Epsilon Archive for Student Projects

Abstract

Ice encasement can damage perennial forage grasses during winter and reduce spring growth. Ice cover restricts gas exchange, which can lead to oxygen depletion and the accumulation of harmful metabolites. Controlled screening can help compare plant responses, but the treatment must produce ice-related injury without mainly becoming a test of freezing tolerance. This study evaluated a controlled ice-encasement protocol, tested image-based biomass measurements, and compared controlled responses with field observations.

Module 1 developed and assessed a controlled ice-encasement protocol for meadow fescue, tall fescue, and timothy. Plants were established in a greenhouse, cold acclimated, placed in freezers set to approximately −5°C, and covered with a shallow ice layer. Treatment durations were 5, 9, and 15 days for the two fescue species and 10, 22, and 30 days for timothy. Plants were photographed repeatedly during greenhouse recovery, and final plant cover was measured by image analysis. Module 2 evaluated whether image analysis could reliably reflect plant biomass. Image-derived measurements were compared with harvested green and dry biomass in a subset of 40 timothy pots. Module 3 used a semi-controlled field ice-encasement experiment at Lännäs, Sweden, as a field reference for the controlled experiment.
In Module 1, final plant cover differed among cultivars, but longer ice treatments did not always lead to lower cover. Mean cover in meadow fescue fell from 2.5% after 5 days to 0.6% after 15 days. Tall fescue had almost no cover after 5 days but higher cover after 9 and 15 days. Timothy had its highest mean cover, 18.2%, after 22 days. These differences were not tested for statistical significance. Treatment durations and recovery times differed among species, so the results could not show which species was most tolerant of ice encasement.

In Module 2, image-derived measurements were positively correlated with harvested green biomass (r = 0.61, p < 0.001) and dry biomass (r = 0.50, p = 0.001). The correlation was higher for green biomass than for dry biomass. These results showed that image analysis could detect some of the differences in plant biomass.
In the field experiment, Grindstad, a timothy cultivar, and Karolina, a tall fescue cultivar, were consistently among the greenest ice-treated subplots. Meadow fescue generally showed little green growth. Karolina performed relatively well in both the controlled and field experiments. However, the cultivar rankings for timothy and meadow fescue differed between the two experiments.
The controlled protocol was feasible, but several factors, including temperature differences among freezer locations and differences in recovery time, made the results difficult to interpret. The shallow laboratory ice layer also differed from the field treatment. Image analysis can support repeated assessment of plant recovery and growth without harvesting the plants. More uniform temperatures, equal recovery times, and further field testing are needed before the protocol can be used for reliable ice-encasement screening.