Hicter Pauline, Beeckman Hans, Luse Belanganayi Basile, De Mil Tom, Van den Bulcke Jan, Kitin Peter, Bauters Marijn, Lievens Kévin, Musepena Donatien, Mbifo Ndiapo José, Luambua Nestor K, Laurent Félix, Angoboy Ilondea Bhély, Hubau Wannes
Wood Biology Service, Royal Museum for Central Africa, Leuvensesteenweg 13, 3080, Tervuren, Belgium.
UGent-Woodlab-Laboratory of Wood technology, Department of Environment, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium.
BMC Plant Biol. 2025 Mar 12;25(1):317. doi: 10.1186/s12870-025-06314-2.
Xylogenesis is synchronous among trees in regions with a distinct growing season, leading to a forest-wide time lag between growth and carbon uptake. In contrast, little is known about interspecific or even intraspecific variability of xylogenesis in tropical forests. Yet an understanding of xylogenesis patterns is key to successfully combine bottom-up (e.g., from permanent forest inventory plots) and top-down (e.g., from eddy covariance flux towers) carbon flux estimates.
Here, we monitor xylogenesis development of 18 trees belonging to 6 abundant species during 8 weeks at the onset of the rainy season from March to April 2022 in a semideciduous rainforest in the Yangambi reserve (central Democratic Republic of the Congo). For each tree, the weekly cambial state (dormant or active) was determined by epifluorescence microscopy.
We find interspecific variability in the cambial phenology, with two species showing predominant cambial dormancy and two species showing predominant cambial activity during the monitoring period. We also find intraspecific variability in two species where individuals either display cambial dormancy or cambial activity. All trees kept > 60% of their leaves throughout the dry season and the monitoring period, suggesting a weak relationship between the phenology of the cambial and foliar. Our results suggest that individual trees in Yangambi asynchronously activate their cambial growth throughout the year, regardless of leaf phenology or seasonal rainfall.
These results are consistent with global analysis of gross primary productivity estimates from eddy covariance flux towers, showing that tropical biomes lack a synchronous dormant period. However, a longer-term monitoring experiment, including more species, is necessary to confirm this for the Congo Basin. As Yangambi is equipped with facilities for microscopic wood analysis, a network of inventory plots and a flux tower, further research in this site will reveal how xylogenesis patterns drive annual variability in carbon fluxes and how ground-based and top-down measurements can be combined for robust upscaling analysis of Congo basin carbon budgets.
在生长季节分明的地区，树木的木质部形成是同步的，这导致整个森林在生长和碳吸收之间存在时间滞后。相比之下，对于热带森林中木质部形成的种间甚至种内变异性知之甚少。然而，了解木质部形成模式是成功结合自下而上（例如，来自永久森林清查地块）和自上而下（例如，来自涡度协方差通量塔）碳通量估计的关键。
在此，我们于2022年3月至4月雨季开始时，在扬甘比保护区（刚果民主共和国中部）的半落叶雨林中，对属于6个优势物种的18棵树的木质部形成发育情况进行了为期8周的监测。对于每棵树，每周通过落射荧光显微镜确定形成层状态（休眠或活跃）。
我们发现形成层物候存在种间变异性，在监测期内，有两个物种表现出主要的形成层休眠，两个物种表现出主要的形成层活动。我们还在两个物种中发现了种内变异性，其中个体要么表现出形成层休眠，要么表现出形成层活动。在整个旱季和监测期内，所有树木保留了超过60%的叶子，这表明形成层和叶物候之间的关系较弱。我们的结果表明，扬甘比的个体树木全年异步激活其形成层生长，无论叶物候或季节性降雨如何。
这些结果与涡度协方差通量塔对总初级生产力估计的全球分析一致，表明热带生物群落缺乏同步休眠期。然而，需要进行包括更多物种的长期监测实验来为刚果盆地证实这一点。由于扬甘比配备了用于微观木材分析的设施、清查地块网络和通量塔，在该地点的进一步研究将揭示木质部形成模式如何驱动碳通量的年度变化，以及如何将地面和自上而下的测量结合起来，对刚果盆地碳预算进行可靠的尺度放大分析。
