Larger diurnal temperature range undermined later autumn leaf senescence with warming in Europe

Aim: Climate change regulates autumn leaf senescence date (LSD), exhibiting a strong phenological control of plant carbon uptake. Unlike the delaying effect of daily mean temperature (T-mean) on LSD, the impact of warming asymmetry in daytime and nighttime, as evidenced by variations of the diurnal temperature range (DTR), remains elusive. The objectives of this study were to investigate physiological and ecological impacts of DTR on LSD using long- term in situ observations and to predict the future trends of LSD under warming.Location: Europe.Time period: 1950-2015. Major taxa studied: Plant phenology. Methods: We used partial correlation analysis, multiple linear regression and ridge regression to explore the impacts of DTR on LSD. To quantify the importance of potential drivers of LSD, we trained random forest models and applied the SHapley Additive ex-Planations method to isolate the marginal contributions of each predictor on LSD. For LSD modelling and projection, we first evaluated two temperature-driven LSD models [i.e., cooling-degree- day (CDD, without DTR effect) and day- night-temperature CDD (DNCDD, with DTR effect)], then applied them to predict future LSDs.Results: We found that observational increases in T-mean and DTR had contrasting effects on LSD. Increased T-mean delayed the LSD, whereas larger DTR overall had an advancing effect. Considering the DTR effect, the T-mean sensitivity of LSD was 14% lower than presently estimated (2.4 vs. 2.8 days degrees C-1). Warming asymmetry-related drought stress and plant functional traits (i.e., plant isohydricity and water- use efficiency) potentially explained the advancing effect of DTR on LSD. We found that current projections of future LSD are overestimated because the DTR effect is discounted, suggesting the need for an adequate understanding of how plant phenology responds to warming asymmetry.Main conclusions: Our findings highlight the importance of DTR in controlling LSD variations with an advancing-dominant effect and call for the improvement of phenology modelling incorporating the DTR effect. Given that DTR showed a globally narrowing trend over the last several decades, more efforts are needed to understand the potential ecological impacts of warming asymmetry and vegetation response to climate change.

Automated summary

This study investigates the impacts of diurnal temperature range (DTR) on autumn leaf senescence date (LSD) and predicts future trends of LSD under warming. The results show that increased DTR has an advancing effect on LSD, whereas increased mean temperature delays LSD. These findings highlight the importance of considering DTR in phenology modeling and call for a better understanding of the ecological impacts of warming asymmetry.