Changes of bacterial versus fungal community composition along a forest degradation gradient of logged-over tropical rain forests, and their consequences on soil enzyme activities in Malaysian Borneo

Background and aim

Soil bacterial and fungal communities play different but mutually interrelated roles in releasing enzymes that catalyze organic matter decomposition. In Malaysian Borneo, decreasing litter inputs caused by forest degradation lead to reductions in soil organic carbon (SOC) and C/N ratio. Enzyme activities also decrease with forest degradation. However, it is unclear if/how changes in microbial community compositions affect soil enzymes, despite their importance in ecosystem processes. We investigated how reduced SOC substrate affects microbial community compositions and further influences enzyme activities during forest degradation.

Methods

We used 16S and ITS amplicon sequencing and ergosterol extraction to derive microbial absolute and relative abundances. A principal coordinate analysis was performed on absolute abundances to analyze patterns of bacterial and fungal community compositions. Structural equation modeling (SEM) was conducted to investigate how SOC affects enzyme activities via microbial community compositions.

Results

Fungal community composition shifted more distinctly than bacterial community composition along the forest degradation gradient. SEM suggested that reduced SOC influenced bacterial and fungal community compositions, while fungal community composition affected activities of acid phosphatase, β-glucosidase, and leucine aminopeptidase.

Conclusion

Changes in fungal community composition may be due to different responses of fungal phyla to changing quality of bulk soil organic matter with decreasing litter input during forest degradation. Variations in fungal community composition subsequently induced changes in enzyme activities. By contrast, bacterial community composition did not change because labile organic matter of bacterial substrates was available throughout degradation course, particularly such matter being supplied as fungal decomposition by-products.