Measuring and managing energy in soil organic matter
Abstract
The community of heterotrophic soil biota (soil food webs) perform fundamental ecological functions and provide critical ecosystems services. The decomposition of soil organic matter (SOM) provides energy to heterotrophs and nutrients to primary producers. If the energy provided by SOM is a currency in soil biological function (i.e. soil health), then energy should be measured by scientists and managed for agriculture. This study uses the chemical information from carbon-13 NMR spectroscopy to estimate thermodynamic quantities, macronutrients, and decomposition indices for SOM. We conducted NMR measurements in soils from a switchgrass field experiment with nitrogen fertilizer and harvesting treatments. The Gibbs free energy (ΔGo) of switchgrass root systems and SOM responded significantly to both fertilizer and harvesting treatments. Energy-stability relationships in the root biomass showed energy for stability tradeoffs that varied by fertilizer and harvesting treatment. The severity of the energy-stability tradeoff in roots predicted the decomposability of the SOM across treatments. The unprotected (free particulate) SOM had less ΔG° in plots where roots exhibited a high energy-stability tradeoff. Mid-season harvesting was more detrimental to the ΔG° of SOM than N fertilizer and was associated with lower carbohydrate and peptide inventories. SOM in N-fertilized plots had higher carbohydrates inventories, consistent with microbial mining theory. Across all treatments, the ΔG° budget declined linearly with indices of SOM decomposition, a trend that we interpret as the outcome of trophic energy transfer in the soil food web. Energy and macronutrient budgets provide insight to function of the soil food web and could have utility as tools for managing SOM decomposition.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B43A..08H
- Keywords:
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- 0402 Agricultural systems;
- BIOGEOSCIENCES;
- 0465 Microbiology: ecology;
- physiology and genomics;
- BIOGEOSCIENCES;
- 0470 Nutrients and nutrient cycling;
- BIOGEOSCIENCES;
- 0486 Soils/pedology;
- BIOGEOSCIENCES