Dynamics of earthworm taxonomic and functional diversity in ploughed and no-tilled cropping systems
Résumé
No-till has been proposed to limit the negative impacts of intensive agriculture. Soil organisms such as earthworms are good indicators of soil tillage effects. The aim of this study was to assess the dynamics of both taxonomic and functional diversity of earthworm communities after switching from ploughing i.e. deep tillage at 25–30 cm depth inducing soil inversion in this paper, to no-till. We assumed (i) that this transition led to increased diversity and (ii) that both taxonomic and functional indices indicated changes in tillage practices. Earthworms were sampled at three experimental sites in France on a Cambisol, a Luvisol, and a Fluvisol over several years (from 1995 to 2011), comparing both tillage systems. Standardized mean differences (Cohen’s indices) were calculated on several taxonomic and functional indices to quantify the influence of tillage practices within each site. We generally found a neutral or positive effect of the no-till on taxonomic and functional indices. The temporal responses of earthworm diversity were stronger in earliest stages (less than 6 years) than in oldest ones (more than 8 years) revealing transitory effects on diversity. In site III, for instance, a positive effect of no-till was observed on species and functional richness during the first 5 years but a negative effect was shown in year 6. Thus, no clear continuous increase of taxonomic and functional diversity was found in no-tilled fields, but positive and negative effects according to sites and years. More marked differences were found for taxonomic than for functional indices, suggesting that individuals settling the fields shared a similar combination of functional traits to those previously present. As transitory effects have been observed, this study highlighted that long-term trials are needed to assess the effects of cropping systems on earthworm biodiversity