Abstract
Root exudation is a key interface in plant-soil interactions and strongly influences nutrient cycling within orchard ecosystems. However, how root exudation varies with orchard age and what ecological factors drive these shifts remain insufficiently understood. Therefore, we quantified the relationships between root exudation and root traits, rhizosphere soil properties, and microbial biomass across a six-age orchard chronosequence of Citrus reticulata 'Chachi' . We found that the specific root length (SRL), root tissue density (RTD), specific root tip number (RTN), and root nitrogen concentration (RN) increased with orchard age, whereas the root diameter (RD), root carbon concentration (RC), and the root C:N ratio decreased. Principal component analysis (PCA) revealed that root traits varied significantly along the orchard-age gradient on PC1. Root exudation rates also differed significantly among orchard ages ( p < 0.05) and were most strongly associated with soil dissolved organic carbon (DOC) and the DOC:total dissolved nitrogen (TDN) ratio. Specifically, along the orchard-age gradient, the exudation rates of carbon (CEr), nitrogen (NEr), sugars (SEr), and organic acids (OAEr) initially increased and then decreased, with peaks at 3 or 5 years. However, root exudation was not significantly related to root chemical traits. Partial least squares path modeling (PLS–PM) further revealed that orchard age was associated with variation in root exudation both directly and indirectly through its influences on root traits, rhizosphere soil properties, and microbial biomass. With increasing orchard age, root traits became more strongly associated with variation in CEr, whereas NEr shifted from being primarily linked to soil nutrient availability to being more closely influenced by microbial biomass. These results suggest that soil nutrient availability and root traits jointly shape how strongly root exudation responds along the orchard-age gradient. These findings enhance our understanding of belowground C processes associated with root exudation along the orchard-age gradient and offer practical insights for fertilization strategies in long-term perennial orchard systems. • Absorptive root acquisition strategy shifts from structural emphasis to efficiency optimization. • Exudate compositional profile persists while exudation rates diverge ontogenetically. • The control of root exudation reconfigures along the stand developmental trajectory. • DOC and DOC:TDN dominate soil control of root exudation rates.
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Claims 14
Claim · model-written summary
Specific root length, tissue density and tip number increased with orchard age.
- Taxon
- Citrus reticulata 'Chachi'
.jpg?width=60)
Citrus reticulatae1 - Treatment
- orchard agee0
- Outcome
- specific root length (SRL), root tissue density (RTD), specific root tip number (RTN)e0
- Direction
- increasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
e0“the specific root length (SRL), root tissue density (RTD), specific root tip number (RTN), and root nitrogen concentration (RN) increased with orchard age”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Root nitrogen concentration increased with orchard age.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Treatment
- orchard agee0
- Outcome
- root nitrogen concentration (RN)e0
- Direction
- increasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“root nitrogen concentration (RN) increased with orchard age”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Root diameter, carbon concentration and C:N ratio decreased with age.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae2
- Treatment
- orchard-age gradiente1
- Outcome
- root diameter (RD), root carbon concentration (RC), and the root C:N ratioe0
- Direction
- decreasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“whereas the root diameter (RD), root carbon concentration (RC), and the root C:N ratio decreased”
e1“root traits varied significantly along the orchard-age gradient on PC1”
e2“Citrus reticulata 'Chachi'”
Claim · model-written summary
Root traits varied significantly on PC1 along the age gradient.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Treatment
- orchard-age gradiente0
- Outcome
- root traitse0
- Qualifier
- on PC1e0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“root traits varied significantly along the orchard-age gradient on PC1”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Root exudation rates differed significantly among ages and were most strongly associated with DOC and DOC:TDN.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Treatment
- orchard agese0
- Compound
- soil dissolved organic carbon (DOC)e0
- Outcome
- Root exudation ratese0
- Qualifier
- the DOC:total dissolved nitrogen (TDN) ratioe0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Root exudation rates also differed significantly among orchard ages ( p < 0.05) and were most strongly associated with soil dissolved organic carbon (DOC) and the DOC:total dissolved nitrogen (TDN) ratio”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Carbon, nitrogen and sugar exudation initially increased then decreased, peaking at 3 or 5 years.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Treatment
- orchard-age gradiente0
- Outcome
- exudation rates of carbon (CEr), nitrogen (NEr), sugars (SEr)e0
- Direction
- initially increased and then decreasede0
- Value
- 3 or 5 yearse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“along the orchard-age gradient, the exudation rates of carbon (CEr), nitrogen (NEr), sugars (SEr), and organic acids (OAEr) initially increased and then decreased, with peaks at 3 or 5 years”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Organic acid exudation initially increased then decreased, peaking at 3 or 5 years.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Treatment
- orchard-age gradiente0
- Outcome
- organic acids (OAEr)e0
- Direction
- initially increased and then decreasede0
- Value
- 3 or 5 yearse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“along the orchard-age gradient, the exudation rates of carbon (CEr), nitrogen (NEr), sugars (SEr), and organic acids (OAEr) initially increased and then decreased, with peaks at 3 or 5 years”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Exudation was not significantly related to root chemical traits.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Organ / stage
- roote0
- Outcome
- root exudatione0
- Qualifier
- root chemical traitse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“root exudation was not significantly related to root chemical traits”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Path modeling linked age to exudation directly and indirectly through traits, soil properties and microbial biomass.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Treatment
- orchard agee0
- Outcome
- variation in root exudatione0
- Qualifier
- both directly and indirectly through its influences on root traits, rhizosphere soil properties, and microbial biomasse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“orchard age was associated with variation in root exudation both directly and indirectly through its influences on root traits, rhizosphere soil properties, and microbial biomass”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Root traits became more strongly associated with carbon exudation as age increased.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Treatment
- orchard agee0
- Outcome
- variation in CEre0
- Qualifier
- root traits became more strongly associatede0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“With increasing orchard age, root traits became more strongly associated with variation in CEr”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Nitrogen exudation shifted from links to nutrient availability toward microbial biomass.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Outcome
- NEre0
- Qualifier
- shifted from being primarily linked to soil nutrient availability to being more closely influenced by microbial biomasse0
Not reportedOrgan / stageDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“NEr shifted from being primarily linked to soil nutrient availability to being more closely influenced by microbial biomass”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Nutrient availability and root traits jointly shape age-related exudation responses.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Outcome
- root exudatione0
- Qualifier
- soil nutrient availability and root traitse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“soil nutrient availability and root traits jointly shape how strongly root exudation responds along the orchard-age gradient”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Absorptive root acquisition shifts from structural emphasis to efficiency optimization.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Outcome
- Absorptive root acquisition strategy shifts from structural emphasis to efficiency optimizatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Absorptive root acquisition strategy shifts from structural emphasis to efficiency optimization.”
e1“Citrus reticulata 'Chachi'”
Claim · model-written summary
Exudate composition persists while rates diverge with development.
- Taxon
- Citrus reticulata 'Chachi'Citrus reticulatae1
- Outcome
- Exudate compositional profile persistse0
- Qualifier
- while exudation rates diverge ontogeneticallye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Exudate compositional profile persists while exudation rates diverge ontogenetically.”
e1“Citrus reticulata 'Chachi'”