FROST-RESISTANCE OF WINTER CEREALS AS A F UNCTION OF ATMOSPHERIC CO2-CONCENTRATION, TEMPERATURE AND SOIL-MOISTURE CONTENT

The effect of atmospheric CO2 concentration, freezing temperature and soil moisture content on the hardening and frost resistance of winter cereals was tested under controlled conditions. The frost resistance o f winter wheat rye and triticale varieties grown and hardened at an at mospheric CO2 concentration of 700 mu mol x mol(1) was better than tha t of plants grown at normal atmospheric CO2 concentration (350 mu mol x mol(1)). The increase in the CO2 level had a favourable effect on th e hardening process, thanks to which the mean survival rate was signif icantly better than that of the control plants. In all the varieties t he increased CO2 concentration caused an increase in the leaf area and in the majority of cases the dry mass was also significantly greater. The varieties gave differing responses to freezing for a short period at a very low temperature or for a longer period at a somewhat higher temperature. The wheat variety Martonvasari 4 survived better when tr eated at a higher freezing temperature (-12 degrees C) for a longer pe riod (72 hours) than at a lower temperature (-18 degrees C) for a shor ter time (24 hours). The opposite behaviour was observed for Martonvas ari 8. An increase in the moisture content of the soil caused only a s light increase in the killed plant rate for varieties with good frost resistance, but led to considerably greater damage in varieties with m edium or poor frost resistance.