Soil microbial community restructuring and functional changes in ancient kauri (Agathis australis) forests impacted by the invasive pathogen Phytophthora agathidicida

Abstract New Zealand's culturally iconic, ancient kauri (Agathis australis) forests are threatened with extinction as a result of dieback caused by an invasive and highly virulent soil-borne pathogen (Phytophthora agathidicida). Kauri trees function as a foundation species in their forests, supporting an ecologically distinct plant and soil environment. The impacts of disease outbreak and subsequent tree dieback on kauri forest ecosystems, in particular soil microbial communities, remains unknown. Using high throughput amplicon sequencing and GeoChip 5 S microarray analysis we analysed the differences in diversity, taxonomic composition and functional genes related to C and N cycling of soil microbial communities associated with asymptomatic and symptomatic mature kauri. Our results found significant differences in the fungal diversity and both fungal and bacterial community composition between asymptomatic and symptomatic kauri. Several microbial taxa known in the literature for their roles in disease suppression, such as Penicillium, Trichoderma, Enterobacteriacae and Pseudomonas, were identified as being significantly higher in asymptomatic kauri soils. These findings have provided a promising direction for the discovery of disease suppressive microbial taxa against kauri dieback. In addition, the composition and abundances of microbial genes related to C and N cycling also differed significantly. These findings highlight the potential long term impacts that dieback disease may have on the health and functioning of kauri forests.