Responses of Spartina alterniflora and Spartina patens to rhizosphere oxygen deficiency

摘要

Spartina alterniflora and S. patens plants were subjected to soil redox (Eh) levels of+ 400, +50, - 60 and - 240 mV under controlled environmental conditions in a series of laboratory microcosms. Photosynthetic and growth responses of the two species to the intensity of soil reduction were measured. An initial significant (p<0.05) decrease in net photosynthesis was noted in both species in response to low Eh treatments followed by substantial recovery in S. alterniflora but limited partial recovery in S. patens. The average photosynthetic rates over the experimental period showed no significant reductions for S. alterniflora across Eh treatments except for plants grown under the most reducing treatment (- 240 mV). S. patens was more responsive to soil reduction, significant reductions in net photosynthesis were found under -60 and -240 mV treatments. Photosynthetic data indicated differences between responses of the two species at the lower range of soil redox conditions. The adverse effect on net photosynthesis was more dramatic for S. patens under moderate and highly reduced conditions than for S. alterniflora. Both species showed significant reductions in height growth under -60 and -240 mV treatments. Foliage and root dry weight increments were reduced significantly at -240 mV treatment in both species. However, S. alterniflora maintained significantly greater foliage and root dry weight increments than S. patens under all treatments. The present study suggests that hydrology and the resultant intensity of soil reduction (low soil Eh conditions) has profound effects on physiological functions and growth of S. alterniflora and S. patens, major species that occur in US coastal wetlands. Based on the observed short-term physiological responses, S. alterniflora may have a competitive advantage over S. patens under continuous moderate to highly reducing conditions in the brackish-saltmarsh transition zone.