Terrestrial Morphotypes of Aquatic Plants Display Improved Seed Germination to Deal with Dry or Low-Rainfall Periods

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.

Keywords: Callitriche brutia; Mediterranean wetlands; Ranunculus peltatus subsp. saniculifolius; germination; reproductive strategies; seeds; temporary ponds.

Figure 1

Location of the study area.

Figure 2

The studied species: Ranunculus peltatus subsp. saniculifolius (left) and Callitriche brutia (right).

Figure 3

Event-specific and cumulative percent germination for Ranunculus peltatus subsp. saniculifolius seeds produced by aquatic and terrestrial morphotypes.

Figure 4

Percentage of germinated and ungerminated Callitriche brutia seeds at the end of the inundation experiment (aquatic morphotype seeds = 587, terrestrial morphotype seeds = 214). The ungerminated seeds were visually assessed and classified as undamaged or damaged.

Figure 5

Results of the Ranunculus peltatus subsp. saniculifolius seed production simulations. The starting number of seeds was 100. Seed production patterns were then modeled across four years with different sets of climatic conditions (dwww: one dry year followed by three wet years; ddww: two dry years followed by two wet years; dddw: three dry years followed by a wet year; dddd: four dry years). Annual seed production was estimated using the percent germination values from the experiment. Percent germination values for aquatic morphotype plants were applied in wet years (G1 = 0.0606, G2 = 0.3397, G3 = 0.1892, and G4 = 0.04), and percent germination values for terrestrial morphotype plants were applied in dry years (G1 = 0.3605, G2 = 0.4711, G3 = 0.3332, and G4 = 0.0850). It was assumed that the survival of the aquatic morphotype plants was 100%. The simulations also examined the effect of reducing the area available for terrestrial morphotype growth by setting the relative size of the terrestrial morphotype population (i.e., the number of terrestrial morphotype plants relative to the number of aquatic morphotype plants that grow in a wet year) to 100%, 50%, or 10%. For the sake of comparison, maximum seed production by aquatic morphotype plants across four wet years (blue line) has been included in each figure.