Seedling Stage Strategies as a Means of Habitat Specialization in Herbaceous Plants

Abstract

The regeneration niche has been little investigated in studies of community assembly and plant distribution. We examined adaptive associations between seedling traits and habitat specialization. Two habitat contrasts were investigated across several evolutionary lineages of angiosperms: species specialized to forest vs. open habitats and to dry vs. wet habitats. We also tested whether effects of shade and drought vary independently or, alternatively, if shade may amplify effects on drought-stressed plants. Seedling response in terms of growth rate, height, slenderness, specific leaf area (SLA) and degree of elongation (longest internode; petiole or leaf-sheath depending on species' morphology) to light and watering treatments was assessed. We used a factorial design involving three light regimes and two watering frequencies. The open-shaded habitat contrast and the dry-wet habitat contrast were investigated using six and five pairs of congeneric species, respectively. The congeneric species pair design controlled for confounding effects of evolutionary history prior to divergence in habitat specialization. Seedling growth rate generally decreased with shade and reduced watering frequency. Plant height was generally largest at intermediate light. Specialization to shaded habitats was associated with a more conservative growth strategy, i.e. showing a more modest growth response to increasing light. Species from all habitats showed the highest relative elongation at intermediate light, except for the moist-habitat species, for which elongation increased with shade. Contrary to our expectations, species from dry habitats grew bigger than species from moist habitats in all treatments. SLA responded to the light treatment, but not to watering regime. The contrasting light and moisture conditions across habitats appear to not have selected for differences in SLA. We conclude that seedling phase strategies of resource allocation in temperate herbs contribute to their habitat specialization. Habitat-specific seedling strategies and trade-offs in response to resource availability and environmental conditions may be important to adaptive specialization.

Habitat specialization through germination cueing: a comparative study of herbs from forests and open habitats

“…5). Our findings are not incompatible with studies showing forest species to have adaptive traits in the seedling or adult phase to survive in shaded habitats, such as shade avoidance or shade tolerance syndromes (Henry and Aarssen, 1997;ten Brink and Bruun, 2011). It remains, however, to be investigated to what degree germination strategy and attributes of the established phase, such as shade tolerance, are coevolved (Silvertown, 1981).…”

Germination of shrub species from Chinese subtropical forests: implications for restoration

“…These interact with microclimatic conditions to determine plant growth, by affecting the photosynthetic capacity to use light and altering herbivory and microbial activity (Valladares, 2003). Consequently, light and temperature conditions vary according to habitat conditions, thus driving germination and seedling establishment strategies (ten Brink & Bruun, 2011). Shrubs grow under many different forest canopy densities, and face wide variations in microclimate according to the forest type/canopy composition.…”

Fine‐tuned ability to predict future competitive environment inAmbrosia artemisiifoliaseeds

“…The most often cited negative effects of native species on invasives are caused by competition (Levine et al ., ). Although competition from resident species takes place at all plant life‐cycle stages (ten Brink & Bruun, ), the vast majority of studies have studied adult plant biomass or fecundity as response variables (Leger & Espeland, ). However, factors affecting seed germination and recruitment also have the potential to affect plant demography and long‐term survival of populations (Tielbörger & Prasse, ; Orrock & Christopher, ; ten Brink & Bruun, ).…”

“…Although competition from resident species takes place at all plant life‐cycle stages (ten Brink & Bruun, ), the vast majority of studies have studied adult plant biomass or fecundity as response variables (Leger & Espeland, ). However, factors affecting seed germination and recruitment also have the potential to affect plant demography and long‐term survival of populations (Tielbörger & Prasse, ; Orrock & Christopher, ; ten Brink & Bruun, ). It has been reported that germination and initial root and shoot development may be particularly sensitive to competition (Foster & Gross, ).…”