DOI: 10.5061/dryad.xwdbrv1t7
title: Data from: Stage-specific biological nitrogen fixation depends on distinct carbon and nitrogen availability in long-term fertilized paddy fields

description: 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.
description: # Data from: Stage-specific biological nitrogen fixation depends on
 distinct carbon and nitrogen availability in long-term fertilized paddy
 fields Dataset DOI:
 [10.5061/dryad.xwdbrv1t7](https://doi.org/10.5061/dryad.xwdbrv1t7) ##
 Description of the data and file structure This dataset contains soil
 biological nitrogen fixation (BNF) activity, basic soil physicochemical
 properties, and diazotrophic community composition summarized at the
 phylum and genus levels. The data were generated from a long-term nitrogen
 fertilization field experiment in paddy fields and were used to examine
 stage-specific drivers of BNF across rice growth stages. All analyses
 presented in the associated article were based on the data provided in the
 three files described below. ### Files and variables #### File:
 Soil_BNF_and_physicochemical_properties.csv **Description:** Soil
 biological nitrogen fixation (BNF) activity and basic soil physicochemical
 properties for all treatments and rice growth stages. ##### Variables *
 Stage: Rice growth stages include the tillering and the maturation stage *
 Treatment: Three treatments with different N fertilization rates: (i) N~0~
 (control), without N fertilization; (ii) N~75~, moderate N fertilization
 at a rate of 75 kg N ha^-1^; and (iii) N~150~, high N fertilization at a
 rate of 150 kg N ha^-1^ * BNF (C~2~H~4~/g h): Soil biological nitrogen
 fixation activity * nifH (copies/g): Soil nifH gene copies * CO~2~ (μg
 C/g): Carbon dioxide emissions * SOC (g/kg): Soil organic carbon * TN
 (g/kg): Soil total nitrogen * C/N ratio: The ratio of soil carbon to
 nitrogen * DOC (mg/kg): Soil dissolved organic carbon * NH~4~^+^-N
 (mg/kg): Soil ammonium nitrogen  * NO~3~^-^-N (mg/kg): Soil nitrate
 nitrogen * INN (mg/kg): Soil inorganic nitrogen * DOC/INN: The ratio of
 soil dissolved organic carbon to inorganic nitrogen * MBC (mg/kg): Soil
 microbial biomass carbon * MBN (mg/kg): Soil microbial biomass nitrogen *
 MBC/MBN: The ratio of soil microbial biomass carbon to microbial biomass
 nitrogen * organic acid (μg/g): Soil organic acid * citric acid (μg/g):
 Soil citric acid * Total free amino acids (μg/g): Soil total free amino
 acids * pH : soil pH #### File: Genus.csv **Description:** Relative
 abundance of diazotrophic communities at the genus level. ##### Variables
 * Stage: Rice growth stages include the tillering and the maturation stage
 * Treatment: Three treatments with different N fertilization rates: (i)
 N~0~ (control), without N fertilization; (ii) N~75~, moderate N
 fertilization at a rate of 75 kg N ha^-1^; and (iii) N~150~, high N
 fertilization at a rate of 150 kg N ha^-1^ * Explanation of taxonomic
 column names Column names in the tabular data files represent microbial
 taxonomic assignments derived from sequence annotation. Each column
 corresponds to a taxonomic unit, with taxonomy levels separated by
 semicolons in the following order: **k__**: kingdom **p__**: phylum
 **c__**: class **o__**: order **f__**: family **g__**: genus For example:
 k__Bacteria;p__Proteobacteria;c__Alphaproteobacteria;o__Rhizobiales;f__Bradyrhizobiaceae;g__Bradyrhizobium represents sequences assigned to the genus *Bradyrhizobium* within the family *Bradyrhizobiaceae*. ### File: Phylum.csv **Description:** Relative abundance of diazotrophic communities at the phylum level. ##### Variables * Stage: Rice growth stages include the tillering and the maturation stage * Treatment: Three treatments with different N fertilization rates: (i) N~0~ (control), without N fertilization; (ii) N~75~, moderate N fertilization at a rate of 75 kg N ha^-1^; and (iii) N~150~, high N fertilization at a rate of 150 kg N ha^-1^ * Explanation of taxonomic column names Column names in the tabular data files represent microbial taxonomic assignments derived from sequence annotation. At the phylum level, column names such as *Proteobacteria* and *Firmicutes* indicate sequences that were successfully classified to a known phylum. Columns labeled as *Unassigned;__* represent sequences that could not be confidently assigned to any recognized phylum based on the reference database.