Soil distribution of Phytophthora cinnamomi inoculum in oak afforestation depends on site characteristics rather than host availability

Abstract

The decline and mortality of Quercus species worldwide are interpreted through the interactions of several factors in space and time. Among these factors, Phytophthora cinnamomi has been identified as a major biotic agent triggering mortality of Quercus ilex and Q. suber in the Mediterranean basin. However, there are few examples in the literature studying the interaction between P. cinnamomi and site environmental factors or assessing the effects of environmental drivers on the host-pathogen system. In this study, we examined how both characteristics and spatial distribution of soil and topography influence the effects of P. cinnamomi over the disease status of Q. ilex and Q. suber plantations using spatial analysis by distance indices and structural equation modelling. Results showed the high influence of soil (texture, nutrients, chemical composition and moisture) and topography (orientation, solar incidence and hydrology) over the pathogen availability, as well as lower mortality and defoliation of Q. suber, but more related to the colony forming units (cfu) distribution, compared with Q. ilex. These differences highlighted the convenience of mixed afforestation compared with monospecific ones, increasing afforestation resilience, and the importance of a precise scale for the characterization of soil and topography, preventing afforestation failure.