Experimental study reveals that cumulative winter chilling drives seedling development and survival in Mediterranean orchids, highlighting species-specific thermal thresholds.
Key Points
To determine how cold exposure and specific thermal thresholds regulate seedling survival, growth, and tuber development across dormancy in Mediterranean terrestrial orchids.
Exposed in vitro protocorms of four Mediterranean orchid species (Anacamptis coriophora, A. laxiflora, Himantoglossum hircinum, and H. robertianum) to eight thermal treatments for eight weeks in controlled laboratory conditions and along an outdoor altitudinal gradient.
Quantified survival, shoot growth, and tuber formation before and after summer dormancy, analyzing temperature relationships using a model selection approach.
Cumulative chilling exposure predicted seedling performance better than mean temperature alone, with moderate cold (10–12 °C) governing pre-dormancy survival and chilling below 6–7 °C doubling post-dormancy shoot length in responsive taxa.
Post-dormancy thermal responses diverged markedly among species: increased chilling reduced survival by ~50% in A. coriophora but increased survival twofold in A. laxiflora, whereas H. robertianum developed leaves only after chilling exposure.