[Effects of moisture and heat coupling on xylem growth of Pinus tabuliformis in Shenyang, China].

Based on the micro-core technology, we can accurately examine the tree cambium phenology and the radial growth at the cellular scale, and reveal the relationship between tree growth and climate. Pinus tabuliformis is one of the constructive species in forests of northern China. We investigated the growth pattern of P. tabuliformis in Shenyang and the changes in cambium and xylem cells throughout the growing season (April to November) in 2020. Results showed that the dividing activity in cambium started in early April and ended at the end of September. Xylem began to grow from the appearance of enlargement cells (mid April) to the end of the disappearance of lignified cells (late October), with a growth trajectory of 'S' shape curve. Approximately 53 xylem cells per row in radical direction were produced in 2020. The maximum growth rate (0.55 ind/row/day) occurred at the end of May, while the change of earlywood and latewood cells occurred at the end of July. When the minimum temperature above 0 ℃ in Shenyang, the cambium began to divide. The minimum critical temperature that affected the beginning and ending of xylem growth was 2-3 ℃. Precipitation promoted the growth in the growing season. The high temperature and insufficient water supply at the end of July were the main factors driving the differentiation of xylem cells to form earlywood and latewood.