Synergistic soil response to nitrogen plus phosphorus fertilization in hardwood forests

Background/Question/Methods

Interactions among nutrients exert control on the stoichiometry of available nutrients, potentially influencing ecosystem responses to nitrogen enrichment and other perturbations that alter resource availability.   We tested whether an excess of one nutrient influenced the availability of another, to learn the net outcome of various feedbacks on mineralization and uptake processes.   We examined resin-available nitrogen and phosphorus availability in the first growing season of fertilizing with 30 kg/ha N, 10 kg/ha P, or N and P together.

Results/Conclusions

Fertilizing with a single nutrient raised the availability of the added nutrient and had no detectable effect on availability of the other nutrient.  However, the availability of N was raised substantially more by adding N+P than it was by adding N alone.  This effect of N+P was either to reduce the biotic uptake of N or to increase its mineralization, and suggests that N loss following forest disturbances will be enhanced if N and P availability increase in stoichiometric proportion.  That P interacts with N to enhance N availability, by whatever mechanism, could help explain observations of N and P co-limitation in ecosystems and calls attention to the need to carefully elucidate mechanisms underlying co-limitation of forest productivity.