Seedling growth rates can have important long-term effects on forest dynamics. Environmental variables such as light availability and edaphic factors can exert a strong influence on seedling growth. The aim of a new article by Offord et al., published in AoB PLANTS, was to uncover the drivers of seedling growth in a rare rainforest conifer. Wollemia nobilis is limited to canyons, characterized by deeply shaded understories and acid soils. In a glasshouse experiment, the authors grew seedlings at a range of pH and light levels. Growth increased with increasing light, and was higher at low pH, regardless of light. The number of stems, however, was greatest in lower light. Thus Wollemia nobilis seedlings may vary their architecture – growing up when light is high, and growing out when light is lower. Nevertheless, low light is likely the key limitation of W. nobilis growth in the wild.
The coexistence of forest tree species has often been linked to differences in their response to light availability during the regeneration stage. Van Couwenberghe et al. study natural regenerated shade-tolerant Fagus sylvatica and shade-intermediate Quercus petraea seedlings and find that no rank reversal occurs between the two species along a light gradient, or along density, mixture or seedling-size gradients. The results thus do not support the classical assumption that spatial heterogeneity in a canopy opening would explain the coexistence of the two species studied. Instead, it is suggested that the main driver of the dynamics of these mixed stands is spatial variation in local size hierarchies among seedlings, which may be caused by differences in seedling emergence time or initial seedling performance.
Early life-history stages of cacti can benefit from the facilitative effects of nurse plants that reduce solar radiation and water stress. Miranda-Jácome et al. conduct a reciprocal transplant experiment, coupled with the artificial manipulation of sun/shade conditions, to test for the effects of local adaptation on germination, seedling survival and growth of the columnar cactus Pilosocereus leucocephalus. They find that significant local adaptation is mainly detected under full sunlight conditions, indicating that sun/shade acts as a selective agent in water-limited environments. Facilitation provided by nurse plants in these environments can attenuate the patterns of local adaptation among plants benefiting from nurse plant effects.