祁连山中部祁连圆柏年内径向生长对气候因子的响应

通过对祁连山中部葫芦沟流域的祁连圆柏连续采集微树芯，对其形成层活动和径向生长动态进行了连续两年的监测研究。结果表明，2012年细胞壁加厚和细胞成熟阶段开始时间分别发生在6月26日和7月24日，比2013年细胞壁加厚（6月22日）和细胞成熟阶段（6月26日）开始时间分别晚5 d和28 d。2012年细胞扩大、细胞壁加厚和细胞成熟阶段结束时间分别为7月16日、8月9日和9月8日，比2013年各阶段结束时间分别晚7、28 d和24 d。2012年最大细胞分裂速率为0.33细胞/d，共形成20.9个细胞，细胞分裂速率和木质部细胞总数均高于2013年。通过与附近气象站记录的气象数据进行对比，发现祁连圆柏生长开始时间在温暖年份显著早于寒冷年份，说明祁连圆柏的径向生长开始时间与温度有关。但2013年春季和夏初的高温导致区域干旱程度加剧，使祁连圆柏生长结束时间显著早于2012年，并导致2013年的木质部细胞总量和生长速率都小于2012年。研究表明，在寒冷干旱地区，尽管升温会使生长季提前，但升温导致的干旱胁迫可能对树木的生长速率和木质部细胞总量产生重要影响。

Intra-annual radial growth responses of Qilian juniper (Juniperus przewalskii) to climate factors in the central Qilian Mountains, northwest China

Studies on cambial phenology and wood formation dynamics (xylogenesis) can provide mechanistic understandings that how climate influence wood production and carbon sequestration at cellular level. The Qilian Mountains is an important ecological security barrier in northwest and even the whole China. However, there is very little in-depth information on the physiological responses of trees to changing climate, especially at individual level. Here, we analyzed phenological traits related to the observed cambial phenology and xylogenesis over two extreme hydroclimatic years from the central Qilian Mountains, northwestern China. The cambial phenology and xylogenesis were assessed biweekly from microcores of five Qilian juniper (Juniperus przewalskii) trees. Results showed that the onset of cell wall-thickening and the first mature cell occurred on June 26 and July 24 in 2012 growing season, 5 and 28 days later than those in 2013 growing season, respectively. In 2012, the end of cell enlargement, cell wall thickening, and cell lignification phase occurred on July 16, August 9, and September 8, respectively, which were 7 days, 28 days and 24 days later than the end of each developing phase in 2013 growing season. In 2012, the maximum rate of wood production was 0.33 cells/d, higher than that in 2013 growing season (0.28 cells/d). Accordingly, a total of 21 cells were formed in 2012 growing season, four cells higher than that in 2013. By comparison with meteorological data recorded at a nearby meteorological station, we found that the cambial phenology and xylogenesis of Qilian juniper were sensitive to changing climate. The onset of xylogenesis in the warm year (2013) was significantly earlier than that in the colder year (2012), indicated that the onset of the growing season was mainly related to temperature. In contrast, warm conditions in 2013 led to an intensification of regional drought in spring and early summer, resulted into a 24 days earlier at the end of the growing season than that in 2012. Our results indicated that strong shifts in water availability during the growing season were crucial to the growth rate and final wood production. Our findings suggested that while warming promoted an early growing season, it also had a strong influence on tree growth and productivity in cold and arid regions due to the decrease in moisture availability. Our study provides new evidence on the malleable nature of tree growth in response to climatic variations in cold and arid region.