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

由于水通过植物的流动对我们生物圈和人类的功能至关重要，大多数人会非常惊讶地得知，植物究竟是如何完成长距离水运输的。虽然有大量的证据表明在负压下植物木质部中的水运输，但仍然不知道空气进入引起的水力破坏是常见的还是罕见的。本研究旨在探讨干旱诱导木本被子植物栓塞的频率，以及导水细胞中有界纹孔水平栓塞的潜在机制。通过在德国的温带森林和中国的萨凡纳和季节性雨林中对30种被子植物进行实地考察，我们将检验以下假设：尽管对干旱引起的栓塞的绝对抵抗力存在明显差异，但不同种类的被子植物对水力衰竭的相对风险相似。我们预计，现场的液压故障在很大程度上限于极端事件。比较茎和叶的栓塞阻力将使我们能够测试水力脆弱性分割假说，这表明，木质部在叶中更容易液压故障比茎木质部，此外，我们将测试栓塞阻力与潜在的正根/茎压力的发生，和/或与木质部汁液脂质的季节性变化。虽然正的根/茎压力在春季温带森林的各种物种中是已知的，但尚不清楚根/茎压力在萨凡纳和季节性雨林地区的植物中是否常见。由于不溶性的，两亲性脂质最近被发现在被子植物的木质部汁液，我们假设，季节性干旱决定了这些脂质的数量和/或质量，这可能会发挥作用，在栓塞avoidation.Finally，孔膜之间的水传导细胞的功能特性将调查其孔隙度和空气播种疲劳，以更好地了解栓塞背后的机制。水力测量和超微结构观测将被整合到一个空间显式模型中，以模拟纳米孔孔膜上的流动和栓塞形成，这一创新项目将有助于我们了解木本被子植物木质部组织中干旱诱导栓塞的频率和空间分布。该应用是与中国广西大学曹坤芳教授的联合项目，双方团队互惠互利，包括工厂液压技术的互补专业知识，博士生培训以及对两国的研究访问。这一提议可能对仿生应用产生影响，并将增加我们对植物水分利用和耐旱性的理解，考虑到目前对气候变化的担忧，这一点尤其重要。

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.