Departamento de Ciência Florestal, Solos e Ambiente, Universidade Estadual Paulista (UNESP), Faculdade de Ciências Agronômicas, Avenida Universitária, Botucatu, SP, Brazil.
Departamento de Botânica, Instituto de Biologia, Universidade Estadual de Campinas (UNICAMP), Campinas, SP, Brazil.
Ann Bot. 2022 Sep 19;130(3):445-456. doi: 10.1093/aob/mcac095.
Xylem is a crucial tissue for plant survival, performing the functions of water transport, mechanical support and storage. Functional trade-offs are a result of the different assemblages of xylem cell types within a certain wood volume. We assessed how the volume allocated to different xylem cell types can be associated with wood functional trade-offs (hydraulics, mechanical and storage) in species from the Cerrado, the Brazilian savanna. We also assessed the xylem anatomical characters linked to wood density across species.
We analysed cross-sections of branches collected from 75 woody species belonging to 42 angiosperm families from the Cerrado. We estimated the wood volume fraction allocated to different cell types and performed measurements of vessel diameter and wood density.
The largest volume of wood is allocated to fibres (0.47), followed by parenchyma (0.33) and vessels (0.20). Wood density is positively correlated to cell wall (fibre and vessel wall), and negatively to the fractions of fibre lumen and gelatinous fibres. We observed a trade-off between hydraulics (vessel diameter) and mechanics (cell wall fraction), and between mechanics and storage (parenchyma fraction). The expected positive functional relationships between hydraulics (vessel diameter) and water and carbohydrate storage (parenchyma and fibre lumen fractions) were not detected, though larger vessels are linked to a larger wood volume allocated to gelatinous fibres.
Woody species from the Cerrado show evidence of functional trade-offs between water transport, mechanical support and storage. Gelatinous fibres might be potentially linked to water storage and release by their positive relationship to increased vessel diameter, thus replacing the functional role of parenchyma and fibre lumen cells. Species can profit from the increased mechanical strength under tension provided by the presence of gelatinous fibres, avoiding expensive investments in high wood density.
木质部是植物生存的关键组织，具有运输水分、提供机械支撑和储存物质的功能。不同木质部细胞类型的组合会导致功能上的权衡，这与一定木材体积内的细胞类型有关。我们评估了不同木质部细胞类型在巴西塞拉多地区物种中的体积分配与木材功能权衡（水力、机械和储存）之间的关系。我们还评估了与跨物种木材密度相关的木质部解剖特征。
我们分析了来自塞拉多地区 42 个被子植物科的 75 个木本物种的分支横切面。我们估计了不同细胞类型分配的木材体积分数，并测量了导管直径和木材密度。
木材的最大体积分配给纤维（0.47），其次是薄壁组织（0.33）和导管（0.20）。木材密度与细胞壁（纤维和导管壁）呈正相关，与纤维腔和凝胶纤维的分数呈负相关。我们观察到水力（导管直径）和力学（细胞壁分数）、力学和储存（薄壁组织分数）之间存在权衡。水力（导管直径）与水和碳水化合物储存（薄壁组织和纤维腔分数）之间预期的正功能关系没有被发现，尽管较大的导管与分配给凝胶纤维的更大木材体积有关。
来自塞拉多的木本物种表现出水分运输、机械支撑和储存之间的功能权衡。凝胶纤维可能通过与导管直径的正相关关系与水储存和释放有关，从而替代薄壁组织和纤维腔细胞的功能作用。由于凝胶纤维的存在提供了更大的张力机械强度，物种可以从增加的机械强度中受益，而不必在高木材密度上进行昂贵的投资。
