Influence of microclimatic conditions under high tunnels on the physiological and productive responses in blueberry 'O'Neal'

Blueberry (Vaccinium corymbosum L.) production under tunnels has spread in recent years. However, there is little information on the productive and physiological responses of blueberry grown under high tunnels. The objective of this research was to evaluate the effect of high tunnel microclimate on the physiological and productive responses of blueberries. A total of 1296 plants of highbush blueberry 'O'Neal' were grown in high tunnels, leaving the same amount of plants under open fields (control). Environmental temperature (T, degrees C) and relative humidity (RH, %), diffuse and total photosynthetically active radiation (PAR(diffuse) and PAR(total), mu mol m(-2) s(-1)), stomatal conductance (g(s), mmol m(-2) s(-1)) and maximum photochemical efficiency of photosystem II (F-v/F-m) of the leaf were measured. Fruit yield, date of harvest initiation and fruit growth rate were also determined. The maximum T was on average 10-12 degrees C higher inside the high tunnel than the control, whereas the minimum T averaged only 2-5 degrees C higher. PAR(total) decreased an average of 25% under tunnel, while levels of PAR(diffuse) increased more than 150%. The gs ranged between 42% and 99% higher in the high tunnel compared to the control, and was positive and statistically related (r(2) = 0.69**) to PAR(diffuse) variations. Blueberries under high tunnel recorded an accumulated yield 44% higher, while harvest started 14 d earlier compared to control. The results suggest that high tunnels in blueberries increases fruit yield and improves precocity due to higher temperatures during the flowering stage and fruit set. Particular light conditions under tunnels would favor higher leaf stomatal conductance in this crop.