Abstract
Root-zone nitrogen fertilization (RZF) can increase crop N uptake and yield, yet the underlying rhizosphere N-cycling functional mechanisms remain insufficiently resolved. In a field experiment with winter oilseed rape (Brassica napus L.), RZF was compared with conventional fertilization (CF) under the same N input rates, alongside a zero-N control (N0). Compared with CF, RZF significantly increased seed yield (by 0.44 t ha−1) and aboveground N uptake (by 20.45 kg ha−1), while simultaneously enriching rhizosphere mineral N pools (NH4+–N and NO3−–N by 54.50% and 56.02%, respectively). Shotgun metagenomics revealed that RZF reprogrammed rhizosphere N-cycling functional potential, characterized by enhanced nitrogen fixation, reduced nitrification and denitrification, and a tendency toward increased assimilatory nitrate reduction. These module-level shifts were supported by concordant changes in key functional genes, indicating greater genetic potential for N retention and assimilation (nifD, glnA, gltB, nasA, napB, nrfA) and reduced potential for nitrification- and denitrification-driven N losses (amoB/C, narI, nirK, norB). Taxonomic composition analysis showed enrichment of Bradyrhizobium and suppression of key nitrifier taxa (Nitrosospira and a Nitrososphaeraceae-affiliated taxon) under RZF. Rhizosphere pH exhibited the strongest Mantel correlation with multiple N-cycling modules, and rhizosphere available N (AN; sum of NH4+–N and NO3−–N) was positively associated with plant N traits and yield. Structural equation modeling supported a pathway in which a functional balance index (retention/assimilation vs. loss/oxidation) increased AN (0.22), and AN strongly promoted yield (0.90). Collectively, these results elucidate a rhizosphere-centered mechanism whereby localized N placement strengthens soil–plant N coupling and enhances crop productivity through reprogramming microbial N-cycling functional potentials, positioning rhizosphere N processes as a key mechanistic bridge for microbiome-informed optimization of root-zone fertilization.
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Claims 15
Claim · model-written summary
Root-zone fertilization increased oilseed rape seed yield relative to conventional fertilization by 0.44 t ha−1.
- Taxon
- winter oilseed rape
_Brassica_napus_-_Habit.jpg?width=60)
Brassica napuse1 - Treatment
- Root-zone nitrogen fertilizatione2
- Outcome
- seed yielde0
- Direction
- increasede0
- Value
- 0.44 t ha−1e0
- Comparator
- conventional fertilizatione3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
_Brassica_napus_-_Habit.jpg?width=500)
Verbatim
e0“Compared with CF, RZF significantly increased seed yield (by 0.44 t ha−1)”
e1“winter oilseed rape (Brassica napus L.)”
e2“Root-zone nitrogen fertilization (RZF)”
e3“conventional fertilization (CF)”
Claim · model-written summary
Root-zone fertilization increased aboveground nitrogen uptake by 20.45 kg ha−1.
- Taxon
- winter oilseed rapeBrassica napuse1
- Treatment
- Root-zone nitrogen fertilizatione2
- Outcome
- aboveground N uptakee0
- Direction
- increasede0
- Value
- 20.45 kg ha−1e0
- Comparator
- conventional fertilizatione3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Compared with CF, RZF significantly increased seed yield (by 0.44 t ha−1) and aboveground N uptake (by 20.45 kg ha−1)”
e1“winter oilseed rape (Brassica napus L.)”
e2“Root-zone nitrogen fertilization (RZF)”
e3“conventional fertilization (CF)”
Claim · model-written summary
Root-zone fertilization enriched rhizosphere ammonium nitrogen by 54.50%.
- Taxon
- winter oilseed rapeBrassica napuse1
- Treatment
- Root-zone nitrogen fertilizatione2
- Outcome
- rhizosphere mineral N pools (NH4+–Ne0
- Direction
- enrichinge0
- Value
- 54.50%e0
- Comparator
- conventional fertilizatione3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“enriching rhizosphere mineral N pools (NH4+–N and NO3−–N by 54.50% and 56.02%, respectively)”
e1“winter oilseed rape (Brassica napus L.)”
e2“Root-zone nitrogen fertilization (RZF)”
e3“conventional fertilization (CF)”
Claim · model-written summary
Root-zone fertilization enriched rhizosphere nitrate nitrogen by 56.02%.
- Taxon
- winter oilseed rapeBrassica napuse1
- Treatment
- Root-zone nitrogen fertilizatione2
- Outcome
- NO3−–Ne0
- Direction
- enrichinge0
- Value
- 56.02%e0
- Comparator
- conventional fertilizatione3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“enriching rhizosphere mineral N pools (NH4+–N and NO3−–N by 54.50% and 56.02%, respectively)”
e1“winter oilseed rape (Brassica napus L.)”
e2“Root-zone nitrogen fertilization (RZF)”
e3“conventional fertilization (CF)”
Claim · model-written summary
Root-zone fertilization enhanced rhizosphere nitrogen fixation potential.
