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Microbial nitrogen use efficiencies and their molecular controls in carbon sequestering soils


EMSL Project ID
60194

Abstract

Present-day agriculture faces a major challenge to sustain food production in the face of a changing climate while mitigating greenhouse gas (GHG) emissions. One way to rise to this challenge is to enhance soil carbon (C) content through climate smart agricultural practices which build sustainability and resilience by improving soil health. Whole orchard recycling (WOR), the on-site grinding and incorporation of woody biomass into soil prior to replanting, is one such practice that has strong potential to be a C negative by retaining >20 years of tree growth in new orchards and building soil organic matter. GHG flux measurements in recycled and unamended soils suggest a shift in degradability of organic matter in WOR soils over time. However, the role of soil microbes in mediating these fluxes and C and nitrogen (N) transformations is unknown. Woody biomass provides soil microbes with very high C:N substrates, which may result in microbial immobilization of N and altered rates of nitrification and denitrification. We posit that microbial N use efficiency (NUE), which reflects the partitioning of organic N taken up between microbial biomass (growth) and N mineralization, is a key parameter for understanding organic matter accumulation in recycled soils. Hence, we propose to use stable isotope probing to discern molecular controls of microbial N uptake and elucidate their impact on NUE in soils in response to differential C availability using a combination of metabolomic and metatranscriptomic approaches along with quantitative determinations of NUE and gross N mineralization. The proposed research will be conducted in an experimental almond orchard with treatments of WOR or control (unamended soils) at high or low N fertilization rates. Our overall hypothesis is that WOR soils will have higher NUE than unamended soils and N fertilization rates will determine the predominant N uptake pathways. We will test this hypothesis through the following specific aims: (1) Quantify rates of N mineralization and levels (high or low) of NUE in recycled vs. control soils. (2) Determine isotopically resolved metabolite transformations in response to organic vs. inorganic N amendments. (3) Profile the metatranscriptome pertaining to soil N cycle in response to organic and inorganic N additions. This research will benefit BER’s Biological Systems research and Earth and Environmental Systems research missions by discovering microbial metabolic pathways in newly established soil systems and their role in C sequestration and nutrient cycling.

Project Details

Project type
Exploratory Research
Start Date
2021-12-01
End Date
2022-09-30
Status
Closed

Team

Principal Investigator

Amisha Poret-Peterson
Institution
United States Department of Agriculture - Agricultural Research Service

Co-Investigator(s)

Taniya Roy Chowdhury
Institution
Woodwell Climate Research Center

Team Members

David Robles
Institution
University of California, Davis

Brent Holtz
Institution
University of California Agriculture and Natural Resources

Suduan Gao
Institution
University of California Agriculture and Natural Resources

Catherine Culumber
Institution
University of California Agriculture and Natural Resources