Seasonal changes in climate are accompanied by shifts in carbon allocation and phenological changes in woody angiosperms, the timing of which can have broad implications for species distributions, interactions and ecosystem processes. During critical transitions from autumn to winter and winter to spring, physiological and anatomical changes within the phloem could impose a physical limit on the ability of woody angiosperms to transport carbon and signals. There is a paucity of the literature that addresses tree (floral or foliar) phenology, seasonal phloem anatomy and seasonal phloem physiology together, so our knowledge of how carbon transport could fluctuate seasonally, especially in temperate climates is limited. We review phloem phenology focussing on how sieve element anatomy and phloem sap flow could affect carbon availability throughout the year with a focus on winter. To investigate whether flow is possible in the winter, we construct a simple model of phloem sap flow and investigate how changes to the sap concentration, pressure gradient and sieve plate pores could influence flow during the winter. Our model suggests that phloem transport in some species could occur year-round, even in winter, but current methods for measuring all the parameters surrounding phloem sap flow make it difficult to test this hypothesis. We highlight outstanding questions that remain about phloem functionality in the winter and emphasize the need for new methods to address gaps in our knowledge about phloem function.

中文翻译：

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温带木本植物韧皮部解剖学和生理学的季节变化：对长途运输的影响


气候的季节性变化伴随着木本被子植物碳分配和物候变化的变化，其时间变化可能对物种分布、相互作用和生态系统过程产生广泛影响。在从秋季到冬季以及从冬季到春季的关键转变期间，韧皮部内的生理和解剖学变化可能会对木本被子植物运输碳和信号的能力施加物理限制。很少有文献同时讨论树木（花或叶）物候学、季节性韧皮部解剖学和季节性韧皮部生理学，因此我们对碳运输如何季节性波动（尤其是在温带气候下）的了解有限。我们回顾韧皮部物候学，重点关注筛元素解剖结构和韧皮部液流如何影响全年的碳可用性，重点是冬季。为了研究冬季是否可能发生流动，我们构建了一个简单的韧皮部汁液流动模型，并研究了汁液浓度、压力梯度和筛板孔隙的变化如何影响冬季的流动。我们的模型表明，某些物种的韧皮部运输可能全年发生，甚至在冬季，但目前测量韧皮部液流所有参数的方法使得很难检验这一假设。我们强调了有关冬季韧皮部功能的突出问题，并强调需要新的方法来弥补我们对韧皮部功能的了解空白。