NITROGEN LIMITATION OF NET PRIMARY PRODUCTIVITY IN TERRESTRIAL ECOSYSTEMS IS GLOBALLY DISTRIBUTED

TLDR

The study tested whether nitrogen limitation of net primary production is widespread across biomes and varies with geography and climate. The authors conducted a meta‑analysis of 126 nitrogen‑addition experiments to evaluate nitrogen limitation of net primary production in terrestrial ecosystems. Across the 126 studies, most ecosystems exhibited nitrogen limitation with an average 29% growth response; significant responses were observed in temperate and tropical forests, grasslands, wetlands, and tundra but not deserts, with tropical forest responses strongest on young volcanic soils and a negative correlation between response and latitude, suggesting geography mediates nitrogen limitation.

Abstract

Our meta-analysis of 126 nitrogen addition experiments evaluated nitrogen (N) limitation of net primary production (NPP) in terrestrial ecosystems. We tested the hypothesis that N limitation is widespread among biomes and influenced by geography and climate. We used the response ratio (R ≅ ANPPN/ANPPctrl) of aboveground plant growth in fertilized to control plots and found that most ecosystems are nitrogen limited with an average 29% growth response to nitrogen (i.e., R = 1.29). The response ratio was significant within temperate forests (R = 1.19), tropical forests (R = 1.60), temperate grasslands (R = 1.53), tropical grasslands (R = 1.26), wetlands (R = 1.16), and tundra (R = 1.35), but not deserts. Eight tropical forest studies had been conducted on very young volcanic soils in Hawaii, and this subgroup was strongly N limited (R = 2.13), which resulted in a negative correlation between forest R and latitude. The degree of N limitation in the remainder of the tropical forest studies (R = 1.20) was comparable to that of temperate forests, and when the young Hawaiian subgroup was excluded, forest R did not vary with latitude. Grassland response increased with latitude, but was independent of temperature and precipitation. These results suggest that the global N and C cycles interact strongly and that geography can mediate ecosystem response to N within certain biome types.