Understanding salinity tolerance of select wildflower species in a hydroponic setting
Water quality and quantity are critical issues in the Southwest US and many other locations in the world. Use of reclaimed water for landscape irrigation can signiﬁcantly conserve potable water and possibly reduce fertilizer application. A potential concern of using alternative water sources is elevated salt levels, which can have adverse effects on plant growth and aesthetic appearance. The majority of Texas native wildflowers are known to be hardy, easy to maintain, and drought tolerant after establishment. In addition, native wildflowers provide wildlife habitat and support native pollinators. However, little information is available on salinity tolerance of many Texas native wildflower species. In this study, two separate hydroponics experiments were conducted to determine salt tolerance of three Texas native wildflower species: sleepy daisy (Xanthisma texanum), standing cypress (Ipomopsis rubra), and gaura (Gaura villosa). Species were suspended in a hydroponics setting using a randomized complete block design with a control (municipal reverse osmosis (RO) water with a nutrition solution at an electrical conductivity (EC) of 3.0 dSm-1), and three salinity treatments: 5.0 dSm-1, 7.0 dSm-1, and 11.0 dSm-1 EC. Sixty days after salinity treatments were initiated, percent survival, visual rating, fresh weight, and length measurements were recorded on root and shoot tissue. To determine tissue percentage Ca2+, Na+, and Cl-, shoot and root tissues were dried and ground for tissue analysis. At the conclusion of each experiment total percent survival for X. texanum, G. villosa, and I. rubra were 100, 94, and 76, respectively, with greatest mortality rate at the highest salinity treatment. For all three species shoot dry weights and plant growth indexes (PGI) decreased as EC of irrigation water increased. Visual qualities of all plant species were mainly compromised at the highest salinity level. Ion concentrations of root and shoot tissue were affected by salinity levels, and varied among species. Several mechanisms of salt tolerance have been observed among wildflower species, including restriction of ion uptake, ion exclusion, salt excretion, and tissue tolerance to high concentrations of Na+ or Cl-. Results indicate standing cypress could be identified as moderately salt tolerant plant species (EC up to 7.0 dSm-1), whereas, sleepy daisy and gaura can be classified as salt tolerant plants (EC up to 11.0 dSm-1). Although additional research is needed, these native Texas wildflowers have great potential in landscapes utilizing limited quality irrigation water, or in areas with soil salinity concerns.