A comparative study on temperature and water potential thresholds for the germination ofBetula pendulaand two Mediterranean endemic birches,Betula aetnensisandBetula fontqueri

Abstract

The influence of temperature and water availability on seed germination can vary across the geographic range of species with a large distribution. Betula pendula is a widely spread European tree that has differentiated into two narrowly distributed taxa, endemic to Mediterranean mountains: Betula aetnensis in Sicily and B. fontqueri in Spain and Morocco. We tested the hypothesis that the regeneration niche, expressed by temperature and water potential thresholds, varies across these species and is influenced by the local climate. Seeds were collected from six populations of B. pendula, one of B. fontqueri and two of B. aetnensis. Germination tests were conducted between 5 and 30°C. The thermal thresholds were calculated before and after cold stratification. The osmotic potential tested ranged from 0 to −1.5 MPa. Time to reach 30 and 50% of germination was calculated by fitting non-linear models. Germination was promoted by high temperatures, but the response to stratification was heterogeneous. Tb and Ψb differed between and within species. Tb ranged between 2.22 and 8.94°C for unstratified seeds. Mediterranean species had higher drought tolerance, while B. pendula showed contrasting responses to low water potential. Ψb reached a minimum value of −1.15 MPa in B. fontqueri. High temperatures influenced the Tb of unstratified seeds negatively, while, after stratification, the Tb increased with precipitation in the driest month. The heterogeneity observed could reflect higher genetic variability in marginal populations of silver birch. Knowledge of their germination ecology may be useful to mitigate future impacts of climate change on core populations of B. pendula.

Sensitivity of Eurasian Rear-Edge Birch Populations to Regional Climate and Local Hydrological Conditions

“…The isolation of birch populations in the central-southern Spanish mountains, which might have persisted here as glacial relicts, has led to their taxonomic differentiation and local adaptation to warmer and drier climates [28]. Though local adaptation can reduce the adaptability of genotypes to rapid environmental changes [33,74], the rear-edge population can provide drought-tolerant genotypes to more central distributions considering predicted species range shifts [37,75]. However, these populations face multiple threats, including drastic habitat fragmentation, warmer and drier conditions, or reduction of water supply due to human land uses.…”

Comparison of the effect of temperature and water potential on the seed germination of five Pedicularis kansuensis populations from the Qinghai–Tibet plateau

“…Different populations of the same species may demonstrate different germination abilities when they germinate under water stress (Baskin and Baskin, 2014;Lima and Meiado, 2017). Previous studies found that the seed germination of Pilosocereus catingicola, Betula pendulai, and Pinus brutia from dry habitats was higher than that of the same plants from wet habitats with low water potentials (Lima and Meiado, 2017;Tilki and Dirik, 2007;Ranno et al, 2020). Similarly, Zhang et al (2017) reported that the germination of Stipa bungeana from Western China's Loess Plateau decreased with decreased water potential in eight populations, and that sensitivity to water stress varied among the populations.…”