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The electrogenic properties of plant–microbial fuel cells (P-MFCs) assembled into a battery are studied. The operation of a single cell is studied experimentally in comparison with parallel and series connections of cells, which are two options for connection in an electrical circuit. A potential difference of ~70 mV, which gradually vanishes, is registered in a P-MFC that does not include a plant organism. We hypothesize that the root system, with involvement of electrogenic chemoorganotrophic microorganisms, gives rise to diffusional electromotive force. We show that in series connection of three fuel cells the bioelectric potential generated by an individual cell, which is 170 mV, increases only by a factor of 1.5. In parallel connection of three cells, the current produced under a load increases, but also only by a factor of 1.5, and this takes place at later developmental stages of the plants, which is presumably caused by triggering certain compensatory mechanisms that diminish the electrogenic properties of the plants.

The paper concerns influence of water distribution on the bioelectric potential in the soil–plant system. Two methods for measuring bioelectric potentials (BEPs) of plants have been compared, namely an invasive installation of needle electrodes (a) and a noninvasive method of providing contact due to root intergrowth through a metal grid (b). It has been shown that needle electrode installation into plant tissue leads to a decrease in the biopotential difference from 70 mV to a noise level within ~ 30 minutes; in fact, this means measuring the potentials generated by the plant organism due to the stress caused by the damage. On the contrary, noninvasive electrode installation provides long-term measurements for months and even longer. A specific system is suggested for automated electrophytogram based on the noninvasive method. It allows one long-term measurement of the plant electrophysiological signal directly under normal living conditions for the rhizosphere; it indicates the current functional state of a plant. An equivalent BEP measurement scheme has been proposed accounting for both electrical properties of the plant and root–inhabited medium. BEPs have been measured under conditions of varying water content in the root zone and water movement along and against the root growth direction. The biopotential is constant on average and fluctuates stochastically in the range from 245 to 275 mV at 60–70% of the total water capacity of the soil substrate. The bioelectric potential decreases almost twice when the soil dries. It is restored after irrigation and the restoration delay time increases with increasing water-deficit period. A model is proposed describing the effects in the system during a water-deficiency regime and irrigation.

We investigate the effects that the spectral composition of radiation that plants are exposed to during their development has on the fractionation of carbon isotopes between atmospheric carbon dioxide and the primary products of photosynthesis in plant tissues. The difference in carbon isotope composition between carbon in air near the leaves and carbon in the leaves varies in the range of 7 to 19 depending on the spectral composition of incident light, with an increase in the red component resulting in enrichment of the leaves with the light isotope 12C. This differences are (i) the measure of isotope fractionation during the vital activity of plants and (ii) the rate of carbon assimilation due to photosynthetic reactions.

—The efficiency of light absorption with different spectral compositions by lettuce leaves and the choice of optimal conditions of the lighting environment for increasing the productivity and quality of plant products grown under artificial lighting conditions were investigated. Lettuce of the Typhoon variety was grown by a thin-layer panoponic method in an automated growth chamber with five variants of different light sources. A non-damaging method developed by the authors for the measurements of the absorption spectra of leaves in vivo made it possible to determine the influence of the spectral composition of the radiation on the optical characteristics that reflect the physiological state of the plants. The amount of absorbed photon energy increased by ~140 μmol m–2 s–1 with an increment in lettuce leaf biomass by 1 g for 10 days under maximum productivity conditions; the values of the light absorption index below 70 μmol m–2 s–1 corresponded to the samples with minimum results in growth characteristics. The similarity of the spectral characteristics of lighting in the region of photosynthetically active radiation of HPS lamps (High-Pressure Sodium lamps) and LED lamps, which emit yellow light, and almost the same proportion of photosynthetically active photons in the blue, green, and red regions of the spectrum led to the same increment of light absorption in the process of plant development. However, a significant difference in the productivity of lettuce (~50%), as well as the growth, development, and biochemical composition indicated a better effect of the HPS lamps on the properties of the plant culture. The obtained data indicated that the illumination with an intensity of ~25 μmol m–2 s–1 in the range of 400–500 nm, ~150 μmol m–2 s–1 in the range of 500–600 nm, and ~150 μmol m–2 s–1 in the range of 600–700 nm led to high productivity of the lettuce.

The experimental plant-microbial fuel cell based on the gradient of bioelectric potentials created in the rhizosphere and compatible with the production of plant products was created and tested.

The screening of protective radiations that occur during laser radiation of biological tissues have been experimentally studied. The metallic and dielectric screens with different shape have been used for screening. The physical model of generation of the secondary radiation that generates the protective effects, which lead to a substantial increase in the environmental resistance of living organisms placed nearby, has been suggested. It has been assumed that this radiation is mainly concentrated in the frequency range lower than 10 GHz.

Absorption spectra of pigments derived from the plants that were illuminated by light with different spectral composition during their growth are presented. The role of the spectrum of LED lighting in the life of plants has been estimated, and its influence on pigment absorption has been noted. It has been recommended to use a full range of lighting in the range of 400–700 nm with the domination of the red component when growing oats in protected ground. It has been found that the recording of absorption spectra of pigments allows the monitoring of the influence of lighting on the processes of plant growth and development. It has been assumed that the use of sources with a controlled spectrum in a greenhouse will allow directed influence on the nature of biochemical reactions occurring in plants during their development: photosynthesis and photomorphogenesis.

The paper describes a new developed method of sample gasification using yeast oxidation of monosaccharides in plant tissue for 13C/12C isotope ratio mass spectrometric analysis. Variations in the carbon isotopic composition of the leaf surface have been shown; the δ13C value for chlorophytum varies from -37 ‰ to -32 ‰ from the tip of the leaf to its base. It has been shown first that the spectral composition of radiation affects the ratio of carbon isotopes in plant leaves: the predominance of blue component in the spectrum results in accumulation of heavy 13C isotope up to δ13C = -25 ‰.