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To test the hypothesis that the effect of daily root zone temperature (RZT) variations would affect strawberry plant performance, root systems of Control ‘Albion’ strawberry plants Treatment 1 (T1) were maintained at 20 °C (no stress), while plants in other treatments were exposed to different diurnal temperature swings about the daily mean of 20 °C. In treatment 2 (T2), temperature swing was 5 °C (mild) which had a total variation of 10 °C (Tvar-10) with a minimum of 15 °C and maximum of 25 °C, treatment 3 (T3) had a variation about the mean of 10 °C (moderate) with a total variation of 20 °C (Tvar-20) with a minimum of 10 °C and maximum of 30 °C, or 15 °C (severe) swings about the mean in treatment 4 (T4) with a diurnal total variation of 30 °C (Tvar-30) with a minimum of 5 °C and maximum of 35 °C. Leaf area and shoot dry weight of plants in the severe treatment were 30% lower than Controls. Root dry weight in the severe treatment was 30% lower than in the mild treatment. Fruits in the moderate and severe treatments were 22% smaller than in the mild treatment. Fruit soluble sugar content was elevated slightly by RZT fluctuation. Shoot concentrations of N, Mg, Fe, B, Zn were not affected by RZT, but there were small differences in concentrations of P, K, Ca, Mn, and Cu. Nutrient uptake of N and Ca were not affected, but P, K and Mg were about 35% less in Tvar-20 and Tvar-30. RZT variation had no effect on chlorophyll content or number of leaves, maximum carboxylation rate, photosynthetic electron transport rate, maximum CO2 assimilation rate, or fluorescence parameters (Fv/Fm and ϕ PSII ) . There was little effect of RZT on predawn or midday stem water potential (SWP), but the SWP was substantially lowered in the severe treatment at mid-morning when RZT was about 5 °C and air vapor pressure deficit was at its daily maximum. We attributed the reduced shoot and root growth to the transient reduction in SWP when RZT was near 5 °C. Overall, the consequences of diurnal RZT fluctuations for strawberry production appear to be small if the minimum temperature is above 7 °C. |
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