Cellular characteristics of a traumatic frost ring in the secondary xylem of Pinus radiata

The effect of a short-term low temperature on cellular characteristics of a frost ring in radiata pine (Pinus radiata) secondary xylem was investigated using various microscopic techniques. Cell walls in the frost ring, that formed in the earlywood due to an abrupt drop in the temperature one night in the Spring, were poorly developed, lacking in the proper thickness and the proportion of wall constituents. In majority of the cases, the cell walls were highly convoluted and the secondary walls developed poorly and incompletely. Judging by irregular deposition of lignin, it appears that the control mechanism ensuring an orderly deposition of monolignols failed to function properly. The highly porous texture of some secondary walls indicated that cellulosic and hemicellulosic framework was affected, which would explain irregular lignification of cell walls. Thus the frost ring constitutes a serious defect in the timber, being a zone of weakness along which the wood is likely to split during processing, such as drying.