Surviving after an eruption: Ecosystem dynamics and mycorrhizae in Nothofagus pumilio forests affected by the 2011 Puyehue Cordon-Caulle tephra

Volcanic eruptions affect ecosystems drastically, and ectomycorrhizal fungi (EM) may play a critical role in forest regeneration. Nothofagus species are usually ectomycorrhizal. The 2011 Puyehue Cordon-Caulle volcanic complex (PCCVC) eruption covered vast areas of N. pumilio forests with thick tephra deposits. The main objectives of this work were to characterize the forest environment following tephra deposition, and to analyze the natural regeneration and development of N. pumilio and associated EM communities. Three study sites were selected and sampled two and three years after the PCCVC eruption. Two sites had a thick tephra layer (50 cm); in one of them most of the tree layer was dead (Highly Affected-Tephra) whereas in the other, most of the adult trees were alive (Affected-Tephra). The third site had minimal tephra deposition (Non-Affected). Physicochemical properties of the substrate, biological environmental factors and EM behavior of N. pumilio seedlings and adults were evaluated in all three sites. The physicochemical properties of the substrate and environmental characteristics differed among sites. Both seedlings and adults had EM in all three sites. The frequency of six-month-old seedlings with EM (40%) and their colonization values (< 12%) were significantly lower in both tephra-affected sites than in the Non-affected site (100% and 80 %, respectively). However, all the 18-month-old seedlings from the tephra-affected sites had EM and their colonization increased almost to the value of the seedlings from the Non-Affected site. In both tephra-affected sites N. pumilio seedlings were associated with some exclusive fungal species, which could have a primary successional role. The early, increasing EM colonization recorded in seedlings after the eruption supports the idea of the strong dependence of Nothofagus trees on this symbioses, and highlights that this mutualism could be an effective adaptive mechanism under stressful conditions. Our findings also suggest that EM symbiosis in N. pumilio persists even after a severe disturbance and is regulated by several factors such as time after eruption, availability and type of mycorrhizal inoculum, plant development and physicochemical substrate composition.

Automated summary

The volcanic eruption in 2011 heavily impacted Nothofagus forests, where ectomycorrhizal fungi may play a crucial role in natural regeneration and development. The presence and colonization of ectomycorrhizal fungi in N. pumilio seedlings were significantly lower in tephra-affected areas, but increased with age, suggesting a strong dependence of Nothofagus trees on this symbiosis. The study highlights the importance of ectomycorrhizal symbiosis as an effective adaptive mechanism under stressful conditions, with fungal communities potentially playing a key role in forest recovery after disturbances like volcanic eruptions.