RELATIONSHIP OF SOIL HYDROGEN-SULFIDE LEVEL TO NET CARBON ASSIMILATION OF PANICUM-HEMITOMON AND SPARTINA-PATENS

Panicum hemitomon Schult and Spartina patens (Ait) Muhl. plants from Louisiana Gulf Coast fresh and brackish marshes were subjected to hydrogen sulfide under controlled sediment redox conditions. Net carbon assimilation responses of both species to the combined sediment anaerobiosis and hydrogen sulfide concentrations was measured. Panicum hemitomon was more sensitive to hydrogen sulfide as compared to Spartina patens. Initiation of reduction in net carbon assimilation in P. hemitomon began when H2S concentrations of soil solution exceeded 0.22 mg l-1. Reductions in net carbon assimilation in S. patens were also noted at H2S concentrations exceeding 0.34 mg l-1. The reduction in net carbon assimilation of both species measured at elevated H2S concentrations suggests that extreme anaerobiosis and elevated sulfide could contribute to the growth reduction of these species under certain conditions. However based on H2S concentration in fresh and brackish marsh soil profiles, levels were too low to cause any adverse effects of Panicum hemitomon. In brackish marsh soils containing hydrogen sulfide of 3.4 mg l-1 in soil solution, sulfide could be a major factor limiting growth of S. patens.