Collaborative Research: The risks of safety: xylem anatomy and tradeoffs between reproduction, growth, and drought survival in conifers

在许多地区，日益严重和频繁的干旱威胁着树木的健康。影响树木能否在干旱中存活的关键因素包括传导水分和组成木材的细胞(木质部)的解剖结构，以及树木如何将资源投资于木材生长和繁殖，而不是保护自己免受虫害。这些因素在不同的树木中都可能有所不同。该项目旨在通过结合所有这些功能的测量，提高对碳资源投资如何影响严重干旱中的生存的科学理解。研究人员将利用加利福尼亚州内华达山脉的森林地块，其中许多林地显示出在具有历史意义的2012-2016年干旱期间树木高度死亡。一个小圆柱体的木材将从活的和死亡的树上移除，以测量总体生长、木质部细胞解剖、木材中的碳和防御性树脂的生产。活的树枝将被用来测量与木质部水分运动相关的其他特征。由活松树产生的球果也将被计算几年，以比较分配、繁殖和木材生长量。这些测量将结合起来评估生长如何与温度和降水(气候)相关，生长、木质部解剖和防御如何影响树木在干旱中死亡的可能性，以及这些关系是否在地点或物种之间有所不同。这些结果将与生长与繁殖的分析相结合，以确定哪些资源投资战略在不同的干旱情况下效果最好，从而帮助确定在未来气候下表现良好的针叶树种子来源。该项目将为博士生和本科生提供树突年代学和细胞解剖学数据的收集、处理和/或分析方面的研究经验和培训。研究人员将与CalTeach项目合作开发学习模块，向学生传授树木生理学和森林生态学，同时加强其他STEM技能。干旱期间树木死亡的两个驱动因素受到最大的理论关注是水力故障和碳耗竭/饥饿，但生物制剂也是一个重要的死亡原因。该项目将A)确定7种内华达山脉针叶树的径向生长、木质部解剖和树脂道生产与干旱相关死亡风险之间的关系，B)确认较厚的木质部壁是否始终包含更多的碳资源，C)测试松树球果生产与碳投资和松干抗栓塞性之间是否存在权衡，以及D)模拟不同水平的投资对总体生长、管胞壁、树脂道和繁殖在不同水平干旱胁迫下的终生适宜性结果。通过碳分配透镜检查多个性状也将使茎中的碳分配与种子生产的潜在权衡联系起来。这些结果将是以多代生态进化方式模拟干旱易发森林的森林动态的重要一步。这项研究的结果将通过为水力安全或树脂生产等性状的现实后果提供证据，帮助识别在未来气候下表现良好的针叶树种来源的努力。这一奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Increasingly severe and frequent droughts threaten tree health in many regions. Key factors that affect whether a tree survives a drought include the anatomy of the cells (xylem) that conduct water and make up the wood, and how the tree invests resources toward wood growth versus reproduction versus defending itself from insects. These factors can all vary between individual trees. This project aims to improve scientific understanding of how investment of carbon resources affects survival in a severe drought by combining measurements of all these functions. The researchers will make use of forest plots in the Sierra Nevada mountains of California, many of which exhibited high tree death in the historic 2012-2016 drought. A small cylinder of wood will be removed from living and dead trees to measure overall growth, xylem cell anatomy, carbon in the wood, and production of defensive resins. Live twigs will be used to measure other traits related to water movement through the xylem. Cones produced by living pines will also be counted for several years to compare allocation to reproduction to amount of wood growth. These measurements will be combined to assess how growth relates to temperature and precipitation (climate) and how growth, xylem anatomy, and defense affect the chance that a tree will die in a drought, as well as whether these relationships differ between locations or species. These results will in turn be combined with the analysis of growth versus reproduction to identify which resource investment strategies work best under different drought scenarios, helping to identify conifer seed sources that will perform well under future climates. The project will provide research experience and training in the collection, processing, and/or analysis of dendrochronology and cell anatomy data for PhD students and undergraduates. The investigators will collaborate with the CalTeach program to develop learning modules that teach students about tree physiology and forest ecology while reinforcing other STEM skills.The two drivers of tree mortality during drought that have received the most theoretical attention are hydraulic failure and carbon depletion/starvation, but biotic agents are also an important cause of death. This project will A) determine the relationships between tree radial growth, xylem anatomy, and resin duct production and drought-related mortality risk in seven species of Sierra Nevada conifers, B) confirm whether thicker xylem walls consistently embody more carbon resources, C) test whether there are tradeoffs between cone production and carbon investment and embolism resistance in the stem in pines, and D) model the lifetime fitness consequences of different levels of investment in overall growth, tracheid walls, resin ducts, and reproduction under different levels of drought stress. Examining multiple traits through a carbon-allocation lens will also enable connection of carbon allocation in the stem to potential tradeoffs with seed production. Results will be an important step in modeling forest dynamics in drought-prone forests in a multigenerational eco-evolutionary manner. The findings of this study will help inform efforts to identify conifer seed sources that will perform well under future climates by providing evidence for the real-world consequences of traits such as hydraulic safety or resin production.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.