Effects of temperature and watering regime on growth, gas exchange and abscisic acid content of canola (Brassica napus) seedlings

Global climate change, including global warming, will likely reduce soil moisture in many parts of the world. Few studies have examined the combined effects of temperature and watering regime on plant growth and physiological parameters, on time-course basis in early developmental stages. We grew canola (Brassica napus L. cv. 45H72) plants under lower (22/18°C) and higher (28/24°C) temperature regimes in controlled-environment chambers. One half of the plants were watered to field capacity and the other half at wilting point. In three separate experiments, we determined growth, gas exchange and endogenous abscisic acid (ABA) content in 1-week-old seedlings grown for another 1, 5 or 10days under the above-mentioned conditions. Higher temperature decreased stem height, leaf area, leaf area ratio (LAR) and water-use efficiency (WUE), but increased specific leaf weight (SLW), leaf weight ratio (LWR) and transpiration (E). Water stress reduced stem height, leaf number, leaf area, dry matter of individual organs and whole plant, LAR, net CO ₂ assimilation, E and WUE, but increased SLW and LWR. Overall, plant growth, dry matter, shoot:root weight ratio and ABA content increased with exposure duration, especially by day 10. However, higher temperature inhibited water stress-induced increases in ABA content. Interaction between watering regime and exposure duration was significant for all parameters of growth and dry matter as well as for LWR, WUE and ABA. No significant interaction was found between temperature and watering regime, between temperature and exposure duration, or among temperature, watering regime and exposure duration for any of the measured parameters. This study revealed that water stress strongly, but higher temperature to a lesser extent, affected canola seedlings, leading to reduced growth and dry matter, and the negative effects increased with time.