Collaborative Research: Mineral-associated organic matter: An overlooked source and mediator of bioavailable nitrogen

Plants need nitrogen (N) to survive, but it remains a mystery exactly where, when, and how plants acquire enough N from the soil. This N dilemma limits productivity and leads to challenges in predicting and managing N cycling in natural and managed systems. This project examines a new, more holistic perspective on the terrestrial N cycle that encompasses multiple sources of N from the soil.

The research focuses on the previously overlooked role of mineral-associated organic matter (MAOM) as a potential major driver of N supply to plants. Long-standing theories consider MAOM to be largely inaccessible to plants and microbes, but emerging evidence highlights the need to re-examine this wholesale classification. This work examines the potential N-supplying capacity of MAOM in the zone of soil surrounding roots, a critical nutrient hotspot.

Ultimately, the results provide new insights into the role of MAOM as a mediator of bioavailable N, which will challenge our fundamental understanding of the processes that regulate soil N cycling in terrestrial ecosystems. The work involves participation in a program at Oklahoma State University, which aims to increase the participation of under-represented populations in STEM disciplines.

The project also supports a collaboration with the Oklahoma Conservation Commission to develop a student-led workshop and video series on soil biogeochemistry with specific relevance to soil organic matter and MAOM management.

The overarching objective is to quantify and characterize the intrinsic and plant-mediated capacity of MAOM to supply bioavailable N. The guiding hypothesis emphasizes the dependence of MAOM-N supply on the intrinsic physical-chemical properties of MAOM, the bioavailability of MAOM relative to other forms of soil organic matter, and plant-microbial mechanisms that can facilitate the mobilization of N from MAOM.

The project pursues the following objectives: 1) Examine edaphic factors regulating plant and microbial access to MAOM-N; 2) Identify mechanisms driving MAOM-N mobilization; 3) Assess feedbacks between plant investment in belowground carbon and MAOM-N mobilization. The study assesses soils varying in geochemical properties using laboratory and greenhouse experiments.

Experimental manipulations combined with stable isotope tracing allow for the tracing of MAOM-derived N into bioavailable pools, as well as uptake by microbes and plants.

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.