Chlorophyll fluorometry sheds light on the role of desiccation resistance for vegetative overland dispersal of aquatic plants

Submerged aquatic plant species predominantly spread through vegetative propagules, particularly shoot fragments. While it is known that the successful establishment of fragments in isolated water bodies is largely determined by retention of fragment viability during overland transport (i.e. desiccation resistance), detailed information on species‐specific desiccation resistance is still scarce and the underlying mechanisms remain uncharted. We combined measurements of chlorophyll a fluorescence (Fv/Fm: maximum quantum yield of photosystem II) with determination of water loss and post‐desiccation survival and regeneration to examine the desiccation resistance of shoot fragments without and with apical tips for six submerged aquatic plant species (Myriophyllum spicatum, Myriophyllum heterophyllum, Ceratophyllum demersum, Lagarosiphon major, Elodea canadensis, Hydrilla verticillata). Overall, the relationship between Fv/Fm and relative water loss was nonlinear, and a decrease in Fv/Fm was significantly related to reduced fragment survival and regeneration. We determined an overall critical minimum of 0.40 in Fv/Fm and a critical maximum of 84% in water loss for regeneration. Differences in the relationships between water loss and desiccation time and between Fv/Fm and water loss were species‐specific rather than fragment type‐specific. Plant fragments of M. spicatum (fragments without apices excluded), M. heterophyllum, and C. demersum maintained a high Fv/Fm even after losing a large proportion of the initial water content, while the Fv/Fm for L. major, E. canadensis, and H. verticillata decreased more rapidly with advancing water loss. Maintaining the function of the photosynthetic apparatus at high water loss can prolong fragment viability during overland transport. Our results suggest that aquatic plants have species‐specific mechanisms to cope with water deficit. Measurements of chlorophyll fluorescence can precisely predict the likelihood of fragment regeneration and constitute a useful tool to assess the spread potential of aquatic plants.