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

该项目将提供有关一个生态上重要的蚂蚁协会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蚂蚁。尽管切叶蚁很突出，但人们对切叶蚁在热带生态系统中对碳循环和营养循环的整体贡献知之甚少。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。切叶虫是热带森林生态系统中的优势食草动物，将周围10%-50%的植被带进巢中，给巢土施肥，并促进二氧化碳和甲烷向大气中释放。切叶蚁的足迹网络延伸到整个森林，工蚁们排成一排，把一片片树叶带进他们的巢穴，在那里特殊的真菌分解植物材料并产生菌丝，蚂蚁以此为食。切叶蚁巢的体积很大，在筑巢和维护过程中，蚂蚁会将叶子颗粒混合到土壤中，改变土壤化学成分。切叶蚁的活动有可能控制生态系统动态的各个方面，尽管它们的影响程度尚未量化。该项目将侧重于切叶蚁巢作为二氧化碳和甲烷排放热点的作用，以及蚁巢在改变土壤化学和在整个景观中创造土壤中碳(C)、氮(N)和磷(P)的异质性方面的作用。这项工作将在哥斯达黎加的La Selva生物研究站进行，这里是热带科学研究的震中，接待了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的碳动态，并区分二氧化碳和甲烷排放的来源，区分蚂蚁、真菌、蚁穴微生物群落以及根和菌丝的活动。对活跃的切叶蚁巢的N、P生物地球化学以及废弃后的土壤遗留效应进行了量化。该项目采用了多方面的方法，包括将土壤二氧化碳排放量的连续测量与甲烷流出量的离散测量相结合，以确定二氧化碳的稳定碳同位素来源、土壤碳和氮库和通量、根和真菌生物量的估计以及微生物群落和功能指数。将在蚂蚁巢穴、成对的非蚁穴地点以及过去不同时间被遗弃的一系列蚂蚁巢穴上进行测量，以量化生物地球化学变化的影响在蚁穴占据的区域持续多久。这些生物地球化学通量将被纳入一个生态系统模型，以估计局部到区域尺度上的碳通量。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年度研讨会，向学生和研究人员介绍尖端的现场仪器和分析技术，并在La Selva提供使用这些新方法的机会。拉塞尔瓦生物研究站是热带科学研究的震中，接待了来自世界各地的大量学生团体、研究人员，并作为生态旅游中心，因此拟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.