Abstract
(1) Background: Planting density is an important factor affecting the yield of poplar per unit area. Therefore, determining the optimal height of the photosynthetic canopy layer for different planting densities is critical. (2) Methods: This study takes Populus euramericana ‘N3016’ × Populus ussuriensis as the research object. According to on the average tree height, diameter at breast height, and crown width of the stand, one standard tree was selected from each planting density for the experiment. The canopy of the standard tree was divided into five canopy layers from top to bottom, and the first-order lateral branches of each canopy layer were divided into three sites from outside to inside. The photosynthesis and leaf traits at various positions in different canopy layers were measured. (3) Results: The results revealed significant differences in photosynthetic and leaf traits at different positions of different canopy layers under different planting densities. As the canopy layer gradually declined, photosynthetic traits revealed that instantaneous photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) gradually decreased, while intercellular CO2 concentration (Ci) increased. Moreover, water use efficiency (WUE) initially increased and then decreased under an 825 trees·ha−1 (D3) planting density. Leaf traits revealed that as leaf length (LL) gradually decreased, leaf width (LW), leaf area (LA), and leaf water content (LWC) gradually increased. Under three planting densities, leaf traits were negatively correlated with Pn, Tr, WUE, and Gs, but positively correlated with Ci. (4) Conclusions: As the planting density decreased, the photosynthetic capacity of poplar gradually increased. With a planting density of D3, all canopy layers were able to carry out efficient photosynthesis, and all living branches within the canopy were functional. However, under the planting density of 1650 trees·ha−1 (D1) and 1089 trees·ha−1 (D2), canopy layers 1 to 4 could perform effective photosynthesis, while the photosynthetic capacity of canopy layer 5 was relatively weak. This study reveals the interactive effects of canopy position and stand density on leaf physiological and morphological traits, providing new insights into the photosynthetic efficiency and growth strategies of poplar under different planting densities. It also offers theoretical support for optimizing stand management and enhancing productivity.
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Claims 13
Claim · model-written summary
Photosynthetic and leaf traits differed significantly across canopy positions and planting densities.
- Outcome
- photosynthetic and leaf traitse0
- Qualifier
- different positions of different canopy layers under different planting densitiese0
PopulusOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“significant differences in photosynthetic and leaf traits at different positions of different canopy layers under different planting densities”
t0“Poplar”
Claim · model-written summary
Instantaneous photosynthetic rate, transpiration rate and stomatal conductance decreased toward lower canopy layers.
- Organ / stage
- canopy layere0
- Outcome
- instantaneous photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs)e0
- Direction
- gradually decreasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“As the canopy layer gradually declined, photosynthetic traits revealed that instantaneous photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) gradually decreased”
t0“Poplar”
Claim · model-written summary
Intercellular CO2 concentration increased toward lower canopy layers.
Not reportedOrgan / stage
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“while intercellular CO2 concentration (Ci) increased”
t0“Poplar”
Claim · model-written summary
Water use efficiency first increased then decreased down the canopy at D3 density.
- Outcome
- water use efficiency (WUE)e0
- Direction
- initially increased and then decreasede0
- Setting
- 825 trees·ha−1 (D3) planting densitye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“water use efficiency (WUE) initially increased and then decreased under an 825 trees·ha−1 (D3) planting density”
t0“Poplar”
Claim · model-written summary
Leaf length decreased down the canopy.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“as leaf length (LL) gradually decreased”
t0“Poplar”
Claim · model-written summary
Leaf width, area and water content increased down the canopy.
- Organ / stage
- leafe0
- Outcome
- leaf width (LW), leaf area (LA), and leaf water content (LWC)e0
- Direction
- gradually increasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“leaf width (LW), leaf area (LA), and leaf water content (LWC) gradually increased”
t0“Poplar”
Claim · model-written summary
Leaf traits were negatively correlated with Pn, Tr, WUE and Gs.
- Outcome
- leaf traitse0
- Direction
- negatively correlatede0
- Qualifier
- Pn, Tr, WUE, and Gse0
- Comparator
- Pn, Tr, WUE, and Gse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“leaf traits were negatively correlated with Pn, Tr, WUE, and Gs”
t0“Poplar”
Claim · model-written summary
Leaf traits were positively correlated with Ci.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“leaf traits were negatively correlated with Pn, Tr, WUE, and Gs, but positively correlated with Ci”
t0“Poplar”
Claim · model-written summary
Poplar photosynthetic capacity increased as planting density decreased.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“As the planting density decreased, the photosynthetic capacity of poplar gradually increased”
Claim · model-written summary
All D3 canopy layers performed efficient photosynthesis.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“With a planting density of D3, all canopy layers were able to carry out efficient photosynthesis”
t0“Poplar”
Claim · model-written summary
All living D3 canopy branches were functional.
- Outcome
- all living branches within the canopy were functionale0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“all living branches within the canopy were functional”
t0“Poplar”
Claim · model-written summary
Canopy layers 1 to 4 photosynthesized effectively at D1 and D2 density.
- Organ / stage
- canopy layers 1 to 4e0
- Outcome
- effective photosynthesise0
- Setting
- 1650 trees·ha−1 (D1) and 1089 trees·ha−1 (D2)e0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“under the planting density of 1650 trees·ha−1 (D1) and 1089 trees·ha−1 (D2), canopy layers 1 to 4 could perform effective photosynthesis”
t0“Poplar”
Claim · model-written summary
The fifth canopy layer had relatively weak photosynthetic capacity at D1 and D2.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“photosynthetic capacity of canopy layer 5 was relatively weak”
t0“Poplar”