Decoding the Hidden Mechanisms of Soil Carbon Cycle in Response to Climate Change Restricted; Files Only

Abstract

Climate change is rapidly redefining the biogeochemical dynamics of our planet, particularly in relation to soil organic carbon (SOC) storage and loss. We aim to isolate confounding elements and elucidate the principal mechanisms underpinning SOC dynamics under diverse environmental scenarios: warming (ambient, +1.5°C, and +2.5°C), and nutrient (nitrogen and phosphorus) and carbon addition treatments. Samples were collected from a low-latitude soil warming experiment where warming commenced in 2010 (Whitehall Forest, Athens, Georgia). Under laboratory conditions, we incubated soil samples (22 days) at their respective field temperatures at the time of sample collection. Core aspects of the soil carbon cycle, including particulate (and mineral-associated) organic carbon, microbial biomass carbon, and microbial necromass carbon, as well as critical processes such as soil microbial respiration and enzyme kinetics were examined. Our systematic evaluations helped separate the direct and indirect effects of warming (e.g., the inherent and apparent temperature sensitivity of SOC formation and loss). Our findings indicate that warming has a minor influence on soil carbon storage in substrate-limited ecosystems. However, as carbon and nutrient inputs increase, soil carbon loss accelerates. This study sheds light on the delicate balance between underlying mechanisms that control SOC dynamics in the face of climate change, emphasizing the nuanced interdependence of temperature, substrate resource availability, and soil carbon dynamics.

Table of Contents

1. Introduction

2. Material and Methods

2.1. Study Site and Field Sampling

2.2. Experimental Design

2.3. CO2 Mineralization

2.4. Soil Organic Content

2.5. Physical Fractionation of SOM

2.6. Microbial Biomass Carbon

2.7. Amino Sugar Extraction and Microbial Residual C (necromass)

2.8. Enzyme Kinetics

2.9. Statistics

3. Results

3.1. Temporal variability in CO2 mineralization across treatments

3.2. Carbon content distribution among soil organic matter (SOM) fractions

3.3. Microbial biomass C (MBC) and residual C (necromass) response to incubation

3.4. Enzyme activities and kinetics

3.5. Correlations among measured soil properties before and after incubation

4. Discussion

4.1. Substrate (C and nutrient) amendment but not temperature rise affects CO2 mineralization

4.2. Temperature but not treatment change affects SOC fractions 

4.3. MBC responses to temperatures and treatments

4.4. Microbial residual C responses to temperatures and treatments

4.5. Enzyme kinetics and activity response to treatments and temperatures

4.6. Correlation matrix interpretations

5. Conclusions and Future Implications

6. References

7. Appendix

About this Master's Thesis

Rights statement

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School	Laney Graduate School
Department	Environmental Sciences
Degree	M.S.
Submission	Master's Thesis
Language	English
Research Field	Environmental Sciences Agriculture, Soil Science
Mot-clé	Substrate Availability Temperature Sensitivity Soil C Cylce Climate Change
Committee Chair / Thesis Advisor	Dr. Debjani Sihi, Emory University
Committee Members	Dr. Shaunna Donaher, Emory University Dr. Jacqueline Mohan, University of Georgia

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