Response of Alnus glutinosa to Phytophthora bark infections at ambient and elevated CO2 levels

Introduction: Mortality of the riparian alder population caused by Phytophthora pathogens has been studied for over 20 years throughout Europe, recently gaining more importance in the context of evident climate change. The main objective of this study was to examine the pathogenicity of species from the "Phytophthora alni complex" present in the Czech Republic (P. x alni and P. uniformis) and P. plurivora to Alnus glutinosa seedlings grown at ambient and elevated CO2 concentration. Methods: An underbark inoculation test was performed with seedlings grown from seeds collected from two Czech alder populations, one suffering from severe Phytophthora decline and the other disease-free. Results: The results showed significant differences in lesion development and seedling mortality. After a 13-week experimental period, at both CO2 levels P. x alni and P. uniformis showed high aggressiveness to A. glutinosa seedlings causing lesions of variable sizes and mortality of 33.3%, and 45.8% of plants, respectively. In contrast, P. plurivora did not cause mortality to any plant, and lesion sizes did not differ significantly from those in control plants. Physiological measurements did not reveal any significant differences between Phytophthora species except for plants inoculated with P. plurivora showing increased values in specific physiological parameters 4 weeks post-inoculation. Net photosynthesis decreased over the measurement period in all treatments with significant differences found between measurements conducted 2 and 4 weeks after the inoculation. Transpiration showed a decreasing trend in all inoculated plants with no significant differences between Phytophthora species at both CO2 levels. Chemical analyses of root samples showed high variability in sugars and phenolic compounds related to the plant's health status. Discussion: This is the first study to examine the response of alder seedlings to Phytophthora pathogens at different CO2 levels. The findings demonstrate high aggressiveness of P. x alni and P. uniformis and weaker aggressiveness of P. plurivora to alder seedlings regardless of the CO2 level.O

Influencia de "Phytophthora cinnamomi" Rands en el decaimento de "Quercus ilex L." y su relación con las propiedades del suelo y las ectomicorrizas

El decaimiento de la encina (“Quercus ilex” L.) afecta a todo el Mediterráneo, y entre los factores implicados, se han descrito la degradación del suelo, el estrés hídrico y los cambios en la humedad edáfica y en la abundancia de micorrizas. El principal factor biótico es el oomiceto “Phytophthora cinnamomi” Rands. El presente trabajo analiza la influencia de “P. cinnamomi” en el decaimiento de la encina y, cómo las propiedades físico-químicas del suelo, las ectomicorrizas y la humedad edáfica afectan la infección de las encinas por “P. cinnamomi”. Se realizaron tres tipos de estudios en el sudoeste peninsular: (i) uno en 96 focos, donde se seleccionaron tres encinas con decaimiento y tres asintomáticas y se analizaron la presencia de “P. cinnamomi” y “Pythium spiculum”, la abundancia de ectomicorrizas, varias propiedades del suelo y la densidad radical; (ii) otro contemplando un seguimiento temporal de la humedad edáfica, el nivel freático, la presencia de “P. cinnamomi”, la abundancia de ectomicorrizas y varios parámetros fisiológicos, y (iii) otro en invernadero. Los resultados mostraron que la pudrición de raíces causada por “P. cinnamomi” en combinación con factores que influyen en su actividad (una menor densidad del suelo, una textura fina y espesores gruesos del horizonte Ah, propiedades relacionadas con los valores de humedad) afectan el vigor de la encina. Las alteraciones en la abundancia y diversidad de ectomicorrizas también se relacionan con el decaimiento de la encina. Asimismo, una sequía prolongada afecta a la encina y aumenta su posterior susceptibilidad a “P. cinnamomi”.Holm oak (“Quercus ilex” L.) decline is extended in the Mediterranean region and among the factors involved, soil degradation, water stress, changes in soil moisture and shifts in mycorrhizal symbiosis have been described. The main biotic factor associated with holm oak decline is the oomycete “Phytophthora cinnamomi” Rands. The present work aims to assess the influence of “P. cinnamomi” on holm oak decline, and how soil properties, ectomycorrhizae, soil water content and water table affect “P. cinnamomi” infections of holm oak. The work comprises three types of assessments in southwestern Spain: (i) an extensive including 96 declining stands, where three declining and three non-declining trees were selected and sampled for analyzing “P. cinnamomi” and “Pythium speculum” presence, abundance of ectomycorrhizae, physical and chemical soil properties and fine root density; (ii) a temporal assessment of soil water content, soil water table, “P. cinnamomi” presence, ectomycorrhizal fungi abundance and the physiological status of trees in 5 stands, and (iii) one performed under greenhouse conditions including 140 seedlings submitted to different watering regimes and subsequently inoculated with “P. cinnamomi”. Results showed that root rot caused by “P. cinnamomi” infection in combination with factors which favour the pathogen activity (lower soil bulk densities, fine textured soils and a thicker Ah horizon, properties which influence soil moisture values) play an important role in the vigour of holm oak. Disturbances in ectomycorrhizal abundance and diversity also related to holm oak decline. Long drought events also affected Q. ilex performance and increased subsequent susceptibility to “P. cinnamomi”.- Junta de Extremadura y Universidad de Extremadura. Convenio “Prospecciones de focos de “seca de Quercus”. - Junta de Extremadura (proyectos regionales III-PRI 08-A78 y IV-PRI IB10088) - Realizado dentro del marco de la acción COST “Established and emerging Phytophthora: increasing threats to woodland and forest ecosystems in Europe” (FP0801)

