Data from: Stage-specific biological nitrogen fixation depends on distinct carbon and nitrogen availability in long-term fertilized paddy fields

Industrial Haber-Bosch provides 32 Tg nitrogen (N) per year to global
croplands. Such large amounts of N fertilization will reshape soil N
cycles. One uncertainty is whether and how these long-term N inputs impact
soil biological N2 fixation (BNF) associated with plant growth, a crucial
microbial-driven process to decipher the balance between soil N and plant
N in paddy fields. To fill this gap, we conducted a 10-year field
experiment to systematically evaluate the impacts of three N fertilization
rates (0, 75, and 150 kg N ha-1) on soil BNF activity, diazotrophic
communities, and environmental dynamics at two typical rice growth stages
(tillering and maturation) in paddy fields. Moderate N fertilization at a
75 kg N ha-1 rate significantly stimulated BNF activity and nifH gene
abundance at the tillering stage, with increases of 20.9% and 49.7%,
respectively. This enhancement was primarily due to the supply of
available carbon (C) sources from organic acids, which promoted the BNF
process to meet the N requirement from rice at the early stage. In
contrast, BNF activity and nifH gene abundance decreased with increasing N
levels at the maturation stages, reflecting the negative impact of N
enrichment on diazotrophs. The accumulation of inorganic N and amino acids
reduced the dependence on the BNF process. Stage-specific key diazotrophs,
such as Rhizobium at tillering and Azoarcus at maturation, played pivotal
roles in the soil BNF. Soil dissolved organic C and inorganic N were
positively correlated with BNF at the tillering stage, but negatively at
the maturation stage. Random Forest analysis further revealed that the BNF
was primarily regulated by available nutrients at the tillering stage,
while closely associated with the key diazotrophs at the maturation stage.
This study highlights that the stage-specific BNF process depends on C
availability and key diazotrophs with long-term N fertilization, providing
a basis for optimized N management in paddy fields.