Trade‐off relationship between productivity and thallus toughness in Laminariales (Phaeophyceae)

Abstract

Trade-off relationships are considered key to understanding the mechanisms supporting the coexistence of multiple species within kelp beds. Thus, information on trade-offs is expected to contribute to conservation of kelp bed diversity. To test the existence of a trade-off between productivity and thallus toughness, thallus traits and relationships between the traits were examined for seven species of Laminariales including 24 populations. For each population, photosynthetic capacity per unit biomass (as A mass ) and nitrogen (i.e., photosynthetic nitrogen-use efficiency, PNUE), nitrogen content (as N mass ), thallus mass per unit thallus area (as TMA) and force required to penetrate the thallus (as F p , a common index of leaf toughness in land plants by punch test) were determined. A mass increased with increasing N mass . Blades with high N mass showed high A mass . These blades may invest a large proportion of nitrogen to the photosynthetic parts, and consequently exhibit high metabolic rates. Moreover, blades with high N mass tended to be associated with low TMA, and N mass decreased with increasing TMA. A significant negative correlation was observed between TMA and A mass because of the linkage of high A mass with high N mass and high N mass associated with low TMA, while a significant positive correlation was observed between TMA and F p . The two correlations indicate the existence of a trade-off between productivity and thallus toughness in Laminariales. PNUE showed a significant negative correlation with TMA, which also showed a significant positive correlation with F p as the index of thallus toughness, and therefore a trade-off relationship between productivity and thallus toughness.

Productivity and thallus toughness trade‐off relationship in marine macroalgae from the Japan Sea

“…Non‐metric multi‐dimensional scaling ordination analysis based on four thallus traits of 28 populations in the 20 species of warm and cold temperate marine macroalgae. Filled circle, the 13 species of macroalgae from the Japan Sea; open circle, 15 populations in 7 cold temperate kelps (Sakanishi et al ) from the eastern Pacific coast of Hokkaido. AP, Alaria praelonga ; CC, Costaria costata ; LY, Laminaria yezoensis ; SC, Saccharina coriacea ; SG, S. gyrata ; SL, S. longissima ; SS, S. sachalinensis .…”

“…In the 13 macroalgal species there was a significant correlation between A mass or PNUE and F p , which was the toughness of the thallus assessed by a punch test (Aranwela et al ; Onoda et al ; Sakanishi et al ). This relationship indicates the occurrence of a trade‐off between productivity and toughness in warm temperate macroalgae, as described in tropical and cold temperate marine macroalgae (Littler et al ; Sakanishi et al ) as well as for land plants (Reich et al ; Wright et al ).…”

“…From pair‐wise relationships between chemical, structural and physiological thallus traits, trade‐offs between productivity and thallus toughness were found for several species of phylogenetically closely related kelps with similar morphologies recently (Sakanishi et al ), as reported in land plants. Also in the kelps, a strong interdependency between the thallus traits was found.…”

“…For the thallus trait measurements, thallus segments cut out from a thallus were used as samples. In species with membranous and blade shaped thalli ( P. undulatum , U. arasakii , U. linza , U. pinnatifida , E. stolonifera and S. dubyi ), tissue discs of 1.5 cm 2 were cut out from the healthy peripheral portion in the middle part of a thallus or a blade using a cork borer (Sakanishi et al ). In C. nipponicus and G. cornea with narrow branched thalli, branched thallus segments were cut out from the healthy part of a thallus.…”

“…Also in the kelps, a strong interdependency between the thallus traits was found. The ordination by nMDS of the thallus traits and the result (high variance of 90% described in PCA axis 1) of PCA indicate that the thallus traits of kelps interdependently vary across a single axis based on the trade‐off between productivity and thallus toughness (Sakanishi et al ).…”