Indirect monitoring of root activity in soybean cultivars under contrasting moisture regimes by measuring electrical capacitance

Abstract

The applicability of root electrical capacitance (EC) measurement for in situ investigation of root activity and drought tolerance was tested in soybean cultivars. Well-watered and drought-stressed plants were grown in pots with repeated EC measurements, followed terminally by harvest to determine root dry mass (RDM), shoot dry mass (SDM), root/shoot ratio (RSR) and leaf area (LA). EC measurement showed the cultivar differences in root growth and biomass production. EC increased till the beginning of flowering, then became nearly constant. Terminal EC was highly correlated with RDM for non-stressed (R 2 = 0.844) and stressed plants (R 2 = 0.936). Drought reduced the EC of cultivars by 28.8–50.5 %, consistently with the corresponding changes of SDM (25.5–49.1 %) and LA (23.6–51.5 %), but considerably exceeded the loss of RDM (12.6–47.3 %) in some cultivars. The reason is drought increased the RSR (by 3.9–21.9 %), leading to decreased water uptake, and thus EC per unit of RDM. This was confirmed by the significantly decreased slope of EC–RDM regression line from 0.437 to 0.317 nF g−1 RDM calculated for well-watered and drought-stressed plants, respectively. As EC referred to root uptake activity, it was better indicator of the actual root status than RDM. EC measurement was adequate for monitoring the cultivar-specific differences in root growth and for estimation of biomass loss caused by drought. By supplementing the conventional methods, this in situ technique could be useful for various fields of agriculture, including cultivar selection or stress tolerance studies.