Abstract
Sympatric closely-related species co-occur within heterogeneous environments by occupying separate ecological niches as result of adaptive differentiation. Soil salinity is one of the most relevant drivers leading plant zonation in salt marshes, where germination is a critical stage in the life cycle of many halophytes. Salinity influence on germination patterns was evaluated for six sympatric Limonium species (L. admirable, L. caesium, L. cossonianum, L. delicatulum, L. supinum and L. tobarrense), which grow under arid environmental conditions in an inland salt marsh from the southeastern Spain. Experiments were conducted to determine the effects of different salinities (0–6% NaCl) on seed germination under 12 h in light at 25 °C and for 12 h in dark at 20 °C. Best seed germination was obtained under non-saline conditions, and germination was delayed and significantly reduced by increasing the salinity levels for all the studied taxa. The germination variables related to final germination percentage, mean time to germination and recovery were directly influenced by salinity. Seeds recovered their germination capacity after transferring the seeds from saline solutions to distilled water, especially those seeds previously treated under high salinity conditions. Our results suggest that the successful establishment of Limonium communities depends on the germination strategy which implies a rapid germination velocity when the soil salinity decreases. Two different germination syndromes based on germination percentage and germination recovery have been found. Hence, these germination strategies would favour the adaptation of different Limonium species under favorable conditions, shaping the plant asssembly within the saline habitat.
Highlights
Salt marshes provide an appropriate model ecosystem to study divergent trait responses among closely-related species in sympatry to specific abiotic factors
Pearson coefficients between the five variables showed that only final germination percentage at 21 days (FGP21) and recovery percentage (RP) were strongly correlated between them (r = 0.92, P < 0.001; Appendix A in Supplementary material)
The an alyses of variance (ANOVA) results showed that these differences for taxa and salinity treatments for the five germination variables were significant (P < 0.001), as well as the interaction between these two factors (P < 0.01; Table 1), except in the case of RP
Summary
Salt marshes provide an appropriate model ecosystem to study divergent trait responses among closely-related species in sympatry to specific abiotic factors. Some functional traits (e.g. salt resistance or life form) have appeared clearly assembled in the different saltmarsh zones, suggesting the existence of an environmental filtering along the salinity gradient and establishing a marked functional trait turnover in Mediterranean salt marshes (Moreno et al, 2020) This strong abiotic pattern, led by soil salinity, holds a noticeable influence over biotic interactions and conceal their effects (Moreno et al, 2020). Sympatric closely-related species co-occur within heterogeneous habitats by occupying separate ecological niches as the result of adaptive differentiation This specific divergent selection is led by adaptive phenotypic differentiation to enhance performance in response to local environmental conditions (Weissing et al, 2011). These evidences may suggest that different morphological species (‘morphotypes’ sensu Moreno et al, 2018a) have different survival strategies under the extreme conditions of saline habitats
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