Plant growth

The maize cultivar Earligold F1 (VSW041, Moles Seeds, UK) was used. In experiment one, 280 seeds (0.15–0.19 g per seed) were soaked in deionized water for 48 h and then pre-germinated on wet paper towels for 72 h in a controlled-environment (CE) room in the dark (temperature, 24 °C/18 °C; photoperiod, 14 h/10 h; relative humidity, 40%; light density, 350 μmol m⁻² s⁻¹). Then seedlings with a root length of 4–10 cm were transplanted into 155 pots (height, 24 cm; diameter, 6.4 cm; with stainless wire mesh at the bottom) with one seedling per pot. Each pot was filled with 785 g of moist soil (~628 g of dry soil) to make a 22 cm tall soil column. The soil was sieved (1 cm sieve) John Innes No.2 (Foremost, UK). After transplanting, each pot was watered thoroughly by adding 200 ml of water. Seedlings became visible on the next day and another 20 ml of water was added to each pot. The soil column was then drained for 1 h and weighed to determine the pot capacity for water (54% of soil water content, w/w soil dry weight). All pots were weighed and watered to the pot capacity every day until the 15th day, except on the seventh day after transplantation when 50 ml of Hoagland’s nutrient solution (pH 5.8–6.0) was given to each pot. The third leaf was expanded fully (the leaf collar became visible) by the 15th day after transplantation, which was set as the last watering day (Day 0) for the soil drying treatment.

One hundred and four plants at a similar growth stage were selected: 48 plants for the soil drying treatment and another 48 plants as the well-watered control during the following 6 d; in addition to these, 8 plants were sampled on Day 0 as the starting reference. Control plants were watered daily to pot capacity. Eight pots of each treatment were destructively harvested every day during Days 1–6. All of the pots were moved every other day to ensure a uniform growth environment.

This experiment was repeated once (experiment two). In experiment two, 170 seeds (0.15–0.19 g per seed) were pre-germinated and 95 seedlings were transplanted into pots. On the last watering day (the 15th day, Day 0), 65 plants at a similar growth stage were selected: 30 plants for each treatment (soil drying and well-watered) and 5 plants were sampled on Day 0. The growth condition and other processes in these two experiments were the same. Similar results were seen in these two experiments. The data presented here were combined results by treating every sample in either experiment as one replicate.