Influencia de "Phytophthora cinnamomi" Rands en el decaimento de "Quercus ilex L." y su relación con las propiedades del suelo y las ectomicorrizas

El decaimiento de la encina (“Quercus ilex” L.) afecta a todo el Mediterráneo, y entre los factores implicados, se han descrito la degradación del suelo, el estrés hídrico y los cambios en la humedad edáfica y en la abundancia de micorrizas. El principal factor biótico es el oomiceto “Phytophthora cinnamomi” Rands. El presente trabajo analiza la influencia de “P. cinnamomi” en el decaimiento de la encina y, cómo las propiedades físico-químicas del suelo, las ectomicorrizas y la humedad edáfica afectan la infección de las encinas por “P. cinnamomi”. Se realizaron tres tipos de estudios en el sudoeste peninsular: (i) uno en 96 focos, donde se seleccionaron tres encinas con decaimiento y tres asintomáticas y se analizaron la presencia de “P. cinnamomi” y “Pythium spiculum”, la abundancia de ectomicorrizas, varias propiedades del suelo y la densidad radical; (ii) otro contemplando un seguimiento temporal de la humedad edáfica, el nivel freático, la presencia de “P. cinnamomi”, la abundancia de ectomicorrizas y varios parámetros fisiológicos, y (iii) otro en invernadero. Los resultados mostraron que la pudrición de raíces causada por “P. cinnamomi” en combinación con factores que influyen en su actividad (una menor densidad del suelo, una textura fina y espesores gruesos del horizonte Ah, propiedades relacionadas con los valores de humedad) afectan el vigor de la encina. Las alteraciones en la abundancia y diversidad de ectomicorrizas también se relacionan con el decaimiento de la encina. Asimismo, una sequía prolongada afecta a la encina y aumenta su posterior susceptibilidad a “P. cinnamomi”.Holm oak (“Quercus ilex” L.) decline is extended in the Mediterranean region and among the factors involved, soil degradation, water stress, changes in soil moisture and shifts in mycorrhizal symbiosis have been described. The main biotic factor associated with holm oak decline is the oomycete “Phytophthora cinnamomi” Rands. The present work aims to assess the influence of “P. cinnamomi” on holm oak decline, and how soil properties, ectomycorrhizae, soil water content and water table affect “P. cinnamomi” infections of holm oak. The work comprises three types of assessments in southwestern Spain: (i) an extensive including 96 declining stands, where three declining and three non-declining trees were selected and sampled for analyzing “P. cinnamomi” and “Pythium speculum” presence, abundance of ectomycorrhizae, physical and chemical soil properties and fine root density; (ii) a temporal assessment of soil water content, soil water table, “P. cinnamomi” presence, ectomycorrhizal fungi abundance and the physiological status of trees in 5 stands, and (iii) one performed under greenhouse conditions including 140 seedlings submitted to different watering regimes and subsequently inoculated with “P. cinnamomi”. Results showed that root rot caused by “P. cinnamomi” infection in combination with factors which favour the pathogen activity (lower soil bulk densities, fine textured soils and a thicker Ah horizon, properties which influence soil moisture values) play an important role in the vigour of holm oak. Disturbances in ectomycorrhizal abundance and diversity also related to holm oak decline. Long drought events also affected Q. ilex performance and increased subsequent susceptibility to “P. cinnamomi”.- Junta de Extremadura y Universidad de Extremadura. Convenio “Prospecciones de focos de “seca de Quercus”. - Junta de Extremadura (proyectos regionales III-PRI 08-A78 y IV-PRI IB10088) - Realizado dentro del marco de la acción COST “Established and emerging Phytophthora: increasing threats to woodland and forest ecosystems in Europe” (FP0801)