Do morphological hillslope features affect soil properties and processes promoting chestnut ink disease? The study case of the Northern Apennine mountains

Abstract. Ink disease caused by the soil-borne Phytophthora cambivora and Phytophthora cinnamomi is threatening sweet chestnut (Castanea sativa) groves in Europe. This study aims to explore whether soil morphology and its related properties influence the development of chestnut ink disease considering the whole soil depth. In C. sativa stand in Northern Italy, along a small altitudinal transect, soil profiles were dug close to ink diseased plants (INK1 at 978 m a.s.l.) and healthy plants (INK2 988 m a.s.l. and INK3 at 998 m a.s.l.) and each soil horizon evaluated for its properties. Further, INK1, INK2 and INK3 had a slope of 3, 9 and 30 %, respectively. The results showed that the lower slope position of INK1 combined with the lower slope gradient than INK2 and INK3 might have promoted the transport of clay particles and water from the latters to the former. Such process allowed the accumulation of clay within the whole INK1 soil profile increasing the saturated hydraulic conductivity and the wilting point. Such soil features might promote the water accumulation within the deeper soil horizons of INK1 which would explain the presence of Phytophthora spp. DNA. The presence of the root pathogen in INK1 might have affected the microbial functionality as observed by the higher abundance of the contact and medium-distance exploration ectomycorrhizal fungal community than the long-distance types. Finally, such study highlighted the pivotal role of soil processes (i.e., clay and water transport) to shape the soil microbial community and soil-borne pathogens because of the changes of edaphic properties.