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

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      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 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.

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          A global analysis of root distributions for terrestrial biomes

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            Author and article information

            Affiliations
            [1 ]simpleSchool of Biological, Earth and Environmental Sciences, The University of New South Wales Sydney, NSW 2052, Australia
            [2 ]simpleEnvironmental Sciences Division, Oak Ridge National Laboratory Oak Ridge, Tennessee 37831-6301
            [3 ]simpleResearch School of Biology, The Australian National University Canberra, ACT 0200, Australia
            [4 ]simpleDepartment of Biological Sciences, Macquarie University North Ryde, NSW 2109, Australia
            [5 ]simpleDepartment of Forest Ecology and Management, Swedish University of Agricultural Sciences Umeå, Sweden
            Author notes
            Ross E. McMurtrie, School of Biological, Earth and Environmental Sciences, The University of New South Wales, Sydney, NSW 2052, Australia. Tel: +61-425 306272; Fax: +61-2-9385 1558; E-mail: r.mcmurtrie@ 123456unsw.edu.au
            Journal
            Ecol Evol
            Ecol Evol
            ece3
            Ecology and Evolution
            Blackwell Publishing Ltd (Oxford, UK )
            2045-7758
            2045-7758
            June 2012
            : 2
            : 6
            : 1235-1250
            3402197
            22833797
            10.1002/ece3.266
            © 2012 The Authors. Published by Blackwell Publishing Ltd.
            Categories
            Original Research

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