Most recommendations about salt tolerance state that plants have low, medium, or high salt tolerance. Salt tolerance can be assessed in terms of plant growth rate, which is appropriate for many plant species (Munns, 2002). We expect to observe a decrease in growth and yield when roots are exposed to high salt levels, because the water potential is reduced in the soil, leading to a reduction in water uptake by the roots (Boursiac et al., 2005). Under normal growing conditions, the water potential in root cells is less than in the outer environment, and water moves into the roots (Luu and Maurel 2005; Tournaire-Roux et al., 2003). However, when the salt concentration is greater outside the plant root than some arbitrary value, salt stress occurs.
Most salt stress in nature is a result of the presence of Na salts (Levitt, 1980). Some water sources may have high Na levels resulting from to saltwater intrusion, the use of reclaimed wastewater, or seasonal variation from snowmelt products. Well water in Massachusetts’ greenhouses had Na levels ranging from 1 to 544 mg·L−1 whereas Na levels in wastewater range from 124 to 384 mg·L−1 (Karleskint et al., 2011). Wastewater effects on field, forage, wetland, forest, and ornamental crops have been the subject of many investigations, with varied plant response resulting from differences in the salt tolerance of the plants investigated (Brister and Schultz, 1981; Day et al., 1981; Fitzpatrick, 1985; Fitzpatrick et al., 1986; Yeager et al., 2009).
Because plant response mechanisms involved in salt tolerance are complicated, there is no standard method for evaluating salt tolerance. One method for measuring salt tolerance is to correlate changes in yield associated with soil EC levels. Other methods monitor changes in osmotic potential in the leaves or the uptake and translocation of Na in the plants (Levitt, 1980; Niu and Cabrera, 2010). However, these methods may be challenging to implement in a greenhouse setting because of the lack of resources or the need for specialized equipment.
We questioned whether we could design a quick and easy test to screen plants based on EC and Na levels in solution that would confirm observational data classifying plants as low, medium, or high salt-tolerant. We monitored changes in leaf water potential and plant quality of sea hibiscus, a high salt-tolerant plant, exposed to increasing EC and Na levels. Because measuring water potential is impractical for a grower, for additional testing we compared plant quality and growth of low to medium salt-tolerant plants—specifically, coleus, copperleaf, ficus, jasmine, and plumbago—in solutions exposed to increasing EC and Na levels.
Al-KarakiG.N.2000bGrowth, water use efficiency, and sodium and potassium acquisition by tomato cultivars grown under salt stressJ. Plant Nutr.2318
BoursiacY.ChenS.LuuD.T.SorieulM.van den DriesN.MaurelC.2005Early effects of salinity on water transport in arabidopsis roots: Molecular and cellular features of aquaporin expressionPlant Physiol.139790805
BroschatT.K.MeerowA.W.1996Betrock’s reference guide to Florida landscape plants. Betrock Information Systems Hollywood FL
FitzpatrickG.E.1985Container production of tropical trees using sewage effluent, incinerator ash and sludge compostJ. Environ. Hort.3123125
FitzpatrickG.E.DonselmannH.CarterN.S.1986Interactive effects of sewage effluent irrigation and supplemental fertilization on container-grown treesHortScience219293
LevittJ.1980Responses of plants to environmental stresses. Vol. II: Water radiation salt and other stresses. Academic Press New York NY
PetersonF.H.1996Water testing and interpretation p. 31–49. In: D.W. Reed (ed.). Water media and nutrition for greenhouse crops. Ball Publications Bataivia IL
RolfeC.YiasoumiW.KeskulaE.2000Managing water in plant nurseries. 2nd ed. NSW Agriculture Orange NSW Australia
Tournaire-RouxC.SutkaM.JavotH.GoutE.GerbeauP.LuuD.T.BlignyR.MaurelC.2003Cytosolic pH regulates root water transport during anoxic stress through gating of aquaporinsNature425393397
WeinholdF.ScharpfH.C.1997Tolerance of ornamental plants to salt, sodium, and chloride in potting substrates containing compost made of separately collected organic residuesActa Hort.450221228
YeagerT.LarsenC.von MerveldtJ.IraniT.2009Use of reclaimed water for irrigation in container nurseries. Univ. Florida Inst. Food Agr. Sci. Florida Coop. Ext. Serv. ENH 1119