Plant responses to simulated and naturally variable winter temperatures: a within vs. among species comparison

Background/Question/Methods

Variation within versus among plant species’ responses to freezing stress may be an important factor influencing species composition changes in the face of climate change. We conducted a winter warming experiment and a transplant experiment to explore variation within and among species’ freezing responses. Eight ecotypes of Arrhenatherum elatius from 4 European countries and 8 grassland species (n=6 per ecotype and species) from Germany were used in the experiments. In the winter warming experiment, plants were acclimated to winter temperature and photoperiod in a growth chamber. In February, plants were thawed for 0, 2 or 6 days at 10 °C, before being frozen to ‐10 °C for 1 day, simulating predicted increases in winter temperature fluctuations. Plants were then grown in a greenhouse at 10‐15 °C for three weeks and their final biomass quantified. In the transplant experiment, plants were planted at two different altitudes around Bayreuth, Germany in the fall to expose the plants to different mean winter temperatures. Mean soil temperature was 1.44°C  lower and soil frost lasted 17 days longer in the upland site than in the lowland site. All plants were transplanted into a common garden in March. Biomass was measured in June.

Results/Conclusions

In the winter warming experiment, frost after the 6 day thaw period reduced green biomass by 56% while dead leaf biomass increased by 62% compared with the control. Within-species variance was higher than among-species variance in green biomass and dead leaf biomass. In the transplant experiment plants that overwintered in the higher altitude site had 39% lower biomass than the plants from the lower latitude site. Within-species biomass variance was as great as among-species variance with respect to upland and lowland sites. In both experiments within-species variability was mainly caused by the Spanish ecotypes which showed greater sensitivity to frost after the 2 day thaw as well as after overwintering at the higher altitude. The results indicate that variation in stress responses within a single plant species can be greater than variation among different plant species stemming from the same environment. This intraspecific variation should be considered in attempts to model plant community responses to climate change. The data also further imply that increased variability in winter temperature conditions can result in considerably higher frost damage in plants.