Electrical Capacitance versus Minirhizotron Technique: A Study of Root Dynamics in Wheat-Pea Intercrops

Abstract

This study evaluated the concurrent application and the results of the root electrical capacitance (C_R) and minirhizotron (MR) methods in the same plant populations. The container experiment involved three winter wheat cultivars, grown as sole crops or intercropped with winter pea under well-watered or drought-stressed conditions. The wheat root activity (characterized by C_R) and the MR-based root length (RL) and root surface area (RSA) were monitored during the vegetation period, the flag leaf chlorophyll content was measured at flowering, and the wheat shoot dry mass (SDM) and grain yield (GY) were determined at maturity. C_R, RL and RSA exhibited similar seasonal patterns with peaks around the flowering. The presence of pea reduced the maximum C_R, RL and RSA. Drought significantly decreased C_R, but increased the MR-based root size. Both intercropping and drought reduced wheat chlorophyll content, SDM and GY. The relative decrease caused by pea or drought in the maximum C_R was proportional to the rate of change in SDM or GY. Significant linear correlations (R²: 0.77-0.97) were found between C_R and RSA, with significantly smaller specific root capacitance (per unit RSA) for the drought-stress treatments. C_R measurements tend to predict root function and the accompanying effect on above-ground production and grain yield. The parallel application of the two in situ methods improves the evaluation of root dynamics and plant responses.

Keywords: cereal–legume intercrops; drought stress; grain yield; in situ root methods; root growth.

Figure 1

Changes in the apparent root electrical capacitance (C_R*; in nanofarads, nF) of wheat with plant age (DAP: days after planting) under (a) well-watered and (b) drought-stressed conditions. Bars show standard deviations (n = 30). Treatment codes: N: wheat cv. Mv Nádor; K: cv. Mv Kolompos; C: YQCCP population; 0: wheat sole crop; P: wheat–pea intercrop; (+): well-watered; (–): drought-stressed.

Figure 2

(a,d) Root length (RL), (b,e) root surface area (RSA) and (c,f) average root diameter (ARD), obtained by minirhizotron image analysis, in relation to plant age (DAP: days after planting) under well-watered (a–c) and drought-stressed (d–f) conditions. RL and RSA are sums from the three soil depths (20, 50 and 80 cm), ARD is a weighted average. For treatment codes, see Figure 1.

Figure 3

Maximum root length (RL) at 20, 50 and 80 cm soil depths, obtained by minirhizotron image analysis, under (a) well-watered and (b) drought-stressed conditions. For treatment codes, see Figure 1.

Figure 4

(a) Leaf chlorophyll content as SPAD value (mean ± SD; n = 15), (b) total shoot dry mass (SDM) and (c) total grain yield (GY) under well-watered (white columns) and drought-stressed (grey columns) conditions. For treatment codes, see Figure 1.

Figure 5

Percentage changes in the apparent root electrical capacitance (C_R*), total shoot dry mass (SDM) and total grain yield (GY) of wheat and in the root surface area (RSA) caused by (a) pea intercropping and (b) drought stress. In the case of C_R* and RSA, maximum values (detected at the wheat flowering stage) were used for calculation. For treatment codes, see Figure 1.

Figure 6

Linear relationships between the apparent root electrical capacitance (C_R*) and root surface area (RSA) in well-watered (filled symbols and solid lines) and drought-stressed (empty symbols and dashed lines) treatments. Only data obtained up to the flowering stage of the wheat genotypes were considered, and were pooled over the two pea treatments. For treatment codes, see Figure 1.