The effect of water stress on cold hardiness was examined in evergreen azaleas, `Coral Bell' (CB), `Hinodegiri' (HD), and `Red Ruffle' (RR). Plants were well-watered between 8 Aug. and 1 Nov. (wet) or were subjected to 3 weeks of reduced water supply starting on one of three dates, 1 Aug. (dry 1), 29 Aug. (dry 2), and 19 Sept. (dry 3). Cold hardiness of leaves and lower, middle, and upper stems was tested on 29 Aug., 19 Sept., 10 Oct., 1 Nov. By the end of each 3-week period, water potential of water stressed plants reached –1.5 to –1.8 MPa compared to around –0.8 MPa of well-watered plants. Reducing the water supply significantly increased cold hardiness of all tested plant parts in all cultivars regardless of timing of watering reduction, with two exceptions, CB middle stems on 29 Aug. and HD leaves on 19 Oct. Three weeks after rewatering cold hardiness of water-stressed plants did not differ significantly from well-watered plants, except for HD plants under dry three treatment, which continued to be 1.0 (middle stems) to 4.3 (upper stems) more cold hardy.
On the role of soil water retention characteristic on aerobic microbial respiration
