RESUMEN
Habitats that differ in soil resource availability are expected to differ for selection on resource-related plant traits. Here, we examined spatial and temporal variation in phenotypic selection on leaf ecophysiological traits for 10 Helianthus populations, including two species of hybrid origin, Helianthus anomalus and Helianthus deserticola, and artificial hybrids of their ancestral parents. Leaf traits assessed were leaf size, succulence, nitrogen (N) concentration and water-use efficiency (WUE). Biomass and leaf traits of artificial hybrids indicate that the actively moving dune habitat of H. anomalus was more growth limiting, with lower N availability but higher relative water availability than the stabilized dune habitat of H. deserticola. Habitats differed for direct selection on leaf N and WUE, but not size or succulence, for the artificial hybrids. However, within the H. anomalus habitat, direct selection on WUE also differed among populations. Across years, direct selection on leaf traits did not differ. Leaf N was the only trait for which direct selection differed between habitats but not within the H. anomalus habitat, suggesting that nutrient limitation is an important selective force driving adaptation of H. anomalus to the active dune habitat.
Asunto(s)
Ecosistema , Helianthus/genética , Helianthus/fisiología , Hojas de la Planta/genética , Hojas de la Planta/fisiología , Carácter Cuantitativo Heredable , Selección Genética , Biomasa , Hibridación Genética , Fenotipo , Dinámica Poblacional , Factores de TiempoRESUMEN
Upon rewetting, lichens lose polyols through leaching. We quantified leaching losses for 21 species under simulated rainfall. Polyol concentrations in these lichens range from 1.0 to 8.8%, with a mean of 2.8%. Leaching losses range up to about 7.5 mg (polyol)/g (lichen dry weight) in a typical rain event. The rate of polyol leaching declines exponentially, becoming negligible within 1 hour of continuous rain. The response of polyol leaching rate to rainfall intensity and amount varies between species-six species showed no response, one had increased leaching with increased rainfall intensity, four had increased leaching with increased amount of rainfall, and one had decreased leaching with increased total amount of rainfall. Polyol leaching rates are positively correlated with polyol concentration for 20 species. Literature values of average daily growth rates for subarctic lichens are of the same order of magnitude as leaching rates, suggesting that polyol leaching is an important part of the carbon budget of lichens.
