Water Use Regulation in Pre- and Post-Freeze Avicennia germinans Populations Reveal Mangrove Ecosystem Resilience

Mangrove forests provide critical ecosystem services, including coastline stabilization, habitats for marine life, and carbon storage. However, climate change introduces extreme temperatures and precipitation shifts that threaten their survival. The ability of mangroves to regulate their water use efficiently through plasticity in their hydraulic strategies will determine their resilience and capacity for range expansion. On the Texas coast, the northernmost range of the black mangrove Avicennia germinans, we investigated the short-term physiological responses to environmental fluctuations across the 2024 growing season, comparing juvenile mangroves that survived winter storm Uri in 2021 and saplings that established after the freeze event. From late spring to early fall, we measured leaf water potential, transpiration, carbon assimilation, and stomatal conductance and analyzed their relationships with temperature, vapor pressure deficit (VPD), photosynthetically active radiation (PAR), and salinity. We found that water use efficiency (WUE) was positively associated with variability in VPD at low VPD stress. A. germinans optimized carbon uptake while minimizing water loss during relatively higher VPD months through strategic regulation of stomatal conductance. Age class/disturbance history played only a small role in the mangroves’ hydraulic responses to environmental stress. No significant WUE differences were observed between saplings and juveniles, suggesting consistent resilience across age classes and disturbance history. These findings indicate that A. germinans can maintain physiological stability under fluctuating conditions, supporting their long-term survival in a warming climate. Their ability to recover after extreme events, such winter storm Uri, underscores the potential for continued range expansion and mangrove ecosystem persistence in the Gulf of Mexico.