Xylogenesis of Pinus radiata D. Don growing in New Zealand

Key MessagePinus radiataD. Don growing in the central North Island of New Zealand did not show full winter cambial dormancy. While there was a brief cessation of cambial cell division during June (winter), cell wall thickening, secondary wall deposition, and lignification of tracheids continued throughout the year.ContextThe xylogenesis of Pinus radiata showing only partial winter dormancy has not previously been reported.AimsTo verify the absence of winter dormancy of P. radiata growing in the mild cool climate of the central North Island. To characterise the intra-annual dynamics of xylem cell formation (cell division and enlargement as well as cell wall thickening and lignification) and growth rates and identify the main drivers of growth.MethodsXylogenesis was monitored by microcore sampling while radial growth was monitored by dendrometers, which was then related to rainfall and temperature.ResultsXylem cell formation started by mid-July and continued until late May of the following year and peaked in spring and early autumn with minimum activity in Southern Hemisphere winter solstice (June 21, DOY 172). A higher correlation was found between the radial stem growth and temperature than with rainfall.ConclusionThere was a winter period of about 30 days where there was no cambial cell division and the differentiation of latewood cells was stalled. This slow-down was supported by dendrometer measurements. This is likely due to the relatively mild winter temperatures and absence of drought conditions that are characteristic of the central North Island climate.