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Cranberries were grown under controlled environmental conditions to determine the effects of soil waterlogging on cranberry gas exchange in three growth stages and to investigate the recovery time after waterlogging. Photosynthesis declined by 28% after the first day of waterlogging at the bud elongation stage and was 46% lower after the fifth day. At the flowering stage, the reduction in photosynthesis started to be significant only after the fifth day, whereas no reduction was observed at the fruit development stage. Stomatal limitations were responsible, in part, for the observed decrease in photosynthesis since stomatal conductance (gS) declined by 68% and 45% after the fifth day of waterlogging during bud elongation and flowering, respectively. After water drained away in the saturated treatments, leaf photosynthesis remained lower than in the unsaturated control treatment for 1 to more than 10 days at the bud elongation stage. Our results demonstrate that short-term hypoxic soil conditions can alter cranberry gas exchange depending on plant growth stage, and suggest that adequate drainage or control of the water table depth is required to avoid the negative effects of soil waterlogging on cranberry yield. The cultivated cranberry (Vaccinium macrocarponAit.) is a perennial plant native from North America (Eck, 1990). Its productivity is maximized when soil water potential in the root zone (at 10-cm depth) is maintained between –3.0 and –7.5 kPa (Caron et al., 2016; Laurent, 2015; Pelletier et al., 2013), and growers can use overhead irrigation to avoid water stress when the lower threshold is reached. Most of the cranberry beds are equipped with drain tiles for removing excess water after rainfall or sprinkler frost protection, but drainage systems can also be used for subirrigation where the water table depth is controlled by adding water in drain tiles. Historically, cranberries were grown under wet conditions with shallow water tables around 23–38 cm below the ground surface (Eck, 1990), but there is evidence that higher yields can be attained when the water table is 60 cm deep (Pelletier et al., 2015). Although drainage problems could induce significant yield limitation (Baumann et al., 2005), the time to remove the excess of water greatly depends on the water table depth before rainfall (Pelletier et al., 2015). Recent improvements in water management and the outcome of efforts at promoting the benefits of drier soil conditions could explain in part the yield increases observed in recent years in the province of Qu ebec (Canada). Indeed, the average yield in conventional production systems increased by 38% over the last decade (from 24,000 kg·ha in 2004 to 33,000 kg·ha in 2014) (APCQ, 2015). A decline in photosynthesis is one of the first physiological responses to soil waterlogging (Liao and Lin, 2001). Poor aeration in the root zone generally leads to a reduction in root cellular respiration and permeability, followed by a decline in water absorption (Bhattarai et al., 2005). Stomata then close gradually, transpiration is reduced, and carbohydrate translocation from leaves to roots is inhibited (Liao and Lin, 2001). The extension of root axes can be severely reduced as a result of ethylene production under anaerobic conditions resulting in injury to the plant (Smith and Restall, 1971). It has been shown in many crops, such as blueberries (Davies and Flore, 1986a), cherries (Beckman et al., 1992), and sunflowers (Grassini et al., 2007), that leaf gas exchange is affected by the lack of oxygen in the rhizosphere. Depending on the growth stage at which soil waterlogging occurs, such reduction in CO2 assimilation may reduce the number of fruiting uprights, number of flowers, fruit set, and fruit size (Kozlowski, 1997). Hence, lower carbon assimilation under saturated soil conditions could reduce plant growth and lead to significant yield loss. The magnitude of these impacts will depend on the time required to recover and return to preflooding values when waterlogging ends. However, although the reduction in plant gas exchange under soil waterlogging and the recovery time are species dependent (Kozlowski, 1997), little is known about these relationships in cranberry production—yet essential to improve the design of drainage systems and avoid yield limitations caused by inadequate drainage. Therefore, the objectives of the present study were to determine the effect of soil waterlogging duration on cranberry gas exchange and to investigate the recovery time after removing the excesswater. Materials and Methods The experiments were carried out in an 18-m controlled growth chamber (BDW80, Conviron, Winnipeg, Manitoba, Canada) located at Universit e Laval in Qu ebec City, Canada (lat. 46 46# N, long. 71 16# W). Mature ‘Stevens’ cranberry plants were collected as 0.06-m square mats of vines from a fine sand field in October and grown in 0.27-m containers filled with fine to medium sand. Particular attention was