Legacy of plant-parasitic nematode communities from past ecosystems and shift by recent afforestation

Ancient ecological legacies and past land use changes may inform on the present structure of biological communities. However, regions providing such successive ecosystems are scarce. In France, the ‘Landes de Gascogne’ area provides such ecological shifts since a few ancient moorland, peatland and oak areas prior the afforestation with maritime pine (Pinus pinaster) 160 years ago still remain. Focusing on soil-borne parasites such as plant-parasitic nematodes (PPN), because forests were recently increasingly impacted by the introduction of intensive agriculture, this study is therefore aimed at comparing the diversity and the community patterns of these organisms at different scales (intra- and intersites) and between different successive ecosystems. The understory vegetation as well as the pedo-climatic characterization of the sampled sites were also considered. Common diversity indices were not impacted by this transition from ancient to past ecosystems. Although the most colonizer nematodes prevailed in all the ecosystems, PPN community structures significantly diverged between both ecosystems. In the logged pine forests, the sediment legacy could have primarily impacted the diversity. Moreover, the PPN diversity would mainly respond to the soil hydromorphicity that determined the associated understory vegetation. Consequently, a significant shift in community structure from moorlands to logged pine to logged pine forests was observed, regarding especially high pathogenic species such as Pratylenchus spp. Thus, analyzing PPN community structure highlights the PPN potential risk to consider during the introduction of intensive cropping systems.