Conversa Giulia, Bonasia Anna, Lazzizera Corrado, La Rotonda Paolo, Elia Antonio
Department of Agriculture, Food, Natural Resources and Engineering, University of Foggia, Foggia, Italy.
Front Plant Sci. 2021 Apr 29;12:645671. doi: 10.3389/fpls.2021.645671. eCollection 2021.
Soilless cultivation systems are efficient tools to control nitrates by managing nutrient solution (NS) salinity and nitrogen availability, however, these nitrate-lowering strategies require appropriate calibration based on species/genotype-specific responses interacting with climate and growing conditions. Three experiments were carried out on lettuce and grown in ebb-and-flow (EF) and floating (FL) systems at two levels of NS salinity (EC = 2.5 and 3.5 dS m) (EC2.5, EC3.5, respectively) under autumn and early-spring (lettuce) and winter and late-spring conditions (). Nitrogen deprivation (NS withdrawal a few days before the harvest) was tested at EC2.5, in the autumn and winter cycles. The EF-system caused an increase in salinity in the substrate where roots mainly develop so it mimicked the effect of the EC3.5 treatment. In the winter-grown lettuce, the EF-system or EC3.5 treatment was effective in reducing the nitrate level without effects on yield, with the EF baby-leaf showing an improved quality (color, dry matter, chlorophylls, carotenoid, vitamin C, phenol). In both seasons, the EF/EC3.5 treatment resulted in a decline in productivity, despite a further reduction in nitrate content and a rise in product quality occurring. This response was strictly linked to the increasing salt-stress loaded by the EC3.5/EF as highlighted by the concurrent Cl accumulation. In early-spring, the FL/EC3.5 combination may represent a trade-off between yield, nitrate content and product quality. In contrast, in winter-grown endive/escarole the EC3.5, EF and EC3.5/EF reduced the nitrate level with no effect on yield, product quality or Cl uptake, thus proving them to be more salt-tolerant than lettuce. High temperatures during the late-spring cycle promoted nitrate and Cl uptake, overcoming the nitrate-controlling effect of salinity charged by the EF system or EC3.5. The nitrate level decreased after 3 day-long (lettuce) or 6 day-long () NS withdrawal. In and EF-grown lettuce, it provoked a decrease in yield, but a concurrent improvement in baby-leaf appearance and nutritional quality. More insights are needed to fine-tune the duration of the NS removal taking into account the soilless system used and species-specific characteristics.
无土栽培系统是通过管理营养液（NS）盐度和氮素有效性来控制硝酸盐的有效工具，然而，这些降低硝酸盐的策略需要根据与气候和生长条件相互作用的物种/基因型特异性反应进行适当校准。在生菜上进行了三项实验，分别在秋季和早春（生菜）以及冬季和晚春条件下，在潮汐流（EF）和漂浮（FL）系统中，以两种营养液盐度水平（EC = 2.5和3.5 dS m）（分别为EC2.5、EC3.5）种植。在秋季和冬季周期的EC2.5条件下测试了氮素剥夺（收获前几天停止供应营养液）。EF系统导致根系主要生长的基质中盐度增加，因此它模拟了EC3.5处理的效果。在冬季种植的生菜中，EF系统或EC3.5处理有效地降低了硝酸盐水平，且对产量没有影响，EF小叶生菜的品质（颜色、干物质、叶绿素、类胡萝卜素、维生素C、酚类）有所改善。在两个季节中，尽管硝酸盐含量进一步降低且产品质量有所提高，但EF/EC3.5处理导致了生产力下降。这种反应与EC3.5/EF施加的盐胁迫增加密切相关，同时积累的氯离子也突出了这一点。在早春，FL/EC3.5组合可能代表了产量、硝酸盐含量和产品质量之间的权衡。相比之下，在冬季种植的苦苣/菊苣中，EC3.5、EF和EC3.5/EF降低了硝酸盐水平，对产量、产品质量或氯离子吸收没有影响，因此证明它们比生菜更耐盐。晚春周期的高温促进了硝酸盐和氯离子的吸收，克服了EF系统或EC3.5施加的盐度对硝酸盐的控制作用。在停止供应营养液3天（生菜）或6天（未提及作物）后，硝酸盐水平下降。在未提及作物和EF种植的生菜中，这导致了产量下降，但同时小叶生菜的外观和营养品质有所改善。需要更多的研究来根据所使用的无土栽培系统和物种特异性特征来微调停止供应营养液的持续时间。
