Determination of Alkalinity Toxicity Limits in Greenhouse Plants

1. Determination of Alkalinity Toxicity Limits of Selected Greenhouse Ornamental Plants Luis A. Valdez-A. and David Wm. Reed Dept. of Horticultural Sciences Texas A&M University

2. Alkalinity Concentration of soluble alkali Alkali have capacity to neutralize acids Major contributors: HCO3- CO32- Minor contributors: OH-, NH3 Phosphates, Silicates, Borates

3. Buffer Capacity Capacity to resist sudden changes in pH CO2 HCO3- H2CO3 H+ OH- H+ H2O OH- H+ H+

4. Effect of pH on Activity of Nutrients Lindsay, 1981

5. Alkalinity-induced Fe Deficiency Whipker et al., 2001

6. Objectives • Provide information about the limits of tolerance to alkalinity • Determine the effects of HCO3- in irrigation water on the growth of selected greenhouse ornamental plants • Determine the mechanisms of tolerance to alkalinity

7. Experiment 1: Tolerance to Alkalinity on Selected Greenhouse Crops

8. Materials and Methods • Species: Chrysanthemum ‘Miramar’ Rosa ‘Pink Cupido’ C. roseus ‘Apricot Delight’ H. rosa-sinensis ‘Mango Breeze’ H. rosa-sinensis ‘Bimini Breeze’

10. Rose Chrysanthemum 0 mM 2.5 mM 5 mM 2.5 mM 0 mM 5 mM 7.5 mM 10 mM 10 mM 7.5 mM 5 mM 0 mM 2.5 mM Vinca 10 mM 7.5 mM

11. 5 mM 5 mM 2.5 mM 2.5 mM 0 mM 0 mM 10 mM 7.5 mM 10 mM 7.5 mM Hibiscus ‘Mango Breeze’ Hibiscus ‘Bimini Breeze’

12. Rose NS * * * 0 % Change NS * * Shoot dry mass * SPAD index NaHCO3(mM)

13. 50 16 14 12 40 10 8 30 6 4 2 20 0 0 2 4 6 8 10 10 0 0 2 4 6 8 10 Rose SPAD index Shoot dry mass (g) Y=45.3-6.01X+0.40X2 R2=0.86 Y=12.4-0.61XR2=0.94 NaHCO3 (mM)

14. Chrysanthemum NS NS NS NS % Change NS * * Shoot dry mass SPAD index * NaHCO3 (mM)

15. 70 20 60 16 50 12 8 40 4 30 0 0 2 4 6 8 10 20 10 0 0 2 4 6 8 10 Chrysanthemum SPAD index Shoot dry mass (g) Y=62.8-0.76X-0.38X2 R2=0.99 Y=17.6+ 0.20XR2=0.87 NaHCO3 (mM)

16. Vinca NS NS NS NS % Change 0 NS NS * * Shoot dry mass SPAD index NaHCO3 (mM)

17. 12 50 10 40 8 6 30 4 2 20 0 0 2 4 6 8 10 10 0 0 2 4 6 8 10 Vinca SPAD index Shoot dry mass (g) Y=45.3-6.01X+0.40X2 R2=0.86 Y=8.79-0.14XR2=0.32 NaHCO3 (mM)

18. Hibiscus ‘Mango Breeze’ * NS % Change * * NS * * Shoot dry mass * SPAD index NaHCO3 (mM)

19. Hibiscus ‘Bimini Breeze’ % Change NS NS NS NS NS NS * * Shoot dry mass SPAD index NaHCO3 (mM)

20. 60 50 40 30 20 Bimini Breeze Mango Breeze 10 0 0 2 4 6 8 10 Hibiscus 12 Y=55.0-1.30XR2=0.96 Y=8.92-0.05XR2=0.20 10 8 SPAD index Shoot dry mass (g) Y=52.2-2.50XR2=0.95 Y=8.16-0.40XR2=0.93 6 4 Bimini Breeze 2 Mango Breeze 0 0 2 4 6 8 10 NaHCO3 (mM)

21. % Shoot Mass Decrease as a Function of NaHCO3 Concentration *NS growth reduction up to 10 mM NaHCO3tested

22. % SPAD Index Decrease as a Function of NaHCO3 Concentration

23. Experiment 2: Mechanisms of Tolerance to Alkalinity of Hibiscus

24. Materials and Methods Cultivars ‘Bimini Breeze’ ‘Carolina Breeze’ Growing Medium pH Fe-Reductase Assay Rosenfield et al., 1991

25. Growing Medium pHBottom Container Layer pH NaHCO3 (mM)

26. 12 Bimini Breeze 10 Carolina Breeze 8 6 4 2 0 0 2 4 6 8 10 Iron Reductase Activity c a b b ab (µM Fe3+.g-1.h-1.x10-3) a a b b b NaHCO3 (mM)

27. Conclusions • Vinca>‘Bimini Breeze’>Mums>‘Mango Breeze’>Rose 6.0 mM 4.2 mM 3.2 mM 2.1 mM 0.8mM • ‘Bimini Breeze’ exhibits • a higher acidification of the growing medium • a higher Fe-reductase activity