Abstract
In temporary ponds, seed germination largely determines how well aquatic plant assemblages recover after dry periods. Some aquatic plants have terrestrial morphotypes that can produce seeds even in dry years. Here, we performed an experiment to compare germination patterns for seeds produced by aquatic and terrestrial morphotypes of Ranunculus peltatus subsp. saniculifolius over the course of five inundation events. During the first inundation event, percent germination was higher for terrestrial morphotype seeds (36.1%) than for aquatic morphotype seeds (6.1%). Seed germination peaked for both groups during the second inundation event (terrestrial morphotype: 47%; aquatic morphotype: 34%). Even after all five events, some viable seeds had not yet germinated (terrestrial morphotype: 0.6%; aquatic morphotype: 5%). We also compared germination patterns for the two morphotypes in Callitriche brutia: the percent germination was higher for terrestrial morphotype seeds (79.5%) than for aquatic morphotype seeds (41.9%). Both aquatic plant species use two complementary strategies to ensure population persistence despite the unpredictable conditions of temporary ponds. First, plants can produce seeds with different dormancy periods that germinate during different inundation periods. Second, plants can produce terrestrial morphotypes, which generate more seeds during dry periods, allowing for re-establishment when conditions are once again favorable.
Highlights
Aquatic plants form a species-rich group whose members display marked differences in morphology, physiology, reproduction, and life history
In Mediterranean temporary ponds, unpredictable rainfall can be catastrophic for submerged plants if flooding triggers seed germination, but the hydroperiod does not last long enough for plants to produce a new generation of seeds
We explored five different scenarios: (a) a series of four wet years during which the ponds were flooded and only the aquatic morphotype was produced; (b) an initial dry year during which there were only terrestrial morphotype plants producing seeds, followed by three wet years during which aquatic morphotype plants produced seeds; (c) two dry years followed by two wet years; (d) three dry years followed by one wet year; and (e) four dry years
Summary
Aquatic plants form a species-rich group whose members display marked differences in morphology, physiology, reproduction, and life history. In Mediterranean ecosystems, the timing and quantity of precipitation can be highly unpredictable It is common for years of heavy rains, during which ponds display very long hydroperiods (>8 months), to alternate with very dry years, during which ponds are ephemeral or may not even flood [4,5]. In Mediterranean temporary ponds, unpredictable rainfall can be catastrophic for submerged plants if flooding triggers seed germination, but the hydroperiod does not last long enough for plants to produce a new generation of seeds. After such “bad years”, seed banks can help re-establish aquatic plant populations in future “good years” [14,15], reducing the risk of plant extinction [16]
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