基于日均温度的华山松径向生长敏感温度研究

树干木质部形成周期与温度密切相关,存在影响形成层活动的敏感温度,但是尚未研究尝试从树木年轮中探索影响径向生长的敏感温度。华山主峰的华山松径向生长对气候变化较敏感,且华山西峰的气象站记录了1953年以来气象资料,这为探索树木径向生长与温度的关系提供了宝贵的材料。以华山主峰的华山松年轮资料和日值温度资料为基础,通过分析历年日平均温度的变化过程和年轮宽度、早材宽度、晚材宽度、最小密度以及最大密度的相关性,尝试探索华山松径向生长与日均温度变化的关系。结果表明春季一定温度的初日时间对华山松径向生长有较大的影响,其中3 ℃和8 ℃初日时间和持续时间对年轮宽度的促进作用最明显,而3 ℃对早材宽度影响较大,8℃初日时间对晚材的影响较大;高于11 ℃的温度会对华山松的径向生长造成限制,其中以11 ℃的作用最明显;而温度的终日时间对年轮特征影响较小。说明3 ℃是早材形成的敏感温度,8 ℃是晚材形成的敏感温度,温度高于11 ℃会对华山松的径向生长构成胁迫。这证明华山松年轮特征中包含了较多的气候信息,形成层活动和木质部的生长存在阈值温度,通过分析不同温度的生长期与年轮特征的关系可以找到影响华山松径向生长的敏感温度。这些敏感的温度是通过什么生理过程影响木质部的形成尚无法得知,但是这为解释树木生长对全球温度升高的响应以及利用华山松年轮重建历史气候提供了重要依据。

The critical temperature to Huashan Pine (Pinus armandi) radial growth based on the daily mean temperature

Tree rings provide a record of radial growth throughout a tree′s life,so much information can be obtained from tree rings.Many studies have been undertaken to study the relationship between tree rings and monthly temperature,but few have focused on the relationship with daily temperature.Although the phenology of stem xylem development and temperature are closely related,many studies indicate that threshold temperatures determine the beginning of cambial activity in spring,but few have attempted to explore the temperatures impacting on radial growth from tree rings.Radial growth of Huashan pine on the Huashan peaks was sensitive to climate change and was mainly limited by water supply in early summer and temperature in spring.In addition,thermal conditions were also a limited factor at this high-altitude site.In this study,tree ring chronology of Huashan pine and climate data recorded at a nearby weather station were used to investigate the relationship between radial growth of Huashan pine and daily mean temperature.The onset date,end date,duration and the cumulative temperature from different initial temperatures were calculated.Correlations between the changes in daily mean temperature over 36 years and the ring width,early-wood width,late-wood width,minimum density and maximum density were analyzed.The onset date of a specific temperature in spring significantly impacted the radial growth of Huashan pine.The onset date and duration of 3 ℃ and 8 ℃ were significantly negatively correlated with ring width,which indicated that the earlier onset date would promote growth in ring width.Early-wood width was sensitive to the onset date of 3 ℃,while late-wood width was more sensitive to the onset date of 8 ℃.However,temperatures higher than 11 ℃ limited the ring width both of early-wood and late-wood,and the most obvious temperature was 11 ℃.The end date of 10 ℃ and lower temperatures were little related to ring width.The duration of 3 ℃ and 8 ℃ were also significantly positively associated with ring width.Ring density and width responded similarly to changing temperature.These results indicated 3 ℃ was the threshold temperature for early-wood formation in spring,8 ℃ was critical for formation of late wood,but daily temperatures higher than 11 ℃ may cause water stress,which negatively affected radial growth.Collectively,the results indicated the tree ring chronology of Huashan pine contained abundant climate information,and that threshold temperatures determined the growth of Huashan pine xylem and cambial activity.By analyzing the relationship between growth phases at different temperatures and ring characteristics,the critical temperatures influencing radial growth of Huashan pine could be identified.Though the physiological processes corresponding to the critical temperature were unclear,this study provided useful information for understanding the tree growth response to rising temperature and historical climate reconstruction.