Trade‐off relationship between productivity and thallus toughness in Laminariales (Phaeophyceae)
2017
Sakanishi, Yoshihiko | Kasai, Hiromi | Tanaka, Jirō
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.
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