Environmental Stresses in Cranberry Production: Critical Thresholds and Physiological Effects

Abiotic stresses are known to cause substantial yield losses in crop productions worldwide. Critical thresholds of the main environmental factors affecting plant physiological processes have been established for several plant species, yet little is known about these relationships in cranberry production. While overhead irrigation and subsurface drainage systems have been used respectively to avoid the effects of heat and water stress and to reduce the risks of hypoxic conditions in the root zone, the definition of critical thresholds based on leaf gas exchange parameters is important to improve the efficiency of such cultural operations. We investigated the effects of soil matric potential, air temperature and flooding times on cranberry physiology to determine the set points where stresses typically occur. Experiments were conducted in a growth chamber using cranberry plants collected from the field (as 0.06 m² mat of vines) and grown in 27-litre containers filled with sand. For experiment 1, cranberries were grown under constant matric potential conditions, with treatments varying between -1 and -9 kPa. For experiment 2, the photosynthetic and transpiration rates of current year and 1- to 2-year-old leaves were measured over a range of leaf temperature (from 21 to 37 °C). For experiment 3, treatments consisted of flooding time ranging from 24 to 120 hours and gas exchange measurements were performed each day during treatments. All measurements were carried out on fruiting uprights. Photosynthesis was optimal when soil matric potential ranged between -3 and -7 kPa, whereas at -9 kPa, leaf photosynthesis declined by 16%. The highest CO₂ assimilation rates were observed at a leaf temperature of 29 °C, with photosynthesis decreasing by 6 and 17% at 33 and 37 °C, respectively. After 24 hours of flooding conditions, the rate of photosynthesis had dropped by 20%, with an average reduction of 4.5% over each of the next four days. The responses of stomatal conductance and transpiration to soil matric potential, temperature and flooding time were similar to photosynthesis in all three experiments. Our results show that over the ranges investigated, hypoxic conditions may be more critical for cranberry production and should thus be avoided. Water stress and heat stress nevertheless resulted in an important loss of carbon assimilation. Hence, cranberry growers may achieve significant increases in yield by focusing more thoroughly on irrigation and drainage.