A canker disease caused by the fungus Quambalaria coyrecup is devastating marri (Corymbia calophylla) trees throughout much of its native range in the southwest of Western Australia. Disease incidence is higher in remnant stands that border cleared land such as road edges where there is greater anthropogenic disturbance. It is likely that a combination of factors is predisposing marri to canker disease: the use of pesticides on road edges, the introduction of exotic soil-borne pathogens, and climate change. These factors can have detrimental effects on concentrations of nutrients in the soil, soil composition, and communities of mycorrhizal fungi. The aim of this project was to examine these potential predisposing factors and how they may interact with marri along a disturbance gradient. Seventeen sites were surveyed. Each site consisted of a disturbance gradient of 3 transects: remnant stand bordering cleared land and a road, a forest edge, and the middle of an intact forest. Soil was collected from ten trees along each transect and the nutrient composition was tested. This soil was used in a glasshouse experiment from which roots were harvested to test mycorrhizal composition.
Results/Conclusions
Results demonstrated differences in soil nutrition between the disturbed and intact forest transects. Quantities of both macro- (nitrogen, phosphorus, potassium) and micro-nutrients (iron, manganese, and copper) were nearly double along the disturbed edge than that along the other transects. The mycorrhizal communities were significantly different among the three transects with the community along the disturbed edge having a unique community assemblage. Soil temperature was lower along disturbed edges than within intact forest and leaf litter depth was significantly higher along disturbed edges than intact forest.
Nutrient composition can play a key role in the community composition of mycorrhizal fungi. Mycorrhizal fungi are fundamental to the health of trees and different species are critical for nutrient acquisition. It is possible that in addition to the differences in microclimate along this disturbance gradient, marri is more susceptible to canker disease due to the joint effects of temperature, nutrients and mycorrhizal fungi. This study demonstrates the importance of using multivariate studies to determine the causes of the decline and will assist in formulating a management plan to mitigate marri decline.