Periodicity of Fine Root Growth in Jarrah (Eucalyptus marginata Donn Ex Sm.)

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Abstract
The timing of new surface root growth in jarrah (Eucalyptus marginata) was followed for a 15-month period in the field. The periodicity of new root growth was similar for long roots, non-mycorrhizal and mycorrhizal root clusters. Root growth was initiated during two peak periods in spring (September-October) and following autumn rain (May-June). Little new root activity was recorded in late winter (August) or during summer drought. Rapid root growth occurred within 2 days of a storm (47 mm rain) in February. In addition, short roots formed after very light showers of rain (<5 mm) in late summer. Much of the framework for fine feeder roots was built up after autumn rain. In contrast to new long root growth which was equally spread between spring and late autumn, the majority of new mycorrhizal roots were produced from May to July. Root growth ceased when warm surface soils dried out and commenced when the soils were moist after rain. Much of the new root growth in jarrah occurred when the root pathogen Phytophthora cinnamomi was active in the soil.