Hydroclimate, Thallus Dynamics and Multi-Seasonal Reproductive Phenology in Mannia triandra

Poikilohydric plants are closely coupled to atmospheric moisture, but their responses to hydroclimate may differ among life cycle phases. We investigated vegetative and reproductive dynamics of the thallose liverwort Mannia triandra in Gesäuse National Park, Austria, using surveys at approximately 14-day intervals over one annual cycle in two quantitatively monitored populations, combined with continuous near-surface temperature and relative humidity measurements. We quantified relative thallus area change, frost exposure, carpocephalum emergence, and post-emergence development. At the site × survey interval scale, median relative thallus area change declined with increasing 14-day mean vapour pressure deficit (standardised β = -0.58, 95% CI [-1.00, -0.16]), whereas temperature had no independent association. Cold-season dynamics did not support a simple frost damage response: longer frost duration was not associated with greater thallus loss, and frost exposure did not increase the probability of negative area change. Reproductive development was multi-seasonal. Carpocephala occurred on thalli persisting from the previous growing season, newly recorded carpocephala were concentrated in early spring, and subsequent development progressed seasonally towards maturation and dehiscence. These findings suggest a potential carry over across life cycle phases: short-term atmospheric drying was reflected in vegetative thallus dynamics, while subsequent reproductive development occurred on gametophytic tissue that persisted across seasons.