Martinez-Vilalta, J. | bioRxiv Science

bioRxiv2026

The PSInet Plant Water Potential Database: advancing new perspectives on plant water status, traits, and hydraulic processes

Water potential gradients drive water flow within and between soils and plants, and the internal plant water potential controls a wide range of physiological processes including photosynthesis, growth, and mortality. Notwithstanding this clear relevance for many critical aspects of ecosystem function, water potential data have historically been relatively inaccessible and unnetworked. The absence of a centralized repository for plant water potential time series limits our ability to integrate a wealth of ecophysiological information from other networks and from remote sensing. Closing this gap is necessary to address unresolved questions about plant responses to drought and heat stress, and to make confident predictions about plant and ecosystem function in a warming world. Here, we introduce the PSInet database -- a global collection of plant water potential time series from 285 datasets representing 523 species. We present the workflow that guided database development and evaluate its key features. Through a series of preliminary analyses, we then highlight the potential of the PSInet database for applications including: a) advancing plant water use strategy frameworks; b) disentangling the impacts of soil versus atmospheric drought stress; c) assessing the long-held assumption of pre-dawn equilibration of ecosystem water potential; d) understanding the risk of drought-driven mortality; and e) benchmarking remote-sensing data products and land-surface models.

plant biology↗

bioRxiv2025

Living on the edge: warmer climate reduces leaf thermal safety margins and causes gas exchange decoupling in Mediterranean shrubs

Global warming pushes plants close to their leaf thermal limits, altering carbon uptake, growth and survival. Therefore, investigating leaf thermal tolerance adjustment is essential to understand future vegetation dynamics, especially in high-risk Mediterranean shrubs facing hot and dry summers. We measured dark-adapted leaf fluorescence (Fv/Fm), thermal thresholds (Tcrit, T50, Tmax), optimal assimilation temperature (Topt), thermal safety margin (TSM), leaf and air- temperatures (Tair, Tleaf) and gas exchange (A, gs, E) in six shrub species in six sites along a climatic gradient in Catalonia, Spain. We found that Topt increased as conditions warmed, while Fv/Fm and Tmax showed quadratic responses decreasing in the warmest sites. Hence, TSM declined and approached 0 at the hottest sites, indicating that shrubs were operating close to their thermal limits. Warmer Tair under high levels of solar radiation raised Tleaf, though some species maintained Tleaf < Tair during daytime, suggesting a passive or active leaf cooling at high temperatures exceeding solar energy. Moreover, E remained high despite low A at higher Tleaf, revealing a decoupling of gas exchange at high temperatures. Incorporating leaf thermal tolerance adjustments and gas exchange decoupling at extreme temperatures into vegetation models could improve predictions of shrub function and dynamics under warmer climates. HighlightOur study highlights that Mediterranean shrubs have limited capacity to adjust leaf thermal tolerance at warmer sites, resulting in narrower thermal safety margins. The decrease in leaf temperatures through evaporative cooling may not compensate for the more frequent and intense heatwaves, leading to irreversible damage. These findings highlight the importance of incorporating leaf thermal tolerance adjustment and gas exchange decoupling into future vegetation models.

ecology↗