Physiological and structural trade-offs as a basis for the coordination of functional traits in marine macroalgae

To assess physiological and structural trade-offs in thalli of marine macroalgae, the feasibility of using a single axis representing and visualizing trade-offs and pairwise correlations among functional traits relating to the trade-offs was examined. Additionally, patterns of pairwise correlations among functional traits related to the trade-offs were compared with those for terrestrial plants. These analyses were performed using data for 12 species of macroalgae: light-saturated photosynthetic and dark respiration rates per dry mass ( A mass , R mass ), thallus nitrogen concentration ( N mass ), thallus dry mass per area (TMA), force to punch per fracture length ( F p ), and C:N ratio (C/N) based on 15 datasets including different seasons. Results of the analyses confirmed that the single axis represents multi-dimensional data on the six functional traits and a continuum in the trait combination based on trade-offs from the conservative to the acquisitive end along the single axis. Additionally, pairwise correlations among key traits relating to trade-offs were confirmed to be qualitatively consistent with those reported in leaves of terrestrial plants. The extremely high A mass and extremely low TMA for marine macroalgae compared with terrestrial plants probably reflect their habitats, and can be regarded as one of the key trait combinations that represent their differences from terrestrial plants.