Report on the Effect of Microbial Agent M44 on Straw Decomposition in Cold Soils with Emphasis on Sustainable Development Goals (SDGs)

Abstract

The application of compound microbial agents is a vital strategy to optimize soil quality and sustain soil microbial activity, aligning with SDG 15: Life on Land. This study investigated the low-temperature degradation microbial agent M44 and its impact on corn straw decomposition, nutrient release, enzyme activity, and soil microbial regulation under indoor pot conditions simulating cold and arid environments. Results demonstrated that M44 enhanced straw degradation efficiency by 8.9% and increased nutrient release rates for carbon, nitrogen, phosphorus, and potassium by 6.7%, 12.8%, 7.4%, and 9.6%, respectively. Soil enzyme activities significantly improved, promoting organic carbon transformation. The microbial community structure was notably altered, enriching beneficial genera such as Pseudomonas and Penicillium, which facilitated rapid straw degradation. These findings support sustainable agricultural practices and contribute to SDG 2: Zero Hunger and SDG 13: Climate Action by enhancing nutrient cycling and soil health in challenging climates.

Introduction

Crop straw, rich in lignocellulose and essential nutrients, represents a renewable biomass resource crucial for sustainable agriculture (SDG 12: Responsible Consumption and Production). Returning straw to fields improves soil fertility and biological activity but faces challenges in cold and arid regions due to low decomposition efficiency. Microbial-driven lignocellulose degradation is key to nutrient transformation; however, environmental stresses limit microbial activity. Natural synthetic microbial consortia, such as M44, offer stability and synergistic degradation capabilities, making them promising agents for enhancing straw decomposition under adverse conditions.

Materials and Methods

Experimental Design

1. T1: Sterilized soil + microbial agent M44
2. T2: Non-sterilized soil + microbial agent M44
3. T3: Non-sterilized soil without microbial agent (control)

Each treatment involved 35 pots with soil and corn straw segments incubated at 15°C under controlled moisture conditions. The microbial agent dosage was 0.1 g per pot.

Experimental Materials

• Microbial agent M44: Composed mainly of Pseudomonas, Brevundimonas, and Flavobacterium, with 1×10⁹ CFU viable bacteria.
• Soil and Straw: Sandy loam soil and corn straw (Xianyu 696) collected from Inner Mongolia Agricultural University experimental fields.

Measurements

• Straw degradation rate and lignocellulosic content analysis.
• Nutrient release rates for carbon, nitrogen, phosphorus, and potassium.
• Organic carbon structure via 13C-NMR spectroscopy.
• Soil enzyme activities including β-glucosidase, β-xylosidase, laccase, acetyl glucosaminidase, and leucine aminopeptidase.
• Soil microbial biomass carbon and nitrogen.
• Soil microbial community structure and diversity using Illumina MiSeq sequencing.

Results and Analysis

Straw Degradation and Lignocellulosic Components

The microbial agent treatments (T1 and T2) significantly increased straw degradation rates compared to control (T3), following a logarithmic decay model. Fast decay constants increased by up to 18.52% with microbial agent application, enhancing cellulose, hemicellulose, and lignin degradation. Microscopic analysis revealed structural disruption of straw surfaces in microbial treatments, facilitating decomposition.

Nutrient Release

Carbon, nitrogen, phosphorus, and potassium release rates were significantly higher in microbial agent treatments throughout the 16-week period, with the non-sterilized soil plus microbial agent (T2) showing the best performance. This nutrient cycling supports SDG 2: Zero Hunger by improving soil fertility and crop nutrient availability.

Organic Carbon Structure

13C-NMR analysis indicated that microbial agent M44 accelerated the degradation of easily decomposable carbon components (alkoxy and methoxy carbons) while increasing resistant carbon fractions, contributing to soil organic matter stability and carbon sequestration, relevant to SDG 13: Climate Action.

Soil Enzyme Activity

Enzyme activities involved in lignocellulose degradation were significantly enhanced by microbial agent application, peaking at week 8. Enhanced enzyme activity promotes efficient nutrient cycling and soil health, supporting SDG 15: Life on Land.

Soil Microbial Biomass

Microbial biomass carbon and nitrogen increased significantly in microbial agent treatments, indicating enhanced microbial growth and activity, which is essential for sustainable soil ecosystems.

Microbial Diversity and Community Structure

• Microbial agent M44 altered soil bacterial and fungal diversity, enriching key lignocellulose-degrading genera such as Pseudomonas, Stenotrophomonas, and Penicillium.
• Principal coordinate analysis showed distinct clustering of microbial communities in treated soils, indicating microbial agent influence on community composition.

