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回收为生物可以使用的碳形式。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，用来防御敌人或者给他们提供营养树木用碳来回报这些服务提供者，也就是所谓的互利主义者。因此，树木互利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。这项研究旨在确定有多少来自树木的碳投资于互利主义者，这些碳来自哪里，以及当互利主义被人类驱动的动物群变化破坏时，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，这种关系非常适合实地实验和景观建模，以确定互惠关系如何促进碳循环。这项研究将通过一个基于网络的教育平台传达给全国的K-12学生，该平台旨在通过主动学习来教授生物学。共生蚁群保护肯尼亚稀树草原上的金合欢树免受食草动物的侵害，以换取住房和碳水化合物，但这种互利共生关系因大型食草动物的消失和入侵蚂蚁物种而被破坏。蚂蚁互利减少树木的生长和繁殖的草食动物的情况下，但这种明显的蚂蚁的碳成本从来没有被调查相对于其他关键的树木碳汇，包括分配到根和微生物互利。本论文拟对A. drepanolobium在树的生物相互作用的变化的背景下，发现如何互利影响树木的碳分配。使用现场实验来操纵蚂蚁互利主义者，大型食草动物，和入侵蚂蚁，这项研究将评估多少树木投资于他们的互利主义者相对于树木的碳供应，以及新的碳同化物是如何分配互利主义者和树汇之间。碳分配将通过测量生物量、非结构性碳水化合物、次级代谢产物、互惠回报和新同化物的脉冲标记来评估。因为A. drepanolobium是东非大面积的单优势树木，这些测量将是重要的预测生态系统水平的碳储量的变化。这个奖项反映了NSF的法定使命，并已被认为是值得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的支持。

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.