Diurnal Root Zone Temperature Fluctuations Affect Strawberry Water Relations, Growth, and Fruit Quality

Root zone temperature (RTZ) variation in soilless production of strawberries has the potential to cause changes in growth, nutrient uptake, gas exchange, stem water potential (SWP), and yield, particularly for strawberries in solution culture. Root systems of control plants were kept at 20 °C, while plants in other treatments were exposed to diurnal temperature swings of 5 ºC (mild), 10 °C (moderate), or 15 °C (severe), each with a daily mean of 20 °C. After 12 weeks, maximum carboxylation rate, photosynthetic electron transport rate, maximum CO₂ assimilation rate, and fluorescence parameters (F_v/F_m and  were unaffected by temperature regime. Likewise, there was no effect on chlorophyll content, number of leaves, or fruit yield. There was little effect of RZT on predawn or midday SWP, but the severe treatment had substantially lower (–0.5 MPa) SWP compared to all other treatments at mid-morning, when RZT was ~5 °C and air vapor pressure deficit was at its daily maximum. Shoot concentrations of N, Mg, Fe, B, Zn were similar across treatments, but, in the moderate treatment, P, Ca, and Mn concentrations were lower. Shoot K concentration was significantly higher in the severe treatment. Fruit in the moderate and severe treatments were significantly smaller than in the mild treatment, which had the largest fruits. Fruit soluble sugar content was elevated slightly by RZT fluctuation. Leaf area and shoot dry weight of plants in the severe treatment were over 30% lower than controls. Root dry weight in the severe and moderate treatments was 30% less than in the mild treatment. The reduced shoot and root growth may be explained by the transient reduction in SWP when RZT was ~5 °C. The consequences of diurnal RZT fluctuations for strawberry production appear to be small if the minimum temperature is above 5 °C.