Bioeletrogenesis in the root environment of leaf, fruit and root vegetable crops

Bioelectrogenic processes occurring in the root environment of plants associated with the generation of potential difference during oxidation-reduction reactions and ion diffusion that accompany the development of the root system serve as a basis for creating alternative devices for obtaining renewable environmentally friendly resource-saving energy - bioelectrochemical systems (BES). The search for biocompatible, energy-generating, high-performance BES components, including technical elements, root environments and plants is an urgent task, the solution of which will increase the autonomy and efficiency of plant production. At present, there are practically no BES developments based on vegetable crops, or unsuccessful attempts to create them have been reported. In the presented work, for the first time in a comprehensive study of electrogenic processes in original root environment-vegetable plants BES, more stability of electrical properties is shown in lettuce (leaf crop), higher electricity output in small radish (root crop) and longer electricity generation in tomato (fruit vegetable crop). The aim of the work was to measure a set of parameters - electrogenic properties of the root environment, reflectance and fluorescence spectra of leaves, morphometric indicators, biochemical composition, characterizing the efficiency of electricity generation, the ability to convert light energy, yield and quality of plant products obtained when growing various vegetable crops in bioelectrochemical systems. The phytotest objects were lettuce ( Lactuca sativa L.) variety Ballet, small radish ( Raphanus sativus L.) cultivar Peterburgskiy fioletovyy and dwarf tomato ( Solanum lycopersicum L.) variety Natasha. The plants were grown in 2023-2024 under controlled conditions of intensive light culture at the agrobiological testing ground of the FGBNU AFI with controlled microclimate conditions. The light sources were our own AFI-5000 LED lamps simulating sunlight, and the root environment was peat soil. The nutrition was carried out with Knop's solution. The BES was a growing container with a biocompatible corrosion-resistant system of electrodes made of a porous conductive material, providing superficial electrical contact with the root and its environment. The volume of the BES was 440 cm3 for lettuce, 320 cm3 for small radish and 3000 cm3 for tomato. Electrodes of 6×6 cm in size were placed horizontally in the root environment. To form the root crop, the upper electrode was modified by adding a round hole of 3 cm in diameter. The potential difference was recorded automatically every 15 min using an automated voltmeter (Arduino, Arduino Software, China). Polarization curves were recorded at the end of the vegetation period of lettuce and radish and on the 64th day of tomato cultivation. Lettuce and radish plants were harvested on day 28, tomato on 110 day from sowing the seeds. During harvesting, the weight of leaves, fruits and roots, the height of the above-ground part of plants and the yield were taken into account. The biochemical composition (the content of dry matter, nitrates, sugars, vitamin C, pigments, macro- and microelements) was determined by generally accepted methods (thermogravimetric, ionometric, titrimetric, photometric). The photosynthetic activity indices (spectra of radiation reflected from the leaf surface and fluorescence parameters) were estimated non-invasively using a spectrometric system («Ocean Optics», USA) and fluorimeter MINI-PAM-II («Heinz Walz GmbH», Germany). The average potential difference formed in the root environment of lettuce plants was 289±27 mV, the maximum value reached 391 mV. For small radish plants, the potential difference in the root environment averaged 394±50 mV with a maximum value of 532 mV. The average potential difference in the root environment of tomato was 257±123 mV: during the initial development of the aboveground mass and roots, a stable voltage generation of 317±17 mV was observed, but during the fruit filling phase, the potential difference dropped to 120±34 mV, and during the transition to the ripening phase, a reverse increase to 340±74 mV was observed. The overall productivity of the studied crops when grown taking into account the possible number of harvests from one tier per year was similar, 73.5±10.3 kg/m2 for lettuce, 68.6±3.8 kg/m2 for radish and 71.2±9.2 kg/m2 for tomato, and exceeded that when grown in standard systems for lettuce and tomato. The quality of plant products corresponded the sanitary and hygienic requirements of the Russian Federation. Thus, the nitrate content in lettuce leaves was 1597.0±214.7 mg/kg fresh weight (FW) (MPC 2000 mg/kg FW), in radish taproots 1206.0±144.8 mg/kg FW (MPC 1500 mg/kg FW), and in tomato fruits 70.2±9.3 mg/kg FW (MPC 300 mg/kg FW).