Plant root distributions and nitrogen uptake predicted by a hypothesis of optimal root foraging
Article first published online: 21 MAY 2012
© 2011 The Authors. MicrobiologyOpen published by Blackwell Publishing Ltd.
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Ecology and Evolution
Volume 2, Issue 6, pages 1235–1250, June 2012
How to Cite
McMurtrie, R. E., Iversen, C. M., Dewar, R. C., Medlyn, B. E., Näsholm, T., Pepper, D. A. and Norby, R. J. (2012), Plant root distributions and nitrogen uptake predicted by a hypothesis of optimal root foraging. Ecology and Evolution, 2: 1235–1250. doi: 10.1002/ece3.266
- Issue published online: 12 JUN 2012
- Article first published online: 21 MAY 2012
- Received: 20 March 2012; Accepted: 26 March 2012
- Elevated CO2;
- nitrogen-uptake efficiency;
- nitrogen-uptake fraction;
- nitrogen-uptake model;
- nitrogen-use efficiency;
- optimal foraging by roots;
- optimal rooting depth;
- root distributions;
- root strategies
CO2-enrichment experiments consistently show that rooting depth increases when trees are grown at elevated CO2 (eCO2), 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 CO2-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.