Maurice, I thought Ken raised an interesting question. When I looked at Arisumi's paper it does not appear he lowered the temperature at night. This could affect net photosynthesis (although I have a feeling I read somewhere that this is not necessarily now thought to always the case, it used to be we were told that night temperatures had to be lower so that respiration rate didn't equal or exceed photosynthesis otherwise the plants would decline or at the very least not grow).
In nature the night temperatures are almost always going to be less than day temperatures. Anyway, disregarding that, are you basing your assessment regarding detrimental temperature on air or soil temps since, as Ken surmised, with the potted plants in Arisumi's study they would both have been the same 24/7?
Several articles note different effects between high air and high soil temps. Here is one abstract (non-daylily) for example:
"High air or soil temperature is a major factor limiting growth of cool-season grasses during summer months in the transition zone and warm climate regions. Knowledge of how cool-season grasses respond to differential high air and soil temperatures would facilitate our understanding of heat tolerance mechanisms. The objectives of this study were to compare the influence of air versus soil temperature on turf quality, physiological activities, and root growth of creeping bentgrass (Agrostis palustris Huds. cv. Penncross), and to investigate whether shoot and root growth could be improved by reducing soil temperature at high air temperatures. Shoots and roots were exposed to four air/soil temperature regimes (20/20, 20/35, 35/20, and 35/35°C) for 56 d in growth chambers. High soil (20/35°C) and high air/soil (35/35°C) temperatures reduced canopy photosynthetic rate (Pn), turf quality, and the number of roots. High air/soil temperatures also reduced photochemical efficiency (Fv/Fm). The adverse effects of high air/soil temperatures were more pronounced than either high soil or air temperature alone for turf quality, Fv/Fm, Pn, and root growth. High soil temperature was more detrimental than high air temperature. Lowering soil temperature at high air temperatures (35/20°C) increased root growth, canopy Pn, Fv/Fm, and turf quality, compared with high soil temperature at low or high air temperatures (20/35 and 35/35°C). The results demonstrated that roots mediated shoot responses to high temperature stress in creeping bentgrass, and that reducing root-zone temperature could help maintain quality creeping bentgrass under supraoptimal ambient temperatures."
https://dl.sciencesocieties.or...
