Ingestion of charcoal by the Amazonian earthworm Pontoscolex corethrurus: A potential for tropical soil fertility

摘要

Pontoscolex corethrurus (Annelida: Oligocheata: Glossoscolecidae) is a small terrestrial earthworm which commonly inhabits rain forest soils over the whole Amazonian basin (Rmbke et al., 1999). Its important burrowing activity through the topsoil, associated with its efficient digestive system (Zhang et al., 1993; Barros et al., 2001), allows it to thrive in soils poor in organic matter, such as those found in areas now deforested for the need of agriculture. In the absence of organic input to the soil, excessive casting activity of this species may cause damage to permanent pastures through the coalescence of earthworm casts, leading to appearance of a thick compact surface crust (Chauvel et al., 1999). However, the detrimental influence of this species may be questioned when the agricultural use of the land is only temporary, as in slash-and-burn shifting agriculture, or when available carbon is regularly added to the soil. We hypothesized that P. corethrurus could be responsible for the observedincrease in soil fertility which has been reported to occur in Amazonian Dark Earths formed during Pre-Colombian times (Myers et al., 2003; Steiner et al., 2004). Using a quantitative optical method (Topoliantz et al., 2000), we investigated the distribution of humus components in soils under shifting cultivation, still practised by Wayana and Aluku people settled along the Maroni river, French Guiana (Topoliantz et al., 2005b). This method allowed us to estimate the relative volume of components of the soil matrix, including plant tissues at varying stages of decomposition, mineral particles of varying size and nature, aggregates of varying colour, size and shape.