Growth, regeneration and colonisation of Egeria densa fragments: the effect of autumn temperature increases

The present study analysed the influence of higher temperatures on the growth, regeneration and colonisation abilities of apical shoot fragments from three naturalised and one cultivated population of Egeria densa. Our hypotheses were that (1) increased temperatures would favour the growth, regeneration and colonisation of E. densa shoots and (2) fragments from naturalised populations would have higher establishment success than fragments from cultivated plants. We tested the effect of average minimal autumn temperature (9 °C), average maximal autumn temperature (16 °C) and an increase of 3 °C above these values, on apical shoots of these four populations of E. densa under controlled conditions in two growth chambers. Our results showed that temperature and the origin of the population had an effect on the growth rate of E. densa fragments, on their regeneration and colonisation abilities at the maximal autumn temperature. An increase of 3 °C stimulated the growth rate of E. densa at low temperatures but had no effect on the plant colonisation and regeneration abilities. The responses of populations to low temperatures (9–12 °C) were more similar than expected. In contrast, at higher temperatures (16–19 °C) the cultivated population showed lower apical growth, higher regeneration and similar colonisation abilities to the naturalised populations. At these higher temperatures, the responses also differed among the naturalised populations. These results suggest that global warming has implications for the invasiveness of E. densa.