The response of Mediterranean species to waterlogging : using salvia officinalis as a case study
King, Claire Margaret
PublisherUniversity of Reading
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Many popular UK garden plants have their origins in the Mediterranean Basin. Adapted for hot summers with prolonged periods of drought they exhibit features that conserve water. Climate change is predicted to bring warmer drier summers to the UK over the next century but also wetter winters: winter rainfall is predicted to increase by up to 30 % by the 2080s. It is uncertain how these species will tolerate the increased flooding associated with greater winter rainfall, or possible summer flooding resulting from high rainfall intensity storms. This research sought to assess the impact of waterlogging on Mediterranean species through a series of glasshouse and field experiments investigating plant growth and physiological changes, in response to increasing soil water content and decreasing oxygen status. In initial potplant experiments using four species, all plants survived winter flooding, whereas a 17-day summer flood (22 -39°C) resulted in the death of about one third Salvia officinalis and Cistus hybridus. Root growth and stomatal conductance were found to be key factors in survival. Previous workers have shown that some species survive waterlogging through the formation of aerenchyma and the development of shoot borne roots: responses found to be initiated by hypoxia. In hydroponic experiments considered here, Salvia officinalis also showed an ability to acclimate to anoxia by a preceding period of hypoxia, achieved largely through the rapid production of lateral roots close to the stem base: 60 % of the lateral roots were located within 40mm compared to 10% in the control. These results were supported by experiments in soil columns where the rate of root production doubled in the unsaturated zone above a rising water table. Such adaptation responses show an ability to withstand short flooding events in the predicted warmer and wetter winters of the future.