Collaborative Research: Quantifying the footprint of a dominant organism: Biogeochemical impacts of leaf cutter ants in a lowland tropical forest ecosystem

该项目将提供生态上重要的蚁群对碳循环的贡献的信息，并将有助于改进对热带森林未来碳动态的预测。热带森林最显著的特征之一是大量的切叶蚁。尽管它们很重要，但人们对切叶蚁对热带生态系统碳和养分循环的总体贡献知之甚少。这些热带和亚热带森林生态系统覆盖了地球陆地面积的17%，储存了大约40%的碳，是全球碳循环的重要决定因素。切叶蚁是热带森林生态系统中的主要食草动物，它们将周围10- 50%的植被带入巢穴，使巢穴土壤肥沃，并促进二氧化碳和甲烷释放到大气中。切叶蚁的足迹网络遍布整个森林，工蚁们排成一列，带着树叶进入它们的巢穴，在那里特殊的真菌会分解植物材料并产生菌丝，蚂蚁以菌丝为食。切叶蚁的巢穴体积巨大，在建造和维护巢穴的过程中，蚂蚁将树叶颗粒混合到土壤中，改变土壤的化学成分。切叶蚁活动具有控制生态系统动力学方面的可能性，尽管其影响程度尚未被量化。该项目将重点关注切叶蚁巢穴作为二氧化碳和甲烷排放热点的作用，以及巢穴在改变土壤化学和造成整个景观中土壤中碳(C)、氮(N)和磷(P)异质性方面的作用。这项工作将在哥斯达黎加的La Selva生物研究站进行，该研究站是热带科学研究的中心，拥有来自世界各地的大量学生团体和研究人员。该项目将描述切叶蚁巢穴上的碳动态特征，并区分蚂蚁、真菌、巢穴微生物群落、根和菌丝活动中二氧化碳和甲烷排放的来源。定量分析了活跃切叶蚁巢穴的N、P生物地球化学特征以及弃巢后的土壤遗留效应。该项目采用多方面的方法，包括将土壤二氧化碳排放的连续测量与甲烷流出的离散测量相结合，二氧化碳的稳定C同位素以确定来源，土壤C和N库和通量，根和真菌生物量的估计，以及微生物群落和功能指数。测量将在蚁巢，成对的非蚁巢地点，以及在过去不同时间被遗弃的蚁巢序列上进行，以量化改变的生物地球化学影响在蚁巢占据的地区持续多久。这些生物地球化学通量将被纳入一个生态系统模型，以估计局地尺度上的碳通量。该项目将通过与来自美国、哥斯达黎加和新西兰的研究人员和学生合作，加强国际合作。除了培训一名博士后研究员和指导几名REU学生外，项目科学家还将举办一年一度的研讨会，向学生和研究人员介绍最前沿的现场仪器和分析技术，并提供在La Selva使用这些新方法的机会。La Selva生物研究站是热带科学研究的中心，拥有大量的学生团体，来自世界各地的研究人员，并作为生态旅游中心，因此建议的研究将得到广泛传播。

This project will provide information on the contribution of an ecologically important ant guild to the carbon cycle and will help improve predictions of future carbon dynamics in tropical forests. One of the most conspicuous features of a tropical forest is the abundance of leaf cutter ants. Despite their prominence, little is known about the overall contribution of leaf cutter ants to carbon and nutrient cycles in tropical ecosystems. These tropical and subtropical forested ecosystems cover 17% of the Earth's land mass and store approximately 40% of all carbon and are an important determinant of the global carbon cycle. Leaf cutters are the dominant herbivores in tropical forest ecosystems, bringing 10-50 % of all surrounding vegetation into the nest, fertilizing nest soils, and promoting the release of carbon dioxide and methane into the atmosphere. The network of leafcutter ant trails extend throughout the forest and workers walk single-file, carrying pieces of leaves into their nests, where special fungi break down the plant material and produce hyphae, on which the ants feed. Leaf cutter ant nests are massive in size and during nest construction and maintenance ants mix leaf particles into the soil and alter soil chemistry. Leaf cutter ant activities have the possibility of controlling aspects of ecosystem dynamics, though the degree of their influence has not been quantified. The project will focus on the role of leafcutter ant nests as hotspots of carbon dioxide and methane emissions and the role of nests in altering soil chemistry and creating heterogeneity in carbon (C), nitrogen (N), and phosphorus (P) in the soil across the landscape. The work will be conducted at La Selva Biological Research Station, Costa Rica, which is an epicenter of tropical scientific research, hosting a large number of student groups, researchers from all over the world. The project will characterize C dynamics on leafcutter ant nests and differentiate the sources of carbon dioxide and methane emissions between the activities of ants, fungi, the nest microbial community, and roots and hyphae. The N, and P biogeochemistry of active leafcutter ant nests will be quantified as well as the soil legacy effects after nests are abandoned. The project uses a multi-faceted approach, including coupling continuous measurements of soil carbon dioxide emissions with discrete measures of methane efflux, stable C isotopes of carbon dioxide to determine sources, soil C and N pools and fluxes, estimates of root and fungal biomass, and microbial community and functional indices. Measurements will be performed on ant nests, paired non-nest sites, and along a sequence of nests abandoned at different times in the past to quantify how long the impact of altered biogeochemistry persists in areas occupied by nests. These biogeochemical fluxes will be incorporated into an ecosystem model to estimate C flux at local-to-regional scales. The project will strengthen international collaborations by working with researchers and students from the US, Costa Rica, and New Zealand. In addition to training a postdoctoral researcher and mentoring several REU students, project scientists will conduct an annual workshop to introduce students and researchers to cutting edge field instrumentation and analysis techniques and provide opportunities to use these new approaches at La Selva. La Selva Biological Research Station is an epicenter of tropical scientific research, hosting a large number of student groups, researchers from all over the world, and serving as a center for ecotourism, thus the proposed research will be widely disseminated.