LAUSR

Abstract: To test the influence of light and temperature on intraspecific gyrogonite variation, two common European charophyte species, Chara vulgaris and Chara globularis, were studied indoors under controlled environmental conditions. A total of 60 plants of each species were incubated under different combinations of four irradiances (L1 = 30 μmol PAR m−2 s−1; L2 = 150 μmol PAR m−2 s−1; L3 = 500 μmol PAR m−2 s−1 and L4 = 1000 μmol PAR m−2 s−1) and three water temperatures (T1 = 15°C; T2 = 25°C and T3 = 35°C). These parameters simulate temporary ponds from the Mediterranean region in the summer and help in understanding charophyte reproduction in shallow temporary ponds of past geological periods. After 102 days, gyrogonite productivity was evaluated, and a morphometric analysis of the gyrogonites produced was performed. Our results indicated that both irradiance and water temperature play a key role in C. vulgaris intraspecific gyrogonite variation. Gyrogonites tended to increase their size as irradiance and temperature increased. However, in extreme conditions (L4 and T3), an opposite trend was observed, with gyrogonites becoming significantly smaller. Our results agree with the distribution patterns of fossil gyrogonite assemblages. Using the present data, we hypothesise that charophytes in historic temporary floodplain water bodies produced smaller gyrogonites in response to the stressful environments induced by high irradiances and temperatures.