5.2.8Effects of Heat Stress on Root

5.2.8Effects of Heat Stress on Root Water RelationsAlthough effects of heat stress on various shoot water relations parameters isrelatively commonly examined (e.g., [17,18,25,26], Tables 5.1 and 5.2, andreferences therein), few studies have investigated effects of heat stress on rootwater relations (Tables 5.1 and 5.2) [27]. For example, Liu and Huang [59] observeddecreases in root water content, and Lal [58] observed decreases in root wateruptake, with heat stress. BassiriRad et al. [50], Dodd et al. [53], and Morales et al.[39] observed decreases in root hydraulic conductivity with heat stress. Importantly,decreases in shoot or root water status, root hydraulic conductivity, or leaf stomatalconductance typically do not occur (or are small) initially during heat stress, or arenot observed during moderate heat stress (i.e., modest versus severe temperatures);only after extended heat stress or during severe temperatures do such decreasestypically occur (Tables 5.1 and 5.2, and references therein). These results indicatethat root, and hence shoot, water stress is not caused by short-term moderate?temperature heating, but that longer duration heating or more-severe temperaturescan cause root water stress. Increases in root water stress with heat stress might becaused by direct temperature effects or indirectly by increased water demand fromthe shoot. In either case, heat-related decreases in root hydraulic conductivity orroot water status will likely impact the shoot, causing stomatal closure, and so on.