A study on the anatomical and physiological characteristics of the cold resistant Eucalyptus cloeziana

The global significance of eucalypts as sources of wood and fiber, but inadequate cold tolerance of Eucalyptus cloeziana has limited a broader deployment beyond subtropical regions of the China. Cold temperature tolerance can be a valuable trait in cultivated plants. This study investigated the effects of the application of under different environment conditions eighteen morphological and six physiological indices were measured in 26 E. cloeziana clones cultivars. Field investigations and analysis of a leaf anatomical structure index were used to define the anatomical and structural characteristics of E. cloeziana leaves, then explored the relationship between a leaf biochemical characteristics and leaf cold tolerance, using a comparative analysis of the changes in leaf physiological indicators. Results of the principal component analysis indicated that some of the 18 morphological indices (including midrib vascular bundle area, main vein xylem area, main vein thickness, leaf area, the lower epidermis thickness, leaf cell tense ratio, and leaf thickness) could be screened out by stepwise regression and could be used to evaluate the low temperature resistance. Moreover, the 26 E. cloeziana clones cultivars were divided into five types: highly cold resistant, cold resistant, moderately cold resistant, low cold resistant, and cold intolerant. The cold resistance of seven selected E. cloeziana cultivars (one cold resistant cultivars, and two each of cold resistant, low cold resistant, and two cultivars) with contrasting low-temperature sensitivities were further verified by physiological analysis. Results showed that various E. cloeziana clone materials had different abilities to adapt to cold temperatures due to their complex genetic backgrounds because the scavenging capacity of reactive oxygen species in the middle leaves was strong enough to eliminate an excessive accumulation of free radicals, and thus reduce the amount of cell membrane leakage. The characteristics of resistance to low-temperature stress in E. cloeziana were, at least partially, dependent on its relatively high leaf cell tense ratio, main vein thickness, and leaf thickness, in addition to its antioxidant capacity and the malondialdehyde and proline content, which can be used as ideal experimental materials to study the characteristic of cold resistance of different E. cloeziana clone cultivars with contrasting low-temperature in responses to low-temperature stress.