Department of Biology, California State University, Bakersfield, CA, USA.
BIOAPLIC, Departamento de Botánica, EPSE, Universidade de Santiago de Compostela, Campus Terra, 27002 Lugo, Spain.
Ann Bot. 2022 Sep 19;130(3):355-365. doi: 10.1093/aob/mcac032.
The onset of spring growth and vessel formation were examined within three deciduous woody plant species, Acer rubrum, Populus balsamifera ssp. trichocarpa and Quercus rubra. We were broadly interested in the lag between the onset of girth expansion and the formation of mature and hydraulically conductive vessels within the new xylem.
Dendrometers were installed on 20 trees (6-7 per species), and expansion of both bole and distal stems was monitored throughout the growing season in a common garden. For each species, four to six distal stems were harvested every other week for anatomical examination of vessel formation. Additionally, for Populus and Quercus, hydraulic conductivity measurements and active xylem staining were completed on all stem samples.
For all three species, the timing of girth expansion was similar. Expansion of distal branches occurred 12-37 d earlier than that of the bole. Vessel formation initiated several weeks prior to leaf-out, but no new earlywood vessels were mature at the time of bud break for Acer and Populus and only a few were present in Quercus. Initial stem girth expansion occurred 2 to >6 weeks before the maturation of the first current-year vessels, and there was an additional delay of up to 4 weeks before mature vessels became hydraulically functional. Hydraulic conductivity was strongly correlated with the number and diameter of stained vessels.
Bud break and leaf expansion relied predominantly on water supplied by vessels formed during prior seasons. Early-season activity is likely affected by the function of older xylem vessels and the environmental factors that influence their structure and function. Understanding the functional lifespan of vessels and the varying contributions of new and older vessels to conductivity are critical to understanding of the phenology and vascular function of long-lived woody plants in response to changing climates.
在三种落叶木本植物中，即 A. rubrum、P. balsamifera ssp. trichocarpa 和 Q. rubra 中，观察了春树生长和导管形成的开始时间。我们广泛关注的是，在新木质部中，周长膨胀的开始与成熟和水力传导导管的形成之间的时间差。
在一个共同花园中，在 20 棵树上（每个物种 6-7 棵）安装了树木生长锥，监测了整个生长季节的树干和远端茎的膨胀情况。对于每个物种，每隔一周收获四到六个远端茎，用于导管形成的解剖学检查。此外，对于 P. 和 Q.，对所有茎样本进行了水力传导率测量和活跃木质部染色。
对于所有三种物种，周长膨胀的时间相似。远端枝条的膨胀比树干早 12-37 天。导管形成在叶子展开前几周开始，但 Acer 和 P. 的芽破裂时没有新的早材导管成熟，只有少数在 Q. 中存在。初始茎周长膨胀发生在第一个当年导管成熟前 2 至>6 周，在成熟导管具有水力功能之前，还会有长达 4 周的延迟。水力传导率与染色导管的数量和直径强烈相关。
芽破裂和叶子展开主要依赖于前一季形成的导管提供的水分。早期活动可能受到较老木质部导管的功能以及影响其结构和功能的环境因素的影响。了解导管的功能寿命以及新导管和旧导管对传导率的不同贡献，对于理解长寿命木本植物对气候变化的物候学和血管功能至关重要。
