From physiology to salt marsh management challenges with sea level rise: the case of native Spartina foliosa, invasive S. densiflora and their hybrid

Authors: GALLEGO-TEVAR, BLANCA - University Of Seville; PEINADO-TORRUBIA, PROCOPIO - University Of Seville; ALVAREZ, ROSARIO - University Of Seville; Grewell, Brenda; CASTILLO, JESUS - University Of Seville

Submitted to: Conservation Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2020
Publication Date: 6/30/2020
Citation: Gallego-Tevar, B., Peinado-Torrubia, P., Alvarez, R., Grewell, B.J., Castillo, J.M. 2020. From physiology to salt marsh management challenges with sea level rise: the case of native Spartina foliosa, invasive S. densiflora and their hybrid. Conservation Physiology. 8(1). Article coaa053. https://doi.org/10.1093/conphys/coaa053.
DOI: https://doi.org/10.1093/conphys/coaa053

Interpretive Summary: Knowledge of plant physiological trait responses to sea level rise can inform coastal ecosystem management. Phosphoenolpyruvate carboxylase (PEPC) catalyzes reactions for photosynthetic carbon fixation, and other metabolic pathways. In a greenhouse mesocosm experiment, we measured PEPC activity and related trait responses in native, invasive and hybrid Spartina cordgrasses from San Francisco Estuary under experimentally-imposed increasing tidewater salinity and inundation regimes. Results demonstrate the PEPC activity supports invasiveness of Spartina hybrids and reveal the enzymatic mechanism for limitations to salt tolerance of invasive S. densiflora. The applied significance of this results suggests targeted eradication of this weed should initially target the most benign habitats to inhibit spread. The relative stress tolerance of S. foliosa is supported by PEPC activity, that suggests recolonization of this taxa may be successful during marsh transgression to higher elevations where adjacent habitat can accommodate sea level rise, or in restoration efforts that enhance marsh elevations through engineered sediment placement.

Technical Abstract: Sea level rise imposes increasing salinity and inundation stresses in salt marshes, which are also being invaded by exotic plant species. Knowledge of plant physiological trait responses to sea level rise can inform coastal ecosystem management. Phosphoenolpyruvate carboxylase (PEPC) enzyme catalyzes reactions for photosynthetic carbon fixation, and other metabolic pathways. PEPC enzymatic activity is regulated by reversible protein phosphorylation. This regulatory phosphorylation depends on light, but also depends on several abiotic factors such as salinity, carbon dioxide or inundation levels. Therefore, PEPC activity, and the photosynthetic process and other biochemical pathways it supports can be altered by rising sea level in coastal ecosystems, and functional trait responses may vary by species. In a mesocosm experiment, we measured and compared phosphoenolpyruvate carboxylase (PEPC) activity and related functional trait responses of California-native Spartina foliosa, invasive S. densiflora and their hybrid S. densiflora x foliosa in response to increasing levels of salinity and inundation. S. foliosa was moderately sensitive to salinity in relation to PEPC functional traits. This native species somewhat compensated for the reduction of PEPC activity with increased salinity through higher enzyme activation by phosphorylation. PEPC functional traits responses of S. foliosa were mostly independent of inundation depth. In view of these results, managers should conserve undeveloped lands for accommodation space above current high tide lines to facilitate natural migration and colonization of stress-tolerant S. foliosa with estuarine transgression. Our results on functional responses of PEPC traits to salinity provide mechanistic insight for previous results showing low tolerance of invasive S. densiflora to salinity. Given limited resources for weed management, these results suggest prioritized eradication of newly colonizing populations of S. densiflora in lower salinity habitats, where growth rates and spread will be highest. Further spread of this invader also increases the risk of further hybrid formation where contact is made with the native taxa. Measured PEPC responses support the high stress tolerance of the S. densiflora x foliosa hybrid to increasing salinity, inundation and their interaction. Therefore, eradication of the hybrid should the highest management priority. Our study shows that the responses of key functional physiological traits to environmental stresses may work as biological indicators orientating our ecosystem management practices in a scenario of climate change.