The snow must go on: Ground ice encasement, snow compaction and absence of snow differently cause soil hypoxia, CO2 accumulation and tree seedling damage in boreal forest

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A COMPARISON OF COLD HARDINESS AND ICE ENCASEMENT TOLERANCE OF TIMOTHY GRASS AND WINTER WHEAT

In the falls of 1979 and 1980 Salvo timothy grass (Phleum pratense L.) showed cold hardiness similar to Norstar winter wheat (Triticum aestivum L.) but significantly greater hardiness than Fredrick winter wheat. Ice tolerance of Salvo, with LI50 values of 29 and 45 days in the 2 yr, was more than twice that of the wheats. In controlled environments, seedlings of three timothy cultivars showed relatively low cold hardiness, but about threefold greater ice tolerance than the wheats. An Icelandic timothy cultivar, Korpa, showed greater ice tolerance than the Norwegian Engmo, and the Canadian cultivar Salvo. Fredrick wheat, and Korpa timothy cold hardened at a similar rate for 4 wk, but Korpa continued to harden to − 18 °C up to 6 wk of low temperature growth. Korpa rapidly attained a high tolerance to ice encasement in 2 wk of low temperature growth while Fredrick attained relatively low ice tolerance reaching a maximum at 3 wk of growth. There is little association between cold and ice tolerance in timothy, and there is a major difference in the ice tolerances of timothy and winter wheat. This high ice tolerance is likely to be a major cause of the superior survival of timothy in conditions of high winter stress. Key. words: Triticum, Phleum, acclimation, resistance, low temperature, frost </jats:p

COLD HARDINESS AND ICE TOLERANCE OF PASTURE GRASSES GROWN AND TESTED IN CONTROLLED ENVIRONMENTS

A number of forage grass species were tested for cold hardiness and ice tolerance after growth and cold hardening under controlled conditions. Tests exposing cold-hardened plants to a single level of stress separated species into statistically similar groups but, in a number of cases, the stress was not sufficient to kill plants so the true cultivar rankings were obscured. Derivation of the 50% kill point from a wide range of levels of stress served to identify cold hardiness and ice tolerance levels of cultivars of 10 species. Ranked according to the most hardy cultivar of the species tested were: timothy (Phleum pratense L.), Kentucky bluegrass (Poa pratensis L.), meadow foxtail (Alopecurus pratensis L.), red fescue (Festuca rubra L.), meadow fescue (Festuca pratensis L.), tufted hairgrass (Deschampsia caespitosa L.), creeping foxtail (Alopecurus arundinaceus L.), berings hairgrass (Deschampsia beringensis L.), orchardgrass (Dactylis glomerata L.), reed canarygrass (Phalaris arundinaceae). LT50 values varied from −15.7 °C for timothy to −4.7 °C for reed canarygrass. Cold hardiness and ice tolerance were only loosely associated (r = 0.36). The most ice-tolerant species were berings and tufted hairgrasses and timothy with LI50 values of 50, 39 and 44 d, respectively.Key words: Acclimation, encasement, freezing, resistance </jats:p

Identification of phytotoxic substances in soils following winter injury of grasses as estimated by a bioassay

Under northern conditions, winter survival of grass species for hay production is quite uncertain because of winter stresses to plants. Damage to plants may be caused by variability in snow cover, low temperatures, ice encasement and pathogens. Compared to renovation by ploughing, direct drilling without ploughing has some beneficial aspects and may be an alternative method for renovating hay fields. However, successful establishment of grasses without ploughing has been difficult to achieve both in scientific studies and under practical conditions. The objective of this investigation was to study whether a dead grass sod, killed by different winter injuries, may leak phytotoxins into the soil, thus causing the poor results observed by direct drilling in hayfields. Experiments, including soil water extraction and the use of bioassays, were conducted in growth chambers, to study the effects of the winter stresses frost, ice encasement, and snow mould on the accumulation of potentially phytotoxic biochemical compounds in the soil. Snow mould did not kill the grasses in the experiments and no phytotoxicity was measured. Although both ice encasement and low temperatures killed the grasses, only ice encasement caused phytotoxicity. The present investigation shows that the occurrence of phytotoxic substances, especially butyrate, after ice encasement may be a cause of poor establishment of direct-drilled grass plants after winter injuries. In serious cases of ice encasement this may justify a 1-2 wk delay of sowing, which in turn may result in reduced soil water for germination and may cause increased competition from other species. Key words: Hay fields, grassland, winter injuries, phytotoxic substances, allelochemicals </jats:p