Root depth distribution and the diversity–productivity relationship in a long-term grassland experiment

Authors

  • Kevin E. Mueller,

    Corresponding author
    1. University of Minnesota, Department of Ecology, Evolution and Behavior, 100 Ecology Building, 1987 Upper Buford Circle, Saint Paul, Minnesota 55108 USA
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  • David Tilman,

    1. University of Minnesota, Department of Ecology, Evolution and Behavior, 100 Ecology Building, 1987 Upper Buford Circle, Saint Paul, Minnesota 55108 USA
    2. University of California, Bren School of the Environment, Santa Barbara, California 93106 USA
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  • Dario A. Fornara,

    1. University of Ulster, School of Environmental Sciences, Coleraine BT52 1SA United Kingdom
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  • Sarah E. Hobbie

    1. University of Minnesota, Department of Ecology, Evolution and Behavior, 100 Ecology Building, 1987 Upper Buford Circle, Saint Paul, Minnesota 55108 USA
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  • Corresponding Editor: P. B. Adler.

Abstract

The relationship between plant diversity and productivity in grasslands could depend, partly, on how diversity affects vertical distributions of root biomass in soil; yet, no prior study has evaluated the links among diversity, root depth distributions, and productivity in a long-term experiment. We used data from a 12-year experiment to ask how plant species richness and composition influenced both observed and expected root depth distributions of plant communities. Expected root depth distributions were based on the abundance of species in each community and two traits of species that were measured in monocultures: root depth distributions and root-to-shoot ratios. The observed proportion of deep-root biomass increased more than expected with species richness and was positively correlated with aboveground productivity. Indeed, the proportion of deep-root biomass explained variation in productivity even after accounting for legume presence/abundance and greater nitrogen availability in diverse plots. Diverse plots had root depth distributions that were twice as deep as expected from their species composition and corresponding monoculture traits, partly due to interactions between C4 grasses and legumes. These results suggest that the productivity of diverse plant communities was partly dependent on belowground plant interactions that caused roots to be distributed more deeply in soil.

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