Changes in species assemblages and diets of Collembola along a gradient of metal pollution

Abstract

Springtails (Hexapoda: Collembola) are known to live in a wide range of soil conditions, but changes occurring in their communities under the influence of heavy metal pollution are still poorly documented. The present study was undertaken in order to discern main coenological trends along a gradient of metal pollution, downwind of a zinc smelter located in the north of France. Three sites were compared within an abandoned field planted with poplar 20 years ago. The total zinc content of the topsoil varied from 4000 to 35 000 mg/kg according to distance to the smelter outlet. Changes in humus forms (shift from mull to mor) and in the degree of opening of the poplar stand (mainly caused by death or stunting of planted trees in the vicinity of the smelter) explained most of the observed variation in abundance and species composition. Sun species living at the ground surface appeared at the most polluted sites where poplar declined and was replaced by a sward of metal-tolerant herb species. The increase in abundance of the whole collembolan community was mainly due to Mesaphorura macrochaeta, the gut contents of which indicated that this species avoided the root mat and fed mainly in the mineral soil underneath. Shifts in food habits and/or in habitat were observed in several other common species, pointing to the importance of avoidance behaviour as a mechanism by which collembolan species may endure heavy metal pollution.