Growth regulation by air stream-based mechanical stimulation in tomato (Solanum lycopersicum L.) – Part II: Phenotypic and physiological responses

Abstract

Plant responses to mechanical stimulation have a great potential for growth control of ornamentals plants and vegetable seedlings and is a major requirement to ensure plant compactness and stability. 21 days old tomato (Solanum lycopersicum cv. ‘Romello’) plants were exposed to regularly applied mechanical stimuli for 14 days by applying of a defined air stream through a custom-built air stream applicator. Air stream application gradually reduced total plant leaf area by 14% and promoted radial growth relative to internode length compared to the untreated control, resulting in a more compact and stable plant phenotype, which was also related to an increased stem dry matter content of the air stream-treated plants. The reduction in total plant leaf area was compensated for the translocation of proportionally more assimilates to light-harvesting tissues and to stems at the expense of dry mass accumulation in petioles. Total stem, leaf and root dry mass of air stream-treated plants were unaffected. The specific leaf area of the air stream treated plants was reduced compared to the control, resulting in an increased relative leaf greenness and consequently in an 8% higher net carbon assimilation rates on average compared to the control. Thereby, air stream-treated plants were able to maintain overall biomass accumulation at the same level as the control. Leaf transpiration rate of air stream treated plants was not markedly affected in the long-term. The technique presented should be easily transferable to other plants, such as ornamentals where the application of chemical plant growth regulators is still the most common technique for plant growth control.