FIGURE 4 Linear regression analysis showing the relationship between RCS and root growth, root metabolic costs, and aboveground growth under drought stress. (A) Total root length, (B) root dry weight, (C) root tissue density, (D) root respiration at 6 cm from the root tip, (E) root respiration at 9 cm from the root tip, (F) root respiration at 12 cm from the root tip, (G) leaf water potential, (H) leaf relative water content, and (I) the ratio of variable to maximum fluorescence (F v/F m ).