Seasonal Dynamics of Fungi Associated with Healthy and Diseased Pinus sylvestris Needles in Northern Europe

Abstract

The relationship between the ecological success of needle pathogens of forest trees and species richness of co-inhabiting endophytic fungi is poorly understood. One of the most dangerous foliar pathogens of pine is Dothistroma septosporum, which is a widely spread threat to northern European forests. We sampled two Pinus sylvestris sites in Estonia and two in Norway in order to analyse the relations between the abundance of D. septosporum and overall fungal richness, specific fungal species composition, time of season, needle age and position in the canopy. In both countries, the overall species richness of fungi was highest in autumn, showing a trend of increase with needle age. The overall species richness in the second-year needles in Estonia and third-year needles in Norway was similar, suggesting that a critical colonization threshold for needle shed in P. sylvestris is breached earlier in Estonia than in Norway. The fungal species richness in P. sylvestris needles was largely affected by Lophodermium conigenum. Especially in older needles, the relative abundance of L. conigenum was significantly higher in spring compared to summer or autumn. The timing of recruitment and colonization mechanisms of different foliage endophytes are shortly discussed.

The Native Hymenoscyphus albidus and the Invasive Hymenoscyphus fraxineus Are Similar in Their Necrotrophic Growth Phase in Ash Leaves

“…The PCR products were sequenced using PacBio platform at the University of Oslo, Norway. PacBio has been recently used successfully in metabarcoding analysis of microorganisms in different plant, tree, and insect species, with the lesson that the long DNA barcodes (500–1500 bp) enabled by the platform substantially improve the resolution in species identification ( Loit et al, 2019 ; Tedersoo and Anslan, 2019 ; Tedersoo et al, 2019 ; Agan et al, 2020 , 2021 ; Jürisoo et al, 2021 ). The primer ITS1catta was originally designed to differentiate H. albidus from H. fraxineus , and to avoid amplification of plant DNA and the long intron in the 3′ end of the rRNA 18S gene of Hymenoscyphus species (see Tedersoo and Anslan, 2019 ; Agan et al, 2020 ).…”

Changes in the foliar fungal community between oak leaf flushes along a latitudinal gradient in Europe

“…The lack of a difference in species richness between leaf flushes in our study contrasts with the two previous studies on this topic, which all found a higher species richness on leaves from the first flush than on leaves from the second flush. Unterseher et al ( 2018 ) found a higher species richness of foliar fungi in leaves from the first flush than in those from the second flush in tropical plants in Thailand, and Agan et al ( 2021 ) found a higher species richness in Pinus sylvestris ‐needles from the current year than in needles produced in previous years in Estonia and Norway. While very speculative, this might suggest that there are differences in the effects of the production of multiple leaf flushes on the species richness of the foliar fungal community between tropical and temperate regions, or between coniferous trees (where leaves from different years co‐exist) and deciduous trees.…”

“…These fungi are known to cause plant diseases, induce plant defences in response to biotic and abiotic stresses (Arnold et al, 2003 ; Jaber & Enkerli, 2017 ) and influence leaf senescence and decomposition (Vacher et al, 2016 ). While these fungi are crucial for plant health and ecosystem functioning, we lack insights into the patterns and drivers of within‐ and among‐tree variation in the foliar fungal community (Agan et al, 2021 ; Allen et al, 2020 ; Millberg et al, 2015 ; Moler & Aho, 2018 ; Piepenbring et al, 2015 ; Sokolski et al, 2017 ; Terhonen et al, 2011 ; Unterseher et al, 2018 ). One factor that might explain within‐tree variation in the foliar fungal community is the co‐existence of leaves from different leaf flushes within individual trees.…”

“…One factor that might explain within‐tree variation in the foliar fungal community is the co‐existence of leaves from different leaf flushes within individual trees. Many plant species produce multiple leaf flushes during the growing season, and newly produced leaves might differ from older leaves in chemistry and resistance against plant enemies (Agan et al, 2021 ; Piepenbring et al, 2015 ; Unterseher et al, 2018 ). At larger spatial scales, the foliar fungal community might vary along the distributional range of the host plant.…”

“…As an illustrative example, the severity of oak powdery mildew on Quercus robur has been found to be lower on leaves from the first flush than on leaves from the second flush (Call & St. Clair, 2017 ). The only two studies that we are aware of that assessed the impact of the production of multiple leaf flushes on the foliar fungal community have found the highest species richness in leaves from the first leaf flush as well as differences in community composition between leaf flushes (Table S1 ; Agan et al, 2021 ; Unterseher et al, 2018 ). Knowing which guilds are more likely to grow in each leaf flush would further help us to understand how foliar fungal communities are distributed and structured within trees.…”