The frequency and mechanisms behind drought-induced hydraulic failure in woody angiosperms from temperate to tropical biomes

由于流经植物的水对我们的生物圈和人类人口的运行具有极其重要的作用，大多数人会非常惊讶地得知，植物到底是如何完成长途水分运输的还不清楚。虽然有大量证据表明植物木质部在负压下进行水分运输，但由于空气进入而导致的水力失灵是常见的还是罕见的，目前还不清楚。本项目旨在研究木本被子植物在干旱诱导下发生栓塞症的频率，以及在导水细胞中邻近纹孔水平发生栓塞症的潜在机制。通过在德国的温带森林和中国的热带草原和季节性雨林场地对总共30种被子植物进行实地考察，我们将检验这样一种假设，即不同的物种显示出类似的水力失败的相对风险，尽管对干旱诱导的血栓的绝对抵抗力存在明显差异。我们预计，该领域的水力故障在很大程度上仅限于极端事件。比较茎和叶的栓塞性将使我们能够检验水力脆弱性分段假说，表明叶中的木质部比茎木质部更容易发生水力故障。此外，我们将测试栓塞性与根/茎正压力的潜在发生相关，和/或木质部汁液脂的季节性变化。虽然在春季的各种温带森林中都知道根/干压力为正，但尚不清楚根/干压力在热带大草原和季节性雨林地区的植物中是否普遍存在。由于最近在被子植物的木质部汁液中发现了不溶的两亲性脂类，我们推测季节性干旱决定了这些脂类的数量和/或质量，这可能在避免血栓方面发挥作用。最后，我们将从孔隙率和充气疲劳的角度研究导水细胞之间的孔洞膜的功能特征，以更好地了解栓塞背后的机制。水力学测量和超微结构观察将整合在一个空间显式模型中，以模拟穿过纳米孔穴膜的流动和栓塞物的形成。这一创新项目将有助于我们理解干旱诱导的栓塞物在木本植物木质部组织中的频率和空间分布。该应用程序是与广西大学中国分校曹坤芳教授合作的项目，对双方都有好处，包括在工厂液压方面的互补专业知识，对博士生的培训，以及对两国的研究访问。这项提议可能会对仿生应用产生影响，并将增加我们对植物水分利用和抗旱性的理解，鉴于目前对气候变化的担忧，这一点尤其相关。

As the flow of water through plants has utmost importance for the functioning of our biosphere and the human population, most people would be extremely surprised to learn that it is still unknown how exactly plants accomplish long-distance water transport. While there is massive evidence for water transport in plant xylem under negative pressure, it is still unknown whether hydraulic failure by air entry represents a common or rare occurrence. This project aims to investigate the frequency of drought-induced embolism in woody angiosperms and the underlying mechanisms of embolism at the bordered pit level in water conducting cells. By conducting field work at a temperate forest in Germany and a savannah and seasonal rainforest site in China for a total of 30 angiosperm species, we will test the hypothesis that a diverse range of species show a similar relative risk to hydraulic failure, despite clear differences in absolute resistance to drought-induced embolism. We expect that hydraulic failure in the field is largely limited to extreme events. Comparison of embolism resistance in stems and leaves will allow us to test the hydraulic vulnerability segmentation hypothesis, suggesting that xylem in leaves is more prone to hydraulic failure than stem xylem.Moreover, we will test the idea that embolism resistance is associated with the potential occurrence of positive root/stem pressure, and/or with seasonal changes in xylem sap lipids. While positive root/stem pressure is known in various species of temperate forests during spring, it is unclear if root/stem pressure is common in plants from the savannah and seasonal rainforest areas. Since insoluble, amphiphilic lipids were recently discovered in xylem sap of angiosperms, we hypothesize that seasonal drought determines the quantity and/or quality of these lipids, which could play a role in embolism avoidance.Finally, functional characteristics of pit membranes between water conducting cells will be investigated with respect to their porosity and air-seeding fatigue to better understand the mechanisms behind embolism. Hydraulic measurements and ultrastructural observations will be integrated in a spatially explicit model to simulate flow and embolism formation across nanoporous pit membranes.This innovative project will contribute to our understanding of the frequency and spatial distribution of drought-induced embolism in xylem tissue of woody angiosperms. The application is a joint project with Prof. Dr. Kun-Fang Cao at Guangxi University in China, with mutual benefits for both teams, including complementary expertise in plant hydraulics, training of PhD students, and research visits to both countries. This proposal could have implications for biomimetic applications, and will increase our understanding of plant water use and drought tolerance, which is especially relevant given current concerns about climate change.