3.2 Root hair traits in maize
We further computed the root hair length and density for Tak Fa 1, Tak Fa 2 and Tak Fa 3 under all four treatments (Figure 3, columns a,b,c). In each replicate, which had more than one image, we calculated the mean root hair length as the mean of all root hairs from all images and the density as the total number of root hairs from all images divided by the total length of the root edge from all images. Despite root hairs in the Tak Fa 3 control group being on average 384.1μm long and thus, 73.7μm and 58.0μm longer than Tak Fa 1 control and Tak Fa 2 control, respectively, the difference was not statistically different. We further did not observe significant differences in density between all three genotypes, despite Tak Fa 2 being 69% and Tak Fa 3 44% denser than Tak Fa 1. We did not observe any significant differences in density between all treatments to the control group in Tak Fa 1 and Tak Fa 3. Only in Tak Fa 2 we observed a decrease in root hair length by 112.0μm under reduced nitrogen with weak significance (p =0.057).
To show how our results compare to standard manual root hair measurements, for each image we correlated the mean root hair lengths of all automatically extracted root hairs to the mean of the five representative root hairs (Figure 3, column d). For all three genotypes we obtained high correlations (Tak Fa 1:R 2=0.78, p <.001; Tak Fa 2:R 2=0.85, p <.001; Tak Fa 3:R 2=0.72, p <.001). Similarly, we correlated root hair density from the automatic method to manual measurement and obtained strong correlations as shown in Figure 3, column e (Tak Fa 1: R 2=0.66,p <.001; Tak Fa 2: R 2=0.46,p <.001; Tak Fa 3: R 2=0.38,p <.001).