Interpretive Summary of the Technical Paper:
“Linking soil microbial community structure to potential carbon mineralization: A continental scale assessment of reduced tillage”
Carbon mineralization potential is a commonly used indicator of soil health and is recommended by the Soil Health Institute. Some may be more familiar with the indicator when described as “CO2 burst” or “soil respiration.” The terminology associated with the indicator reflects the methodology used, where a burst of carbon dioxide (CO2) released from microbial activity is measured upon rewetting an air-dried, sieved soil. Reported measurement values are often greater in no-till systems when compared to conventionally tilled systems. While the measurement is known to be driven by soil microbes, little is known about which microbes are responsible for creating the burst of CO2. Understanding which microbes drive these differences will strengthen interpretation of this widely used indicator of soil health.
To better understand the microbes associated with greater carbon mineralization potential in reduced tillage systems, scientists at the Soil Health Institute analyzed soil DNA sequences, collected as part of the North American Project to Evaluate Soil Health Measurements. Soils used in the study were collected from 124 long-term agricultural research sites across the U.S., Canada, and Mexico. Specific DNA sequences were used to identify different microbes found in each soil and research treatment. First, we determined how tillage impacted the abundances of different microbes. Next, we identified groups of soil microbes that flourished in no-till systems and were influential drivers of 24-hour carbon mineralization measurements.
Results indicated that switching from intensive tillage practices (moldboard, chisel plow, etc.) to no-till management consistently changed the abundance of certain microbes, except in systems with wheat-based rotations. We hypothesized that the greater belowground biomass produced in wheat systems may mimic residue incorporation from tillage, resulting in similar microbe populations between the treatments. Results from less intense tillage comparisons (no-till vs. reduced tillage and reduced tillage vs. intense tillage) were mixed. Less intense tillage comparisons at approximately half of long-term sites contained similar microbial fingerprints. However, when grouped by soil pH, we found only soil microbes at sites with slightly acidic soils were unaffected by differences in tillage.
Next, we identified microbes that influenced greater carbon mineralization potential measurements. We found that many of the microbes that influenced greater CO2 bursts were also more abundant in reduced tillage systems. These organisms were often slower growing and adaptive to lower, but consistent nutrient concentrations. This means that the organisms are not reliant on additional outside inputs (organic residues, manures, etc.), but are capable of cycling nutrients from residues contained within stable aggregates and from root exudates when available. Additionally, several of the organisms could produce extracellular polymeric substances, commonly referred to as, “microbial glues.” Many of these substances form biofilms, which help microbes deal with changes in soil moisture over time. Additionally, these “glues” have been shown to enhance aggregation in the soil profile. This study demonstrated how understanding the microbial drivers of carbon mineralization potential strengthens our ability to interpret this widely used measurement. In this particular case, we discovered that reducing tillage resulted in soil microbial communities more capable of thriving under diverse environmental conditions. This means that as more climate extremes are experienced, those microbial
communities present in reduced tillage systems are more resilient to those extremes and can therefore carry on their important functions of building soil aggregates, cycling nutrients, and others.
Read the peer-reviewed manuscript here: https://www.sciencedirect.com/science/article/pii/S003807172200075X