Physiological and oxidative stress responses of baldcypress in response to elevated salinity: linking and identifying biomarkers of stress in a keystone species
2016
Lauer, Nathan | Ross, Cliff
Globally, saltwater intrusion associated with sea level rise is threatening the vitality of coastal freshwater wetland communities. In the current study, we investigated the impacts of salinity stress on Baldcypress (Taxodium distichum (L.) Rich), a tree common to coastal freshwater wetlands within the southeastern USA. Salinity-induced responses of saplings and adult trees were assessed in a greenhouse and field-based study, respectively. In the greenhouse study, saplings maintained under mesohaline conditions (8 g L⁻¹) for 10 weeks exhibited a predictable physiological response characterized by decreased maximum quantum yield of photosystem II (Fv/Fm) and increased non-photochemical quenching. Changes in photochemistry were concomitant with increases in leaf sodium, hydrogen peroxide, and free proline content compared to saplings maintained in freshwater. A strong negative correlation existed between Fv/Fm and leaf hydrogen peroxide content. Salinity-stressed saplings also exhibited decreased activity of a low molecular weight peroxidase isozyme within leaf tissue. Taken together, the evidence suggests that H₂O₂ was maintained at marginally elevated levels in leaf tissue to elicit a physiological response. Adult trees sampled in situ displayed similar stress responses to elevated salinity as saplings from the greenhouse study. Specifically, trees sampled at a basin swamp exhibited decreased Fv/Fm and increased non-photochemical quenching, lipid peroxidation, and free proline content in leaf tissue compared to trees at other sites. Thus, coupling chlorophyll fluorescence parameters with stable biomarkers show promise in detecting sub-lethal salinity stress for plants in situ.
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