Drought response of three ornamental herbaceous perennials

Boltonia asteroides L. 'Snowbank' (Snowbank boltonia), Eupatorium rugosum L . (eastern white snakeroot), and Rudbeckia triloba L. (three-lobed coneflow er) were subjected to drought for 2, 4, and 6 days during the fall and spri ng. Leaf gas exchange, leaf water potential, growth, and carbohydrate parti tioning were measured during drought and throughout the following growing s eason, Leaf gas exchange of B. asteroides was not affected by drought treat ment in the fall, not until day 6 of spring drought, and there were no long -term effects on growth. Transpiration and stomatal conductance of R. trilo ba decreased when substrate moisture decreased to 21% after drought treatme nt during both seasons. Assimilation of drought-treated R. triloba decrease d when substrate moisture content decreased to 12% during spring but was no t affected by drought in the fall. There was a decrease in the root-to-shoo t ratio of R. triloba that had been treated for 4 days, which was attribute d to an increase in the shoot dry weight (DW) of treated plants. Reductions in spring growth of E. rugosum were observed only after fall drought of 6 days, and there were no differences in final DWs of plants subjected to any of the drought durations. Spring drought had no effect on growth index or DW of any of the perennials. Boltonia asteroides and R. triloba had increas es in low-molecular-weight sugars on day 4 of drought, but E. rugosum did n ot have an increase in sugars of lon molecular weight until day 6 of drough t. Differences in drought response of B. asteroides, E. rugosum, and R. tri loba were attributed to differences in water use rates.