Responses to a fluctuating environment: effects of water depth on growth and biomass allocation in Eleocharis cellulosa Torr. (Cyperaceae)

Abstract

Fluctuating water levels, which characterize freshwater marshes of the Florida Everglades, U.S.A., constrain growth in emergent macrophytes. We studied acclimation of Eleocharis cellulosa Torr. (Cyperaceae) in mesocosms to water depths of 7 and 54 cm and to switching between these water depths. After 80 weeks at fixed depths, deepwater plants produced (i) taller, thicker, and fewer shoots; (ii) fewer ramets; (iii) less biomass; and (iv) greater shoot biomass relative to root and rhizome biomass. Despite large differences in shoot lengths between water depths, shoot heights above the water surface were similar. Emergent shoot tissues had thick secondary walls in the epidermal cells and several palisade layers beneath; submerged shoots lacked this anatomy. When shallow-water plants were transferred to deep water, shoots elongated rapidly, with younger shoots elongating more than older ones. When deepwater plants were transferred to shallow water, emergent shoots quickly died and were replaced by new shoots. Overall, plants exposed to rapid changes in water level adjusted biomass allocation patterns after 9 weeks towards those of control plants in their new environment, but deepwater plants responded more slowly than shallow-water plants. These shifts may allow E. cellulosa to produce shoots that optimize biomechanical support and aeration.Key words: biomass allocation, Eleocharis cellulosa, Everglades, gas exchange, shoot demography, wetland plants.