水冷式苗床根际降温效果及其对番茄幼苗生长的影响

Root-zone cooling effect of water-cooled seedling bed on growth of tomato seedling

作为水分和养分吸收运输的主要器官,根系及其代谢直接影响着植株的生长与发育,相对于地上部温度植株对地温更为敏感。根际高温是影响夏季蔬菜集约化育苗主要障碍因子之一,适宜、稳定的根际温度是幼苗根系生长和培育壮苗的重要保证。为了降低夏季集约化育苗时幼苗的根际高温环境,设计了一种低能耗的根际降温方式,该研究利用地下水作为降温媒介,采用梯形排管作为冷却管道,设计了一套水冷式苗床用于集约化育苗根际局部降温。试验结果表明,在番茄育苗期间,水冷式苗床番茄幼苗根际积温、日均温和平均最高温分别比对照苗床降低了154.1、4.5和6.5℃。水冷式苗床平均一天中番茄幼苗根际温度高于25℃历时比对照苗床减少了7.6 h,高于28℃历时比对照苗床减少了7.2 h。水冷式苗床番茄幼苗叶片的蒸腾速率比对照提高了36.3%,提高了叶-气温差。水冷式苗床番茄幼苗根系活力和光合作用显著高于对照苗床,壮苗指数比对照苗床提高了34.9%。因此,水冷式降温苗床能够较好的降低根际温度,缓解夏季高温对番茄幼苗生长的胁迫。

As the main plant organ of absorbing and transporting water and nutrients, root system and its metabolism directly affect plant growth and development.Plant growth is more susceptible to root zone temperature than above ground portion. The root zone temperature greatly affects the growth and physiological metabolism of plant. Optimal and stable rhizosphere temperature is an important factor for root growth and metabolism. The heat stress around rhizosphere during summer season is an important factor limiting the seedling growth. Root-zone cooling is more economical compared with air temperature cooling, it can be an effective solution to alleviate high temperature stress. A new water-cooled seedling bed （WSD） was exploited by using the underground water as the natural coolant to lower the root-zone temperature during summer season. The root cooling system consisted of inlet pipe, cooling tube, return pipe and control valve. The profile of cooling tube with a trapezoidal cross section was used, which could increase the contact area between cooling tube and plug trays. Tomato seedlings were grown in 72-cell plug trays that were cooled by cold water flowing through the cooling tube buried at the bottom of plug trays. The objective of this study was to investigate the cooling effect of water-cooled seedling bed and its effect on the growth of tomato seedling. The root zone temperature, growth and physiological characteristics of tomato seedling were analyzed in this study. The results showed that the cumulative temperature, mean daily temperature and mean daily maximum temperature of the root-zone in WSD were on average, 154.1, 4.5 and 6.5℃ lower than those of non-cooled seedling bed （NSD） during tomato seedling period, respectively. The mean temperature diurnal variation of WSD （8.5℃） was milder than that of NSD （13.6℃）. The root-zone temperature was analyzed. The results showed that the mean high temperature duration of WSD above 25 and 28℃were 8.0 and 3.1 h per day, respectively. However, the mean high temperature duration of NSD reached 15.6 and 10.3 h. The run length of WSD was shortened by 7.6 and 7.2 h at the fixed level 25 and 28℃, respectively. The leaf evaporating rate of tomato seedling in cooled treatment was enhanced by 36.3%compared with that of non-cooled treatment, which improved the temperature difference between leaf and air. Root activity and the net photosynthetic rate of tomato seedling were also improved significantly. Plant height, dry mass of shoot and root of tomato seedling in cooled treatment were increased by 35.8%and 72.6%compared with seedling of non-cooled treatment, while no significant difference was observed in the stem diameter of seedling between two treatments. Tomato seedling healthy index in the water-cooled seedling bed was improved by 57.1%compared with a non-cooled treatment. This study indicated that the water-cooled seedling bed is an effective method to alleviate heat stress around rhizosphere and improve the seedling growth during summer season.