Plant root distributions and nitrogen uptake predicted by a hypothesis of optimal root foraging

Ross E. McMurtrie*, Colleen M. Iversen, Roderick C. Dewar, Belinda E. Medlyn, Torgny Näsholm, David A. Pepper, Richard J. Norby

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    64 Citations (Scopus)

    Abstract

    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 annualNuptake. 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.

    Original languageEnglish
    Pages (from-to)1235-1250
    Number of pages16
    JournalEcology and Evolution
    Volume2
    Issue number6
    DOIs
    Publication statusPublished - Jun 2012

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