Open AccessPlant root distributions and nitrogen uptake predicted by a hypothesis of optimal root foraging
Author(s) -
McMurtrie Ross E.,
Iversen Colleen M.,
Dewar Roderick C.,
Medlyn Belinda E.,
Näsholm Torgny,
Pepper David A.,
Norby Richard J.
Publication year - 2012
Publication title -
ecology and evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.17
H-Index - 63
ISSN - 2045-7758
DOI - 10.1002/ece3.266
Subject(s) - root (linguistics) , foraging , plant root , nitrogen , biology , mathematics , ecology , chemistry , horticulture , philosophy , linguistics , organic chemistry
Abstract CO 2 ‐enrichment experiments consistently show that rooting depth increases when trees are grown at elevated CO 2 (eCO 2 ), leading in some experiments to increased capture of available soil nitrogen (N) from deeper soil. However, the link between N uptake and root distributions remains poorly represented in forest ecosystem and global land‐surface models. Here, this link is modeled and analyzed using a new optimization hypothesis ( MaxNup ) for root foraging in relation to the spatial variability of soil N, according to which a given total root mass is distributed vertically in order to maximize annual N uptake. MaxNup leads to analytical predictions for the optimal vertical profile of root biomass, maximum rooting depth, and N‐uptake fraction (i.e., the proportion of plant‐available soil N taken up annually by roots). We use these predictions to gain new insight into the behavior of the N‐uptake fraction in trees growing at the Oak Ridge National Laboratory free‐air CO 2 ‐enrichment experiment. We also compare MaxNup with empirical equations previously fitted to root‐distribution data from all the world's plant biomes, and find that the empirical equations underestimate the capacity of root systems to take up N.