Mechanical stimulation modifies canopy architecture and improves volume utilization efficiency in bell pepper: Implications for bioregenerative life-support and vertical farming

Abstract

Mechanical stimuli or stress has been shown to induce characteristic morphogenic responses (thigmomorphogenesis) in a range of crop species. The typical mechanically stimulated phenotype is shorter and more compact than non-mechanically stimulated plants. This dwarfing effect can be employed to help conform crop plants to the constraints of spaceflight and vertical agriculture crop production systems. Capsicum annum (cv. California Wonder) plants were grown in controlled environment chambers and subjected to mechanical stimulation in the form of firm but gentle daily rubbing of internode tissue with a tightly wrapped cotton swab. Two studies were conducted, the first being a vegetative growth phase study in which plants were mechanically stimulated until anthesis. The second study carried the mechanical stimulation through to fruit set. The response during the vegetative growth experiment was consistent with other results in the literature, with a general reduction in all plant growth metrics and an increase in relative chlorophyll (SPAD) content under mechanical stimulation. In the fruiting phase study, only height and stem thickness differed from the control plants. Using the data from the fruiting study, a rudimentary calculation of volume use efficiency (VUE) improvements was conducted. Results suggest that VUE can be improved, particularly in terrestrial vertical agriculture systems that can take advantage of moderate height reductions by exploiting much greater vertical capacity in the production system. Mechanical stimulation can also improve VUE in spaceflight applications by reducing vertical system requirements or by expanding the species range that can be grown in a fixed production volume. Mechanical stimulation is also discussed as a microgravity countermeasure for crop plants.