetation (Neyland et al, 2009), but eucalypt seedlings often are poor competitors for soil resources needed to achieve the rapid growth of which they are capable (Withers, 1979). With its intolerance of shade and belowground competition, and a capacity for dense recruitment (Ashton, 1986) and rapid early growth, E. obliqua essentially is a long-persistent, pioneer species in rainforest environments where the primary disturbance is landscape fire (Tng et al, 2012)
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