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Ephemeral root modules in Fraxinus mandshurica

Authors

  • Mengxue Xia,

    1. Department of Ecology, College of Urban and Environmental Sciences and the Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing 100871, China
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  • Dali Guo,

    1. Department of Ecology, College of Urban and Environmental Sciences and the Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing 100871, China
    2. The Key Laboratory of Science and Technology of Urban Environment, Peking University Shenzhen Graduate School, Shenzhen 518055, China
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  • Kurt S. Pregitzer

    1. Department of Natural Resources and Environmental Science, University of Nevada, Mail Stop 186, 1000 Valley Road, Reno, NV 89512, USA
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Author for correspondence:
Dali Guo
Tel: +86 10 62753063
Email: dlguo@urban.pku.edu.cn

Summary

  • Historically, ephemeral roots have been equated with ‘fine roots’ (i.e. all roots of less than an arbitrary diameter, such as 2 mm), but evidence shows that ‘fine roots’ in woody species are complex branching systems with both rapid-cycling and slow-cycling components. A precise definition of ephemeral roots is therefore needed.
  • Using a branch-order classification, a rhizotron method and sequential sampling of a root cohort, we tested the hypothesis that ephemeral root modules exist within the branching Fraxinus mandshurica (Manchurian ash) root system as distal nonwoody lateral branches, which show anatomical, nutritional and physiological patterns distinct from their woody mother roots.
  • Our results showed that in F. mandshurica, distal nonwoody root branch orders die rapidly as intact lateral branches (or modules). These nonwoody branch orders exhibited highly synchronous changes in tissue nitrogen concentrations and respiration, dominated root turnover, nutrient flux and root respiration, and never underwent secondary development.
  • The ephemeral root modules proposed here may provide a functional basis for differentiating and sampling short-lived absorptive roots in woody plants, and represent a conceptual leap over the traditional coarse–fine root dichotomies based on arbitrary size classes.

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