Beyond poikilothermy: Habitat and sex shape thermoregulation and its impact on resilience to heat in the liverwort Marchantia inflexa

Premise: Elevated air temperatures subject plants to heat stress, impairing their physiology and productivity. Because most studies on heat resilience have focused on ambient air rather than tissue temperatures, our understanding of how plants perceive and respond to heat remains limited. We evaluated how tissue temperature and thermoregulation varied during heat stress, quantified the damage and recovery of photosystem II (PSII), and related thermoregulation to recovery. Methods: We grew male and female plants of the thalloid liverwort Marchantia inflexa that originated from two contrasting habitats (streamsides and roadsides) in common conditions to capture natural variation in temperature parameters; 42 plants were placed in an oven for 45 min at 55°C, and tissue temperatures were recorded every 10 s. Thermoregulation was assessed as mean fluctuations of tissue temperatures, and damage and recovery were assessed using PSII efficiency. Results: Thallus temperatures mirrored thermoregulatory patterns; they were higher on roadsides and in females and more variable in males. Although recovery patterns across habitats aligned positively with thermoregulation, streamside males exhibited the opposite pattern. Conclusions: We posit these patterns reflect stronger selection for thermoregulation in plants on roadsides than on streamsides, and stronger selection in females to optimize photosynthesis to support maturing offspring.