Does fire drive fatty acid composition in seed coats of physically dormant species?

Abstract

Seed dormancy is the key driver of seed germination regulation, hence is fundamental to the seedling recruitment life-history stage and population persistence. However, despite the importance of physical dormancy in timing post-fire germination, the mechanism driving dormancy-break within seed coats remains surprisingly unclear. We suggest that seed coat chemistry may play an important role in controlling dormancy in species with physical dormancy. In particular, seed coat fatty acids are hydrophobic, and have melting points within the range of seed dormancy-breaking temperatures. Furthermore, melting points of saturated fatty acids increase with increasing carbon chain length. We investigated whether fire could influence seed coat fatty acid profiles and discussed their potential influence on dormancy mechanisms. Seed coat fatty acids of 25 species within the Faboideae, from fire-prone and fire-free ecosystems, were identified and quantified through gas chromatography-mass spectrometry. Fatty acids profiles were interpreted in the context of species habitat and inter-specific variation. Fatty acid compositions were found to be distinct between species from fire-prone and fire-free habitats. Fire-prone species tended to have longer saturated fatty acid chains, a lower ratio of saturated to unsaturated fatty acids, and a slightly higher relative amount of fatty acids compared to fire-free species. The specific fatty acid composition of fire-prone species seed coats indicated a potential role of fatty acids in dormancy mechanisms. Overall, the distinct fatty acid composition between fire-prone and fire-free species suggests that the chemistry of the seed coat may be under selection pressure in fire-prone ecosystems.