Germination capability of four charophyte populations (Characeae) from Mediterranean brackish ponds under warm experimental conditions

ABSTRACT The diaspore banks from two brackish ponds within the Albufera de València Natural Park (Spain) containing oospores of Chara hispida, C. aspera, C. canescens and Nitella hyalina were analysed and their germination capability studied under controlled temperature conditions. The top layer of sediment from each meadow was collected and sequentially sieved to isolate the charophyte oospores, subsequently identified and counted under the microscope. The density of apparently viable fructifications varied largely within the studied ponds and within specific meadows. In general, but not always, the most abundant oospores belonged to the species forming the meadow. An additional set of surficial sediment samples were collected to perform germination trials in an indoor culture room under three temperature treatments (21, 25 and 29°C). For each species, 219–272 fructifications were allocated inside small perforated packages that were placed in Petri dishes (n = 3) and submerged for 40 days in plastic containers. Germination rates were low for the four species in all temperatures (0–7%), with no large differences detected amongst treatments. C. aspera was the first species to germinate and the one with the most germlings. Higher temperatures negatively affected its germination; the same trend was shown by C. canescens. Dense oospore banks and low germination rates have been previously described for charophytes from temporary habitats. However, it seems that the recovery of charophyte meadows after droughts will be hindered by a warmer climate. Further studies concerning the optimal conditions for germination are needed to understand the future capability of charophyte meadows to re-establish in Mediterranean ecosystems.