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Effects of fire on the growth, nutrient content and rate of nitrogen fixation of the cycad Macrozamia riedlei



Effects of fire on the growth, nutrient content and rate of nitrogen fixation of the cycad Macrozamia riedlei



Australian Journal of Botany 28(3): 271-281



The response of M. riedlei (Gaud.) C.A. Gardn. to fire and its contribution to the input of N to the jarrah (Eucalyptus marginata Donn ex Sm.) forest ecosystem of southwestern Australia were studied by measuring the biomass and nutrient content of plant parts, and the nitrogenase activity of coralloid roots, in relation to time since burning. Leaf growth was rapid during the 1st yr following fire. In forest burned 1-5 yr previously, the ratio of weight of leaves to weight of bole did not differ significantly between sites. On a site burned 7 yr previously a reduced proportion of leaves in the total plant biomass was attributed to a yellowing and sensescence of leaves. The ratio of weight of corralloid roots to weight of boles was greatest on the most recently burned site. Concentrations of N and P in leaves, and P, K and Zn in corralloid roots, were significantly higher in plants growing in recently burned forest. Concentrations of Ca, Na and Cl in leaves were higher on sites which had not been burned recently. The rate of acetylene reduction, expressed per unit of bole weight, was greatest where forest was burned 1 yr before sampling and decreased to a minimum where burning had occurred 7 yr previously. This trend resulted from a decrease in both the weight and nitrogenase activity of coralloid roots with increasing time since burning. Estimated rates of N fixation were 8.4 and 1.4 kg ha-1 yr-1 on sites burned 1.5 and 7 yr previously. In the period between successive prescribed burns (5-7 yr), M rieldei fixed about 35 kg N ha-1. This may be a significant input in relation to the N balance of the jarrah forest ecosystem.

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Accession: 001580877

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DOI: 10.1071/BT9800271



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