Body size of soil organisms is more sensitive to fertilization than their community structure: Evidence from a rice field trial

•Fertilization significantly affected bacterial community structure and body size.•Fertilization did not affect fungal community diversity and body size.•The body size of soil nematode communities was very sensitive to fertilization.•In total, the body size of soil organisms was sensitive to environmental changes. The effective use of soil biological resources requires a thorough understanding of the ecological roles played by biological communities. The majority of research on soil biological communities has concentrated on their structural aspects, such as diversity and composition. However, further efforts are required to provide a comprehensive understanding of community characteristics. Body size can be used to better understand the ecological activities of soil biological communities, as it is a significant life history feature of organisms. The current study examined alterations to the populations of bacteria, fungi, and nematodes in soil samples that were treated with chemical fertilizer (CF), organic fertilizer (OF), or no fertilizer (CK). The results showed that, in comparison to CK, OF treatments reduced the Shannon diversity of the bacterial community. The fertilization treatments (CF and OF) resulted in a significant increase in the community-weighted mean (CWM) of bacterial body size and the relative abundance of Candidatus koribacter, as compared to the CK treatment. The body size and diversity of the fungal did not significantly differ across the fertilization treatments. Additionally, the CF treatment led to a higher relative abundance of Mortierella in the soil when compared to the CK and OF treatments. The CWM of nematode body size varied dramatically across treatments, whereas there was no discernible variation in diversity or composition. Furthermore, a comprehensive analysis has been carried out utilizing three separate approaches to assess the sensitivity of the soil biological community diversity, composition, and body size to environmental changes. These methods include correlation heatmap, redundancy analysis, and structural equation model. The study consistently showed that the CWM body size of soil organisms is more vulnerable to environmental changes compared to the variety and composition of the community structure. Meanwhile, the current study has revealed that this tendency is less prominent in fungal communities and more apparent in nematode colonies. Our results highlight the importance of body size in characterizing the d