Soil macrofaunal communities along an abandoned rice field chronosequence in Northern Argentina

International audience

English. This study assessed the biodiversity of soil macrofauna along a chronosequence of abandoned rice paddy fields including situations of 2, 4, 7 and 15 years since the last rice harvest, compared to a control without agricultural disturbance. The density of soil macrofauna changed dramatically according to the chronosequence. It was maximum in the 2-year-abandoned rice field (4360 ind m(-2)) and minimum in the natural grassland (397.3 ind m(-2)). A total of 133 morphospecies was found, distributed among 20 main families. The highest species richness was observed in the natural grassland and in the 2-year-fallow with 53 and 59 species, respectively, whereas the lowest richness was found in the 7-year-fallow (39 species). The proportion of shared species was minimum (19.1%) when comparing the natural grassland and the 2-year-fallow and remained surprisingly low between the natural grassland and the 15-year-fallow (23.4%). The species diversity as measured by the Shannon index varied strongly along the chronosequence. It was maximum in the natural grassland (1.98), minimum in the 2-year-fallow (1.01) and increased progressively throughout the chronosequence, although, it was still lower in the fallow after 15 years of abandonment as compared to the natural grassland. The same trend was observed using the evenness index. The indicator value index (Indval) was computed for each species and showed that 14 species out of 133 were statistically associated with a given chronosequence stage. This survey showed that soil macrofauna quickly recolonized the ex-rice fields after the abandonment of rice culture and that the species richness was higher in recent ex-rice fields (2 years) as compared to the natural grassland. The pool of species that colonise the newly abandoned rice fields is substantially different from the one inhabiting the natural grassland, therefore suggesting that most of the successful colonisers probably originate from neighbouring fallow plots. This highlights the possible effects of landscape structure upon the dynamics of the soil macrofaunal biodiversity