Effects of a copper-tolerant grass (Agrostis capillaris) on the ecosystem of a copper-contaminated arable soil

To test how a dysfunctioning ecosystem of a severely metal‐polluted soil responds to renewed plant growth, a pot experiment was conducted with soil from an experimental arable field with pH and copper gradients imposed 13 years ago. In this experiment, four pH/copper combinations from this field were either planted with a pH‐ and copper‐resistant grass cultivar or remained fallow. During a 10‐week period, the dynamics of the microbial activity and of the abundances of bacteria, protozoa, and nematodes were measured, as were the dynamics of several chemical soil parameters. After 13 years of copper (750 kg copper per hectare) and/or pH stress (6.1® 4.7), which had resulted in severely reduced crop growth, no effects were observed on bacterial numbers, respiration, or protozoan numbers, but bacterial growth (measured as [3H]thymidine incorporation into bacterial DNA) was strongly reduced in the low pH plots, and even more so in low pH plots enriched with copper. Of the organisms, only nematodes were negatively affected under conditions of high copper load at low pH. In these plots, numbers belonging to all feeding categories were strongly reduced. Planting of a copper‐tolerant grass variety, Agrostis capillaris L. var. Parys Mountain, resulted within 10 weeks in faster bacterial growth and more protozoa and bacterivorous nematodes in comparison with fallow controls; these effects were markedly strongest in the acidic, copper‐enriched soils. During incubation, fungivorous nematodes increased in all treatments, in fallow and in planted pots and in the pots with high‐copper, low‐pH soil. The results of this experiment suggest that introduction of plant growth is one of the major causes of increased biological activity in acidic contaminated soils (approximately 1.2 times the current EC limits). Planting such soils with metal‐tolerant plant species can reestablish the necessary food base to support soil organism growth, and this can lead to numerous positive effects, reversing the loss of soil functions due to the high copper levels under acidic conditions.