Divergent mechanisms of labile phosphorus accumulation in paddy soils under TPU microplastics versus manure-derived hydrochar: roles of dissolved organic matter and bacterial communities

The availability of phosphorus (P) in paddy soils is essential for sustainable agriculture and labile P (LP) content is influenced by soil dissolved organic matter (DOM) and the soil microbiome. However, the mechanisms by which anthropogenic carbon sources such as hydrochar (HC) and microplastics (MPs) regulate P fraction transformation remain poorly understood. Results showed that HC and MPs increased soil LP content by 21.1% and 14.2%, respectively, and raised soil DOM content by 21.3% and 27.9%. Bacterial communities emerged as the key drivers of these processes, with significant correlations observed between soil DOM features and LP dynamics ( p < 0.05). HC enhanced interspecific competition by increasing carbon bioavailability, which was reflected in the accelerated turnover of bacterial communities ( v = 0.217) and the dominance of copiotrophic bacteria. MPs, on the other hand, boosted microbial network complexity by promoting the secretion of protein-like soil DOM, fostering more interconnected microbial communities. These changes facilitated the conversion of soil LP. These findings highlight the distinct mechanisms by which HC and MPs regulate soil P cycling, emphasizing the importance of soil DOM-microbe interactions for sustainable P management in agriculture.