Plant and Soil

, Volume 296, Issue 1–2, pp 103–113 | Cite as

Early root growth plasticity in seedlings of three Mediterranean woody species

  • Francisco M. Padilla
  • Juan de Dios Miranda
  • Francisco I. Pugnaire
Regular Article

Abstract

Since very young seedlings are sensitive to dehydration, soil desiccation is often responsible for seedling death in water-stressed environments. Roots play a major role in overcoming water stress and plant establishment, thus early root development in response to limited water availability becomes a strategy that may ensure seedling recruitment. We explored whether different water availabilities altered growth patterns of very young seedlings, focussing on root elongation, and hypothesized that seedling responses would depend on species-specific drought tolerance and seed size. We carried out a greenhouse experiment exposing 2-week-old seedlings of three Mediterranean shrubland species, the drought-tolerant and small-seeded Genista umbellata (L’Hér.) Dum. Cours. and Lycium intricatum Boiss., and the drought-sensitive, large-seeded Retama sphaerocarpa (L.) Boiss., to two watering quantities and monitored plant and root growth weekly in glass cases for 5 weeks. We found that at such early stages, reduced water quantity enhanced root growth in all three species, regardless of drought tolerance and seed size, although root plasticity was the highest in the small-seeded and drought-tolerant Genista. In contrast, shoot elongation and mass allocation, root-to-shoot mass (R:S) ratio, was unaffected by watering. Seedlings responded to lower water availability with faster root elongation rate and greater absorptive root surface, which can account for the enhanced relative growth rate (RGR) of the small-seeded Genista and Lycium under reduced watering. By contrast, a larger root absorptive surface did not lead to higher RGR in the large-seeded Retama probably because of its greater independence from external mineral resources. Our data evidence the importance of water availability on the initial developmental stages of these three species regardless of seed size and drought tolerance. Root growth can be interpreted as an adaptive strategy to deal with drying soils and decreasing soil moisture since larger roots enable to exploit unexplored soil areas of soil, which may ensure recruitment success.

Keywords

Cotyledons Drought Mediterranean ecosystems Recruitment Root growth Seedlings 

Notes

Acknowledgments

We are grateful to Kazuhiko Kimura for helping with the root macro, Florentino Mostaza for root scanning and Consejería de Medio Ambiente (Junta de Andalucía) for seed donation. Two anonymous reviewers made valuable comments on an earlier draft. The Spanish Ministry of Education and Science funded this work (grant CGL2004-00090/CLI). FMP was supported by a predoctoral I3P fellowship (CSIC-European Social Fund).

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Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Francisco M. Padilla
    • 1
  • Juan de Dios Miranda
    • 1
  • Francisco I. Pugnaire
    • 1
  1. 1.Estación Experimental de Zonas ÁridasConsejo Superior de Investigaciones CientíficasAlmeriaSpain

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