Reproductive strategies in Mediterranean annual clovers: germination and hardseededness

Abstract

Clovers from 6 sites in the eastern and western Mediterranean were examined for germination and seed dormancy strategies. At least 2 species were collected from each site, such that 4 strategies were compared in 14 accessions of 11 species. The first trait was initial and final hardseededness after 1 summer-autumn (long-term hardseededness), the second was the pattern of hardseed breakdown during this period (short-term hardseededness), the third was the rate of germination at temperatures ranging from 5ºC to 30ºC, and the fourth was the degree to which germination proceeded at high temperatures. Logistic curves were used to describe short-term hardseededness and germination rates, and to calculate half-lives. The seeds of all species exhibited some form of protection against out-of-season rains. In accessions from the eastern Mediterranean the most common strategy was delayed breakdown of hard seed, where most seeds remained hard until mid-to-late autumn. This was the strategy used by Trifolium lappaceum, T. glanduliferum, T. clusii, and T. purpureum. In the western Mediterranean, the accessions also employed slow germination and high temperature dormancy. Examples were T. obscurum and T. clypeatum (slow germination) and T. cherleri and T. isthmocarpum (high temperature dormancy). It was clear that no single germination-regulating mechanism applied to genotypes collected from any 1 site. However, individual species growing at different sites tended to exhibit the same strategies. The results supported the idea of substitutability in reproductive traits, developed by ecological modellers. The efficacy of the 60º/15ºC alternating temperature oven in predicting loss of hardseededness by the clovers in the field was poor except for T. cherleri. The alternating temperature ovens, which are used to predict hardseed breakdown of subterranean clover, are unsatisfactory for most other clovers.