NSFDEB-NERC: MIcrobial Nitrogen cycling in the Tropics (MINT)

Tropical forests are the largest reservoir of terrestrial carbon and strongly influence the flow of nutrients between the Earth's surface and atmosphere. One of the most important of these nutrients is nitrogen. Nitrogen in tropical forests can be assimilated during plant growth and it can also be released from soil to the atmosphere as nitrous oxide. Much of the Earth's nitrogen cycle is controlled by soil microorganisms, which add nitrogen to the soil by removing it from the air and converting it into forms that plants and other organisms can use. How these microbes, and the nitrogen cycle they control, will respond to the changing environment in tropical forests remains largely untested. Increasing the temperature in soil may speed up some nitrogen processes while slowing others, influencing rates of microbial processes involving nitrogen. Small changes matter, because even minor shifts in how much atmospheric nitrogen is removed or released can lead to larger consequences for the Earth as a whole. This project examines how long-term increases in the temperature of tropical forest soils affect the microbial communities that govern the nitrogen balance, and what those changes mean for plant growth and feedbacks on the Earth's atmosphere. This project will also strengthen the Nation's scientific workforce by training undergraduates, technicians, and graduate students in biotechnology and working with artificial intelligence (AI). The research involves a collaboration with counterparts in the United Kingdom funded by the U.K.'s Natural Environment Research Council (NERC). This project examines how long-term soil temperature increase alters nitrogen cycling in lowland tropical forest by influencing nitrogen fixation, soil nitrogen transformation, and nitrous oxide emission. Researchers will test the hypothesis that tropical nitrogen fixation already operates near its upper temperature limit in tropical areas, so that additional increase will reduce fixation and impair plant growth. This study leverages a unique, established, long-term field experiment in which replicated plots heat entire soil profiles by four degrees Celsius to a depth of 1.5 meters, within a one-hectare forest site. Combining meta-transcriptomics, shotgun metagenomics, isotopic nitrogen-fixation assays, and continuous nitrous oxide monitoring, this project will resolve, at high spatial and temporal scales, how environmental change affects the microbes that metabolize nitrogen in the soil and release it as nitrous oxide. The team will also test the consequences of these nitrogen cycling changes for plant communities by studying the growth and physiological responses of different tree species to altered nitrogen cycling in a changing environment. Data will be made publicly available through the National Microbiome Data Collaborative, creating a lasting resource for the scientific community. 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.