EAGER: Tracking carbon allocation to unravel how a mutualism and its breakdown affect the carbon cycle

树木是碳循环中的关键角色，因为它们将大气中的二氧化碳循环成生物可以利用的碳形式。为了获得成功，大多数树木需要动物或微生物为它们提供服务，例如防御敌人或为它们提供营养。树木用碳回报这些服务提供者，即互惠主义者。因此，树木共生者可能对碳循环有很大的影响，但这些影响很少被量化。这项研究旨在确定从树木中获得的碳有多少投资于互惠共生，这些碳来自哪里，以及当互惠共生被人类驱动的动物群变化破坏时，这些碳投资是否会发生变化。该项目将利用肯尼亚树木和防御蚂蚁之间的互惠关系，这种互惠关系非常适合于实地实验和景观建模，以确定互惠关系如何对碳循环做出贡献。这项研究将通过一个基于网络的教育平台传播给全国的K-12学生，该平台旨在通过主动学习来教授生物学。在肯尼亚的稀树草原上，共生蚁群保护金合欢树免受食草动物的侵害，以换取住房和碳水化合物，但这种共生关系被大型食草动物的消失和一种入侵的蚂蚁物种所破坏。在没有草食的情况下，蚂蚁共生减少了树木的生长和繁殖，但蚂蚁的这种明显的碳成本从未被研究过，相对于其他关键的树木碳汇，包括分配给根系和微生物共生。该研究将在树的生物相互作用变化的背景下研究A. drepanolobium的碳库和动态，以发现共生者如何影响树木的碳分配。本研究将利用野外实验对互惠蚁、大型食草动物和入侵蚂蚁进行操作，评估树木对互惠蚁的投资与树木碳供应的关系，以及新的碳同化物如何在互惠蚁和树木汇之间分配。碳分配将通过测量生物量、非结构性碳水化合物、次生代谢物、互惠奖励和新同化物的脉冲标记来评估。因为在东非的大部分地区，a . drepanolobium是一种单优势树，这些测量对于预测生态系统水平碳储量的变化将是重要的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Trees are key players in the carbon cycle because they recycle atmospheric carbon dioxide into forms of carbon that living things can use. To be successful, most trees require animals or microbes to provide them with services, e.g., with defense against enemies or to supply them with nutrients. Trees reward these service providers, known as mutualists, with carbon. Tree mutualists thus probably have large impacts on the carbon cycle, but these impacts have rarely been quantified. This research seeks to determine how much carbon from trees is invested in mutualists, where that carbon comes from, and whether that carbon investment changes when mutualisms are disrupted by human-driven changes in the animal fauna. The project will leverage a mutualism between trees and defensive ants in Kenya that is uniquely well-suited to field experiments and landscape modeling, in order to determine how mutualists contribute to the carbon cycle. This research will be communicated to K-12 students throughout the country using a web-based education platform designed to teach biology through active learning.Symbiotic ant colonies protect Acacia drepanolobium trees against herbivores in Kenyan savannas in exchange for housing and carbohydrates, but this mutualism is disrupted by the disappearance of megaherbivores and by an invasive ant species. Ant mutualists reduce tree growth and reproduction in the absence of herbivory, but this apparent carbon cost of ants has never been investigated relative to other critical tree carbon sinks, including allocation to roots and microbial mutualists. The proposed work will investigate carbon pools and dynamics in A. drepanolobium in the context of variation in the tree's biotic interactions to discover how mutualists affect tree carbon allocation. Using field experiments to manipulate ant mutualists, megaherbivores, and invasive ants, this research will evaluate how much trees invest in their mutualists relative to tree carbon supply, and how new carbon assimilates are partitioned between mutualists and tree sinks. Carbon allocation will be assessed by measuring biomass, nonstructural carbohydrates, secondary metabolites, mutualist rewards, and by pulse labeling of new assimilates. Because A. drepanolobium is a monodominant tree across large areas of East Africa, these measurements will be important to predicting changes in ecosystem-level carbon storage.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.