Effect of soil microbial community structure on the chemical compositions of different soil organic matter fractions in land uses of the Pearl River Estuary

Understanding the interactions between the dynamics of soil organic matter (SOM) and soil microbial communities is important for predicting the stability and fate of estuarine SOM following anthropogenic disturbance. However, current knowledge on the influence of microbial communities on the chemical compositions of different SOM fractions in estuarine land uses still remains incomplete. In this study, we used high-throughput sequencing, Fourier transform infrared spectroscopy, UV-Vis absorption, and fluorescence spectroscopy to investigate soil microbial communities and characterize the chemical compositions of bulk SOM and water-extractable organic matter (WEOM) across different land uses (artificial forests (AF), farmland (FL), natural wetland (NW), construction land (CL), and abandoned land (AL)) in the Pearl River Estuary. The results showed that the bulk SOM in FL and AL exhibited comparable or higher levels of aromatic functional groups (aromatic C-H and aromatic C=C) compared to other land uses. The HIX and SUV254 indexes further confirmed that AF and FL had more aromatic and hydrophobic WEOM. Apart from FL, where anthropogenic humus constituted the largest proportion, the WEOM fraction predominantly consist of three components in the following order across all land uses, ordered as anthropogenic humus < microbial humus < protein humus. The chemical compositions of the different SOM fractions showed a stronger correlation with the dominant bacterial phylum composition, especially for the WEOM fraction, compared to the fungal composition. Meanwhile, our findings demonstrate that bacterial diversity showed a stronger relationship with the chemical composition of WEOM compared to abundance. Overall, this study sheds light on the impact of land use on the quantity and quality of SOM fractions, underscoring the varying influence of microorganisms on the chemical compositions of different SOM fractions within estuarine environments.