Most water and essential soil nutrient uptake is carried out by fine roots in plants. It is therefore important to understand the global geographic patterns of fine-root nitrogen and phosphorus cycling. Here, by compiling plant root data from 211 studies in 51 countries, we show that live fine roots have low nitrogen (N) and phosphorus (P), but similar N:P ratios when compared with green leaves. The fine-root N:P ratio differs between biomes and declines exponentially with latitude in roots of all diameter classes. This is in contrast to previous reports of a linear latitudinal decline in green leaf N:P, but consistent with nonlinear declines in leaf litter N:P. Whereas the latitudinal N:P decline in both roots and leaves reflects collective influences of climate, soil age and weathering, differences in the shape of the response function may be a result of their different N and P use strategies.
Bibliographical noteFunding Information:
We thank Jane Parker for her constructive comments. This work was financially supported by the Natural Science and Engineering Council of Canada (DG283336-09), Ontario Ministry of Research and Innovation Early Researcher Award program, the National Science Foundation LTER Program (DEB-0080382) of the United States, and the Discovery Grant Program of the Institute on the Environment, University of Minnesota.