Assessment of tracer methods for identifying belowground niche differentiation in grassland

摘要

Benefits of grassland mixtures over monocultures are hypothesised to be based on niche complementarity among plant species. Belowground niche differentiation can be assessed by injecting tracers at different soil depths and comparing the resulting tracer concentrations in plant material of individual species. In previous methods, one single tracer was injected to one soil depth per sub-plot, requiring separate sub plots for each depth of injection (single tracer method). A multiple tracer method in which different tracers are injected each at a distinct soil depth within the same sub-plot has been proposed (multiple tracer method). To be valid, this method has to meet the following requirements: 1) tracers have to be reliable markers of the targetedsoil depth, i.e. remain at the injected soil depth throughout the experimental period, and 2) tracers have to allow a quantitative estimate of nutrient uptake. We tested these requirements for four different tracers ~(15)N, lithium, rubidium and caesium. For the combination of tracers and plant species in this experiment, we were unable to determine a set of two or more tracers that meet both requirements for the multiple tracer method.