RESPONSE TO PHOTOPERIOD AND TEMPERATURE BY SPARTINA ALTERNIFLORA (POACEAE) FROM NORTH CAROLINA AND SPARTINA FOLIOSA FROM CALIFORNIA

Abstract

Seedlings of Spartina alterniflora Loisel. from Oregon Inlet, North Carolina were generally taller and produced significantly more culms and total dry weight than those of S. foliosa Trin. from two California populations (Alameda Beach and Marin County) in eight photoperiod‐temperature treatments over a 17‐wk period. Seedlings of S. alterniflora produced maximal biomass in 30–26 C whereas those of S. foliosa produced maximal biomass in 22–18 C, both under long‐day conditions. The average photosynthesis rate for S. alterniflora (3.0 mg C g dry wt−‐ hr−‐1) was 1.6 times higher than that for S. foliosa (1.9 mg C g dry wt−‐1 hr−‐1), but the dark respiration rates (0.3 and 0.4 mg C g dry wt−‐1 hr−‐1, respectively) were not significantly different. The proportion of rhizomes was greater under short than long‐day conditions for both species in most temperature regimes. The average shoot soluble carbohydrate and starch concentrations were higher for S. foliosa (8.4 and 0.9%, respectively) than those for S. alterniflora (6.0 and 0.4%, respectively). The average rhizome soluble carbohydrate concentration (18%) for S. alterniflora under long‐day conditions was significantly lower than that under short‐day conditions (28%) and also lower than those for S. foliosa under both long (26%) and short‐day (25%) conditions. Rhizome starch concentrations of S. alterniflora were significantly higher in the short than in most long‐day temperatures and were generally higher for S. alterniflora than for S. foliosa under short‐day conditions. The root starch concentration of S. alterniflora under short‐day conditions (1.3%) was higher than that under long‐day conditions (0.2%) and also higher than those of S. foliosa under both long (0.2%) and short‐day (0.7%) conditions. The two species exhibited similar patterns of carbohydrate storage in belowground organs, similar flower initiation processes not under strict photoperiod control, and similar respiration rates, but significantly different photosynthetic rates and growth responses with S. alterniflora having the potential to be the more productive species.