Regional projection of winter frost risk on a legume crop due to warming in a temperate climate

Abstract

International audiencePea (Pisum sativum L.) is an important annual legume crop grown in temperate regions for its high seed nitrogenconcentration and environmental benefits. In the recent climate warming, a subtle evolution of the winter cropfrost risk was observed: a paradoxical increase of frost stress events and a frost stress intensity decrease (Castel etal. 2017). Such results are questioning the future winter frost risk for peas. We assessed the winter frost damageevolution along 2006 to 2100 in Burgundy-Franche-Comté (a French region - western part of Europe). The approachis based on the combination of i) a dynamical downscaled climate data of two RCP trajectories (4.5 and 8.5) (Boulardet al. 2016) and ii) a winter frost stress model calibrated and validated for pea (using varieties with different frostresistance levels and acclimation rates) (Lecomte et al. 2003; Castel et al. 2017). Our results show that frost risk willnot disappear with warming climate (Fig. 1). Compared to the historical period (1980-2005), the frost risk for the peavariety with a frost resistance level of -13°C will increase along the near future period (2020-2050) for RCP 8.5: withan increase of both the median and the spread of the cumulative frost degree days (Fig. 1B). With a highest warmingalong the far future period (2070-2100) for RCP 8.5, the results show a significant decrease of the cumulative frostdegree days compared to the near future and the historical periods, but the frost risk will persist (Fig. 1B). It suggeststhat frost risk will significantly increase for an extended winter warming below + 2°C, while it will decrease whenthis threshold will be overpassed (Fig. 1). The figure 2 depicts the evolution of the two components of the froststress with warming: intensity and number of the frost stress events. The increase of the cumulative frost degreedays in the near future period (2020-2050) for RCP 8.5 is determined by the increase of frost stress events intensity(Fig. 2A). By contrast the number of frost stress events slightly decrease during this period (Fig. 2B). This resultdiffers from the past evolution of these components with the observed warming from 1961 to 2018 (Castel et al.2019) and suggests a change in the winter frost risk structure. For the end of the century (period 2070-2100) andfor the RCP 8.5, both intensity and number of the frost stress events will decrease (Fig. 2). Finally the projectionsshow a contrasted geography of the frost risk evolution. This geographic trend depends on the frost resistance leveland acclimation rate of the pea variety. Our results seem to confirm subtle evolutions of winter climate warmingdynamics revealed by the change in the pea crop frost risk structure. Moreover, this work provides leads for breedingand crop management techniques strategies for winter pea adaptation to climate change to avoid the detrimentaleffects of frost while taking advantage of the potential of this crop