Precipitation predictability shapes plant growth trajectories, climate sensitivity, and fitness pathways within and across generations

Katja Springer, Patrick S. Fitze, Lucrezia Laccetti, Guillermo Mercé, Martí March-Salas

Environmental predictability is increasingly altered under climate change, particularly through shifts in the temporal structure and autocorrelation of climatic variables. In plants, the interaction between precipitation predictability and temporal climatic variation can shape the magnitude, timing, and trajectory of growth, with cascading effects on phenological coordination, and ultimately on reproductive success, both within and across generations. Yet, the temporal dynamics and the evolutionary consequences arising from changes in predictability remain poorly understood. To address this, we experimentally manipulated precipitation predictability (i.e., temporal autocorrelation among precipitation events) over four generations of the crop legume Onobrychis viciifolia, and assessed its effects on temporal growth dynamics, fitness pathways, and climate sensitivity to variation in mean temperature and precipitation. We observed that less predictable regimes promoted faster growth trajectories, with treatment differences emerging early in the season and intensifying over time, while more predictable regimes exhibited slower, more gradual growth. Growth responses were also strongly shaped by the interaction between natural climatic variation and predictability treatments, with stronger sensitivity to precipitation under lower predictability and comparatively weaker temperature sensitivity. Furthermore, climatic sensitivity sharply increased across generations, indicating dynamic transgenerational responses to environmental variation amplified under less predictable conditions. Contrary to the common assumption that transgenerational responses build up gradually, we found that climatic sensitivity, to both temperature and precipitation, remained approximately stable across the first three generations and then sharply emerged in the fourth. Finally, structural equation modelling revealed that precipitation predictability reshaped plant fitness indirectly by altering growth rates and phenological development. Together, our results establish that environmental predictability fundamentally shapes the magnitude and temporal dynamics of plant growth response to short-term climatic fluctuations, with cascading effects on fitness pathways and the evolutionary trajectories of plant populations.