Dose-dependent stress responses of the aquatic moss Taxiphyllum barbieri under acute X-ray exposure: implications for environmental risk assessment.

Freshwater ecosystems may experience acute oxidative stress following accidental or localized release of ionizing radiation. In these environments, the responses of aquatic bryophytes remain poorly understood. We investigated dose-dependent physiological, biochemical, and structural responses of the aquatic moss Taxiphyllum barbieri after acute X-ray exposure (1, 10, and 30 Gy), aiming to investigate dose-dependent physiological responses and identify potential functional resilience thresholds. Photosynthetic performance, pigment composition, antioxidant activity, and structural traits were assessed over a 63-day recovery period using an integrated multilevel approach. Low-dose irradiation (1 Gy) stimulated net carbon assimilation, PSII efficiency, electron transport rate, and pigment content, indicating a low-dose stimulatory response consistent with hormesis. In contrast, higher doses (10-30 Gy) progressively constrained photosynthetic performance and pigment concentration, while inducing persistent alterations in phenolic metabolism and shoot architecture. Multivariate analyses showed marked early divergence from controls followed by partial physiological stabilization at 63 days, despite incomplete structural recovery. These findings highlight the capacity of T. barbieri to maintain key functional processes under acute oxidative stress and support the inclusion of ecophysiological endpoints in ecological risk assessment frameworks addressing episodic radiation exposure in freshwater systems.