Differences in nutrient uptake and response among wild and cultivated genotypes of the salt marsh grass Spartina alterniflora
Ecosystem consequences of genetic variation in functional traits are often overlooked in practical use of engineering species for habitat restoration. This is becoming increasingly important as restoration projects now regularly implement agronomic approaches, including reliance on cultivars selected for specific traits to increase performance under targeted conditions. Inthis experiment, we considered the influence of genetic variation among Spartina alternifloracultivars and wild genotypes on ecosystem attributes and functioning following salt marsh restoration in Louisiana.Replicated plots on an eroding shoreline devegetated by the Deepwater Horizon oil spill were restored with plants from one of four sources: two local wild populations and two cultivated clone lines frequently used in restoration projects. We characterized functional differences among genotypes through measures of phenotypic variation (biomass, shoot height and architecture), and indicators of resource use (porewater nutrient dynamics, plant tissue C:N ratios). To test for potential ecosystem consequences of functional differences, we monitored shoreline erosion rates over a two-year period.
We found that cultivars did not outperform wild genotypesaccording to targeted performance traits including high biomass production and high reproductive output. Though significant differences in biomass growth were found,one cultivar and one wild genotype treatment attainedcomparablyhigh biomass and shoot density. Porewater nutrient concentrations tended to be lower in cultivar plots, but no differences in soil nitrogen were observed andtissue C:N ratios suggested that the low-performance wild genotype treatment was more strongly nitrogen limited than other genotype treatments. Erosion rates were significantly higher in the low-performance wild genotype treatmentplots;accelerated erosion was not observed in the cultivar plots with comparable biomass, suggesting that other traits and resource useare stronger determinants of erosion. Not only does this study demonstrate that genotypic variation can result in ecosystem consequences when restoration involves deployment of engineering species,it also suggests that selective cultivation of functional traits may not yield desired outcomes, particularly under stressful conditions.