Root growth response to water and nutrients in the New Jersey Pinelands

Abstract

Resource limitation theory regarding water versus nutrient limitation predicts on the one hand that, because of uptake trade-offs, increases in water will increase limitation by nutrients; on the other hand, because of supply interactions, increases in water will lead to correlated increases in nutrient availability. Using root ingrowth into resource-enriched soil cores as an assay of resource limitation, we report the effect of variable water supply on two experiments in the New Jersey Pinelands. In the first experiment in an upland oak–pine habitat, root ingrowth was highest in nitrogen-enriched cores in a wet year and highest in water-enriched cores in a dry year. In the second experiment in four vegetation types that differ in water table depth, roots grew more into nitrogen-enriched cores in all habitats, but nitrogen cores did not stimulate more ingrowth in wet (pitch pine lowland, hardwood swamp) versus dry habitats (pine–oak upland, oak–pine upland). Experiment 1 is consistent with the expectation that increasing water will increase relative limitation by mineral nutrients, but experiment 2 is not. Experiment 2 is consistent with an alternate hypothesis that long-term plant–soil feedback will result in higher nutrient acquisition in sites of higher water availability.