Bacterial drivers of forest litter decomposition: linking organic acid production to bacterial diversity dynamics

Forest litter, formed from the metabolic by-products of plant growth, plays a key role in nutrient cycling and microbial community dynamics within forest ecosystems. This study investigated the characteristics of organic acid production during leaf litter decomposition and its influence on bacterial diversity over a 90-day decomposition period at room temperature (25 ± 2 ℃). Samples of leaf litter derived from the fallen leaves of Myrica ruba, Bambusa cerosissima, and Pinus sylvestris in Daluo Mountain (Wenzhou) and Machilus thunbergii, Cunninghamia lanceolata, and Quercus acutissima in Wuyanling National Nature Reserve (Zhejiang) were collected and subjected to decomposition, and the resulting organic acid profiles and bacterial diversity were analyzed. The results showed that organic acid levels increased significantly during the early stages of decomposition, peaking before gradually declining over a 90-day period. Bacterial diversity was consistently higher on the leaf interior compared to the surface. Among the species studied, Bambusa cerosissima and Cunninghamia lanceolata supported greater bacterial diversity than Machilus thunbergii and Quercus acutissima. Bacterial abundance increased during early decomposition, reaching its highest point at day 50, before decreasing. Proteobacteria and Sphingomonas were identified as the dominant bacterial groups throughout decomposition. The heatmap of inter‑group correlation analysis revealed that there were highly significant relationships (p < 0.01) between fumaric acid and Proteobacteria at the phylum level, both on leaf surfaces and internally. At the genus level, oxalic, lactic, fumaric, malic, and citric acids showed significant differences with dominant bacteria. These findings highlight the important role of organic acid production and microbial diversity in leaf litter during decomposition, offering new insights into their combined impact on forest ecosystem function and nutrient cycling.