Effects of root damage associated with Phytophthora cinnamomi on water relations, biomass accumulation, mineral nutrition and vulnerability to water deficit of five oak and chestnut species

The effects of root damage associated with Phytophthora cinnamomi on water relations, biomass accumulation, mineral nutrition and vulnerability to water deficit were investigated in pedunculate oak (Quercus robur), red oak (Quercus rubra) and holm oak (Quercus ilex) saplings over two years. Comparison was made with sweet chestnut (Castanea sativa), a susceptible species to infection by P. cinnamomi, and with a resistant hybrid chestnut (Castanea crenata × C. sativa). Trees were inoculated in 1998 and were subjected to water shortage in 1999. All inoculated sweet chestnuts died before the application of water shortage. Hybrid chestnut, pedunculate oak and red oak displayed low root susceptibility to P. cinnamomi. In these species, water relations, aerial growth and mineral nutrition were slightly affected by inoculation. By contrast, holm oak was the most susceptible oak species to P. cinnamomi as inoculated well‐watered trees displayed the highest root loss (67%) and a 10% mortality. Root loss was associated with a decrease in predawn leaf water potential, a 61% reduction in stomatal conductance, a 55% reduction in aerial biomass, a decrease in leaf carbon isotope discrimination and reduced leaf N and P contents in comparison with controls. In hybrid chestnut and pedunculate oak, water shortage resulted in a similar decrease of predawn leaf water potential, stomatal conductance and aerial biomass in inoculated and non‐inoculated trees. In red and holm oaks, soil volumetric water content of inoculated trees subjected to water shortage remained high. The effects observed in those trees were similar to those of inoculated well‐watered trees and were probably the result of root infection only. Effects des dégâts racinaires associés à l’infection par Phytophthora cinnamomi sur le fonctionnement hydrique, l’accumulation de biomasse, la nutrition minérale et la vulnerabilitéà un déficit hydrique de cinq espèces de chênes et châtaigniers Les effets des pertes racinaires associées àPhytophthora cinnamomi sur le fonctionnement hydrique, l’accumulation de biomasse, la nutrition minérale et sur la vulnérabilitéà un déficit hydrique ont étéétudiés chez le chêne pédonculé (Quercus robur), le chêne rouge (Q. rubra) et le chêne vert (Q. ilex) pendant deux ans. Ces espèces ont été comparées au châtaignier (Castanea sativa), espèce sensible àP. cinnamomi et à un châtaignier hybride résistant (C. crenata × C. sativa). Les arbres ont été inoculés en 1998 et ont été soumis à u