The Changes in Soil Microorganisms and Soil Chemical Properties Affect the Heterogeneity and Stability of Soil Aggregates before and after Grassland Conversion

Abstract

The conversion of grasslands to croplands is common in the agro-pastoral ecotone and brings potential risks to soil health and environmental safety. As the forming unit of soil structure, the status of soil aggregates determines soil health and is affected by multiple factors. This study investigated the changes in soil aggregate and main related factors in conversion grasslands with different managed years. Grassland conversion ages were selected as experimental treatments, which included unmanaged grassland, 3 years, 10 years, 30 years, and 50 years since grassland conversion. After grassland conversion, the proportion of large macro-aggregates with a particle size of >2 mm in the 0–10 cm soil layer decreased, small macro-aggregates with a particle size of 2–0.25 mm and micro-aggregates with a particle size of 0.25–0.053 mm increased, while aggregates with a particle size of <0.053 mm had no significant change. Soil chemical properties, most microorganisms and the soil aggregate stability indices MWD and GMD decreased at the early stage (<30 years) of the managed grasslands. After about 50 years of cultivation, soil chemical properties and microorganisms returned to equal or higher levels compared to unmanaged grasslands. However, the stability of aggregates (mean weight diameter (MWD) and geometric mean diameter (GMD)) did not recover to the initial state. MWD and GMD were positively correlated with most bacterial factors (total phospholipid fatty acids (PLFAs), bacteria, Gram-positive bacteria, Gram-negative bacteria, actinomycetes and arbuscular mycorrhizal fungi (AMF)) and some soil chemical properties (carbon, nitrogen and polysaccharides). According to the partial least square structural equation model, soil organic carbon, total nitrogen and phosphorus in the 0–10 cm soil layer explained 33.0% of the variance in MWD by influencing microorganisms. These results indicated that the stability of aggregates was directly driven by microorganisms and indirectly affected by soil organic carbon, total nitrogen and phosphorus.

Multiple Factors Jointly Lead to the Lower Soil Microbial Carbon Use Efficiency of Abies fanjingshanensis in a Typical Subtropical Forest in Southwest China

“…The amount of soil moisture has a significant impact on the growth and activity of soil microorganisms. Fungi are more sensitive than bacteria, indicating that under different soil moisture conditions, different communities of soil microorganisms have different adaptations and regulatory mechanisms [37]. It is generally believed that fungi have an advantage over bacteria in soil lacking water because bacteria are more adaptable to the environment and have a higher tolerance [38], whereas fungi have a single-celled structure, which is more flexible and not limited by water [39].…”

Influence of some polymers and microorganisms on the soil physical properties under drought conditions

“…These results align with the capacity of polymers to absorb water at a rate significantly higher than their weight and emphasize their potential impact on soil water management and irrigation efficiency (Abedi-Koupai and Sohrab, 2004;Yang et al, 2014;Baran et al, 2015;Montesano et al, 2015;Patel et al, 2023). The role of soil microbes, such as Bacillus bacteria and Actinomycetes, in producing polysaccharides that contribute to soil aggregation and water retention is significant (Ren et al, 2022). Also, Trichoderma, a type of soil fungus, can bond to soil particles by mycelium or act as a binding agent in soil particles by secreting insoluble extracellular substances.…”

Native Trichoderma Strains Biocontrol Potential against Soil-Borne Pathogens: Strawberry

“…Azoxystrobin, metalaxyl, and difenoconazole due to the often use of fungicides, these pathogens have developed resistance to these fungicides. As a result, chemical combat is unsuccessful in offering enough control for the disease [75,76]. There is no one-size-matches-all-solution to disease control in soil-based strawberry growing, and a combination of strategies can be useful.…”