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参与者，因为它们将大气中的二氧化碳循环为生物可以利用的碳形式。为了成功，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。树木用碳奖励这些被称为互助者的服务提供者。因此，树木互助者可能对碳循环有很大的影响，但这些影响很少被量化。这项研究试图确定有多少来自树木的碳被投资于互助者，这些碳来自哪里，以及当互助性被人类推动的动物群变化扰乱时，这种碳投资是否会发生变化。该项目将利用肯尼亚树木和防御性蚂蚁之间的互惠关系，这种互惠关系非常适合田间实验和景观建模，以确定互助者如何为碳循环做出贡献。这项研究将通过一个旨在通过主动学习教授生物学的网络教育平台传达给全国的K-12学生。共生蚁群保护相思树免受肯尼亚稀树草原上的食草动物的伤害，以换取住房和碳水化合物，但这种互惠关系因巨型食草动物的消失和一种入侵的蚂蚁物种而被破坏。蚂蚁互助者在没有食草动物的情况下减少树木的生长和繁殖，但相对于其他关键的树木碳汇，包括分配给根和微生物互助者，蚂蚁的这种明显的碳成本从未被研究过。这项拟议的工作将在树的生物相互作用发生变化的背景下，研究树中的碳库和动态，以发现互助者如何影响树的碳分配。利用田间实验来操纵蚂蚁互助者、食草动物和入侵蚂蚁，这项研究将评估相对于树木碳供应，树木在其互助者身上投入了多少资金，以及新的碳同化物如何在互助者和树汇之间分配。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。由于A.drepanolobium是一种横跨东非大片地区的单一优势树，这些测量结果对于预测生态系统层面碳储量的变化将是重要的。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.