Abstract
The effects of nitrogen availability on N cycling and N use efficiency (NUE) were examined in natural and fertilized loblolly pine stands on the upper coastal plain of South Carolina. Indices of N availability, based on potential rates of N mineralization, ranged from 1.6 to 11 kg°ha — 1 (8 wk) — 1 in the stands, and concentrations of N in foliage, wood, fine roots, and needlefall increased with greater N availability. Litterfall dry masses, net aboveground production, and litterfall nitrogen were all positively correlated with N availability, while indices of NUE decreased with increased N availability. Mechanisms that could explain increased NUE in low—N sites were examined in the field and in a phytotron study. First, nitrogen retranslocation on a per needle basis did not change significantly across the N—availability gradient, and thus could not account for the change in NUE efficiency. For the stands as a whole, however, substantially more N was retranslocated at the highest levels of N availability. Second, an increase in N uptake efficiency could not account for an increase in NUE with low N availability, since phytotron—grown seedlings fertilized with N had significantly higher rates of N uptake per unite root mass and lower root: shoot ratios than N—limited seedlings. Third, net production per unit N within pine seedlings was significantly higher in the N—limited plants, suggesting that an increase in the amount of carbon fixed per unit of tissue N could account for the observed increased in NUE in loblolly pine stands at low levels of N availability.
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Claims 11
Claim · model-written summary
Nitrogen availability indices ranged from 1.6 to 11 kg per hectare over eight weeks.
- Taxon
- loblolly pine
Pinus taedat0 - Outcome
- Indices of N availabilitye0
- Value
- 1.6 to 11 kg°ha — 1 (8 wk) — 1e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Indices of N availability, based on potential rates of N mineralization, ranged from 1.6 to 11 kg°ha — 1 (8 wk) — 1 in the stands”
t0“Loblolly Pine”
Claim · model-written summary
Nitrogen concentrations in foliage, wood, fine roots and needlefall increased as nitrogen availability increased.
- Taxon
- loblolly pinePinus taedat0
- Compound
- Ne0
- Outcome
- concentrations of Ne0
- Direction
- increasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“concentrations of N in foliage, wood, fine roots, and needlefall increased with greater N availability.”
t0“Loblolly Pine”
Claim · model-written summary
Litterfall dry mass was positively correlated with nitrogen availability.
- Taxon
- loblolly pinePinus taedat0
- Compound
- Ne0
- Outcome
- Litterfall dry massese0
- Direction
- positively correlatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Litterfall dry masses, net aboveground production, and litterfall nitrogen were all positively correlated with N availability”
t0“Loblolly Pine”
Claim · model-written summary
Net aboveground production was positively correlated with nitrogen availability.
- Taxon
- loblolly pinePinus taedat0
- Compound
- Ne0
- Outcome
- net aboveground productione0
- Direction
- positively correlatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Litterfall dry masses, net aboveground production, and litterfall nitrogen were all positively correlated with N availability”
t0“Loblolly Pine”
Claim · model-written summary
Litterfall nitrogen was positively correlated with nitrogen availability.
- Taxon
- loblolly pinePinus taedat0
- Compound
- Ne0
- Outcome
- litterfall nitrogene0
- Direction
- positively correlatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Litterfall dry masses, net aboveground production, and litterfall nitrogen were all positively correlated with N availability”
t0“Loblolly Pine”
Claim · model-written summary
Nitrogen use efficiency indices declined with greater nitrogen availability.
- Taxon
- loblolly pinePinus taedat0
- Compound
- Ne0
- Outcome
- indices of NUEe0
- Direction
- decreasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“indices of NUE decreased with increased N availability.”
t0“Loblolly Pine”
Claim · model-written summary
Per-needle nitrogen retranslocation did not significantly change across the nitrogen availability gradient.
- Taxon
- loblolly pinePinus taedat0
- Compound
- Ne0
- Outcome
- nitrogen retranslocatione0
- Direction
- did not change significantlye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“nitrogen retranslocation on a per needle basis did not change significantly across the N—availability gradient”
t0“Loblolly Pine”
Claim · model-written summary
Whole stands retranslocated substantially more nitrogen at the highest nitrogen availability.
- Taxon
- loblolly pinePinus taedat0
- Compound
- Ne0
- Outcome
- N was retranslocatede0
- Direction
- substantially moree0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“For the stands as a whole, however, substantially more N was retranslocated at the highest levels of N availability.”
t0“Loblolly Pine”
Claim · model-written summary
Nitrogen-fertilized seedlings had significantly higher nitrogen uptake per root mass than nitrogen-limited seedlings.
- Treatment
- fertilized with Ne0
- Outcome
- rates of N uptake per unite root masse0
- Direction
- highere0
- Comparator
- N—limited seedlingse0
PinusOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“phytotron—grown seedlings fertilized with N had significantly higher rates of N uptake per unite root mass and lower root: shoot ratios than N—limited seedlings.”
t0“Pine”
Claim · model-written summary
Nitrogen-fertilized seedlings had lower root-to-shoot ratios than nitrogen-limited seedlings.
- Treatment
- fertilized with Ne0
- Outcome
- root: shoot ratiose0
- Direction
- lowere0
- Comparator
- N—limited seedlingse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“phytotron—grown seedlings fertilized with N had significantly higher rates of N uptake per unite root mass and lower root: shoot ratios than N—limited seedlings.”
t0“Pine”
Claim · model-written summary
Net production per unit nitrogen was significantly higher in nitrogen-limited pine seedlings.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“net production per unit N within pine seedlings was significantly higher in the N—limited plants”