PS 14-137 - Phenotypic variation of a moderately salt tolerant sunflower (Helianthus annuus) under extreme environmental salinity

Background/Question/Methods

Global salinity is increasing due to anthropogenic change, and is toxic to most plants. Less than 1% of angiosperm species are considered “halophytes”, which tolerate high concentrations of environmental salinity. Helianthus annuus is considered a moderately salt tolerant glycophyte (non-halophyte), although populations occur in the saline Great Salt Lake (GSL) region of Utah. This raises the question: can populations of glycophytes in saline habitats locally adapt to more extreme salinity? Variation in salt tolerance is well known among species, but the potential for intra-specific variation in salt tolerance is less known. To investigate variation in the relation between environmental salinity and phenotypic variation, we conducted a common-garden experiment using H. annuus seeds collected from 20 populations of the species’ range with varying concentrations of environmental salinity. Seedlings were treated with control, moderate (field), and high (field x2) salinity treatment solutions mimicking the ionic composition of H. paradoxus habitat. Phenotypic traits related to salt tolerance (above- and below-ground biomass, plant height, and growth rate) of juvenile plants were measured and compared among populations and treatment groups. Quantitative soil salinity data was collected for ten of these populations, and used to investigate the relation between environmental salinity and salt tolerance.

Results/Conclusions

In the GSL region soil salinity (% sodium) ranged from 1.3 to 37.9 (n = 26 populations); thus, high-saline sites exhibit salinity in the range associated with H. paradoxus. Above-ground biomass differed significantly between the 20 populations that were phenotypically studied in control conditions. However, under both moderate and high salinity we did not detect significant differences among populations. This suggests that plant growth performance under salinity does not significantly vary between populations. Furthermore, performance was not correlated to environmental salinity under control, moderate, or high salinity. Similar results were observed for below-ground biomass, total biomass, growth rate, and plant height: there is significant variation among populations in control conditions, but variation is not significant in moderate or high salinity nor is it correlated to our estimate of environmental salinity. One possible interpretation of the lack of association between variation in performance and environmental salinity is that the evolution of salt tolerance is limited by gene flow between populations occupying the geographic mosaic of saline and non-saline habitats. We are continuing to explore the responses of individual populations to this salinity gradient, and whether these populations exhibit variation in key salt tolerance traits such as succulence and ion sequestration.