Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2017
Publication Date: 9/17/2017
Citation: Goslee, S.C., Gonet, J.M., Skinner, R.H. 2017. Freeze tolerance of perennial ryegrass and implications for future species distribution. Crop Science. 57:2875-2880. https://doi.org/10.2135/cropsci2017.02.0135.
Interpretive Summary: Perennial ryegrass is the most commonly planted forage grass in the world. Although it is both productive and palatable to grazing animals, it is damaged by cold temperatures and not useful in northern regions with severe winters. We grew thirteen cultivars of perennial ryegrass, many sold for use in cold areas, and froze them briefly to -10 C, -15 C, or -20 C, and counted the surviving plants after they recovered. At the coldest temperature between half and all of the plants died, depending on cultivar. Some varieties were much more cold tolerant than others. Using the temperature at which perennial ryegrass died, and predicted climate in the immediate future and long-term future, we found that previously, this forage grass would freeze to death at least 10% of the time in the northeastern United States, but that by 2070-2099, up to three-quarters of the region would no longer be too cold for long-term perennial ryegrass survival. Winter survival is more complicated than simply extreme cold, but these results demonstrate that perennial ryegrass has successfully been bred to tolerate colder winters, and that climate change will increase the suitable area for this very important forage plant.
Technical Abstract: Winter hardiness is one of the factors limiting the use of the palatable and productive cool-season forage grass Lolium perenne L, perennial ryegrass, in the northeastern United States. We performed a screening study to compare freeze tolerance, one component of winter hardiness, among thirteen commercial cultivars of perennial ryegrass. We raised three sets of ten seedlings of each cultivar in a controlled environment chamber. After an acclimation period, plants were chilled to -10, -15, or -20 C for 1 h, then gradually warmed. After 36 d, surviving plants were counted, and plants were harvested and weighed. Mortality rate varied significantly among cultivars (0 - 13.2% at -10 C; 47.2 - 100% at -20 C). A log-logistic curve was used to fit mortality to temperature to estimate the temperature at which 50% of plants would die (LT50). The LT 50 of these cultivars ranged from -12.9 C for the most sensitive cultivar, to -20.8 C for the hardiest. Two climate change scenarios (Hadley Centre Coupled Model version 3, fossil-fuel intensive A1FI and sustainability-focused B2) were used to estimate the 10th percentile extreme minimum temperature for three 30-y periods: baseline 1960-1989, immediate future 2015-2044, and long-term future 2070-2099. During the baseline period, freeze tolerance was strongly limiting: depending on cultivar, only 0 - 7.2% of the northeastern United States was warmer than the LT50 of perennial ryegrass at least 27 out of 30 years. In the more extreme scenario, that percentage increased to 17.1 - 76.4% by 2070-2099, and in the less extreme climate change scenario the suitable area was 3.5 - 42.6%. Minimum temperature alone is not the only climatic factor contributing factor to winter survival. Snow cover can insulate plants from extreme temperatures. Cold acclimation is crucial to allowing survival of extreme temperatures, but as winter temperatures become warmer and more variable, acclimation periods may be less consistent, and deacclimation during warm periods may reduce freeze tolerance. Thus, although consideration of LT50 predicts increased area of suitable habitat of perennial ryegrass in the northeastern US, the actual situation is substantially more complex.