Influence of biological aggregating agents associated with microbial population on soil aggregate stability

doi:10.1016/j.apsoil.2011.01.001

Applied Soil Ecology

Volume 47, Issue 3, March 2011, Pages 153-159

https://doi.org/10.1016/j.apsoil.2011.01.001 Get rights and content

Abstract

In this study, we investigated the effects of plant residue decomposition and biological aggregating agents (microbial extracellular polysaccharides and fungal hyphae) on soil aggregate stability and determined the microbial population at different stages of soil aggregate stabilization. Experiments were conducted in a 40 days incubation period with the following six treatments: the control (soil only), soil + fungicide, soil + bactericide, soil + maize residues, soil + maize residues + fungicide, and soil + maize residues + bactericide. The maize residues treatments greatly enhanced the formation of macroaggregates. In the residue treatments, the addition of fungicide led to a significant suppression of fungal biomass and activity as well as a reduction of soil aggregate stability, which demonstrated the profound influence of fungal activity on aggregate formation. The addition of bactericide also significantly reduced soil aggregate stability, indicating that bacterial activity also played an important role in the macroaggregate formation. However, the effect of microbial extracellular polysaccharides on soil aggregate stability was not significant, which might be attributable to the fast wet sieving method used for aggregate separation. For the treatments of soil + residues and soil + residues + bactericide, the temporal variations of soil aggregate formation with two peak values suggested that other factors, such as hydrophobic compounds and phenolic acids, might be involved in the soil aggregate stabilization process.

Research highlights

▶ The roles of fungi and bacteria in soil aggregation were demonstrated with addition of antibiotics. ▶ Fungi played a more profound role in soil aggregation than bacteria. ▶ A low-energy stress method is necessary to analyze the effects of bacteria on soil aggregation.

Introduction

Soil aggregation affects various soil physical, chemical, and biological processes, such as soil aeration, soil water infiltration, and soil microbial activities. If soil organic matter (SOM) is within soil aggregates, aggregate formation physically protects SOM from biodegradation. Therefore, aggregate formation promotes long term carbon sequestration and soil structural stability (Six et al., 2000b).

Aggregate formation and stabilization are affected by various factors, including clay content, mineralogy of the clay fraction, and types and amount of SOM (Degens, 1997, Denef and Six, 2005). The main agents of aggregate formation and stabilization are organic materials, including persistent cementing agents, such as humic matter involved in stabilizing microaggregates, and transient bonding agents (e.g. polysaccharides derived from plants and microorganisms) as well as temporary binding agents (e.g. fungal hyphae, fine roots, bacterial cells) related to formation and stabilization of macroaggregates. Because of the sensitivity of transient and temporary agents to the change of soil environment, most research activities have focused on the effects of the transient and temporary agents on the soil aggregation. Denef et al. (2001) and De Gryze et al. (2005) showed that fungi significantly affected the macroaggregate formation. Besides physical effects of enmeshment of macroaggregates by hyphae, with extracellular polysaccharides produced by hyphae, microaggregates are attached and bound into stable macroaggregates (Neufeldt et al., 1999). In addition, the hydrophobicity of microbial extracellular polysaccharides contributes to the stabilization of macroaggregates by decreasing their wettability (Liu et al., 2005). Besides fungi, bacteria also exude extracellular polysaccharides to bond soil particles and increase inter-particle cohesion (Degens, 1997).

It is well known that the addition of easily decomposable substrates to soil rapidly stimulates the soil microflora, resulting in a significant increase in aggregate stability (e.g. De Gryze et al., 2005, Abiven et al., 2007). The stimulation of soil microbial community leads to an increase of biological aggregating agents as well, such as fungal hyphae and microbial extracellular polysaccharides. However, the relationships among aggregate stability, microbial population, biological binding and bonding agents in soils amended with organic matter are still poorly understood. Therefore, our objectives were to study the microbial population dynamics at the different stages of soil aggregate stabilization, and to determine the effect of plant residues and biological aggregating agents on soil aggregate stability.

Section snippets

Experimental design

Surface soil (0–20 cm) and maize leaf residues were collected in December of 2008 from a field with long-term maize cropping in Guangzhou (23°03′22.6″N, 113°22′55″E, 300 m H), Guangdong Province in South China. A particle size distribution analysis showed that the soil texture was clay (with sand, silt, and clay particles of 18%, 44%, and 38%, respectively). By using soil core samples, the soil bulk density was determined as 1.2 g cm⁻³. The sample soils were air dried and all macroaggregates were

Carbon mineralization

As shown in Fig. 1, the CO₂ respiration rates were very different between the treatments with and without maize residues. The temporal distributions of CO₂ respiration rates in the SRF and SRB treatments were similar to that in the SR treatment. After 20 days of incubation, the CO₂ production of the SRF treatment was close to those of the three treatments without maize residues and much lower than those of the SR and SRB treatments. The temporal changes of the CO₂ respiration rates were

Discussion

Compared to the treatments without residues, the much higher respiration rates in the treatments with the residues were attributable to the high bioavailability of residues. The maize leaves decayed fast, which might be contributed to a high content of easily available carbon compounds and a low content of recalcitrant compounds (Helfrich et al., 2008). The respiration rate of the SRF treatment was not much lower than that of the SR treatment during the first 2 weeks of incubation, which was

Conclusions

In this study, the effect of biological aggregating agents, including fungal hyphae and microbial extracellular polysaccharides, on soil aggregate stability was investigated and relationships between microbial population and soil aggregate formation were established. Suppressing fungal biomass and activities by fungicide application reduced the soil aggregate stability and the formation of water-stable macroaggregates greatly, which confirmed the important role of fungi on soil aggregate

Acknowledgements

This study was partly supported by grants from the Natural Science Foundation of China (Nos. 51039007 and 50779080) and the Fundamental Research Funds for the Central Universities.

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Influence of biological aggregating agents associated with microbial population on soil aggregate stability

Abstract

Research highlights

Introduction

Section snippets

Experimental design

Carbon mineralization

Discussion

Conclusions

Acknowledgements

Appl. Soil Ecol.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Soil Biol. Biochem.

Geoderma

Soil Biol. Biochem.

Soil Biol. Biochem.

Dynamics of aggregate stability and biological binding agents during decomposition of organic materials

Eur. J. Soil Sci.