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Water logging, Mediterranean plants, lavender, sage, roots, anaerobiosis.
Mediterranean plants originate from habitats typified by hot, very dry summers, moderately wet winters and stony, free-draining soils. With climate change scenarios for the UK predicting warmer summers with higher sunlight hours and periods of drought, Mediterranean species are being promoted as ideal garden plants. There is concern, however, that the predicted wetter winters and increased summer flooding the UK may experience in future, will not be conducive to the successful cultivation of these plants, especially on clay soils prone to waterlogging, that are commonly found in the UK.
A range of experiments are planned to investigate the problem; from the general effects on plant growth at an outdoor site prone to winter flooding, to detailed examination of how plants respond when oxygen levels become low or totally absent in controlled environment chambers. There is a particular emphasis on how roots respond, as changes in growth and structure of the root system under these conditions, is likely to be the key to future growth and survival.
To understand the extent to which Mediterranean species can tolerate waterlogging (flooding), by investigating how these plants respond when oxygen levels are depleted and any subsequent effect on plant growth and survival. To see how season and length of flooding effect plant response.
To find out if our popular Mediterranean species will be suitable candidates in future garden planting, when climate change scenarios predict wetter winters and more frequent unpredictable summer flooding.
Despite evolving in a dry habitat, the four species tested proved remarkably resilient to flooding. All species survived 17 days flooding in winter, with Stachys and Lavandula also surviving equivalent flooding duration during summer. Photosynthesis and biomass production, however, were strongly inhibited by flooding although the most tolerant species, Stachys quickly restored its photosynthetic capacity on termination of flooding. Overall, survival rates were comparable to previous studies on other terrestrial (including wetland) species. Subsequent experiments using Salvia (a species we identified as ‘intermediate’ in tolerance) clearly demonstrated adaptations to waterlogging, e.g. acclimation against anoxia when pre-treated with hypoxia. Despite anecdotal information to the contrary, we found no evidence to suggest that these xerophytic species are particularly intolerant of waterlogging. Other climatic and biotic factors may restrict the viability and distribution of these species within the urban conurbations of north-west Europe, but we believe increased incidence of flooding per se should not preclude their consideration.
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.