Responses of Soil Nitrification Activities To Copper After A Moisture Stress
Abstract Some steps of the soil nitrogen cycle are sensitive to environmental pressures like soil moisture or contamination, which are expected to evolve during the next decades but such a double stress is not yet documented. This study aimed at assessing the importance of the soil moisture on the impact of copper (Cu) contaminations on the N cycling soil function using the potential nitrifying activities (PNA) as bioindicator. A loamy soil was first incubated 6 weeks in either 30, 60, or 90% of its water holding capacity (WHC) or alternating drought and rewetting periods. Thereafter, soil samples were exposed to a gradient of Cu concentrations through a bioassay. The dose-response curves of PNA in function of added Cu were modelled and we compared the different effective Cu concentrations (ECx) producing x % of PNA inhibition to highlight differences in threshold values. The preincubation moisture treatments significantly affected the PNA responses to the secondary Cu stress with, for instance, hormetic responses in all cases except for the dry-rewetting treatment. Small PNA inhibitions were estimated for high Cu doses in the soils with low water contents (30% WHC) or submitted to dry-rewetting cycles, contrarily to the patterns observed for the soils with high water contents (90% WHC) or submitted to a single period of drought. Overall, significant differences were found in estimated ECx values between moisture treatments.