Soil acidity shapes microbial carbon processing, impacting farmland fertility

Soil acidification is a growing challenge in intensive farming, contributing to significant losses of soil organic carbon and diminished fertility. Traditional agricultural management often employs lime materials to neutralize acidic soil, aiming to improve soil health and increase carbon stocks. However, the precise mechanisms by which pH changes influence microbial carbon metabolism, particularly in the breakdown of plant residues, have remained unclear. Researchers, including Xiaodong Zheng and Zhongzhen Liu from the Guangdong Academy of Agricultural Sciences, and Qimei Lin, Hailong Wang, Anna Gunina of University of Kassel and Tumen University, Yunying Fang and Lukas Van Zwieten from Griffith University and Department of Primary Industries, New South Wales, and Nanthi Bolan from The University of Western Australia, set out to clarify these processes.

Investigating Microbial Responses in a Controlled Setting

To investigate the effect of soil pH, the scientists conducted a 60-day incubation experiment using 13C-labeled maize straw. This straw was separated into hydrophilic water-loving and hydrophobic water-repelling fractions. These distinct fractions were then introduced into both naturally acidic Ferralsol and the same soil adjusted to a neutral pH with calcium oxide. Using phospholipid fatty acid PLFA analysis, the team meticulously tracked how different microbial groups—bacteria, fungi, and actinomycetes—processed these carbon sources under varying pH conditions.

Acidic Conditions Drive Faster Breakdown of Simpler Carbon

The study's outcomes revealed that acidic Ferralsol exhibited a greater mineralization of the hydrophilic fraction compared to the neutralized soil. Mineralization, the process where organic matter is converted to CO₂, was initially much higher for hydrophilic compounds in acidic conditions. This suggests that structurally simple carbon compounds are more readily broken down in low pH environments. In contrast, the mineralization of the hydrophobic fraction remained similar across both acidic and neutralized soils, indicating less pH sensitivity for these more complex molecules.

Microbial Preferences Determined by Soil pH

The research also found that soil pH strongly influenced the substrate utilization patterns of different microbial groups. Actinomycetes showed a greater preference for the hydrophilic fraction in neutralized soil, aligning with their known neutrophilic nature. Bacteria consistently preferred hydrophilic compounds in both soil types, while fungi favored hydrophobic compounds. The study determined that the sensitivity of microbial substrate utilization to pH followed a specific order: actinomycetes exhibited the highest sensitivity, followed by bacteria, with fungi demonstrating the most tolerance to pH changes.

Enhancing Carbon Storage Through pH Management

A key finding was the impact of soil pH on microbial substrate use efficiency SUE. The SUE of the hydrophilic fraction was notably higher in the neutralized Ferralsol throughout the incubation period, indicating that microorganisms in neutral soil effectively incorporated more organic carbon into their biomass. This suggests that liming acidic soils can encourage microbes to build more cellular material, thereby retaining carbon within the soil rather than releasing it as CO₂.

Implications for Sustainable Agriculture

This research offers important insights for agricultural practices aiming to improve soil carbon storage. Managing soil pH through liming can direct microbial activity, promoting the incorporation of plant residue carbon into soil organic matter, particularly in Ferralsols common in subtropical regions. The varying utilization strategies observed within and across microbial groups, as identified by Xiang Li, Lan Wei, Lianxi Huang, and Yufen Huang, further suggest that specific microbial species harbor unique carbon metabolization capabilities.

Future Research Directions

The findings confirm that soil pH is a significant regulator of carbon mineralization and microbial utilization strategies. The observed increase in SUE in limed Ferralsol presents a promising pathway for long-term improvements in soil carbon storage. Future studies could concentrate on identifying the specific microbial species responsible for efficient carbon utilization to develop targeted soil management approaches that maximize carbon sequestration and enhance overall soil fertility.

Corresponding Author:

Hailong Wang, Zhongzhen Liu

Original Source:

https://doi.org/10.1007/s44246-023-00075-z

Contributions:

Xiaodong Zheng analysed the data and wrote the article. Anna Gunina, Yunying Fang, Lukas Van Zwieten, and Nanthi Bolan revised the manuscript. Xiang Li, Lan Wei Lianxi Huang, and Yufen Huang collected experimental soil samples and measured related indexes. Qimei Lin, Hailong Wang, and Zhongzhen Liu designed the whole experiment. Zhongzhen Liu submitted the manuscript. The authors read and approved the final manuscript.