The relationship between organic matter and soil microorganisms

Why do some soils have long-lasting fertility and good crop growth? The answer cannot be separated from the tacit cooperation between organic matter and soil microorganisms. From energy supply to nutrient cycling, from soil structure improvement to environmental adaptation, the symbiotic evolution of the two profoundly affects soil health. This article will take you through the two-way symbiotic relationship between the two, unlocking the underlying logic of sustainable soil use.
1、 There is a bidirectional interaction and symbiotic evolution between organic matter and soil microorganisms, which can be summarized as follows: (1) Organic matter is the "food" and "home" of microorganisms Organic matter (including animal and plant residues, humus, root exudates, etc.) is the main carbon and energy source for soil microorganisms (bacteria, fungi, actinomycetes, etc.). Microorganisms obtain energy by decomposing organic matter, while releasing CO ₂ or synthesizing their own biomass. 2. Habitat improvement of organic matter provides a stable microenvironment for microorganisms by improving soil structure (forming granular structures), regulating porosity and water retention. For example, fungal hyphae can expand their network by attaching to organic matter fragments.

（2） Microbial driven transformation and cycling of organic matter 1 Extracellular enzymes secreted by microorganisms for decomposition and mineralization, such as cellulase and lignin peroxidase, break down complex organic matter into simple compounds, such as glucose and amino acids, which are then mineralized into inorganic nutrients, such as NH ₄⁺ and PO ₄³ ⁻, for plant absorption. 2. During the process of humification, some organic matter is re synthesized into humus (such as humic acid and fulvic acid) through microbial metabolism, which relies on enzymatic reactions and metabolic products (such as phenolic oxidase) of microorganisms. 3. Priming Effect: The input of fresh organic matter (such as root exudates) activates microbial activity, accelerating the decomposition of existing organic matter (positive excitation) or fixing carbon through microbial assimilation (negative excitation), thereby regulating the stability of soil carbon pools.

（3） Dynamic equilibrium and feedback mechanism microbial community regulation: The chemical composition of organic matter (C/N ratio, degree of aromatization) selectively enriches specific functional microorganisms (such as high C/N ratio promoting fungal dominance, low C/N ratio promoting bacterial dominance).
Stability maintenance: Microorganisms promote long-term organic matter sequestration by synthesizing recalcitrant microbial residues such as amino sugars and cell wall peptides, forming a "microbial carbon pump" effect.
Environmental response: Under hypoxic or acidic conditions, organic matter decomposition slows down, microbial metabolic pathways shift towards fermentation or methane production, and carbon cycling pathways change.
2、 The relationship between organic matter and soil microorganisms is interdependent and dynamically coordinated, together forming the foundation of soil ecosystems. Its core connection is reflected in the following aspects:

（1） The fundamental role of nutrition and energy 1 Organic matter is the energy reservoir of microorganisms. Soil organic matter (plant residues, animal remains, etc.) provides carbon, nitrogen, and other essential nutrients for microorganisms, and is the material basis for their survival and reproduction. For example, for every gram of organic carbon decomposed by microorganisms, approximately 0.5 grams of biomass can be obtained, forming an energy conversion chain. 2. Microorganisms drive the transformation of organic matter. Microorganisms secrete enzymes to break down large organic molecules (such as cellulose and lignin) into small molecules such as amino acids and sugars, ultimately producing humus (which accounts for 60% -80% of organic matter). This process releases readily available nutrients such as nitrogen, phosphorus, and potassium that plants can absorb.

（2） Synergistic enhancement of ecological functions 1 The combined effect of soil structure improvement is that microbial metabolites (such as polysaccharides and mucus) combine with humus to promote the formation of soil aggregate structure, increase porosity and water retention capacity. Experiments have shown that soil aggregates containing microbial activity have a stability improvement of over 40% compared to sterile soil. 2. Construction of nutrient activation system: Phosphate solubilizing bacteria decompose closed state phosphate ore (such as Ca ₅ (PO ₄) ∝ F), increasing the effective phosphorus content by 2-3 times.
Nitrogen fixing bacteria (such as rhizobia) can fix nitrogen up to 100-300kg per hectare per year.
Potassium solubilizing bacteria can convert 90% of ineffective potassium in soil into available form.

（3） Dynamic balance adjustment mechanism

1. The regulatory hub of carbon to nitrogen ratio (C/N) is that microorganisms preferentially decompose organic matter with a C/N ratio of 25:1. For example, straw (C/N=80:1) requires nitrogen fertilizer supplementation to promote decomposition, while legume plant residues (C/N=20:1) are more easily utilized quickly. 2. Collaborative adaptation of environmental response: Under high temperature (>35 ℃) or drought conditions, microorganisms secrete more extracellular polymeric substances (EPS) to encapsulate organic matter, forming a stress resistant protective layer; When the soil moisture recovers to 60% of the field capacity, the decomposition rate increases by more than twice. （4） The application of modern agriculture inspires the synergy of Organic Fertilizer and bacterial fertilizer: the application of decomposed cow manure (organic matter ≥ 45%)+nitrogen fixing bacterial agent (≥ 5 × 10 ⁸ CFU/g) can increase corn yield by 18% -25%
Cultivation regulation: straw returning combined with deep plowing (25-30cm) can promote aerobic microbial activity and accelerate organic matter mineralization
The essence of the relationship between the two is a closed cycle of "material cycle energy flow functional feedback", and maintaining this balance is the key to sustainable soil use. In actual production, the dual goals of soil health and crop high yield need to be achieved through organic material supplementation, microbial community regulation (such as inoculation with microbial agents), and reasonable cultivation.

3、 Collaborative management in practical applications
Organic fertilizer application: Supplementing with organic matter can enhance microbial diversity and enzyme activity (such as urease and phosphatase), and improve soil fertility.
No tillage and mulching crops: reduce disturbance, protect microbial networks, promote organic matter accumulation and stability.
Microbial agents: Inoculating nitrogen fixing bacteria or phosphate solubilizing bacteria can accelerate the release of nutrients from organic matter, but it needs to be matched with the type of organic matter (such as straw returning to the field with cellulose degrading bacteria).
4、 Summary
The relationship between organic matter and microorganisms is a model of collaborative evolution of "you in me, I in you": organic matter is the "fuel" for microorganisms, and microorganisms are the "engine" driving soil material cycling, jointly maintaining the productivity and sustainability of soil ecosystems.