The root electrical capacitance (CR) method is suitable for assessing root growth and activity, but soil water content (SWC) strongly influences the measurement results. This study aimed to adapt the method for field monitoring by evaluating the effect of SWC on root capacitance to ensure the comparability of CR detected at different SWC. First a pot experiment was conducted with maize and soybean to establish CR–SWC functions for the field soil. Ontogenetic changes in root activity were monitored under field conditions by simultaneously measuring CR and SWC around the roots. The CR values were normalized using SWC data and experimental CR–SWC functions to obtain CR*, the comparable indicator of root activity. The effect of arbuscular mycorrhizal fungi (AMF) inoculation on the CR* and biomass of field-grown soybean was investigated. The pot trial showed an exponential increase in CR with SWC. CR–SWC functions proved to be species-specific. CR showed strong correlation with root dry mass (R2 = 0.83–0.87). The root activity (CR*) of field-grown crops increased until flowering, then decreased during maturity. This was consistent with data obtained with other methods. AMF inoculation of soybean resulted in significantly higher CR* during the late vegetative and early flowering stages, when destructive sampling concurrently showed higher shoot biomass. The results demonstrated that the root capacitance method could be useful for time course studies on root activity under field conditions, and for comparing single-time capacitance data collected in areas with heterogeneous soil water status.

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Appropriate selection and well-timed measurement of plant developmental, morphological and physiological parameters are essential to maximize efficacy and minimize time consumption of experiments. To select for the most sensitive indicators of drought or salt stress, three independent pot experiments with diverse setups were analysed with 20-20 measured parameters. Parameters of plant growth, phenology and symbiotic interactions, visual stress symptoms, photosynthetic activity, nutrient composition and vitality were studied and the result matrices were evaluated with principal component analysis (PCA). Stress effects manifested in PC1 of two experiments and in PC2 of the third one. Traits assumed to be adequate for stress indication were characterized by high PC1 or PC2 loading values. Beside parameters of biomass production, growth and visible stress symptoms, less evident traits e.g. root electrical capacitance, membrane stability index in roots and leaves, relative water content of leaves and SPAD units were identified.

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Soybean (Glycine max L. Merr.) is regarded worldwide as indisputably one of the most important crops for human food and animal feed. The presence of symbiotic bacteria and fungi is essential for soybean breeding, especially in low-input agricultural systems. Research on the cooperation between different microbial symbionts is a key to understanding how the health and productivity of the plant is supported. The symbiotic effectivity of dual and tripartite symbiotic agents was investigated in two pot experiments on different soybean cultivars with special regard to compatibility. In the Selection experiment, two out of sixteen soybean cultivars (Aliz, Emese) were chosen on the basis of their drought tolerance and used in all the other investigations. In the Compatibility experiment, the compatible coupling of symbiotic partners was selected based on the efficiency of single and co-inoculation with two Bradyrhizobium japonicum strains and two commercial arbuscular mycorrhizal fungal (AMF) products. Significant differences were found in the infectivity and effectivity of the microsymbionts. The rhizobial and AMF inoculation generally improved plant production, photosynthetic efficiency and root activity, but this effect depended on the type of symbiotic assotiation. Despite the low infectivity of AMF, inocula containing fungi were more beneficial than those containing only rhizobia. In the Drought Stress (DS) experiment, co-inoculated and control plants were grown in chernozem soil originating from organic farms. Emese was more resistant to drought stress than Aliz and produced a bigger root system. Under DS, the growth parameters of both microbially inoculated cultivars were better than that of control, proving that even drought tolerant genotypes can strengthen their endurance due to inoculation with AMF and nitrogen fixing bacteria. Root electrical capacitance (CR) showed a highly significant linear correlation with root and shoot dry mass and leaf area. The same root biomass was associated with higher CR in inoculated hosts. As CR method detects the absorptive surface increasing due to inoculation, it may be used to check the efficiency of the microbial treatment.

Soil enhancements such as biochar (BC) are gaining attention as tools to mitigate climate change and also to promote crop growth. However, biochar use can disrupt soil ecosystems by changing the soil’s physical, chemical, and biological properties. The study aimed to determine how biochar influences soil physical changes such as specific surface area (SSA) and water vapor sorption, and how these conditions affect arbuscular mycorrhizal fungal (AMF) hyphae growth and glomalin production. The study analyzed these factors at different plant phenological phases (i.e., flowering, development of fruit, and ripening of fruit and seed) to better understand the changes within the system while varying biochar amounts. The study also investigated the effect of different soil physical and chemical parameters on mycorrhizal hyphae growth and glomalin production. Four treatments were investigated: 0, 0.5%, 2.5%, and 5.0% (w/w) biochar amended silt loam soil planted with pepper. Soil samples were taken at the beginning and weeks 6, 10, and 12 of the study. The amount of adsorbed water vapor increased with an increasing amount of biochar added to the soils. Compared to control, SSA was significantly higher in all biochar amended treatments based on adsorption data, and only in the highest biochar amended soils for the desorption data at the end of the experiment. The presence of AMF in the roots appeared at week 6 of the experiment and the intensity of AMF root colonization increased with the age of plants. The AMF colonization parameters were significantly lower in BC2.5 compared to all other biochar amended soils. The abundance of intraradical AMF structures was highly correlated with several physicochemical soil parameters, such as SSA, the geometric mean diameter of soil aggregate, soil aggregate sizes, or pH. Glomalin production was negatively correlated with SSA, water vapor adsorption, aggregate stability, aggregate size, total nitrogen, potassium, and organic carbon content of the soil, while positive correlation was observed with bulk density. Increased biochar amount resulted in a significant decrease in glomalin production, concurrent with the age of the plants. Our results highlight the great complexity of interactions between soil physicochemical and biological parameters, and the importance of the time of sampling when biochar is used in soil, as the effects of biochar additions on the plant, soil physical characteristics, and soil microsymbionts vary over time.

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A pot experiment was designed to demonstrate that the parallel, single-frequency detection of electrical capacitance (C R), impedance phase angle (Φ R), and electrical conductance (G R) in root-substrate systems was an adequate method for monitoring root growth and some aspects of stress response in situ. The wheat cultivars 'Hombar' and 'TC33' were grown in a rhyolite-vermiculite mixture under control, and low, medium, and high alkaline (Na 2 CO 3) conditions with regular measurement of electrical parameters. The photochemical efficiency (F v /F m) and SPAD chlorophyll content were recorded nonintrusively; the green leaf area (GLA), shoot dry mass (SDM), root dry mass (RDM), and root membrane stability index (MSI) were determined after harvest. C R progressively decreased with increasing alkalinity due to impeded root growth. Strong linear C R-RDM relationships (R 2 = 0.883-0.940) were obtained for the cultivars. Stress reduced |Φ R |, presumably due to the altered membrane properties and anatomy of the roots, including primarily enhanced lignification. G R was not reduced by alkalinity, implying the increasing symplastic conductivity caused by the higher electrolyte leakage indicated by decreasing root MSI. F v /F m , SPAD value, GLA, and SDM showed decreasing trends with increasing alkalinity. Cultivar 'TC33' was comparatively sensitive to high alkalinity, as shown by the greater relative decrease in C R , SDM, and RDM under stress, and by the significantly lower MSI and higher (moderately reduced) |Φ R | compared to the values obtained for 'Hombar'. Electrical root characterization proved to be an efficient non-intrusive technique for studying root growth and stress responses, and for assessing plant stress tolerance in pot experiments.