By Michelle DaCosta and Masoud Arghavani, University of Massachusetts-Amherst
As turf managers transition into summer, it is easy to forget concerns related to winter injury, especially in years with limited damage. But our WinterTurf research continues regardless of the temperature outside!
Our team has been working on understanding what makes some turfgrasses like annual bluegrass and perennial ryegrass more sensitive to winter-related stresses, including crown hydration, low temperature kill, and premature deacclimation in response to freeze-thaw events. One of the objectives of our research has been to tease out how these different but related stresses impact turfgrass survival. We can simulate different winter environments in controlled environment growth chambers, which allows us to continue our research throughout the year and not depend on specific winter conditions occurring in the field.
We previously found that grasses coming out from simulated ice encasement were sensitive to high light intensities (Figure 1). The higher light intensity caused a significant loss in percent green cover, which resulted in prolonged recovery period. Some cool-season grasses were more sensitive to high light intensities after simulated ice encasement, with annual bluegrass showing the most damage and velvet bentgrass maintaining a higher percent green cover. In some cases, species differences in the ability to retain green cover was related to the level of protective pigments in the turfgrass leaves. For example, species such as velvet bentgrass and Chewings fescue maintained higher leaf carotenoid pigment content compared to the more sensitive species. However, these could not explain all the variations we observed.
Research this summer will examine additional factors explaining species sensitivity to low temperatures and high light interactions. We recently completed the first round of experiments to evaluate the capacity of different cool-season grasses to photosynthesize at low temperatures. We found that annual bluegrass grown at low temperatures of 40°F had the lowest leaf photosynthetic capacity compared to all other turfgrasses in the study (creeping bentgrass, velvet bentgrass, Chewings fescue, strong creeping red fescue, and perennial ryegrass). When looking at the interaction between low temperature and different light conditions, a higher light intensity (500 µmol m⁻² s⁻¹) caused photosynthesis rates of annual bluegrass to be more suppressed compared to a more tolerant species such as velvet bentgrass (Figure 2). We know that plants usually have decreased photosynthesis rates at low temperatures, and that some plants have better capacity to adjust their photosynthesis machinery depending on temperature and light conditions. Based on our preliminary results, it seems that a reduced photosynthetic capacity in annual bluegrass may predispose this species to winter stress during periods of low temperature and high light intensity. Additional experiments will continue this summer and will hep us to understand the physiological limitations of winter-sensitive grasses like annual bluegrass. The goal will be to use this information to explore management practices to minimize winter injury in these species.