Collaborative Research: Microbial necromass decomposition: moving from predictions to principles

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Microorganisms have been increasingly recognized as significant contributors to the accumulation of organic matter in soil through the inputs of their own dead cell material, collectively referred to as necromass. Despite progress in quantifying the ecological factors affecting the rates of necromass decomposition, which microorganisms actually drive this turnover and how interactions among different functional groups affect degradation dynamics remains poorly understood. The overarching objective of the proposed research is to functionally characterize how bacteria and fungi, both alone and together, degrade microbial necromass and how the carbon and nitrogen from necromass moves into different ecosystem pools (both soils and plants). The cross-disciplinary strengths of the research team will provide a holistic understanding of how decomposer community functioning influences microbial necromass decomposition in ways directly relevant to important ecosystem services such as soil carbon storage and plant nutrient acquisition. Along with enhancing our understanding of the functioning of necromass-associated microbial communities, the project has multiple broader impacts activities focused on sharing knowledge with public audiences and training a diverse pool of STEM-focused students. The specific research aims include: Aim 1: Characterize the genes and metabolic pathways involved in microbial necromass degradation using well-studied fungal and bacterial decomposition systems; Aim 2: Determine which soil microbes use resources derived from microbial necromass and how its decomposition affects soil carbon and nitrogen pools; Aim 3: Track how trees acquire microbial necromass-derived nitrogen via ectomycorrhizal fungal symbioses. These aims will be addressed through an integrated set of experiments that scale from individual microbial cultures to complex communities. In the first aim, RNAseq-based lab experiments will generate a detailed profile of gene expression during the decay of fungal necromass in an ecologically relevant and diverse set of fungi and bacteria. The second aim will couple qSIP analyses of the microbial communities on field-based decaying necromass with isotopic analyses of surrounding soils and roots (using both IRMS and NanoSIMS imaging) to quantitatively track carbon and nitrogen release from necromass types into different ecosystem pools. Finally, in Aim 3, microbial communities present on lab-incubated necromass will be experimentally manipulated to examine how initial substrate chemistry and interspecific competition affect the amount of necromass nitrogen transferred to trees by ectomycorrhizal fungi. Collectively, this research seeks to transition the study microbial necromass decomposition from a largely descriptive to a mechanistically predictive science.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.