Sebastian-Azcona Jaime, Hacke Uwe, Hamann Andreas
Department of Renewable Resources, University of Alberta, Edmonton, AB, Canada.
Front Plant Sci. 2020 Feb 27;11:208. doi: 10.3389/fpls.2020.00208. eCollection 2020.
Xylem anomalies that are caused by unusual climate events have long been used to aid cross-dating in tree ring research. Here, we analyzed a range of xylem anomalies in a 39-year-old common garden experiment of white spruce ( [Moench] Voss) in central Alberta, Canada, designed to investigate local adaptation. We extracted wood cores from trees representing 24 provenances covering much of the species range across the Canadian boreal forest. Using a double stain and light microscopy analysis, four xylem anomalies and their causes could be distinguished: (1) frost rings indicate issues with synchronizing the onset of growth with the start of the growing season, and were prevalent in young trees; (2) light rings represent thin cell walls caused by an insufficient growing season length, most prevalent in southern sources; (3) blue rings were caused by a failure to complete lignification of new wood due to an early end of the growing season; and (4) double rings represent density fluctuations due to drier than normal summers. Local provenances showed the least amount of xylem anomalies, indicating that they are correctly adapted to the environment in which they occur. In contrast, trees moved to the test site from other climate regions showed various types of xylem anomalies depending on their origin. In particular, populations originating from warmer regions showed an increased presence of latewood anomalies, consistent with a more extensive use of the growing season in the fall. We conclude that xylem anomalies may serve as a sensitive early indicator of maladaptation to climate before populations experience tree dieback or mortality. They may therefore be useful to monitor the health of natural populations, or to evaluate the success of assisted migration in reforestation to address climate change.
由异常气候事件导致的木质部异常长期以来一直被用于协助树木年轮研究中的交叉定年。在此，我们分析了加拿大艾伯塔省中部一个39年生白云杉（[Moench] Voss）的常见园实验中的一系列木质部异常，该实验旨在研究局部适应性。我们从代表24个种源的树木中提取了木芯，这些种源覆盖了加拿大北方森林中该物种分布范围的大部分地区。通过双重染色和光学显微镜分析，可以区分出四种木质部异常及其成因：（1）霜轮表明生长开始与生长季节开始的同步性存在问题，在幼树中普遍存在；（2）轻轮代表由于生长季节长度不足导致的细胞壁薄，在南部种源中最为普遍；（3）蓝轮是由于生长季节提前结束导致新木材木质化不完全所致；（4）双轮代表由于夏季比正常情况干燥导致的密度波动。本地种源的木质部异常数量最少，表明它们能正确适应其所处的环境。相比之下，从其他气候区域移栽到试验地点的树木根据其来源显示出各种类型的木质部异常。特别是，来自温暖地区的种群晚材异常的出现频率增加，这与秋季生长季节的更广泛利用一致。我们得出结论，木质部异常可能是种群经历树木死亡或死亡率之前对气候适应不良的敏感早期指标。因此，它们可能有助于监测自然种群的健康状况，或评估造林中辅助迁移应对气候变化的成效。
