Electrical capacitance (EC) measurement in a root–soil system is a suitable technique for the rapid in situ determination of root mass and active root surface area. Pot experiments were designed to test the applicability of the EC method for monitoring of root water uptake activity. In Experiment 1, cucumber and bean plants were grown; half of them were inoculated with Funneliformis mosseae arbuscular mycorrhizal fungi (AMF) beside the non-infected controls. Root EC and daily transpiration (DT) were monitored during plant ontogeny. In Experiment 2, temporal changes in root development and transpiration of four soybean cultivars (cv. Bagera, Martina, Aliz, Emese) were studied.

Phenology-dependent changes of root EC and DT (related to root water uptake) proved to be similar, as they showed increasing trends from seedling emergence to the beginning of flowering (cucumber: day 38; bean: day 33), thereafter decreased continuously during yield formation. A few days after AMF infection and root colonization (on days 18–23), root EC and DT of AMF-infected plants became significantly higher than those of their non-infected counterparts, and the relative increment of the measured parameters was greater for the more mycorrhizal-dependent bean cultivar (75%) compared to that of cucumber (15%). AMF inoculation resulted in significant enhancement in shoot dry mass of cucumber (29%) and bean (69%), and in root dry mass of bean (37%).

Characteristic changes in root extension dynamics for various soybean cultivars were detected by measuring EC. Trends of EC were in conformity with the temporal changes of DT in this case, too. Both parameters increased continuously until the beginning of flowering (days 40–56 for different cultivars) with different intensity depending on plant age, then remained nearly constant. At the end of the experiment (day 60) EC and DT of Bagera, Emese, Aliz and Martina showed a significantly increasing order (EC: 2.39–3.05 nF; DT: 116–147 ml). Biomass weighing revealed similar rank and significance of shoot dry mass for the four cultivars (13.24–17.71 g), nevertheless the root dry mass of Aliz proved to be fully equal to those of Martina (5.48 g). Due to the greater shoot of cultivar Martina, its transpiration rate – thus root water uptake activity – was higher as compared to Aliz, which disparity was clearly indicated by the significantly higher root EC for Martina.

Our results suggest that EC measurement can be an adequate method for in situ monitoring of root growth and water uptake activity, for studying the disparities in root development among various plant cultivars, and for detection of environmental factors influencing root functionality. By supplementing the conventional methods, this simple and rapid technique may be profitable for a wide scope of plant investigations, thus its further development is obviously reasonable.

Keywords: root electrical capacitance, in situ root investigation, mycorrhizal colonization, transpiration, water uptake