Abstract
Causes of differences in photosynthetic nitrogen‐use efficiency (PNUE), the rate of photosynthesis per unit leaf N, were investigated in four species. These were in order of decreasing PNUE; the two herbs Galinsoga ciliata and Origanum vulgare , and the two trees Populus nigra and Quercus robur . Plants were grown in pots outdoors at three levels of nutrient availability. The light‐ and CO 2 response of gas exchange of leaves were measured, and their nitrogen and chlorophyll contents were determined. Furthermore, the internal conductance for CO 2 diffusion was estimated. Nutrients did not have a large effect on PNUE except in Galinsoga . Leaf mass per unit area was negatively correlated with PNUE max , which is likely to be partly caused by N present in cell wall proteins among other non‐photosynthetic N compounds. The trees had a larger fraction of photosynthetic N in light harvesting components compared to the herbs. This contributed also substantially to the difference in PNUE at light saturation (PNUE max ) between the two groups, but not for PNUE calculated for an overcast day. Intercellular CO 2 concentration was high in Galinsoga and Populus , which contributed significantly to their higher PNUE max , particularly at low nutrient availability. The large gradient in CO 2 concentration between intercellular spaces and chloroplasts was another factor that explained a substantial part of the differences in PNUE max between Quercus and the other species that had smaller gradients. Stomatal and internal conductances for CO 2 explained most of the difference in PNUE max between Quercus and Populus at high nutrient availability for which these data were available.
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Claims 9
Claim · model-written summary
Photosynthetic nitrogen-use efficiency decreased in the order Galinsoga ciliata, Origanum vulgare, Populus nigra, Quercus robur.
- Taxon
- two herbs Galinsoga ciliata and Origanum vulgare , and the two trees Populus nigra and Quercus robur
Populus nigra
Quercus robur
Origanum vulgare
Galinsoga quadriradiatae1 - Outcome
- PNUEe1
- Direction
- decreasinge1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“in order of decreasing PNUE; the two herbs Galinsoga ciliata and Origanum vulgare , and the two trees Populus nigra and Quercus robur”
Claim · model-written summary
Nutrient availability did not have a large effect on PNUE except in Galinsoga.
GalinsogaNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Nutrients did not have a large effect on PNUE except in Galinsoga”
Claim · model-written summary
Leaf mass per unit area was negatively correlated with PNUEmax.
Not reportedTaxon
Verbatim
e1“Leaf mass per unit area was negatively correlated with PNUE max”
Claim · model-written summary
The negative correlation between leaf mass per unit area and PNUEmax is likely partly caused by N present in cell wall proteins.
Not reportedTaxon
Verbatim
e1“Leaf mass per unit area was negatively correlated with PNUE max , which is likely to be partly caused by N present in cell wall proteins”
Claim · model-written summary
The trees had a larger fraction of photosynthetic N in light harvesting components than the herbs.
Verbatim
e1“The trees had a larger fraction of photosynthetic N in light harvesting components compared to the herbs”
Claim · model-written summary
The larger light-harvesting N fraction contributed substantially to the PNUEmax difference between trees and herbs, but not to PNUE calculated for an overcast day.
- Outcome
- difference in PNUE at light saturation (PNUE max )e1
- Qualifier
- but not for PNUE calculated for an overcast daye1
Not reportedTaxon
Verbatim
e1“This contributed also substantially to the difference in PNUE at light saturation (PNUE max ) between the two groups, but not for PNUE calculated for an overcast day”
Claim · model-written summary
High intercellular CO2 concentration in Galinsoga and Populus contributed significantly to their higher PNUEmax, particularly at low nutrient availability.
PopulusOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Intercellular CO 2 concentration was high in Galinsoga and Populus , which contributed significantly to their higher PNUE max , particularly at low nutrient availability”
Claim · model-written summary
The large CO2 gradient between intercellular spaces and chloroplasts explained a substantial part of the PNUEmax difference between Quercus and the other species.
- Compound
- CO 2e1
- Outcome
- differences in PNUE maxe1
- Qualifier
- large gradient in CO 2 concentration between intercellular spaces and chloroplastse1
QuercusOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“The large gradient in CO 2 concentration between intercellular spaces and chloroplasts was another factor that explained a substantial part of the differences in PNUE max between Quercus and the other species that had smaller gradients”
Claim · model-written summary
Stomatal and internal conductances for CO2 explained most of the PNUEmax difference between Quercus and Populus at high nutrient availability.
- Treatment
- high nutrient availabilitye1
- Outcome
- difference in PNUE maxe1
- Qualifier
- Stomatal and internal conductances for CO 2e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Stomatal and internal conductances for CO 2 explained most of the difference in PNUE max between Quercus and Populus at high nutrient availability”