UVA Epidermal Transmittance

Epidermal transmittance for UV-A for fava beans grown in a high UV environment on Mauna Kea was found to be significantly affected by both the dimming treatment and UV-B screening (Table 13.1; Fig. 13.3). On average, measured transmittances increased 6.6% with a 13% reduction in PAR (+ UVB full sun vs. + UVB reduced sun). Screening of UV-B fUrther increased epidermal

Table 13.1 Summary of 2-way ANOVA of the global dimming and UV-B reduction experiment conducted with fava bean at the Mauna Kea, HI, USA field station. Dosimetry and meteorological data as described in Fig 13.3. Treatments are described in the text. "mse" refers to mean square error from ANOVA; n is the total number measurements per treatment. Not all plants had internodes 7 - 9

Treatments

Treatments

Table 13.1 Summary of 2-way ANOVA of the global dimming and UV-B reduction experiment conducted with fava bean at the Mauna Kea, HI, USA field station. Dosimetry and meteorological data as described in Fig 13.3. Treatments are described in the text. "mse" refers to mean square error from ANOVA; n is the total number measurements per treatment. Not all plants had internodes 7 - 9

Metric

Units

n

+ UVB full sun

+ UVB - UVB reduced sun reduced sun

mse

p-value

UVA transmittance

%

150

4.521

4.819

5.516

0.097

< 0.0001

Total height

cm

75

19.223

19.191

19.309

0.223

0.927

Total biomass

g

75

0.814

0.804

0.803

0.018

0.903

Leaf biomass

g

75

0.402

0.393

0.388

0.014

0.783

Stem biomass

g

75

0.245

0.229

0.227

0.008

0.221

Branch biomass

g

75

0.162

0.177

0.184

0.016

0.609

Leaf mass per area

g cm 2

75

0.0044

0.0044

0.0043

0.0001

0.796

Number of internodes

n

75

7.68

7.91

8.00

0.10

0.081

Number of branch nodes

n

75

2.49

2.56

2.69

0.10

0.330

Number of leaf nodes

n

75

5.19

5.35

5.31

0.08

0.360

Length of 1st internode

cm

75

0.376

0.415

0.324

0.041

0.294

Length of 2nd internode

cm

75

1.420

1.395

1.227

0.094

0.291

Length of 3rd internode

cm

75

2.405

2.273

2.144

0.114

0.272

Length of 4th internode

cm

75

3.020

2.935

2.840

0.107

0.496

Length of 5th internode

cm

75

2.716

2.584

2.761

0.086

0.319

Height of 1st internode

cm

75

0.068

0.088

0.064

0.017

0.547

Height of 2nd internode

cm

75

0.444

0.503

0.388

0.050

0.275

Height of 3rd internode

cm

75

1.864

1.897

1.615

0.131

0.253

Height of 4th internode

cm

75

4.269

4.171

3.759

0.229

0.250

Height of 5th internode

cm

75

7.289

7.105

6.599

0.308

0.262

Height of 6th internode

cm

75

10.005

9.689

9.360

0.316

0.354

Height of 7th internode

cm

73-75

11.991

11.594

11.406

0.282

0.330

Height of 8th internode

cm

41-50

13.238

12.359

12.443

0.316

0.104

Height of 9th internode

cm

10-22

14.101

12.828

13.036

0.551

0.335

Figure 13.3 Epidermal transmittance for UV-A (375 nm) for mature fava bean leaves grown under simulated global dimming and UV-B exclusion environments at the Mauna Kea, HI field site (see Section 13.2.1). Epidermal transmittance was measured non-destructively with a UVA-PAM fluorometer. Error bars represent 1 standard error. Bars with different letters are significantly different at p < 0.05. Average daily biologically weighted UV doses were: erythemal = 8.97 kJ m 2 d 1 (sd. 1.28, min. 4.90, max. 10.06); UV-BBE71 = 13.8 kJ m 2 d 1 (sd. 2.0, min. 7.5, max. 15.4); and UV-BBE03 = 37.7 kJ m 2 d 1 (sd. 5.4, min. 20.6, max. 42.3). Daily total PAR averaged 46.6 mol m 2 d 1 (sd. 8.3) and daily maximum PAR averaged 2,024 p,mol m 2 s 1 (sd. 332). Daily air temperature averaged 11.8°C (sd. 1.5), daily maximum temperature averaged 17.8°C (sd. 2.0), and daily minimum temperature averaged 5.9°C (sd. 2.1)

