Plant root pathogens over 120,000 years of temperate rainforest ecosystem development

34 35 The role of pathogens, including oomycetes, in long-term ecosystem development has 36 remained largely unknown, despite hypotheses that pathogens drive primary succession, 37 determine mature ecosystem plant diversity, or dominate in retrogressive, nutrient-limited 38 ecosystems. Using DNA sequencing from roots, we investigated the frequency and host 39 relationships of oomycete communities along a 120 000 year glacial chronosequence. 40 Oomycetes were frequent in early successional sites (5 70 yrs), occurring in 38 – 65% of 41 plant roots, but rare (average 3%) in all older ecosystems (280 yrs and older). Oomycetes 42 were highly host specific, and more frequent on plant species that declined most strongly in 43 abundance between ecosystem ages. In contrast, oomycetes were not correlated with plant 44 abundance or plant root traits associated with retrogression. The results support the 45 importance of root pathogens in early succession, but not thereafter, suggesting root 46 pathogen-driven dynamics may be important in driving succession but not long-term 47 diversity maintenance. 48 49 not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/042341 doi: bioRxiv preprint first posted online Mar. 4, 2016;