Many clonal plant species demonstrate plasticity in their allocation to sexual and asexual reproductive strategies in response to external cues. Both reproductive strategies offer context dependent advantages, such as asexual reproduction being favorable under environmentally stressful conditions when the probability of sexual recruitment is low. However, little is known about the ability of plants to adaptively switch between these reproductive strategies. The objective of this study was to determine the ability of the foundational wetland grass Spartina alterniflora to plastically reallocate between reproductive strategies in response to stress. To accomplish this, I conducted a common greenhouse experiment testing the effect of salinity stress on the sexual and asexual reproductive traits of S. alterniflora. Seed was collected from a natural population and 80 individuals were grown under high salinity (35 to 40 ppt) or no salinity (0 to 1 ppt) conditions. An initial harvest of 20 individuals from both treatments was conducted after the emergence of a secondary daughter ramet to determine the characteristics of daughter ramets in relation to parents. An additional 20 individuals from both treatments were harvested after the development of inflorescences to determine relative allocation to sexual and asexual processes. Differences in reproductive traits were compared using ANCOVA.
Results/Conclusions
I found that S. alternflora grown in saline conditions made larger investments in asexual reproduction by producing larger rhizomes and daughter ramets than those found in fresh conditions. Primary daughters produced larger secondary daughters relative to their own biomass in saline than in fresh conditions. Mature S. alterniflora individuals grown in fresh conditions produced more ramets and inflorescences with a higher probability of an individual ramet producing an inflorescence, and greater aboveground total and reproductive biomass. Individuals grown in saline conditions produced less belowground biomass overall but produced proportionately larger reproductive belowground biomass in the form of rhizomes relative to their total biomass. S. alterniflora grown in saline conditions also produced significantly more rhizomes than in fresh conditions. These results demonstrate increased asexual investment of S. alterniflora under highly saline conditions relative to their total biomass, as well as suppression of sexual reproduction. This suggests plasticity in reproductive phenotypes that may scale to population level evolutionary and ecological consequences. Reliance on asexual reproduction can produce decreased genetic diversity in natural populations, and may ultimately lead to sexual extinction and evolutionary dead ends.