Tropical N2-fixers in a world of biogeochemical constraints and rising CO2: The role of light, phosphorus, and molybdenum

Abstract

Tropical forests hold immense ecological value as biodiversity hotspots and due to their capacity to store carbon in quantities that are disproportional to their area. Despite their importance in the global carbon cycle, we do not know the mechanisms or dynamics by which tropical forests will respond to climate change. Whether these forests can store carbon and thus mitigate climate change depends on whether soil nutrients such as nitrogen or phosphorus limit plant productivity and the mechanisms and dynamics of such nutrient limitation. Nitrogen fixing plants may play a particularly important role in tropical forest biogeochemical cycles due to their ability to bring new nitrogen into the ecosystems. To understand how nitrogen fixation controls the tropical carbon sink, we first need to understand what controls nitrogen fixation and how this might change in the future.

My dissertation expands our understanding of how essential soil nutrients – nitrogen, phosphorus, and molybdenum – interact to affect tropical symbiotic fixers, how the demand by plants for nutrients will change in the future at higher CO2 levels, and how weathering and geology play an important role in supplying nutrients. In my dissertation research I address these specific questions: (1) what controls nitrogen fixation (at individual and ecosystem levels) in the tropics now and into the future as global C and N cycles change? (2) How will ecological constraints affect tropical nitrogen fixers’ response to rising CO2? And (3) what controls phosphorus and molybdenum bioavailability in the soil, and how does this translate into nutrient limitation?