Gp. Kraemer et Rs. Alberte, AGE-RELATED PATTERNS OF METABOLISM AND BIOMASS IN SUBTERRANEAN TISSUES OF ZOSTERA-MARINA (EELGRASS), Marine ecology. Progress series, 95(1-2), 1993, pp. 193-203
Production and metabolic features of the rhizomatous marine angiosperm
Zostera marina L. (eelgrass) from a subtidal meadow in Monterey Bay,
Monterey, California, USA, were examined to assess the impact of the s
ubterranean system on whole plant metabolism. Total subterranean bioma
ss of eelgrass was correlated with above-ground (shoot) biomass. The s
ubterranean system presents a gradient in tissue age, from young (prox
imal to shoot) to old (distal). While root biomass was constant, indic
es of metabolic capacity (respiration, soluble carbohydrate content, g
lutamine synthetase activity) decreased with increasing tissue age. Rh
izome internodal biomass and carbohydrate levels were influenced by se
ason and tissue age, and rates of respiration declined with increasing
tissue age. The first 4 (youngest) root bundles along the rhizome acc
ounted 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 d
epths (photosynthesis = respiration) for Monterey Bay eelgrass of 4.2
to 11.6 m depth, given instantaneous shoot P(net):R ratios of 11 to 4.
5. The model also predicted that small changes in both P(net):R and de
pth (light availability) have the potential to effect large changes in
the rate of new tissue production. Although the subterranean tissues
constitute 20 to 26 % of plant biomass, carbon consumed by respiration
in the subterranean tissue represented <15 % of gross photosynthetic
production (P(g)) at depths < 10 m. At the deep edges of the eelgrass
bed, the model predicts that total subterranean respiration increases
to 25 % of P(g). Since respiration by subterranean tissues represents
only 10 to 15 % of total plant respiration, eelgrass carbon balance is
strongly controlled by shoot carbon metabolism.