Document: JOH-3-63-18

Controls of ecosystem nutrient use efficiency: Bottom-up or top-down?

HIREMATH, A.J.* ¹ and J.J.EWEL ²

Harvard University, Cambridge MA 02138 ¹
USDA Forest Service Institute of Pacific Islands Forestry, Honolulu HI 96813 ²

Abstract:
Ecosystem nutrient use efficiency is the ratio of net primary productivity to soil nutrient supply. Ecologists have invoked nutrient use efficiency as an explanation for the distribution of communities along gradients of soil fertility; high efficiency of nutrient use may also be a desirable attribute in human-managed ecosystems. We investigated whether ecosystem nutrient use efficiency could be predicted from plant-level nutrient use efficiency alone (i.e., the ratio of an individual's biomass production to its nutrient uptake), or whether it was primarily determined by soil nutrient supply. We worked in model tropical ecosystems at La Selva Biological Station, Costa Rica. The systems comprised monocultures of three tree species, Hyeronima alchorneoides, Cedrela odorata, and Cordia alliodora, and polycultures in which those tree species were co-planted with large, perennial monocots: A palm and a heliconia. The dominant tree species had a significant effect on nutrient use efficiency at the ecosystem level. Nonetheless, ecosystem nutrient use efficiency was better correlated with soil nutrient supply than with plant-level nutrient use efficiency. Our results suggest that ecosystem nutrient use efficiency is subject to control by both bottom-up and top-down factors, the former related to characteristics of the species involved, the latter related to an environmental factor: Soil fertility.

Keywords: cross-scale linkages, ecosystem, nutrient use efficiency, plant

This abstract is being presented at: 3:30 PM in session:
Poster Session #15: Nutrient Cycling.