08/15/2018

Warmer Temperatures Lengthen Growing Season, Increase Plants’ Vulnerability to Frost

Experimental warming treatments show how peatland forests may respond to future environmental change.

The Science

A warming experiment in a boreal peatland forest in Minnesota resulted in plants greening up earlier in spring, and staying green longer in autumn, indicating potential extension of the growing season by up to 3-6 weeks by the end of the current century. However, as plants greened up earlier, some also lost their winter hardiness: this exposed these individuals to damage when a spring frost hit in early April 2016.

The Impact

Recent warming trends have been shown to lengthen the growing season in temperate and Boreal ecosystems. Whether this trend will continue under future environmental conditions depends on whether other factors—such as day length (photoperiod)—become more limiting. This study resolves that debate by showing that with warming of up to +9°C above ambient, vegetation responses to increased temperature were linear, and not limited by day length.

Summary

The SPRUCE experiment is applying warming (0 to +9°C above ambient) and CO2 (ambient and elevated) treatments to intact communities of mature vegetation in a Boreal black-spruce sphagnum bog in the upper Midwest USA. Digital cameras mounted in each of the 10 experimental plots show that warming treatments linearly extend the period of vegetation activity in both spring and autumn. There was little evidence that daylength (photoperiod) limited these phenological shifts. The camera observations are consistent with ground observations of the timing of flowering and growth by a variety of bog plant species. In spring 2016, unusually warm weather in March was followed by extreme cold in early April. Vegetation in the warmest chambers (+6.75, +9.0 °C) suffered severe frost damage as the temperature dropped to -3 °C, indicating a premature loss of frost hardiness. By comparison, vegetation in the cooler chambers (0, +2.25, +4.5 °C) was undamaged, despite experiencing dramatically colder temperatures (up to -15 °C). Thus, because phenological transitions – including loss of frost hardiness – appear to be temperature-driven, rather than cued by photoperiod, vegetation may be exposed to greater risk of frost damage in a warmer world. These in situ experimental results are of particular significance because Boreal forests have a circumpolar distribution and play a key role in the global carbon cycle.

Principal Investigator(s)

Andrew Richardson
Northern Arizona University
[email protected]

Funding

This research is based upon work supported by the US Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for DOE under contract DE-AC05-00OR22725. Support for PhenoCam has come from the National Science Foundation (EF-1065029, EF-1702697).

References

Richardson, A.D., K. Hufkens, T. Milliman, D.M. Aubrecht, M.E. Furze, B. Seyednasrollah, M.B. Krassovski, J.M. Latimer, W.R. Nettles, R.R. Heiderman, J.M. Warren and P.J. Hanson. “Ecosystem warming extends vegetation activity but heightens vulnerability to cold temperatures.” Nature 560 368-371 (2018). [DOI: 10.1038/s41586-018-0399-1].