Lime-Chlorosis and the Effect of Fire on the Growth of Three Seedling Populations of Eucalyptus obliqua L'hérit.

Abstract

A field experiment confirmed the existence of intraspecific variation in E. obliqua in relation to edaphic factors. A population from an acidic soil showed severe chlorosis, slow growth and low survival when grown on more alkaline calcareous soils, but was the fastest-growing population on fertile acidic soils. Seedling deaths in the field suggested that an interaction between mineral-nutrient and drought stress may be important in the survival of E. obliqua on the calcareous soils. Foliar analysis of seedlings from the acidic populations grown on calcareous soil in the field showed that chlorosis was closely correlated with high levels of phosphorus, low levels of iron and increased phosphorusliron ratios. In contrast, seedlings from the calcareous population showed only a mild chlorosis when grown on alkaline calcareous soils, with seedlings maintaining low levels of phosphorus. higher levels of iron and correspondingly low phosphorus/iron ratios. I t is suggested that lime-chlorosis exhibited by the acidic population may be the result of either an internal inactivation or reduced uptake of iron. A glasshouse experiment showed that the effects of the calcareous soil could be ameliorated by burning. Seedlings from both the acidic and calcareous populations showed increased growth, alleviation of chlorosis and reduced mycorrhizal infection when grown on burnt calcareous soil. Furthermore, the alleviation of chlorosis in seedlings from the acidic population was concomitant with a reduction in phosphorus content and phosphorushron ratios. However, in this experiment trends indicated higher levels of iron in chlorotic tissue compared with green tissue. Seedling establishment and survival on calcareous soils are likely to depend on both the seedling genotype and direct environmental factors, e.g. fire, operating at the time of regeneration.