Study on Regulation Mechanism of Tomato Root Growth in Greenhouse under Cycle Aerated Subsurface Drip Irrigation

Aerobic irrigation can effectively improve the oxygen environment in the root zone, and enhance crop quality and yield. However, how aerobic irrigation regulates root growth has not been elucidated. In this study, tomato plants were irrigated with three levels of oxygen (high, medium, and low) under underground drip irrigation. The morphology, activity, transcriptome, and hormone content of tomato roots under oxygen irrigation were analyzed. We found that the aeration irrigation significantly promoted root development. Notably, in the high-aeration irrigation treatment (HAI), the total root length, total surface area, total volume, and root activity were 12.41%, 43.2%, 79.1%, and 24.15% higher than in the non-aeration irrigation treatment (CK), respectively. The transcriptome of tomato roots under aeration irrigation was determined with a total of 272 differentially expressed genes (DEGs), including 131 up-regulated and 141 down-regulated genes. The Kyoto encyclopedia of genes and genomes (KEGG) analysis revealed that the DEGs were enriched mainly in the metabolic pathways and plant hormone signal transduction. Among the plant hormone signal transduction, 50% of DEGs belonged to IAA signal-related genes and were upregulated. LC-MS analysis showed that the content of auxin hormones in the tomato roots subjected to aeration irrigation was significantly higher than that in CK. The content of Indole-3-acetic acid (IAA), Indole-3-carboxylic acid (ICA) and Indole-3-carboxaldehyde (ICAld) were 2.3, 2.14 and 1.45 times higher than those of the CK, but insignificant effects were exerted on the contents of cytokinins, salicylic acid, jasmonic acid, abscisic acid, and ethylene. Meanwhile, the key enzyme of auxin synthesis flavin monooxygenase (YUCCA) was significantly up-regulated. The aforementioned results show that aeration irrigation may promote the growth and development of roots by auxin regulation.