Terrestrial Oligochaeta communities in a world’s unique longterm bare fallow experiment

The use of fertilizers can impact physical and chemical soil characteristics, but also soil organisms such as Oligochaeta (Clitellata, Annelida) and their activity. We here assessed the impacts of 89 years of different fertilization practices (N, P, K fertilizers, basic and organic amendments, or no input) on the species composition and abundance of earthworm and enchytraeid communities at INRA’s 42-plot design in Versailles (France). This long-term barefallow experiment on silty Luvisols, developed from aeolian loess, includes 16 duplicated treatments that received continuous annual applications of 16 different amendments, leading to highly diverging physical and chemical properties in the soil's surface layer. Enchytraeids (with soil cores) and earthworms (with octet method) were sampled in spring 2017 in these 32 plots and in 5 reference plots that had received no amendments. We also used bait lamina sticks to assess the feeding activity in this trial. Only 14 earthworm individuals were sampled from the 37 plots, belonging to three different species i.e., Aporrectodea giardi, Allolobophora chlorotica, and Allolobophora icterica. Eight individuals of A. chlorotica were found in soils with a pH ranging from 6.5 to 9. The highest number of earthworms (4 individuals of A. chlorotica) was sampled from the plot receiving lime. The other two species were found in plots with a pH between 4.5 and 7.5. For enchytraeids, 256 individuals were found, belonging to 13 species of 6 genera. The most abundant genus was Enchytraeus (95 specimens), then Achaeta (72), Buchholzia (65), Fridericia (23), and lastly Enchytronia (2) and Marionina (2). The most abundant species was Buchholzia appendiculata (Buchholz, 1862) which is common and widespread in neutral to acidic soils (Schmelz and Collado 2010). This species was found in most of the treatments (calcium carbonate, potassium chloride, natural phosphate, lime, ammonium sulfate, calcium nitrate, sodium nitrate, fumier, diammonium phosphate) and reached the highest density (4 840 individuals m-2 in calcium carbonate plots). Enchytraeus bulbosus (Nielsen and Christensen, 1963) was also a widespread species that represented about 7% of the relative abundance. The individuals of this species were mainly present in horse manure treatments, but also in lime, natural phosphate, superphosphate and control treatments. The highest abundance for this species was 1 020 individuals m-2 in horse manure fertilized plots. Achaeta affinis (Nielsen and Christensen, 1959) was also found (6% of the relative abundance) but only in control and horse manure treatments, where the highest density was 3 060 individuals m-2. In natural habitats this species is often found in moderately acidic soils (Schmelz and Collado, 2010). The other species, representing less than 5 % of the total abundance, were: Achaeta bohemica (Vejdovský, 1879); Achaeta eiseni (Vejdovský, 1878); Achaeta pannonica (Graefe, 1989); Buchholzia fallax (Michaelsen, 1887); Enchytraeus buchholzi s.l. (Vejdovský, 1879); Enchytronia parva (Nielsen and Christensen, 1959); Fridericia bulboides (Nielsen and Christensen, 1959); F. isseli (Rota, 1994); F. perrieri (Vejdovský, 1878) and Marionina communis (Nielsen and Christensen, 1959).