Age-related patterns of metabolism and biomass in subterranean tissues of Zostera marina (eelgrass)

Abstract

In a subtidal meadow in Monterey Bay, California, total subterranean biomass of eelgrass was correlated with above-ground biomass. While root biomass was constant, indices of metabolic capacity decreased with increasing tissue age. Rhizome internodal biomass and carbohydrate levels with influenced by season and tissue age, and rates of respiration declined with increasing tissue age. The first four (youngest) root bundles along the rhizome accounted for >90% of total plant NH4+ assimilatory potential, while O2 consumption increased linearly with increasing amount of subterranean tissue. A model of whole plant carbon balance predicted compensation depths (photosynthesis = respiration) for Monterey Bay eelgrass of 4.2-11.6 m depth, given instantaneous shoot Pnet:R ratios of 11 to 4.5. Small changes in both Pnet:R and depth (light availability) have the potential to effect large changes in the rate of new tissue production. Although the subterranean tissues constitute 20-26% of plant biomass, carbon consumed by respiration in the subterranean tissue represented <15% of gross photosynthetic production (Pg) at depths <10 m. At the deep edges of the eel-grass bed, the model predicts that total subterranean respiration increases to 25% of Pg. Since respiration by subterranean tissues represents only 10-15% of total plant respiration, eelgrass carbon balance is strongly controlled by shoot carbon metabolism. -from Authors