The role of earthworm communities in soil mineral weathering: a field experiment

MINERALS are an important component of the soil environment (Dixon et al., 1977). They provide a structural framework which supports plants and contribute to the physical heterogeneity of soil. Minerals also contribute to the fertility of soils. Primary minerals are a source of essential plant nutrients (Harley and Gilkes, 2000). Clay minerals impact on the water-holding capacity of soils, affect the cation exchange capacity of soils (Brown, 1977) and are able to sequester nutrients and contaminants within the soil (Dubbin, 2001). Mineral weathering is an important process in soils and releases nutrients from the mineral structure into a form available for uptake by plants (Harley and Gilkes, 2000). Mineral weathering also increases the number of cation exchange sites, which increases the fertility of soils by improving nutrient retention. The weathering of clay minerals and the expansion of clay layers increases the water-holding capacity of soils (Brown, 1977). Mineral weathering also contributes to the pedological development of soils. Pedologically old soils are highly weathered and have a large proportion of clay minerals and a small proportion of primary minerals (Dubbin, 2001). Highly weathered soils, such as those found in the tropics, tend to be less fertile than less weathered soils (Dubbin, 2001). Earthworms are an important component of the soil ecosystem and have been described as ecosystem engineers because of the major role they play in modifying the soil ecosystem (Lavelle et al., 1997). They play a key role in modifying the physical structure of soils by creating aggregates (Haynes and Fraser, 1998), creating pores which increases infiltration and drainage (Lamande et al., 2003) and contributing to the development of soil horizons by the transport of material and incorporation of organic matter (Marhan and Scheu, 2006). Earthworms are also one of the key drivers of decomposition, particularly in temperate soil ecosystems by comminuting organic matter and incorporating it into the soil (McInerney and Bolger, 2000). Mineral weathering is a biogeochemical process in which organisms are intimately involved. Previous studies have shown that earthworms are capable of accelerating the weathering of soil minerals (Suzuki et al., 2003; Needham et al., 2004; Carpenter et al., 2007). However, this important interaction between two key components of the soil environment has not previously been studied in a field situation. The aim of this study was to evaluate the role of an earthworm community in the weathering of a primary mineral addition to a field soil.