Summary
The role of pathogens, including oomycetes, in long-term ecosystem development has remained largely unknown, despite hypotheses that pathogens drive primary succession, determine mature ecosystem plant diversity, or dominate in retrogressive, nutrient-limited ecosystems.
Using DNA sequencing from roots, we investigated the frequency and host relationships of oomycete communities along a 120 000 year glacial chronosequence, comprising site ages with rapid compositional change (“early succession”; 5, 15, and 70 years old soil); relatively stable higher-diversity sites (“mature”, 280, 500, 1000, 5000, 12000 years); and ancient, nutrient-limited soils with declining plant diversity and stature (“retrogression”, 60 000, 120 000 years).
Oomycetes were frequent in early successional sites occurring in 38 – 65% of plant roots, but rare (average 3%) in all older ecosystems.
Oomycetes were highly host specific, and more frequent on those plant species that declined most strongly in abundance between ecosystem ages.
In contrast, oomycetes were not correlated with plant abundance or plant root traits associated with retrogression.
Synthesis. The results support the potential importance of oomycete pathogens in early succession, but not thereafter, suggesting oomycete pathogen driven dynamics may be important in driving succession but not long-term diversity maintenance.