High resolution imaging to assess oilseed species’ root hair responses to soil water stress

Abstract

An imaging method was developed to evaluate crop species differences in root hair morphology using high resolution scanners, and to determine if the method could also detect root hair responses to soil water availability. High resolution (1890 picture elements (pixels) cm⁻¹) desktop scanners were buried in containers filled with soil to characterize root hair development under two water availability levels (−63 and −188 kPa) for canola (Brassica napus L. cv Clearwater), camelina (Camelina sativa L. Crantz cv Cheyenne), flax (Linum usitatissimum L. cv CDC Bethune), and lentil (Lens culinaris Medik. cv Brewer). There was notable effect of available moisture on root hair geometry (RHG). At −188 kPa, length from the root tip to the root hair initiation zone decreased and root hair length (RHL) became more variable near the root hair initiation zone as compared to −63 kPa. For the response of primary axial RHL, significant main effects were present for both water availability (P < 0.05) and species (P < 0.0001); lateral RHL showed a significant main effect for both water availability (P < 0.05) and species (P < 0.01) as well. For both primary axial and lateral root hair density (RHD), there was a significant effect of species (P < 0.0001), but no significant response to water availability. No water availability x species interaction was present in any case. Low available water reduced RHL in both primary axial and lateral roots. The change in RHL due to water availability was most evident in canola and camelina. Additionally, those with greater RHL $\left( {\text{canola} = \text{camelina} > \text{flax} = \text{lentil}} \right)$ had lower RHD $\left( {\text{canola} = \text{camelina} < \text{flax} < \text{lentil}} \right)$ in primary axial roots and a similar trend was found in lateral RHL. Both water and species had a significant effect on primary axial root surface area (RSA) (P < 0.05) but no significant effect was found for lateral RSA. For primary axial RSA the longest and most dense root hair had the greatest RSA. This novel approach to in situ rhizosphere imaging allowed observation of species differences in root hair development in response to water availability and should be useful in future studies of rhizosphere interactions and crop water and nutrient management.