Physiological Responses of Selected Taxa of Salvia, Taxus, Cephalotaxus, and Syringa to Heat and/or Flooding

Abstract

High-temperature stress impacts plant growth in warm-temperate climates. Landscape plants are subjected to extreme conditions in urban environments, due to reflected light and retained heat from brick and concrete.

Two experiments were conducted to ascertain heat tolerance across a range of Salvia L. taxa. In the first study, Salvia chamaedryoides Cav., S. greggii A. Gray 'Furman's Red', S. guaranitica St.-Hil. ex Benth., S. leucantha Cav., S. nemorosa L. 'Ostfriesland', S. pratensis L., S. splendens Sell. ex Roem. & Schult., and S. x sylvestris L. 'Mainacht' were grown under 15-hour days of 20, 25, 30, 35, or 40 °C and 9-hour nights of 15 or 25 °C. American taxa performed poorly — S. chamaedryoides, S. greggii 'Furman's Red', S. guaranitica, S. leucantha, and S. splendens — exhibiting chlorosis and growth distortions at 35 and 40 °C. European taxa, S. nemorosa 'Ostfriesland', S. pratensis, S. x sylvestris 'Mainacht', maintained shoot and root dry weights at 35 and 40 °C and exhibited lesser physical symptoms. The second study demonstrated that S. x sylvestris 'Mainacht' and S. nemorosa 'Pusztaflamme' were better able to maintain net photosynthetic rates (P[subscript n]) at 35 and 40 °C than S. guaranitica and S. leucantha.

In regions with hot, humid climates, plant growth is limited by tolerance of root systems to hot, wet conditions in poorly drained soils. A third study measured flood and heat tolerance of Taxus canadensis Marsh., T. x media Rehd. 'Brownii', T. x media 'Densiformis', T. x media 'Tauntonii', T. wallichiana Zucc. var. chinensis (Pilg.) Florin, and Cephalotaxus harringtonia (Knight ex Forbes) K. Koch 'Prostrata'. Despite anecdotal evidence that Taxus are intolerant of heat and poor soil drainage, cultivars of T. x media, especially 'Densiformis', survived a 30-day flood and grew better than other taxa at 30/26 °C.

In a fourth study, Syringa x hyacinthiflora (Lemoine) Rehd. 'California Rose', S. x persica L., and S. vulgaris L. were subjected to flooding at 16-hour days/8-hour nights of 25/20, 30/25, or 35/30 °C. No plants survived a 10-day flood. Both S. x persica and S. x hyacinthiflora 'California Rose' exhibited greater growth and higher P[subscript n] rates at day temperatures up to 35 °C, compared to S. vulgaris.