Parched plants: survival and viability of invasive aquatic macrophytes following exposure to various desiccation regimes

Invasive alien species represent a serious worldwide threat to natural and semi-natural ecosystems. Although successful overland transport of invasive aquatic macrophytes can be facilitated by more mobile organisms or anthropogenic activity, tolerance to desiccation is likely a limiting factor. Particularly in the case of vegetative fragmentary propagules. Here we examined survival and subsequent viability (i.e. regeneration by production of new shoot or root growth) for whole plantlets of two floating (Azolla filiculoides, Lemna minuta) and stem fragments of three submerged (Elodea canadensis. E. nuttallii, Lagarosiphon major) invasive macrophytes following exposure to different desiccation regimes. Species were exposed to selected temperature (20, 27, 36 degrees C) and relative humidity (18, 38, 60, 85% RH) combinations for up to six hours. In general, floating plants displayed greater survival and viability than submerged species. Overall, survival and viability decreased significantly for all species with increased desiccation exposure times. In essence, increased vapour-pressure deficit significantly reduced survival of aquatic plants. Although reduced humidity rates particularly decreased survival and viability, increased temperatures were observed to bolster the impact of certain humidity treatments. In particular, when exposed to low RH (<= 38%RH), little or no viability was observed after 2 h. Contrastingly, propagules kept under RH above 60% RH at 20 degrees C retained viability for considerably longer intervals above 4-6 h. Overall, desiccation as a biosecurity tool alone is likely inadequate to prevent the spread of fragmentary propagule stages, as even small desiccated fragments that appear to be dry may still be viable.