Relationships of bacterial-feeding nematodes, phosphatase-producing bacteria, phosphatase activity and their effects on soil organic phosphorus mineralization under straw return

Bacterial-feeding nematodes can affect soil phosphatase activity by influencing phosphatase-producing bacteria and thus may affect soil organic phosphorus (P) mineralization. However, relationships between bacterial-feeding nematodes, phosphatase-producing bacteria, phosphatase activity and their effects on organic P mineralization under straw return remain largely unclear. The present work carried out a field experiment to analyze changes of bacterial-feeding nematodes, phosphatase-producing bacteria, phosphatase, organic P and inorganic P composition under different straw return amounts [0 % (S0), 30 % (S30), 50 % (S50) and 100 % (S100) crop residue incorporation)] as well as the relationships between these features. Compared to S0 treatment, S100 treatment significantly increased the abundances of bacterial-feeding nematode Heterocephalobus, Eucephalobus and Cephalobus; relative abundance of the alkaline phosphatase-producing bacteria Bacillus; phosphodiesterase (PD) and alkaline phosphomonoesterase (AlP) activities; and diester content, but did not change the soil available P (AP) content. Based on the relationships between phosphatase, P composition and AP, the maintenance of soil AP content under S100 treatment was attributed to the promoted mineralization of monoesters by increased AlP activity. Among the alkaline phosphatase-producing bacterial genera, only Bacillus showed significant and positive relation to AlP, structural equation modeling (SEM) showed that this genus also had a significant direct positive effect on AlP. Of diverse genera of bacterial-feeding nematodes, only Heterocephalobus had a significant direct and positive effect on Bacillus. Heterocephalobus also showed significant and positive relation to AlP. Overall, bacterial-feeding nematode Heterocephalobus possibly increased AlP activity by affecting the Bacillus, thus promoting monoester mineralization and indirectly improving soil P availability under straw return.