Phenological events from budburst to leaf senescence are characterized by changes in organ growth and the mobilization of resources in the vascular system. Yet, in seasonally cold climates, many important phenological events (phenophases) occur in the spring and autumn at times when maintaining an active vascular system is risky and transport in the xylem and phloem might be compromised. Understanding plant growth and nutrient remobilization at these critical times requires a comprehension of vascular phenology. Although a handful of studies have shown links between xylem anatomy/physiology and leaf phenology across species (Lechowicz, 1984; Wang et al., 1992; Panchen et al., 2014; Fahey, 2016), few studies exist on the phloem, and they focus on a small set of species (Prislan et al., 2013; Lavrič et al., 2017; Montwé et al., 2019). This underrepresentation of phloem in the literature is surprising considering the phloem's critical role in transporting nutrients, resources, and long‐distance signals important in regulating organ growth and allocation (for review, see Ham and Lucas, 2014). Here, I make the case that studying seasonal changes in the phloem is necessary for understanding physiological limits to plant phenology and propose two potential ways that the phloem could influence leaf and flower phenology in woody, deciduous angiosperms, one in the spring and one in the autumn.

从芽期到叶片衰老的物候事件的特征是器官生长的变化和血管系统资源的动员。然而，在季节性寒冷的气候中，许多重要的物候事件（物候期）发生在春季和秋季，这时维持活跃的血管系统存在风险，木质部和韧皮部的运输可能会受到损害。在这些关键时刻了解植物的生长和养分迁移需要理解血管的物候学。尽管少数研究表明跨物种的木质部解剖学/生理学与叶片物候学之间存在联系（Lechowicz，1984 ; Wang等，1992 ; Panchen等，2014 ; Fahey，2016），关于韧皮部的研究很少，而只关注少数物种（Prislan等，2013 ;Lavrič等，2017 ;Montwé等，2019）。考虑到韧皮部在运输养分，资源和长距离信号中的重要作用，而韧皮部在调节器官的生长和分配中起着至关重要的作用，因此，在文献中这种韧皮部的代表性不足令人惊讶（有关综述，请参见Ham and Lucas，2014）。在这里，我认为研究韧皮部的季节性变化对于理解植物物候的生理极限是必要的，并提出了韧皮部可能影响木质，落叶被子植物的叶片和花物候的两种潜在方式，一种在春季，另一种在春季。秋季。