A new net mineralizable nitrogen assay improves predictions of floristic composition

Question Can a simple measurement of nitrogen (N) availability be related to an ecologically relevant response, i.e. mean Ellenberg N indicator value (E-N)? Location UK (England, Wales and Scotland). Methods Soil cores from a stratified sample of UK habitats were analysed for mineralizable N with a conventional incubation and a new flushing method, which uses a single mineral N extraction. Predictions of mean E-N using mineralizable N and other soil measurements were assessed by fitting linear mixed-effect models, using the Akaike information criterion (AIC) as a measure of model parsimony. Results Mineralizable N measurements using the flushing method described a component of the variation in mean E-N that was more orthogonal to bulk soil properties such as moisture content, total N/C ratio and pH than that described by conventionally measured mineralizable N. Mineralizable N as measured using the flushing method improved the accuracy of predictions obtained using only bulk soil measurements, and appeared in the best two-term and three-term models. Conclusions Much of the variation in mean E-N can be related to soil N/C ratio, pH or moisture content, but mineralizable N distinguishes variation in mean E-N that is independent of these bulk soil properties. The new measure will be useful for studies of the exposure of plants to N, in particular when assessing N pollution effects on plant species composition.