- Taxon
- winter oilseed rapeBrassica napuse1
- Treatment
- Root-zone nitrogen fertilizatione2
- Outcome
- nitrogen fixatione0
- Direction
- enhancede0
- Comparator
- conventional fertilizatione3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“RZF reprogrammed rhizosphere N-cycling functional potential, characterized by enhanced nitrogen fixation, reduced nitrification and denitrification”
e1“winter oilseed rape (Brassica napus L.)”
e2“Root-zone nitrogen fertilization (RZF)”
e3“conventional fertilization (CF)”
Claim · model-written summary
Root-zone fertilization reduced rhizosphere nitrification and denitrification potential.
- Taxon
- winter oilseed rapeBrassica napuse1
- Treatment
- Root-zone nitrogen fertilizatione2
- Outcome
- nitrification and denitrificatione0
- Direction
- reducede0
- Comparator
- conventional fertilizatione3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“reduced nitrification and denitrification”
e1“winter oilseed rape (Brassica napus L.)”
e2“Root-zone nitrogen fertilization (RZF)”
e3“conventional fertilization (CF)”
Claim · model-written summary
Root-zone fertilization tended to increase assimilatory nitrate reduction.
- Taxon
- winter oilseed rapeBrassica napuse1
- Treatment
- Root-zone nitrogen fertilizatione2
- Outcome
- assimilatory nitrate reductione0
- Direction
- increasede0
- Qualifier
- a tendency towarde0
- Comparator
- conventional fertilizatione3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a tendency toward increased assimilatory nitrate reduction”
e1“winter oilseed rape (Brassica napus L.)”
e2“Root-zone nitrogen fertilization (RZF)”
e3“conventional fertilization (CF)”
Claim · model-written summary
Functional genes indicated greater potential for nitrogen retention and assimilation under root-zone fertilization.
- Taxon
- winter oilseed rapeBrassica napuse1
- Gene
- nifD, glnA, gltB, nasA, napB, nrfAe0
- Outcome
- genetic potential for N retention and assimilatione0
- Direction
- greatere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“greater genetic potential for N retention and assimilation (nifD, glnA, gltB, nasA, napB, nrfA)”
e1“winter oilseed rape (Brassica napus L.)”
Claim · model-written summary
Functional genes indicated reduced potential for rhizosphere nitrogen losses.
- Taxon
- winter oilseed rapeBrassica napuse1
- Gene
- amoB/C, narI, nirK, norBe0
- Outcome
- potential for nitrification- and denitrification-driven N lossese0
- Direction
- reducede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“reduced potential for nitrification- and denitrification-driven N losses (amoB/C, narI, nirK, norB)”
e1“winter oilseed rape (Brassica napus L.)”
Claim · model-written summary
Bradyrhizobium was enriched under root-zone fertilization.
- Taxon
- winter oilseed rapeBrassica napuse1
- Interactor
- Bradyrhizobium
Bradyrhizobiume0symbiont - Outcome
- enrichment of Bradyrhizobiume0
- Direction
- enrichmente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“enrichment of Bradyrhizobium”
e1“winter oilseed rape (Brassica napus L.)”
Claim · model-written summary
Nitrifier taxa were suppressed under root-zone fertilization.
- Taxon
- winter oilseed rapeBrassica napuse1
- Interactor
- NitrosospiraNitrosospirae0other
- Second interactor
- Nitrososphaeraceae-affiliated taxone0other
- Outcome
- key nitrifier taxae0
- Direction
- suppressione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“suppression of key nitrifier taxa (Nitrosospira and a Nitrososphaeraceae-affiliated taxon) under RZF”
e1“winter oilseed rape (Brassica napus L.)”
Claim · model-written summary
Rhizosphere pH had the strongest Mantel correlation with multiple nitrogen cycling modules.
- Taxon
- winter oilseed rapeBrassica napuse1
- Outcome
- multiple N-cycling modulese0
- Qualifier
- strongest Mantel correlatione0
- Setting
- Rhizospheree0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Rhizosphere pH exhibited the strongest Mantel correlation with multiple N-cycling modules”
e1“winter oilseed rape (Brassica napus L.)”
Claim · model-written summary
Rhizosphere available nitrogen was positively associated with plant nitrogen traits and yield.
- Taxon
- winter oilseed rapeBrassica napuse1
- Outcome
- plant N traits and yielde0
- Direction
- positivelye0
- Qualifier
- available Ne0
- Setting
- rhizospheree0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“rhizosphere available N (AN; sum of NH4+–N and NO3−–N) was positively associated with plant N traits and yield”
e1“winter oilseed rape (Brassica napus L.)”
Claim · model-written summary
A modeled functional balance index increased available nitrogen with a path coefficient of 0.22.
- Taxon
- winter oilseed rapeBrassica napuse1
- Outcome
- ANe0
- Direction
- increasede0
- Value
- 0.22e0
- Qualifier
- functional balance index (retention/assimilation vs. loss/oxidation)e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a functional balance index (retention/assimilation vs. loss/oxidation) increased AN (0.22)”
e1“winter oilseed rape (Brassica napus L.)”
Claim · model-written summary
Modeled available nitrogen promoted yield with a path coefficient of 0.90.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“AN strongly promoted yield (0.90)”
e1“winter oilseed rape (Brassica napus L.)”
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