Copper effects on soil nematodes and their possible impact on leaf litter decomposition: A microcosm approach

Abstract

Scientists and policy makers have to establish criteria to distinguish ‘acceptable’ from ‘harmful’ levels of pollution. Earlier studies have shown that even amounts of heavy metal pollutants well below LC50 or EC50 concentrations, can affect the fitness of individual bacterivorous nematode species, as well as the balance of the horizontal interactions between them. Species interactions are critical in shaping community structure and promoting ecosystem functions like organic matter decomposition - a key process that drives the flow of energy and nutrients in ecosystems.In this paper, we exposed two bacterial feeding soil nematodes, Plectus acuminatus and Acrobeloides nanus, to different Cu concentrations in monospecific and two-species microcosms containing leaf litter of the common grass species Urochloa mutica for a period of 60 days. We demonstrate that toxicant concentrations well below LC50 not only impair the fitness of the nematodes, but may also affect the interspecific interactions between them as a result of their differential sensitivity to Cu. Both Plectus and Acrobeloides are bacterial feeders and may thus affect the decomposition of leaf litter by impacting on the abundance and composition of bacteria. We observed Cu effects on the decomposition of Urochloa, but in the absence of data on the microbial community, it is not possible to assign these to direct effects of Cu on the bacteria or indirect effects through the Cu impacts on nematodes and their interactions.