Partial rootzone irrigation: Its physiological consequences and impact on water use efficiency

Partial rootzone irrigation (PRI) means that only part of therootzone is wetted as in full irrigation,while the rest is unwatered during certain periods of the growing season of a crop.This practice is predicted to reduce plant water consumption and maintain the biomass production according to two theoretical backgrounds.Firstly,fully irrigated plants usually have widely opened stomata.A small narrowing of the stomatal opening may reduce water loss substantially with little effect on the photosynthesis.Secondly,part of the root system in drying soil can respond to the drying by sending a root-sourced signal to the shoots where stomata may be inhibited so that water loss is reduced.

根系分区灌溉是指仅仅部分根系受到正常的灌溉，其余根系则受到人为的干旱。两项理论根据指出这种措施可减少植物的水分消耗，并保持一定的生物产量。其一是植物蒸腾失水与气孔导性是线性关系，而光合作用与气孔导性则是一种渐趋饱和的关系，如果气孔导性从最大值适当调低，可显著降低蒸腾，但对光合影响应小得多。其二是处于干燥土壤中的根系可感受干旱，产生干旱信号来调节地上部分的气孔开度。显然，这项措施在田间有多大效用值得深入研究。首先是大田作物的蒸腾失水仅部分地受气孔控制，界面层的扩散阻力起很大作用。因此该措施可能对界面层阻力较小的，如果树等作用大些。另外，根系干旱信号可否“长期”地产生和调控气孔仍需试验证明。