Functional intraspecific variation in the base water potential for seed germination along soil microclimatic gradients

The ability of plants to successfully regenerate depends on complex physiological and ecological processes, and one of the first vital stages is seed germination, which depends on temperature, light and water availability. Within species variation in seed germination allows differential responses when facing stimuli and is key for adaptation in the natural world. There has been abundant research about variation in germination responses to temperature changes, but much less is known about responses to water availability, specifically the limits and the potential variation within a single wild species. Under ongoing climate change with increasing drought episodes it is vital to know the minimum amount of water required for germination, as well as if variation and therefore the potential to adapt exists within a species. We focused on a wild carnation (Dianthus langeanus) endemic to the northwestern Iberian Peninsula. We collected seeds from 18 different subpopulations, some only 10 m apart, and with contrasting microclimatic conditions due to topography, slope and orientation. We measured germination responses to water stress using polyethylene glycol (PEG) solutions, a polymer that increases water density and allows to mimic different drought intensities. We found considerable differences in germination under water stress between each subpopulation. Seeds from warmer and drier subpopulations were able to germinate under higher water stress, meaning their germination was more drought tolerant. Our results highlight the importance of germination responses to water availability. Variation within species appears to be important even at small scales, suggesting an important previously unknown potential for seed germination adaptation to future drier conditions.Read the free Plain Language Summary for this article on the Journal blog. La variaci & oacute;n intraespec & iacute;fica es una parte imprescindible de un amplio abanico de procesos biol & oacute;gicos y es la base la adaptaci & oacute;n de las especies a los cambios ambientales. La variaci & oacute;n intraespec & iacute;fica en los l & iacute;mites termales para la germinaci & oacute;n est & aacute; ampliamente extendida en espermatofitos y ha estado objeto de abundante investigaci & oacute;n. Sin embargo, los l & iacute;mites h & iacute;dricos para la germinaci & oacute;n han sido mucho menos estudiados. La distribuci & oacute;n y magnitud de la variaci & oacute;n intraespec & iacute;fica en el potencial h & iacute;drico base para la germinaci & oacute;n (psi b i.e. la cantidad m & iacute;nima de agua requerida para germinar) puede tener un alto significado ecol & oacute;gico en ambientes con limitaci & oacute;n de agua, pero su funcionalidad nunca ha sido testada en escalas de pocos metros. En este estudio testamos la hip & oacute;tesis que los l & iacute;mites h & iacute;dricos para la germinaci & oacute;n muestran variaci & oacute;n intraespec & iacute;fica funcional a lo largo de gradientes microclim & aacute;ticos locales en ambientes alpinos mediterr & aacute;neos con estr & eacute;s h & iacute;drico de la Pen & iacute;nsula Ib & eacute;rica (SW Europa). Muestreamos 18 subpoblaciones de la especie Dianthus langeanus (Caryophyllaceae), separadas a intervalos de 10m, y con condiciones microclim & aacute;ticas contrastantes registradas en campo. Medimos las respuestas de germinaci & oacute;n al estr & eacute;s h & iacute;drico usando soluciones de polietilenglicol (PEG). Ajustamos modelos "hydro-time" para calcular psi b para la germinaci & oacute;n en cada subpoblaci & oacute;n y examinamos la predicci & oacute;n de que semillas de subpoblaciones con condiciones m & aacute;s c & aacute;lidas y secas tendr & aacute;n psi b m & aacute;s bajos (i.e. su germinaci & oacute;n es m & aacute;s tolerante a la sequ & iacute;a). Encontramos diferencias significativas entre los psi b de las subpoblaciones, i.e. hay variaci & oacute;n intraespec & iacute;fica en la respuesta al estr & eacute;s h & iacute;drico. Semillas de subpoblaciones con condiciones m & aacute;s c & aacute;lidas y secas tuvieron psi b m & aacute;s bajos, lo que significa que su germinaci & oacute;n es m & aacute;s tolerante a la sequ & iacute;a. Estos resultados apoyan la hip & oacute;tesis que la variaci & oacute;n intraespec & iacute;fica en psi b para germinaci & oacute;n puede tener un significado funcional, incluso a microescala (aprox. 10 m). S & iacute;ntesis. Nuestros resultados indican que el psi b para germinaci & oacute;n es un car & aacute;cter con importantes implicaciones potenciales para la fenolog & iacute;a, reproducci & oacute;n y fitness de los individuos en ambientes con limitada disponibilidad h & iacute;drica. Estos hallazgos resaltan el potencial de adaptaci & oacute;n de la germinaci & oacute;n a condiciones clim & aacute;ticas actuales y futuras.