Plasticity in the efficiency of nutrient use for forest production potentially contributes to balanced nutrition despite imbalanced nutrient supply. We examined this possibility by quantifying litter nutrient use efficiency (NutrUE), quantified as leaf litter biomass produced per unit nutrient uptake (litter C:nutrient) in a NxP fertilization experiment in hardwood forests in the northeastern US. We tested the hypotheses that litter NutrUE is higher where nutrients are more limiting, and that elevated availability of one nutrient leads to higher NutrUE of the other nutrient.
Results/Conclusions
Fertilizing for 4 growing seasons (30 kg N ha-1 yr-1, 10 kg P ha-1 yr-1) consistently elevated soil resin-available levels of the nutrient that was added. The relative basal area increment of individual trees responded significantly to P but not to N addition, suggesting P limitation of productivity. Consistent with P limitation and supporting our first hypothesis, litter PUE declined strongly in response to P (24% lower than controls; p=0.007). The response of NUE to added N was relatively weak (7% lower than controls; p=0.08), and the NUE response to P was greater than that to N (11%; p=0.005). The effect of P on NUE supports our second hypothesis and is consistent with our observations that P addition has suppressed levels of resin-available N relative to controls. Responses by NutrUE that we show here support the idea that efficient use of limiting resources can contribute to balanced nutrition.