Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853
Performing Department
College of Ag & Life Sciences
Non Technical Summary
Soil organic carbon stocks contain three-times the amount of carbon as the atmosphere, and yet it is still unclear what mechanisms control this critical balance. An emerging mechanism is the molecular diversity, or the richness and evenness of compounds that comprise the whole organic matter composition. Molecular diversity is hypothesized to not only be influenced by microorganism activity, but it likely also impedes the microbial respiration of soil organic carbon. Soil organic matter molecular diversity has the potential to contribute to soil organic carbon sequestration efforts, can contribute to climate change models by introducing a novel variable to the equation, and can also enhance carbon and nutrient retention, therefore increase crop yields,in agricultural activities.To fully investigate the impact that molecular diversity has on soil organic carbon persistence, we will first identify how microbial transformations of plant litter over time impact the molecular diversity of the resulting soil organic matter.Using this information, we will generate a molecular diversity gradient to use as a substrate in mineralization trials, where we will determine if soil microbial communities respire organic matter with lower molecular diversities at faster rates. Additionally, we will test microbial communities from vastly different ecosystems (i.e., deserts, coniferous forests)across the US to identify if microbial diversity can overcome molecular diversity. Finally, we will identify if mineral components of soil have an effect on the relationships between molecular diversity and microbial respiration rates.Through this experimental approach, we ultimately aim to determine how molecular diversity contributes to the retention of soil organic carbon. Increased understanding of the molecular composition and diversity of soil organic matter can improve our societies overall efforts of offsetting the effects of climate change through increased soil organic carbon sequestration.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
The primary goal of this project is to determine how molecular diversity changes as a result of microbial decomposition processes and what affects this will have on soil organic carbon (SOC) persistence, both on their own and in the presence of soil minerals.Objectives:1. Determine how molecular diversity changes over time as a function of microbial decomposition processes.2. Identify how soil organic matter molecular diversity influences microbial mineralizations rates of the carbon stored therein.3. Identifyhow mineralization rates frommicrobial communities that have high beta-diversity across samples respond to low and highmolecular diversity.4. Test how mineralogy affects the relationship between molecular diversity and microbial mineralization rates.
Project Methods
Efforts:The overall experimental approach for this project starts with using a soil microbial community and plant litter to track how molecular diversity changes over time and to generate an organic mattermolecular diversity gradient substrate (Obj. 1). Using the generated substrate, a series of mineralization trials with the same soil microbial community will be conducted to measure the impact of molecular diversity on mineralization rates (Obj. 2). Next, to identify how the soil microbial community diversity is impacted by molecular diversity soil microbial communities sourced from vastly different locations across the US will be used in mineralization trials using the same molecular diversity substrate gradient (Obj. 3). Finally, to determine how mineral surfaces affect these relationships, they will be added to incubations monitoring soil mineralization rates with the soil microbial community used in the first two experiments (Obj. 4).Objective 1.DOM media (~6 L; ~45 mg C L-1), sourced from herbaceous and woody plant material collected from predominately sugar maple, red oak and lowland shrubs (air-dried and milled to < 2cm for homogenization) at the Turkey Hill experimental forest, will be used to generate a molecular diversity gradient and then progressively decomposed by a soil microbial community for one year. Incubations will be continuously stirred to ensure solution oxygenation. To limit confounding effects of buffers (e.g., elongation of microbial cell bodies) and excess nutrients (e.g., favoring non-oligotrophic microbial species), we will not use solution buffers or nutrient additions. We will monitor organic C and N concentrations, aromaticity, using specific ultra-violet absorbance at 254 nm (SUVA254), and DOM composition changes, using ATR-FTIR spectroscopy. We will use LC-MS and FTICR-MS to analyze selected time-point samples and calculate molecular diversity indexes, including number of identified compounds, Chao 1 and Rao's quadratic entropy equation, which will allow us to test how moleculara-diversity changes over time. From these indices we will select 10 time points to include in our moleculara-diversity gradient. Samples will be filtered and freeze-dried.Objective 2.The 10 samples selected that span the greatest differences in molecular diversity (low to higha-diversity) will be used in mineralization incubation experiments to establish the effect of molecular diversity on SOC persistence. Freeze-dried samples will be reconstituted to equal C concentrations using sterile DI-water, while also controlling for N concentrations through inorganic N additions. The media will be inoculated with the same Turkey Hill microbial community (stationary phase) used to generate it, and CO2respiration rates will be monitored using a Picarro automated gas analyzer (G2201-I, Santa Clara, CA, USA) in four replicates over 20 days with high temporal resolution (4 hr frequency). We aim to monitor replicates for 20 days to measure CO2emission rates as a function of molecular diversity, rather than as a function of microbial community shifts that can occur during longer incubations. Hightemporal resolution offered by the Picarro gas analyzer enables us to detect short-term respiration responses as well as changes in respiration rates, rather than solely cumulative CO2emissions. Data will be reported as cumulative mineralized C and mineralization rates over time as a function of moleculara-diversity.Objective 3.The next phase of experiments aims at identifying how microbial communities that have highb-diversity across samples respond to molecular diversity. Microbial communities will be sourced from soil samples that I collected in 2019 across N. America. Based on PCA analysis of 16s rRNA sequencing data, twelve soil-sourced microbial communities, from four soil orders, that span highb-diversity have been chosen from the available locations. The microbial communities will be obtained from frozen A-horizon samples by using a 1:10 slurry wash of soil in sterile DI-water. The inoculum will all be grown to the same optical density within stationary phase growth to ensure samples are inoculated with a similar number of cells. The molecular diversity gradient generated underObj. 1will be used as the substrate, and C mineralization by the microbial communities selected will be measured using the same established protocols. We will test whether molecular diversity has an effect on microbial decomposition irrespective of the composition or diversity of the microbial communities. Higher microbiala-diversity is expected to be better equipped to decompose C with high moleculara-diversity, while general microbial community composition will not be a good indicator to predict C persistence, as there is likely microbial functional redundancy across communities.Objective 4.The presence and composition of soil minerals will likely exhibit an interaction with molecular diversity, where high molecular diversity when met with higher mineral diversity could promote SOC persistence. To test this hypothesis, we will conduct the established molecular diversity incubation protocol(Obj. 2)with the addition of mineral soils that have had residual OC carefully removed with sodium hypochlorite (pH 8, 25°C). The mineral soil additions will be from the same locations selected inObj. 3--enabling us to determine if mineral additions will inhibit C mineralization rates through adsorption of organic compounds onto reactive mineral surfaces. We expect the presence of minerals will further exacerbate the effects of molecular diversity on reducing C mineralization, given that there are more opportunities for adsorption between the mineral and organic components. We anticipate that a higher degree of mineral diversity (i.e., a mixture of crystalline, poorly crystalline, and various types of clay minerals) will show interactive effects with molecular diversity.Evaluation:The primary data generated throughout this experiment are LCMS/MS metabolite data and soil respiration (CO2) data collected using a Picarro gas analyzer. LCMS/MS data analysis will be conducted in Rstudio, using peak heights and intensities to calculate molecular diversity. In addition, LCMS/MS data will be processed with GNPS to identify molecular compounds in the organic matter solutions to track how their abundances change over time. Respiration data will be used to generate cumulative CO2respiration curves as well as rates of respiration over time. Additional data collection of dissolved organic carbon and nitrogen concentrations will be measured with a Shimadzu TOC-V analyzer and analyzed in Rstudio.