Evaluation of the effect of freezing stress tolerance of Phyla lanceolata under some organic mulch in controlled conditions

In order to investigate the effect of frost stress on Phyla lanceolata as a cover plant under the influence of some organic mulches, this experiment was conducted as a factorial experiment based on completely randomized design with four replications at Ferdowsi University of Mashhad. Five levels of freezing temperature (0, -5, -10, -15, and -20 °C) and three types of mulch (manure, leaf needle, and bran) were treated in the experiment. For evaluation of frost tolerance temperatures, some traits such as electrolyte leakage percentage, soluble carbohydrate content, leaf proline content, leaf number, leaf area, and plant dry weight were considered. Results showed that the simple and interaction effects of mulch and temperature on the measured morphological traits, electrolyte leakage, relative water content, spade and photosynthetic pigment content (chlorophyll a, b and total) were significant. All of the organic mulches used in the study increased shoot and root dry weight so that by applying three mulch of bran, leaf needle, and animal manure, shoot dry weight from 2.15 g under non-mulch conditions reached to 2.72, 3.13, and 3.19 g/plant, respectively and root dry weight from 1.50 g reached 1.90, 2.23, and 2.29 g /plant, respectively. The highest electrolyte leakage (80%) was at -20 °C and in plants treated with bran mulch and the highest relative water content (55%) was at 0 °C and in plants treated with needle mulch treatment. Also, total chlorophyll content was 0.11 mg higher than that in control treatment. In general, among the mulches used, animal manure mulch had the greatest effect on mitigating the effects of frost on morphological and biochemical traits of the plant.