Within-species variability and past climatic experience influence the response to late spring frost in five common temperate grass and tree species

Background/Question/Methods

Late frost events in spring are climatic extremes with high ecological and evolutionary importance. Their magnitude is projected to remain constant despite climate warming. Damage to plants may even increase because of earlier phenological development.
We explored the late-frost sensitivity of four common European grass species and one dominant deciduous tree species and investigate whether these species exhibit local adaptations to late frost on a continental scale and whether past climatic experience influences late frost sensitivity.
Ecotypes of the grass species Arrhenatherum elatius, Alopecurus pratensis, Festuca pratensis, and Holcus lanatus from Spain, Italy, Bulgaria, Hungary, Sweden, and Germany and two-year old seedlings of the tree species Fagus sylvatica from six origins in Germany and Bulgaria were exposed to late frost after warming (+1.5°C) and extreme drought manipulations in the preceding growing season in a full-factorial common garden experiment.

Results/Conclusions

Late frost reduced the productivity of the grasses on average by 20%. Ecotypes differed in their late-frost sensitivity in three of the four species and local adaptations to late frost were identified. Previous exposure to drought and warming caused differences in late-frost sensitivity in some cases.
Late frost led to leaf injury and reduced height growth (-7%) in Fagus sylvatica. Ecotypes differed in their late frost sensitivity already at a regional scale and local adaptation was detected. At the continental scale, the Bulgarian provenances showed reduced height growth (-17%) while the German provenances did not exhibit growth reduction. The continuous warming treatment prevented late frost damage while height growth declined by 19% in the reference temperature treatment. This surprising finding was attributed to advanced leaf maturity in the warming treatment.
The impact of late frost events may increase in a warmer world due to an earlier onset of growing and no change in timing of late frost events. Late frost damage strongly depends on timing: An event that injures leaves immediately after leaf flushing appears negligible a few days earlier or later, thereby complicating projections. In addition, the history of climatic exposure can alter the performance of plants, possibly through epigenetic mechanisms. Based on the complex response pattern observed, a maximization of genetic diversity is proposed as a promising adaptation strategy against adverse effects of climate change.