By Kavi Raj Acharya and Shui-zhang Fei, Iowa State University
Every spring after a harsh winter, turfgrass managers face the same question: Will their grasses come back? A hard winter with deep-freezing temperatures can leave lawns, sports fields, and golf courses looking bleak. But what actually determines whether the grass recovers? The answer, it turns out, may have less to do with surviving the freeze itself and more to do with what the plant does afterward.
In our current research on perennial ryegrass, conducted as part of the WinterTurf project, we've been looking closely at the recovery phase that follows freezing temperatures. Most winter stress research focuses on what happens during the cold event, which is certainly important. But we took this a step further by examining what happens during recovery after a freezing event. To do this, we compared two types of perennial ryegrass: one more tolerant of freezing conditions and the other more susceptible. We exposed both to varying lengths of subzero temperatures (-2 °C for 1 or 2 weeks), then tracked their recovery under non-freezing, cold-acclimation conditions (4 °C; Figure 1). We were trying to answer a key question: Is recovery from freezing simply a gradual return to normal (i.e., an attenuation of stress responses), or is it a biologically distinct process?
Our results suggest the latter. When we examined gene expression during recovery, we found that the genes switching on and off were largely distinct from those active during the freezing stress itself (Figure 2). This suggests that recovery is a separate biological phase involving a unique set of molecular processes. More importantly, gene expression patterns differed between the freezing-susceptible plant type and the freezing-tolerant type. This difference matters practically because if recovery is a separate biological process or trait, it can be a target for plant breeding and selection. This may lead to improved grass cultivars that are better at bouncing back after a hard winter, regardless of their initial freezing tolerance. A better understanding of the trait of recovery is a step toward developing turfgrasses that not only survive winter but also come back strong in spring.