Figure 13.3 Epidermal transmittance for UV-A (375 nm) for mature fava bean leaves grown under simulated global dimming and UV-B exclusion environments at the Mauna Kea, HI field site (see Section 13.2.1). Epidermal transmittance was measured non-destructively with a UVA-PAM fluorometer. Error bars represent 1 standard error. Bars with different letters are significantly different at p < 0.05. Average daily biologically weighted UV doses were: erythemal = 8.97 kJ m 2 d 1 (sd. 1.28, min. 4.90, max. 10.06); UV-BBE71 = 13.8 kJ m 2 d 1 (sd. 2.0, min. 7.5, max. 15.4); and UV-BBE03 = 37.7 kJ m 2 d 1 (sd. 5.4, min. 20.6, max. 42.3). Daily total PAR averaged 46.6 mol m 2 d 1 (sd. 8.3) and daily maximum PAR averaged 2,024 p,mol m 2 s 1 (sd. 332). Daily air temperature averaged 11.8°C (sd. 1.5), daily maximum temperature averaged 17.8°C (sd. 2.0), and daily minimum temperature averaged 5.9°C (sd. 2.1)

transmittance by an additional 14.5% under a 13% reduction in PAR (-UVB reduced sun), and a total 22.1% increase in transmittance from the full sun treatment (vs. +UVB full sun). Screening of UV-B under a 6.1% reduction in PAR resulted in a 21.5% (-UVB, "full" sun) increase in epidermal transmittance for UV-A from the full sun treatment (+ UVB full sun).

To determine the relationship between maximum ambient PAR and UV exclusion on leaf epidermal transmittance for UV, we grew fava beans under different PAR and UV environments in Utah. For these plants, relatively small but steady increases in transmittance were observed with declining PAR until maximum daily PAR exposure went below 200 ^mol m- s- where transmittances were observed to increase rapidly per unit quanta. This pattern was found to be consistent whether UV was present or absent, although leaves not exposed to UV radiation had slightly higher transmittances for all levels of PAR exposure (Fig. 13.4 upper). A similar pattern (Fig. 13.4 lower) was found for quaking aspen (Populus tremuloides) leaves grown in Utah under different levels of PAR without UV exclusion.

Figure 13.4 Epidermal transmittance for UV-A (375 nm) for mature fava bean (upper and lower panels) and quaking aspen leaves (lower panel only) grown under different PAR intensities in Logan, Utah measured non-destructively with a UVA-PAM fluorometer. Changes in UV exposure were commensurate with changes in PAR. Both UV-A and UV-B were shielded under the UV exclusion treatment (-UV)

Figure 13.4 Epidermal transmittance for UV-A (375 nm) for mature fava bean (upper and lower panels) and quaking aspen leaves (lower panel only) grown under different PAR intensities in Logan, Utah measured non-destructively with a UVA-PAM fluorometer. Changes in UV exposure were commensurate with changes in PAR. Both UV-A and UV-B were shielded under the UV exclusion treatment (-UV)

The relationship between the concentration of UV absorbing pigments and UV-A epidermal transmittance as measured with the UVA-PAM was also evaluated for the fava beans grown in Utah. Highly significant relationships (p < 0.0001) were found among concentrations of extracted UV absorbing pigments and UV-A epidermal transmittance for both UV-A (Fig. 13.5, upper left) and UV-B (Fig. 13.5, lower left) absorbing compounds. In addition, concentrations of UV-A and UV-B absorbing compounds were highly correlated (R = 0.93, p < 0.0001) and linear in relationship (Fig. 13.5, upper right). The relationship between the concentration of UV-B absorbing compounds and epidermal transmittance were consistent with a relationship (Fig. 13.5, lower right) found for a single quaking aspen growing in Utah.

0 0.2 0.4 0.6 0.8 1.0 ' 0 0.1 0.2 0.3 0,4 0.5 0.6 0.7 0.8 Absorbance 360 nm (cm 2) Absorbance 360 nm (cm

Absorbance 305 nm (cm Absorbancc 305 nm (cm :)

Figure 13.5 Relationship between UV-A transmittance (375 nm) as measured with a UVA-PAM fluorometer and absorbance (at 305 and 360 nm) of flavonoids extracted from same leaves for fava bean (left panels) and quaking aspen growing in Logan, Utah (lower right panel). The relationship between extract absorbance at 305 nm and 360 nm for fava bean is shown in the upper right panel. The quaking aspen relationship was derived from a single tree, while multiple individuals of fava bean were used

Absorbance 305 nm (cm Absorbancc 305 nm (cm :)

Figure 13.5 Relationship between UV-A transmittance (375 nm) as measured with a UVA-PAM fluorometer and absorbance (at 305 and 360 nm) of flavonoids extracted from same leaves for fava bean (left panels) and quaking aspen growing in Logan, Utah (lower right panel). The relationship between extract absorbance at 305 nm and 360 nm for fava bean is shown in the upper right panel. The quaking aspen relationship was derived from a single tree, while multiple individuals of fava bean were used

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