paid to avoid damaging the roots and shoots when removing each mat from the soil. Plants were overwintered in the dark at an air temperature of 4 C and relative humidity (RH) of 80% for 2880 h, satisfying the recommended time of 2500 h (Eady and Eaton, 1972). For the first week of breaking dormancy (d = 1 to d = 7), temperature was set to 15 C from 1300 to 1800 HR and to 6 C from 0100 to 0500 HR with constant hourly steps between these periods. RH was controlled at 50% during the day and 80% during the night, following a time course similar to temperature. From d = 8 to d = 14, the temperature was set to 21 C day/11 C night and from d = 15 to d = 147, to 25 C day/16 C night. Plants were exposed to a 13-h photoperiod during breaking dormancy and a 15-h photoperiod during the growing season. Metal halide high-intensity discharge lamps (n = 33, 400 W each) were used to provide a photosynthetic photon flux density (PPFD) of 600 mmol·m·s at plant level, corresponding to light-saturated conditions for cranberry (Kumudini, 2004). Each experimental unit (EU) of 0.27 m was seated in a 0.76-m container. Water was added in the large container and small holes were drilled in the bottom of the small container to ensure water entering into the soil by upward flux. AMariotte bottle was connected to the large container to replace the water lost by evapotranspiration (Soppe andAyars, 2003). Mariotte bottles were filled each week for maintaining a constant water table depth. Except for fertilization, no water was added to the soil surface. Fertilizers were applied at 10%, 50%, and 100% of flowering for a total dose of 40 kg·ha N, 60 kg·ha P, and 125 kg·ha K. Nutrients were mixed with 250mL of water per EU and manually applied with a commercial watering can. Flowers were hand pollinated each day with a small paintbrush Received for publication 24 Sept. 2015. Accepted for publication 2 May 2016. The paper is a portion of a thesis submitted by Vincent Pelletier in fulfilling a PhD degree requirement. We acknowledge the financial contribution of the Natural Sciences and Engineering Research Council of Canada, Fonds de Recherche Nature et Technologies du Qu ebec, Nature Canneberge, Canneberges Bieler, Transport Gaston Nadeau, Hortau and the Scientific Research and Experimental Development Tax Incentive Program of the Canada Revenue Agency and Revenu Qu ebec. We thank Jonathan Lafond and Benjamin Parys for providing helpful comments on a previous version of the manuscript. Corresponding author. E-mail: vincent.pelletier.8@ ulaval.ca. 910 HORTSCIENCE VOL. 51(7) JULY 2016 from d = 44 to d = 65. This resulted in fruit set ( 40%) similar to that observed in the field (Pelletier et al., 2015), with no significant difference among EUs. Treatments consisted of soil waterlogging time varying from 0 (control) to 5 d (1, 2, 3, and 5 d) and were applied at three different growth stages: bud elongation (d = 24 after dormancy), flowering (d = 51), and fruit development (d = 77; i.e., 2 weeks after fruit set). Soil in the control treatment was never waterlogged. To apply the saturation treatments, the water level in the 0.76-m containers was increased until the soil was completely saturated by capillary rise, as evidenced by a thin layer of water at the soil surface. At the end of each saturation treatment, the water in the large containers was removed. Because of the high saturated hydraulic conductivity of the soil and the absence of restrictive constraints, water drained away in less than 30 min after the treatment period. Measurements of photosynthesis (Pn), gS, and transpiration (E) were performed each day using the same uprights between 1300 and 1600 HR on the day before treatment application and for the next 12 d (except for the 6th, 8th, 10th, and 11th d) using a portable photosynthesis system (LI-6400XT; LI-COR, Lincoln, NE) equipped with a 6-cm chamber and a red/blue light-emitting diode light source (6400-02B, LI-COR). Leaf gas exchange was measured up to 7 d after the termination of the longest saturation treatment to allow estimation of the recovery time. A different set of uprights was selected at each development stage. Oneyear-old leaves were used at the bud elongation stage, whereas current year foliage was used at the flowering and fruit development stages. Leaves were first acclimated under 800 mmol·m·s PPFD, 25 ± 1 C leaf temperature, 400 mmol·mol leaf chamber air CO2, 400 mmol·s air flow rate, and gas exchange variables (Pn, gS, and E) were recorded once they had reached steady state. The leaf-to-air vapor pressure deficit (VPDl) was maintained at 1.2 ± 0.1 kPa during measurements. Because of the difficulty to ensure a good contact between the foliage and the leaf thermocouple, the latter was positioned to measure air temperature instead of leaf temperature and the energy balance method was used for estimating leaf temperature and calculating related gas exchange parameters. After measurements, leaveswerecollectedandd

Cranberry Gas Exchange under Short-term Hypoxic Soil Conditions