Influence of soil-borne pathogens on seedling performance in declining Quercus suber forests: an experimental approach

Tutorres: Kreyling, Jürgen y Gómez Aparicio, LorenaSoil-borne pathogens drive important problems of forest decline worldwide. In the iberian Peninsula in particular, the exotic oomycete pathogen Phytophthora cinnamomi is driving the decline of cork oak (Quercus suber), one of the most abundant oak species in Mediterranean forests. This pathogen might not only influence community structure and composition by causing the death of adult cork oak trees, but also by limiting the establishment of new seedlings. This study aimed to experimentally analyse the effect of oomycete soil-borne pathogens on seedling performance of two different tree species (Q. suber and Olea europaea) that coexist in natural forests in southern Spain and show different susceptibility to P. cinnamomi attack. A greenhouse experiment was set up where seedlings grew on soils collected under trees of different species and health status in a declining cork oak forest. Half of the seedlings were treated with an oomycete-specific fungicide to investigate the impact of P. cinnamomi on aboveground and belowground plant performance. Seedlings were subjected to three competition levels (no competition, intraspecific competition and interspecific competition) to explore how pathogens might modify plantplant interactions. Q. suber seedlings with fungicide showed faster growth and larger fine root biomass than control seedlings, especially on soils with high pathogen abundance sampled under defoliated cork oak trees in the field. The application of fungicide also altered the root morphology as well as the abundance of ecto- and arbuscular- mycorrhizal associations of the studied tree seedlings. Competiveness of oak and Olea seedlings was not strongly modified by oomycete pathogens. The results indicate that seedling performance of Q. suber in declining cork oak forests is strongly reduced by direct and indirect effects of P. cinnamomi. This recruitment limitation might cause difficulties to compensate for the death of adult trees, leading to a reduction in the abundance of this important tree species in Mediterranean regions.Peer Reviewe