Oomycetes along a 120,000 year temperate rainforest ecosystem development chronosequence

The occurrence of plant-associated oomycetes in natural ecosystems and particularly during long-term ecosystem development is largely unknown. Using DNA sequencing, we investigated the frequency and host relationships of plant-root-associated oomycete communities along a 120 000 y glacial chronosequence, comprising site ages with rapid compositional change (early succession; 5-70 y old soil); relatively stable higher-diversity sites (mature, 280-12000 y); and ancient, nutrient-limited soils with declining plant biomass and stature (retrogression, 60 000, 120 000 y). Plant-associated oomycetes were frequent in early successional sites, occurring in 38-65% of plant roots, but rare (mean 3%) in all older ecosystems. Oomycete OTUs occurred non-randomly with plant host species, and were more frequent on those plant species that declined most strongly in abundance between ecosystem ages. While oomycetes were common in early succession, their absence in older sites suggests a limited role in later stages of ecosystem development. (C) 2019 Elsevier Ltd and British Mycological Society. All rights reserved.