A comparison of indicators of sub-lethal nutrient stress in the salt marsh grass, Spartina patens

Wetland plant communities in coastal Louisiana are degrading, resulting in the loss of live emergent vegetation and subsequent succession to open water. Nutrient deprivation caused by compartmentalization of marsh parcels and impaired water exchange is one of the potential sources of sub-lethal stress on plants. Greenhouse experiments were conducted on Spartina patens (Ait.) Muhl. to compare the usefulness of several indicators for the detection of nutrient stress. Responses were measured at the end of 7, 14 and 35 days, with experiments timed to end simultaneously. Leaf expansion rate, aboveground biomass, leaf spectral reflectance, adenine nucleotide levels and CO2 exchange rate all detected significant differences among treatments (0, 25, 50 and 100% Hoagland's solution). All but aboveground biomass were able to detect some treatment differences as early as 7 days after initiation of treatments; aboveground biomass detected differences after 14 days. Adenine nucleotide levels showed the best ability to discriminate among the 0, 25, 50 and 100% Hoagland's treatments, while all other indicators were able to detect differences only between the 0% treatment and the higher levels of nutrient application.