Kauri dieback, caused by Phytophthora agathidicida, is a recent threat to the survival of kauri (Agathis australis) forests in New Zealand. Pathogen induced tree dieback and mortality may alter plant species composition and biogeochemical processes. Previous studies have shown that throughfall and stemflow play an important role in meeting the nutrient requirements of kauri forests. However, the effects of kauri dieback on the amount and transfer of macro- and micronutrients via throughfall and stemflow remains unknown. To address this knowledge gap we measured throughfall and stemflow water yield and nutrient fluxes (potassium, calcium, magnesium, manganese, silicon, sulfur, sodium, iron) of ten kauri trees differing in their infection level over 1 year. Soil P. agathidicida DNA concentration and visual health status were used as indicators of the infection level.
Results/Conclusions
Nutrient concentrations in throughfall and stemflow were up to 10-fold higher (potassium) than nutrient concentrations in bulk precipitation. Normalized to crown projection area, throughfall and stemflow were 65% and 8%, respectively, of bulk precipitation. Although some infected trees showed a considerable loss of foliage we did not observe a relationship between throughfall and stemflow water yield and P. agathidicida infection level. Throughfall nutrient fluxes tend to decrease (up to 50%) with increasing infection level. However, significant correlations were only found for throughfall potassium and manganese fluxes. No relationship was found between stemflow nutrient fluxes and infection level. Changes in throughfall chemistry may be related to P. agathidicida induced changes in leaf chemistry and leachable leaf surface area. The observed alteration in throughfall nutrient fluxes of P. agathidicida infected kauri trees could lead to long-term changes in biogeochemical processes (e.g. mineralization, nutrient availability) in these ecologically unique kauri forests.