Determination of Determination of Alkalinity Toxicity Limits Alkalinity Toxicity Limits of Selected Greenhouse of Selected Greenhouse

Ornamental PlantsOrnamental Plants

Luis A. Valdez-A. and David Wm. ReedLuis A. Valdez-A. and David Wm. ReedDept. of Horticultural SciencesDept. of Horticultural Sciences

Texas A&M UniversityTexas A&M University

AlkalinityAlkalinity• Concentration of soluble alkali• Alkali have capacity to neutralize

acids• Major contributors:

• HCO3-

•CO32-

• Minor contributors: • OH-, NH3

• Phosphates, Silicates, Borates

Buffer CapacityBuffer Capacity

Capacity to resist sudden changes in pH

HCO3-

OH-H+ H+

H+OH- H+

H2CO3

CO2

H2O

Effect of pH on Activity of Effect of pH on Activity of NutrientsNutrients

Lindsay, 1981

Alkalinity-induced Alkalinity-induced Fe DeficiencyFe Deficiency

Whipker et al., 2001

ObjectivesObjectives

• 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

Experiment 1:

Tolerance to Tolerance to Alkalinity on Alkalinity on

Selected Greenhouse Selected Greenhouse CropsCrops

Materials and MethodsMaterials and Methods

• Species: Chrysanthemum ‘Miramar’ Rosa ‘Pink Cupido’

C. roseus ‘Apricot Delight’ H. rosa-sinensis ‘Mango Breeze’

H. rosa-sinensis ‘Bimini Breeze’

Treatment

NaHCO3

mg.L-1

Solution pH

Control - 7.18

2.5 mM 153 8.29

5 mM 305 8.48

7.5 mM 458 8.61

10 mM 610 8.65

Chrysanthemum Rose

Vinca

0 mM 2.5 mM0 mM5 mM

7.5 mM 10 mM

2.5 mM 5 mM

7.5 mM10 mM

7.5 mM 10 mM

0 mM 2.5 mM 5 mM

Hibiscus ‘Mango Breeze’ Hibiscus ‘Bimini Breeze’

0 mM 2.5 mM 5 mM 0 mM 2.5 mM 5 mM

10 mM7.5 mM10 mM7.5 mM

-70

-50

-30

-10

10

0 2.5 5 7.5 10

Shoot dry mass

NaHCO3 (mM)

RoseRose

NS * *

NS

*

*

*

SPAD index

*0

% C

han

ge

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10

RoseRose

SP

AD

ind

ex

0

10

20

30

40

50

0 2 4 6 8 10

Y=45.3-6.01X+0.40X2 R2=0.86

NaHCO3 (mM)S

hoo

t d

ry m

ass

(g)

Y=12.4-0.61X R2=0.94

-80

-60

-40

-20

0

20

0 2.5 5 7.5 10

NaHCO3 (mM)

% C

han

ge

ChrysanthemumChrysanthemum

NS NS NS

NS

*

*

*Shoot dry mass SPAD index

NS

0

4

8

12

16

20

0 2 4 6 8 10

0

10

20

30

40

50

60

70

0 2 4 6 8 10

SP

AD

ind

ex

ChrysanthemumChrysanthemum

Y=62.8-0.76X-0.38X2 R2=0.99

NaHCO3 (mM)S

hoo

t d

ry m

ass

(g)

Y=17.6+ 0.20X R2=0.87

-70

-50

-30

-10

10

0 2.5 5 7.5 10NaHCO3 (mM)

VincaVinca

NS NS NS NS

NS NS

*

*Shoot dry mass SPAD index

% C

han

ge

0

0

2

4

6

8

10

12

0 2 4 6 8 10

NaHCO3 (mM)

SP

AD

ind

ex

VincaVinca

0

10

20

30

40

50

0 2 4 6 8 10

Y=45.3-6.01X+0.40X2 R2=0.86 Sh

oot

dry

mas

s (g

)

Y=8.79-0.14X R2=0.32

-60

-40

-20

0

20

0 2.5 5 7.5 10

NaHCO3 (mM)

Hibiscus ‘Mango Breeze’Hibiscus ‘Mango Breeze’*

NS*

NS

*

**Shoot dry mass

SPAD index

% C

han

ge

*

-60

-40

-20

0

20

0 2.5 5 7.5 10NaHCO3 (mM)

Hibiscus ‘Bimini Breeze’Hibiscus ‘Bimini Breeze’

NS NS NS NS

NS

**

Shoot dry mass SPAD index

NS% C

han

ge

0

10

20

30

40

50

60

0 2 4 6 8 10

Bimini BreezeMango Breeze

HibiscusHibiscusS

PA

D in

dex

NaHCO3 (mM)

Y=55.0-1.30X R2=0.96

Y=52.2-2.50X R2=0.95

Sh

oot

dry

mas

s (g

)

Y=8.16-0.40X R2=0.93

Y=8.92-0.05X R2=0.20

0

2

4

6

8

10

12

0 2 4 6 8 10

Bimini BreezeMango Breeze

RoseRose MumMum VincaVincaHibiscus Hibiscus ‘Mango ‘Mango Breeze’Breeze’

Hibiscus Hibiscus

‘‘Bimini Bimini Breeze’Breeze’

Shoot Shoot MassMass

DecreaseDecreasePredicted mPredicted mMM NaHCONaHCO33

10% 2.0 -* -* 6.4 -*

20% 4.0 - - 7.9 -

30% 6.0 - - 9.0 -

40% 8.0 - - 9.9 -

% Shoot Mass Decrease as a % Shoot Mass Decrease as a Function of NaHCOFunction of NaHCO33 Concentration Concentration

*NS growth reduction up to 10 m*NS growth reduction up to 10 mMM NaHCO NaHCO3 testedtested

RoseRose MumMum VincaVincaHibiscus Hibiscus ‘Mango ‘Mango Breeze’Breeze’

Hibiscus Hibiscus

‘‘Bimini Bimini Breeze’Breeze’

SPAD SPAD Index Index

decreasedecreasePredicted mM NaHCO3

10% 0.8 3.2 6.0 2.1 4.2

20% 1.7 4.8 7.4 4.2 8.5

30% 2.8 6.1 8.4 6.3 12.7

40% 4.2 7.2 9.3 8.4 16.8

% SPAD Index Decrease as a % SPAD Index Decrease as a Function of NaHCOFunction of NaHCO33 Concentration Concentration

Experiment 2:

Mechanisms of Tolerance Mechanisms of Tolerance to Alkalinity ofto Alkalinity of

HibiscusHibiscus

Materials and MethodsMaterials and Methods

• Cultivars•‘Bimini Breeze’•‘Carolina Breeze’

• Growing Medium pH• Fe-Reductase Assay

• Rosenfield et al., 1991

4

5

6

7

8

9

10

0 2.5 5 7.5 10

Carolina Breeze

Bimini Breeze

Growing Medium pHGrowing Medium pHBottom Container Layer

NaHCO3 (mM)

pH

Iron Reductase ActivityIron Reductase Activity

(µM

Fe3+

.g-1.h

-1.x

10-3)

NaHCO3 (mM)

0

2

4

6

8

10

12

0 2 4 6 8 10

Bimini Breeze

Carolina Breeze

a

a

bb

b

bab

b

c

a

ConclusionsConclusions• Vinca>‘Bimini Breeze’>Mums>‘Mango

Breeze’>Rose

6.0 mM 4.2 mM 3.2 mM 2.1 mM 0.8 mM

• ‘Bimini Breeze’ exhibits – a higher acidification of the growing

medium – a higher Fe-reductase activity