Abstract
Ebb-and-flow subirrigation systems are highly efficient, water-saving and environmentally friendly. However, one concern with these recirculating systems is the possible transmission of plant pathogens. Here, through 16S rRNA-targeted Illumina sequencing, the bacterial dynamics in a recirculating nutrient solution were characterized for cucumber plug seedlings cultivated in an ebb-and-flow system in summer and winter. Both the bacterial number and diversity in the nutrient solution increased immediately after the first irrigation cycle; then, these values were gradually stable with recirculating irrigation. In summer and winter, different bacterial compositions and changing patterns were observed. In summer, the predominant genera in the nutrient solution included Comamonas, Pseudomonas, Acinetobacter, Reyranella, Sphingobium, Bradyrhizobium, Sphingomonas, and Acidovorax. Of those genera, during recirculating irrigation, the relative abundance of Bradyrhizobium gradually decreased, whereas those of Pseudomonas, Reyranella, Sphingobium, Sphingomonas, and Acidovorax gradually increased. In winter, the bacterial communities were mainly composed of Nevskia, Bosea, Sphingobium, Acidovorax, Pseudomonas, and Hydrocarboniphaga. Of those genera, the relative abundance of Bosea, Sphingobium, and Acidovorax showed an increasing trend, whereas those of Nevskia and Hydrocarboniphaga decreased overall. Furthermore, in both summer and winter, no plant pathogenic bacteria on cucumber could be detected; however, some potentially beneficial bacteria, including Comamonas testosteroni, Acinetobacter baumannii, Pseudomonas aeruginosa, P. koreensis and Sphingobium yanoikuyae, colonized the nutrient solution and exhibited increased relative abundances during irrigation. The colonization of these bacteria might facilitate the plant growth promotion. Inoculation of the microbes from the effluent nutrient solution also promoted the growth of cucumber seedlings, but did not lead to any disease. The present data elucidate the bacterial dynamics in a cucumber cultivation ebb-and-flow system and provide useful information for biological control during cucumber seedling production.
Highlights
Ebb-and-flow irrigation is a highly efficient, water-saving and environmentally friendly subirrigation technique that is emerging to replace traditional overhead irrigation systems in nursery plant production
Bacterial dynamics in a recirculating ebb-and-flow subirrigation system number of culturable bacteria showed no significant difference between the samples before and after seedling cultivation in both summer and winter (Fig 1B)
The results indicated that the substrate and irrigation water might be the primary sources of bacterial transfer to the nutrient solution
Summary
Ebb-and-flow irrigation is a highly efficient, water-saving and environmentally friendly subirrigation technique that is emerging to replace traditional overhead irrigation systems in nursery plant production. Ebb-and-flow systems use an automatic flood and drain watering technique, in which plants are flooded temporarily and periodically [1]. The drainage water from ebb-and-flow systems is usually recycled to save water and nutrients, thereby preventing fertilizers and pesticides from entering surface and groundwater [5,6]. Ebb-and-flow systems can reduce labor costs by eliminating the need for hand-watering and reducing the incidence of foliar diseases by keeping the foliage dry [2,7]. As a result of these benefits, the supply of and demand for ebb-and-flow systems have dramatically increased in horticultural production [7], especially in the intensive cultivation of plug seedlings
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