Nutrients – especially nitrogen (N) and phosphorus (P) – constrain plant growth; however human activities are drastically changing the nature of such nutrient limitations on land. Here we examine interactions between N and P cycles via meta-analysis of P mineralizing enzyme activities (phosphatase enzymes) across a wide variety of terrestrial ecosystems and conditions. Specifically, we address the response of phosphatase activity to fertilization by N, P, and NxP by evaluating response ratios of phosphatase activity among nutrient fertilized vs. control conditions. The compiled data set includes 124 observations from 19 separate studies, and spans six major biomes, including grassland, shrubland, temperate deciduous forest, tropical rainforest, tundra, and wetland. Moreover, we separately analyze results for external root and free soil phosphatases.
Results/Conclusions
N fertilization enhances phosphatase activity, from the tropics to extra-tropics, and in both roots and soils; overall, added N stimulated phosphatase activity by 63.6% relative to control conditions. By contrast, P fertilizations strongly depress phosphatase production; added P depressed phosphatase activity by 35.5%. Fertilization by N plus P decreases phosphatase activity by 38% compared to controls, showing that P more strongly controls phosphatase activity than N alone. Phosphatase activity measured on plant roots and in the soil showed similar trends, but root-effects were stronger than those of soils. In sum, these results suggest that plants optimize growth via N allocations to phosphatase enzymes, thus delaying the onset of P limitations as induced by human modifications to the cycling of N, regardless of the type of terrestrial ecosystem.