Kauri dieback, caused by Phytophthora agathidicida, is an
ecosystem disturbance that poses a recent threat to the survival of
kauri (Agathis australis) forests in New Zealand. Throughfall and
stemflow play an important role in meeting the nutrient requirements of
kauri forests. However, the effects of kauri dieback on canopy nutrient
deposition remain unknown. Here we measured throughfall, stemflow and
forest floor water yield and nutrient concentrations and fluxes
(potassium, calcium, magnesium, manganese, silicon, sulphur, sodium,
iron) of ten kauri trees differing in soil P. agathidicida DNA
concentration and health status. We did not observe an effect of soil
P. agathidicida DNA concentration on throughfall and stemflow
water yield. Throughfall and forest floor nutrient concentrations and
fluxes tended to decrease (up to 50%) with increasing soil P.
agathidicida DNA concentration. Significant effects were found for
potassium and manganese fluxes in throughfall, and calcium and silicon
fluxes in forest floor leachate. The decline in nutrient input will have
implications on plant nutrition, tree health and susceptibility to
future pathogen infection in these ecologically unique kauri forests.
Given our findings and the increasing spread of Phytophthora
species worldwide, research on the underlying physiological mechanisms
linking dieback and plant-soil nutrient fluxes is critical.