Silva Luciano M, Pfaff Jonas, Pereira Luciano, Miranda Marcela T, Jansen Steven
Institute of Botany, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
Tree Physiol. 2024 Oct 10. doi: 10.1093/treephys/tpae131.
Centrifuges provide a fast approach to quantify embolism resistance of xylem in vulnerability curves (VCs). Since embolism formation is assumingly driven by pressure only, spin time is not standardised for flow centrifuge experiments. Here, we explore to what extent embolism resistance could be spin-time dependent, and hypothesise that changes in hydraulic conductivity (Kh) would shift VCs towards higher water potential (Ψ) values over time. We quantified time-based shifts in flow-centrifuge VCs and their parameter estimations for six angiosperm species by measuring Kh over 15 minutes of spinning at a particular speed, before a higher speed was applied to the same sample. We compared various VCs per sample based on cumulative spin time, and modelled the relationship between Kh, Ψ, and spin-time. Time-based changes of Kh showed considerable increases and decreases at low and high centrifuge speeds, respectively, which generally shifted VCs towards more positive Ψ values. Values corresponding to 50% loss of hydraulic conductivity (P50) became less negative by up to 0.72 MPa in Acer pseudoplatanus, and on average by 8.5% for all six species compared to VCs that did not consider spin-time. By employing an asymptotic exponential model, we estimated time-stable Kh, which improved the statistical significance of VCs in 5 of the 6 species studied. This model also revealed the instability of VCs at short spin times with embolism formation in flow-centrifuges following a saturating exponential growth curve. Although pressure remains the major determinant of embolism formation, spin-time should be considered in flow-centrifuge VCs because not considering the time-dependent stability of Kh overestimates embolism resistance. This spin-time artefact is species-specific, and likely based on relatively slow gas diffusion that is associated with embolism propagation. The accuracy of VCs is improved by determining time-stable Kh values for each centrifuge speed, without considerably extending the experimental time to construct VCs.
离心机提供了一种快速方法来量化脆弱性曲线（VCs）中木质部的栓塞抗性。由于假定栓塞形成仅由压力驱动，因此在流动离心机实验中，旋转时间并未标准化。在此，我们探究栓塞抗性在多大程度上可能依赖于旋转时间，并假设水力传导率（Kh）的变化会使VCs随时间向更高水势（Ψ）值移动。我们通过在特定速度下旋转15分钟测量Kh，然后对同一样本施加更高速度，量化了六种被子植物物种的流动离心机VCs基于时间的变化及其参数估计。我们根据累积旋转时间比较了每个样本的各种VCs，并对Kh、Ψ和旋转时间之间的关系进行了建模。基于时间的Kh变化在低速和高速离心时分别显示出显著增加和减少，这通常使VCs向更正值的Ψ值移动。与未考虑旋转时间的VCs相比，在假挪威槭中，对应于水力传导率损失50%（P50）的值负性降低高达0.72MPa，所有六个物种平均降低8.5%。通过采用渐近指数模型，我们估计了时间稳定的Kh，这提高了所研究的6个物种中5个物种VCs的统计显著性。该模型还揭示了在短旋转时间下VCs的不稳定性，流动离心机中的栓塞形成遵循饱和指数增长曲线。尽管压力仍然是栓塞形成的主要决定因素，但在流动离心机VCs中应考虑旋转时间，因为不考虑Kh随时间的稳定性会高估栓塞抗性。这种旋转时间假象是物种特异性的，可能基于与栓塞传播相关的相对缓慢的气体扩散。通过为每个离心速度确定时间稳定的Kh值来提高VCs的准确性，而无需大幅延长构建VCs的实验时间。
