Abstract
Abstract 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 N 2 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 nif H 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 nif H 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. Read the free Plain Language Summary for this article on the Journal blog.
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Claims 10
Claim · model-written summary
Moderate N fertilization at 75 kg N ha−1 significantly stimulated soil BNF activity at tillering by 20.9%
- Taxon
- rice
Oryza sativae0 - Organ / stage
- tillering stagee1
- Treatment
- Moderate N fertilization at a 75 kg N ha −1 ratee1
- Outcome
- BNF activitye1
- Direction
- stimulatede1
- Value
- 20.9%e1
- Setting
- paddy fieldse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two typical rice growth stages (tillering and maturation) in paddy fields”
e1“Moderate N fertilization at a 75 kg N ha −1 rate significantly stimulated BNF activity and nif H gene abundance at the tillering stage, with increases of 20.9% and 49.7%, respectively”
Claim · model-written summary
Moderate N fertilization at 75 kg N ha−1 significantly increased nif H gene abundance at tillering by 49.7%
- Taxon
- riceOryza sativae0
- Organ / stage
- tillering stagee1
- Treatment
- Moderate N fertilization at a 75 kg N ha −1 ratee1
- Gene
- nif He1
- Outcome
- nif H gene abundancee1
- Direction
- increasese1
- Value
- 49.7%e1
- Setting
- paddy fieldse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two typical rice growth stages (tillering and maturation) in paddy fields”
e1“Moderate N fertilization at a 75 kg N ha −1 rate significantly stimulated BNF activity and nif H gene abundance at the tillering stage, with increases of 20.9% and 49.7%, respectively”
Claim · model-written summary
BNF activity and nif H gene abundance decreased with increasing N levels at the maturation stages
- Taxon
- riceOryza sativae0
- Organ / stage
- maturation stagese2
- Treatment
- increasing N levelse2
- Outcome
- BNF activity and nif H gene abundancee2
- Direction
- decreasede2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two typical rice growth stages (tillering and maturation) in paddy fields”
e2“BNF activity and nif H gene abundance decreased with increasing N levels at the maturation stages, reflecting the negative impact of N enrichment on diazotrophs”
Claim · model-written summary
Accumulation of inorganic N and amino acids reduced the dependence of rice on the BNF process
- Taxon
- riceOryza sativae0
- Compound
- inorganic N and amino acidse3
- Outcome
- dependence on the BNF processe3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two typical rice growth stages (tillering and maturation) in paddy fields”
e3“The accumulation of inorganic N and amino acids reduced the dependence on the BNF process”
Claim · model-written summary
Rhizobium at tillering played a pivotal role in soil BNF
- Taxon
- riceOryza sativae0
- Organ / stage
- tilleringe4
- Outcome
- soil BNFe4
RhizobiumOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two typical rice growth stages (tillering and maturation) in paddy fields”
e4“Stage‐specific key diazotrophs, such as Rhizobium at tillering and Azoarcus at maturation, played pivotal roles in the soil BNF”
Claim · model-written summary
Azoarcus at maturation played a pivotal role in soil BNF
- Taxon
- riceOryza sativae0
- Organ / stage
- maturatione4
- Outcome
- soil BNFe4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two typical rice growth stages (tillering and maturation) in paddy fields”
e4“Stage‐specific key diazotrophs, such as Rhizobium at tillering and Azoarcus at maturation, played pivotal roles in the soil BNF”
Claim · model-written summary
Soil dissolved organic C and inorganic N were positively correlated with BNF at tillering
- Taxon
- riceOryza sativae0
- Organ / stage
- tillering stagee5
- Compound
- dissolved organic C and inorganic Ne5
- Outcome
- BNFe5
- Direction
- positively correlatede5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two typical rice growth stages (tillering and maturation) in paddy fields”
e5“Soil‐dissolved organic C and inorganic N were positively correlated with BNF at the tillering stage, but negatively at the maturation stage”
Claim · model-written summary
Soil dissolved organic C and inorganic N were negatively correlated with BNF at the maturation stage
- Taxon
- riceOryza sativae0
- Organ / stage
- maturation stagee5
- Compound
- dissolved organic C and inorganic Ne5
- Outcome
- BNFe5
- Direction
- negativelye5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two typical rice growth stages (tillering and maturation) in paddy fields”
e5“Soil‐dissolved organic C and inorganic N were positively correlated with BNF at the tillering stage, but negatively at the maturation stage”
Claim · model-written summary
Random Forest analysis indicated that BNF at tillering was primarily regulated by available nutrients
- Taxon
- riceOryza sativae0
- Organ / stage
- tillering stagee6
- Treatment
- available nutrientse6
- Outcome
- BNFe6
- Qualifier
- Random Forest analysise6
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two typical rice growth stages (tillering and maturation) in paddy fields”
e6“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”
Claim · model-written summary
BNF at maturation was closely associated with key diazotrophs
- Taxon
- riceOryza sativae0
- Organ / stage
- maturation stagee6
- Interactor
- key diazotrophse6symbiont
- Outcome
- BNFe6
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two typical rice growth stages (tillering and maturation) in paddy fields”
e6“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”
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Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.