Carbon-phosphorus coupling in reddish paddy fields under long-term organic material input: Temporal dynamics and the...

Long-term organic material input has been shown to enhance soil organic carbon (SOC) and potentially improve phosphorus (P) availability. The pqqC gene that encodes pyrroloquinoline quinone synthase can play a key role in regulating P mobilization and availability.

The temporal dynamics of C-P coupling and microbial mechanisms involving pqqC-harboring bacteria remain insufficiently understood.

Temporal variations in SOC and P fractions along with enzyme activities were examined under long-term pig manure application and straw return for 10, 20, 30, and 43 years, with particular emphasis on the response of pqqC-harboring bacterial communities in the 43rd year.

SOC fractions were primarily influenced by both the timing and type of organic material input. Pig manure consistently increased soil available P (Olsen-P), total P (TP), and P activation coefficient (PAC), thereby enhancing both labile and stable P fractions. Straw return exhibited limited effects in earlier stages but significantly increased Olsen-P, TP, and PAC by the 43rd year. Enzyme activities related to C acquisition exhibited a gradual increase, whereas N- and P-acquiring enzyme activities demonstrated more complex trends. Structural equation modeling revealed that changes in SOC fractions, microbial carbon use efficiency (CUE), ecosystem multifunctionality (EMF), enzyme activities, and pqqC-harboring Rhodanobacter were the major drivers of P dynamics, primarily by modulating moderately labile P (mod-labile P), ultimately enhancing P availability.

Under long-term organic material inputs, SOC fractions were regulated by both timing and type of input. Moreover, the changes in SOC fractions and CUE indirectly influenced pqqC-harboring Rhodanobacter through EMF, initiating a cascade that affected C- and P-acquiring enzyme activities and mod-labile P, ultimately regulating Olsen-P and PAC.