When Soil Goes to Sleep: Simultaneous Changes in Biodiversity and Pedodiversity Along an Anthropogenic Copper Gradient.

Soils are among the most complex systems in nature with interdependent biological, chemical and physical processes taking place simultaneously and varying in space and with time. Healthy soils exhibit a delicate balance between the biotic and abiotic environments, providing the basis for sustained life and welfare on Earth. Anthropogenic forcing (e.g., heavy metal contamination) adversely affects the highly sensitive soil ecosystem, not only deteriorating the living organisms, but also associated soil chemical and physical properties. This study quantitatively demonstrates how copper (Cu) contamination simultaneously impacts soil biodiversity and pedodiversity. Soil biodiversity (bacterial, fungal and nematode richness and diversity, earthworm density, plant species richness) was analysed in conjunction with soil physicochemical properties (total and bioavailable copper, organic carbon, total nitrogen, phosphorous, pH, texture, surface area, soil water characteristics, gas transport) along a legacy Cu pollution gradient (22 to 3800 mg total Cu kg^-1) in a field in Hygum, Denmark. X-ray Computed Tomography (CT) was also applied to directly visualize the impact of Cu contamination on pore network architecture. Simultaneous decline in both biodiversity and pedodiversity with increasing Cu concentration was observed, indicating a strong interdependcy of these two key life entities of soil. All measured parameters indicated that biodiversity, pedodiversity and biophysical life support functions had significantly decreased or disappeared beyond ~500 mg total Cu kg^-1. Combined use of emerging medical, physical, macro- and molecular biological techniques proved to be an essential tool for characterizing soil ecosystem and its response to anthropogenic forcing.