Xylem growth rings and leaf phenological patterns in tree species of a subtropical seasonal forest

ABSTRACT Growth rings have been reported for several tropical species under seasonal precipitation regimes and have often been related to leaf phenology. We investigated growth ring distinctiveness, wood markers, and leaf shedding and flushing patterns of 16 tree species from a subtropical seasonal deciduous forest under abundant and well-distributed rainfall regime in southern Brazil. Distinct growth rings were found in 13 species, 10 of which presented clear anatomical boundaries. Seven species were deciduous, five semideciduous and four perennial. Leaf shedding peaked during winter and spring months for the deciduous species, while it peaked during spring and summer months for the perennial and semideciduous species. Leaf flushing peaked in spring and summer for all species. All the deciduous species exhibited growth rings with clear boundaries. Marginal parenchyma, associated or not with other anatomical markers, was present in deciduous species but was not present in species with other leaf shedding patterns. Growth rings in Allophylus edulis, Erythrina falcata, Jacaranda micrantha and Luehea divaricata were described for the first time. The presence of seasonal leaf phenological patterns and growth rings in most of the species suggests that seasonality of the photoperiod and/or temperature influence the development of trees in moist subtropical seasonal deciduous forests.摘要：已有研究报道，多种热带树种在季节性降水格局下可形成生长轮（growth rings），且生长轮常与叶片物候（leaf phenology）相关联。本研究针对巴西南部一处降雨充沛且分布均匀的亚热带季节性落叶林内的16个树种，探究了其生长轮辨识度、木材解剖标记（wood markers）以及叶片脱落与萌发模式。研究发现，13个树种存在清晰的生长轮，其中10个树种具有明确的解剖学边界。受试树种中，7个为落叶树种、5个为半落叶树种、4个为常绿树种。落叶树种的叶片脱落峰值出现在冬春两季，而常绿与半落叶树种的叶片脱落峰值则集中在春夏两季；所有树种的叶片萌发峰值均出现在春夏季节。所有落叶树种均具有边界清晰的生长轮。边缘薄壁组织（marginal parenchyma）无论是否伴随其他解剖标记，均存在于落叶树种中，但在其他叶片脱落类型的树种中未被检出。本研究首次报道了Allophylus edulis、Erythrina falcata、Jacaranda micrantha及Luehea divaricata的生长轮特征。多数受试树种兼具季节性叶片物候模式与生长轮，这表明光周期（photoperiod）和/或温度的季节变化，可对湿润亚热带季节性落叶林内树木的生长发育产生影响。