Microbial Network and Module Analysis

Network analysis revealed that microbial agent application enhanced microbial interactions and community modularity, increasing the abundance of beneficial microbes that synergistically degrade straw. Structural equation modeling confirmed that these microbial networks positively influenced enzyme activities and nutrient release rates, thereby improving straw degradation efficiency.

Correlation Between Straw Degradation and Environmental Factors

Straw degradation rates correlated positively with soil microbial biomass, enzyme activities, and specific carbon functional groups, highlighting the role of microbial agents in modifying soil environments to favor decomposition.

Discussion and Conclusion

The study demonstrates that microbial agent M44 significantly improves corn straw degradation under cold and arid conditions by:

• Enhancing microbial community structure and enriching lignocellulose-degrading species.
• Increasing enzyme activities critical for cellulose and lignin breakdown.
• Improving nutrient release and soil microbial biomass, thereby supporting soil fertility.
• Modulating microbial interactions to optimize degradation processes.

These outcomes contribute directly to several Sustainable Development Goals:

1. SDG 2: Zero Hunger – by improving soil nutrient cycling and crop productivity.
2. SDG 12: Responsible Consumption and Production – through sustainable biomass recycling and waste reduction.
3. SDG 13: Climate Action – by enhancing soil carbon sequestration and reducing greenhouse gas emissions from straw burning.
4. SDG 15: Life on Land – by maintaining healthy soil ecosystems and biodiversity.

While the study was conducted under controlled indoor conditions, the findings provide theoretical and practical support for applying microbial agents like M44 in sustainable agriculture, especially in cold and arid regions. Future field trials are necessary to validate environmental adaptability and long-term benefits.

Data Availability

All data generated or analyzed during this study are included in the article and supplementary materials. Microbial raw sequence data are deposited in NCBI under accession number PRJNA1205916.

1. Sustainable Development Goals (SDGs) Addressed or Connected

1. SDG 2: Zero Hunger
   • The article discusses improving soil fertility and nutrient release through microbial agents to enhance crop growth and yield, directly contributing to food security.
2. SDG 12: Responsible Consumption and Production
   • Efficient degradation and recycling of crop straw reduce agricultural waste and promote sustainable resource use.
3. SDG 13: Climate Action
   • Improving soil quality and microbial activity can enhance carbon sequestration and reduce environmental risks associated with straw decomposition.
4. SDG 15: Life on Land
   • The study focuses on soil health, microbial biodiversity, and sustainable land management in cold and arid regions.

2. Specific Targets Under the Identified SDGs

1. SDG 2: Zero Hunger
   • Target 2.3: By 2030, double the agricultural productivity and incomes of small-scale food producers through sustainable food production systems and resilient agricultural practices.
   • Target 2.4: Ensure sustainable food production systems and implement resilient agricultural practices that increase productivity and production.
2. SDG 12: Responsible Consumption and Production
   • Target 12.5: Substantially reduce waste generation through prevention, reduction, recycling, and reuse.
3. SDG 13: Climate Action
   • Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters.
   • Target 13.2: Integrate climate change measures into national policies, strategies, and planning.
4. SDG 15: Life on Land
   • Target 15.3: Combat desertification, restore degraded land and soil, including land affected by desertification, drought, and floods, and strive to achieve a land degradation-neutral world.
   • Target 15.5: Take urgent and significant action to reduce the degradation of natural habitats, halt the loss of biodiversity.

3. Indicators Mentioned or Implied to Measure Progress

1. Straw Degradation Rate (DSR)
   • Used to measure the efficiency of straw decomposition under different treatments.
2. Nutrient Release Rates
   • Release rates of carbon, nitrogen, phosphorus, and potassium from straw as indicators of nutrient cycling and soil fertility improvement.
3. Soil Enzyme Activities
   • Activities of β-glucosidase, β-xylosidase, laccase, acetyl glucosaminidase, and leucine aminopeptidase as indicators of microbial activity and soil health.
4. Soil Microbial Biomass Carbon (MBC) and Nitrogen (MBN)
   • Indicators of soil microbial biomass and nutrient availability.
5. Soil Microbial Diversity and Community Structure
   • Alpha diversity indices (Chao, Ace, Shannon, Simpson) and microbial community composition as indicators of soil biodiversity and ecosystem function.
6. Structural Equation Modeling (SEM) Indicators
   • Relationships between microbial network modules, enzyme activities, and nutrient release rates to evaluate microbial interactions and degradation efficiency.

4. Table of SDGs, Targets, and Indicators

Source: nature.com