Lignotubers in Mediterranean basin plants

Abstract

Lignotubers are swollen woody structures located at the root-shoot transition zone and contain numerous dormant buds and starch reserves. This structure enables the plant to resprout prolifically after severe disturbances that remove the aboveground biomass. These are considered adaptive traits in ecosystems with highly frequent and severe disturbances-such as fire-prone ecosystems. In this paper, we aim to contribute to the knowledge of lignotubers in the Mediterranean basin and highlight the evolutionary implications. We first summarise existing knowledge on lignotuber species in the Mediterranean basin. We then provide a detailed morpho-anatomical description of early lignotubers in two common woody species (Arbutus unedo L. and Phillyrea angustifolia L.). Finally, we compare our anatomical results with those obtained in studies conducted with other lignotuberous species from different Mediterranean regions. Lignotubers were verified in 14 species in the Mediterranean basin; all being from lineages with origins dating to the Tertiary and thus pre-dating the Mediterranean climate. In A. unedo and P. angustifolia, lignotubers are macroscopically discernible in 4-and 2-year-old saplings, respectively. In these two species, the lignotubers have numerous buds protected by hypertrophied scales, and have a contorted xylem containing abundant starch. Our results challenge the traditional idea that pre-Mediterranean lineages suffered evolutionary inertia; instead, lignotuberous species may be considered examples of plants that adapted to the increased fire activity that occurred throughout the Tertiary and Quaternary. We also highlight the use of morpho-anatomical traits to unambiguously distinguish between lignotuberous and non-lignotuberous resprouting species.

Postfire responses of the woody flora of Central Chile: Insights from a germination experiment

“…In these ecosystems, many plant species are able to persist after fire by having thick bark [7, 16], resprouting from dormant buds [17–18], and/or recruiting new individuals from the seed bank (located either in the soil or in the canopy; [19–22]) or from new seeds produced after fire-stimulated flowering [23]. High resource availability, weak competition, and low seed predation after fire, increase the success of seedling establishment.…”

Advances in understanding the influence of fire on the ecology and evolution of plants: a tribute to Peter J. Clarke

“…Lignotubers (woody swelling of the root crown) are considered an adaptive trait in ecosystems with highly frequent and severe disturbances, such as fire (Paula et al 2016;this issue). Lignotubers are associated with a basal resprouting response that enables post-fire regeneration (Burrows 2013; Clarke et al 2013c), conferring a degree of resilience to individuals that are prone to being top-killed by fire.…”

“…Species that resprout from lignotubers have a larger bud bank than those resprouting from root crowns (Clarke et al 2013c) with associated higher energy costs. Large bud banks should therefore only be selected when they have a significant effect on survival, as they do in fire-prone environments (Paula et al 2016). Consequently, basal resprouting is prevalent particularly in crown-fire affected ecosystems (Knox and Clarke 2004;Paula et al 2009;Burrows 2013;Paula et al 2016).…”

Flammable Mexico

“…Therefore, in some cases, the pressure that shaped resprouting may not be fire and thus, resprouting could have an adaptive value under recurrent fires but may not be a true adaptation to fire (Keeley et al 2011). This is why resprouting from rhizomes, roots or bulbs may not necessarily be fire adaptations, in contrast with resprouting from lignotubers or epicormic buds that are more related to fire (Keeley et al 2011;Paula et al 2016). Similarly, having high dispersal ability may enable the quick colonisation of burned areas but may not be a direct adaptation to fire.…”