Drought resistance strategies of four native ornamental perennials : Echinacea purpurea L., Rudbeckia fulgida L. var. Sullivantii, Monarda didyma L., and Helianthus angustifolius L.

Plant responses to water stress operate In conjunction with coinciding plant characteristics. These response-characteristic combinations have been termed "strategies." We characterized and compared the drought resistance strategies (avoidance vs. tolerance) of four native ornamental perennials, purple coneflower (Echinacea purpurea), orange coneflower (Rudbeckia fulgida var. Sullivantii), bee-balm (Monarda didyma), and swamp sunflower (Helianthus angustifolius), after assessing stomatal behavior, dehydration tolerance and leaf osmotic adjustment (δΨ_π100) following water withholding from plants growing in a greenhouse. In the stomatal behavior experiment, leaf water potential (Ψ_L), leaf turgor potential (Ψ_p) and leaf relative water content (RWC) were measured daily as stomatal conductance (Cs) approached 0 mm*s-i. In the dehydration tolerance and leaf osmotic adjustment experiment, lethal Ψ_L, lethal soil water potential (Ψ_S) lethal leaf RWC, and leaf δΨ_π100 were determined when only 5-6 living leaves remained on a plant. E. purpurea had the lowest Ψ_L(Ψ_L^→0) near stomatal closure and lethal Ψ_L (high dehydration tolerance), and a low leaf RWC (RWC^→0) near stomatal closure and lethal leaf RWC. R. fulgida var. Sullivantii had a similar low Ψ_L^→0 and low lethal Ψ_L, but displayed a relatively large (δΨ_π100. M. didyma had the highest Ψ_L^→0 and RWC^→0, an intermediate lethal Ψ_L, yet displayed a relatively large δΨ_π100 H. angustifolius became desiccated more rapidly than the other three species despite having a high Ψ_L^→0 it had the highest lethal 'Vl and displayed very little δΨ_π100 (low dehydration tolerance). Despite the observed differences in stomatal behavior, dehydration tolerance and leaf δΨ_π100 among the four species, all four perennials fall predominantly into the drought avoidance category. The understanding of drought resistance strategies in ornamentals can potentially help growers and landscapers to minimize plant water stress following wholesale production.