ISHS Acta Horticulturae 610: V International Symposium on Kiwifruit
EFFECTS OF SHADE LEVEL ON KIWIFRUIT LEAF EFFICIENCY IN A MARGINAL AREA |
| Authors: | P. Allan, C. Carlson |
| Keywords: | Actinidia deliciosa, chlorophyll fluorescence |
| Abstract:
‘Allison’ kiwifruit vines were grown, under 0 to 55% shade, on a T-bar trellis running approx. E-W at Pietermaritzburg, South Africa. The chlorophyll fluorescence of leaves was measured throughout the day, at three times during the year, for leaves on three positions in the canopy: viz. North, Top, and South sides of the T-bar trellis. The ratio of variable fluorescence (Fv/Fm) was calculated as this ratio has been shown to have a high degree of correlation with the quantum yield of photosynthesis. Fv/Fm ratios tended to decrease from about 0.8 after sunrise, to lower levels through the mid day, and then increase again in the late afternoon. Unshaded (0%) leaves on the Top of the trellis were the most stressed (lower Fv/Fm ratios), through most, or all, of the day during summer (December and February, respectively) with Fv/Fm ratios below 0.75 and down to 0.65 at midday. In contrast, all shaded leaves generally had ratios above 0.75 throughout the day in summer, except for some North-facing shaded leaves, which were around this ratio. South-facing leaves generally had higher ratios at all seasons indicating that they were less stressed. In autumn (April) unshaded leaves generally followed similar trends to leaves under shade. Leaf position, month and shading all had significant (p<:0.001) effects on the midday Fv/Fm ratios. The midday (11h00 to 14h30) ratios increased significantly from Top to North to South side; decreased from December to February/April; while increasing shade level gave higher midday ratios. Significant (p<0.001) month-by-shade and position-by-month interactions were found. The photosynthetic photon flux density (PPFD) levels were greatest for the Top and North-facing leaves, while South-facing leaves received very low levels in early summer and especially in autumn. Peak levels were up to 3,000 µmol m-2 s-1 (Top) in summer and 2,500 (North-facing) in autumn. Leaf temperatures rose from approx. 22 °C on summer mornings to 32-38 °C after midday, compared with an increase from 14 to 32 °C in autumn. The greater stress of the unshaded leaves during summer, in this marginal area, helps explain why the best yields were obtained under medium shade. | |
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