Abstract
Summary The soil nitrogen cycle was investigated in a pre‐established Lolium perenne sward on a loamy soil and exposed to ambient and elevated atmospheric CO 2 concentrations (350 and 700 μL L −1 ) and, at elevated [CO 2 ], to a 3 °C temperature increase. At two levels of mineral nitrogen supply, N– (150 kgN ha −1 y −1 ) and N+ (533 kgN ha −1 y −1 ), 15 N‐labelled ammonium nitrate was supplied in split applications over a 2.5‐y period. The recovery of the labelled fertilizer N was measured in the harvests, in the stubble and roots, in the macro‐organic matter fractions above 200 μm in size (MOM) and in the aggregated organic matter below 200 μM (AOM). Elevated [CO 2 ] reduced the total amount of N harvested in the clipped parts of the sward. The harvested N derived from soil was reduced to a greater extent than that derived from fertilizer. At both N supplies, elevated [CO 2 ] modified the allocation of the fertilizer N in the sward, in favour of the stubble and roots and significantly increased the recovery of fertilizer N in the soil macro‐organic matter fractions. The increase of fertilizer N immobilization in the MOM was associated with a decline of fertilizer N uptake by the grass sward, which supported the hypothesis of a negative feedback of elevated [CO 2 ] on the sward N yield and uptake. Similar and even more pronounced effects were observed for the native N mineralized in the soil. At N–, a greater part of the fertilizer N organized in the root phytomass resulted in an underestimation of N immobilized in dead roots and, in turn, an underestimation of N immobilization in the MOM. The 3 °C temperature increase alleviated the [CO 2 ] effect throughout much of the N cycle, increasing soil N mineralization, N derived from soil in the harvests, and the partitioning of the assimilated fertilizer N to shoots. In conclusion, at ambient temperature, the N cycle was slowed down under elevated [CO 2 ], which restricted the increase in the aboveground production of the grass sward, and apparently contributed to the sequestration of carbon belowground. In contrast, a temperature increase under elevated [CO 2 ] stimulated the soil nitrogen cycle, improved the N nutrition of the sward and restricted the magnitude of the soil C sequestration.
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Claims 14
Claim · model-written summary
Elevated carbon dioxide reduced harvested sward nitrogen.
- Taxon
- Lolium perenne
Lolium perennee1 - Treatment
- Elevated [CO 2 ]e0
- Outcome
- total amount of N harvestede0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Elevated [CO 2 ] reduced the total amount of N harvested in the clipped parts of the sward.”
e1“Lolium perenne sward”
Claim · model-written summary
Elevated carbon dioxide reduced soil-derived harvested nitrogen more than fertilizer-derived nitrogen.
- Taxon
- Lolium perenneLolium perennee2
- Treatment
- Elevated [CO 2 ]e1
- Outcome
- harvested N derived from soile0
- Direction
- reducede0
- Comparator
- that derived from fertilizere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The harvested N derived from soil was reduced to a greater extent than that derived from fertilizer.”
e1“Elevated [CO 2 ]”
e2“Lolium perenne sward”
Claim · model-written summary
Elevated carbon dioxide shifted fertilizer nitrogen allocation toward stubble and roots.
- Taxon
- Lolium perenneLolium perennee1
- Organ / stage
- stubble and rootse0
- Treatment
- elevated [CO 2 ]e0
- Outcome
- allocation of the fertilizer Ne0
- Direction
- in favour ofe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“elevated [CO 2 ] modified the allocation of the fertilizer N in the sward, in favour of the stubble and roots”
e1“Lolium perenne sward”
Claim · model-written summary
Elevated carbon dioxide significantly increased fertilizer nitrogen recovery in soil macro-organic matter.
- Taxon
- Lolium perenneLolium perennee2
- Treatment
- elevated [CO 2 ]e1
- Outcome
- recovery of fertilizer N in the soil macro‐organic matter fractionse0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“significantly increased the recovery of fertilizer N in the soil macro‐organic matter fractions”
e1“elevated [CO 2 ] modified the allocation”
e2“Lolium perenne sward”
Claim · model-written summary
Fertilizer nitrogen immobilization in macro-organic matter was associated with lower grass uptake.
- Taxon
- Lolium perenneLolium perennee1
- Outcome
- fertilizer N uptake by the grass swarde0
- Direction
- declinee0
- Qualifier
- increase of fertilizer N immobilization in the MOMe0
Not reportedSetting
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The increase of fertilizer N immobilization in the MOM was associated with a decline of fertilizer N uptake by the grass sward”
e1“Lolium perenne sward”
Claim · model-written summary
Native soil nitrogen showed similar, more pronounced effects.
- Taxon
- Lolium perenneLolium perennee1
- Outcome
- native N mineralized in the soile0
- Direction
- more pronouncede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Similar and even more pronounced effects were observed for the native N mineralized in the soil.”
e1“Lolium perenne sward”
Claim · model-written summary
At low nitrogen supply, more fertilizer nitrogen was organized in root phytomass, causing underestimation of dead-root nitrogen immobilization.
- Taxon
- Lolium perenneLolium perennee1
- Organ / stage
- dead rootse0
- Outcome
- N immobilized in dead rootse0
- Direction
- underestimatione0
- Qualifier
- At N–e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At N–, a greater part of the fertilizer N organized in the root phytomass resulted in an underestimation of N immobilized in dead roots”
e1“Lolium perenne sward”
Claim · model-written summary
At low nitrogen supply, root fertilizer nitrogen caused underestimation of macro-organic-matter nitrogen immobilization.
- Taxon
- Lolium perenneLolium perennee2
- Outcome
- N immobilization in the MOMe0
- Direction
- underestimatione0
- Qualifier
- At N–e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“in turn, an underestimation of N immobilization in the MOM”
e1“At N–, a greater part of the fertilizer N organized in the root phytomass”
e2“Lolium perenne sward”
Claim · model-written summary
A 3 °C temperature increase raised soil nitrogen mineralization under elevated carbon dioxide.
- Taxon
- Lolium perenneLolium perennee1
- Treatment
- 3 °C temperature increasee0
- Outcome
- soil N mineralizatione0
- Direction
- increasinge0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The 3 °C temperature increase alleviated the [CO 2 ] effect throughout much of the N cycle, increasing soil N mineralization, N derived from soil in the harvests, and the partitioning of the assimilated fertilizer N to shoots.”
e1“Lolium perenne sward”
Claim · model-written summary
A 3 °C temperature increase raised soil-derived nitrogen in harvests.
- Taxon
- Lolium perenneLolium perennee1
- Treatment
- 3 °C temperature increasee0
- Outcome
- N derived from soil in the harvestse0
- Direction
- increasinge0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The 3 °C temperature increase alleviated the [CO 2 ] effect throughout much of the N cycle, increasing soil N mineralization, N derived from soil in the harvests, and the partitioning of the assimilated fertilizer N to shoots.”
e1“Lolium perenne sward”
Claim · model-written summary
A 3 °C temperature increase raised fertilizer nitrogen partitioning to shoots.
- Taxon
- Lolium perenneLolium perennee1
- Treatment
- 3 °C temperature increasee0
- Outcome
- partitioning of the assimilated fertilizer N to shootse0
- Direction
- increasinge0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The 3 °C temperature increase alleviated the [CO 2 ] effect throughout much of the N cycle, increasing soil N mineralization, N derived from soil in the harvests, and the partitioning of the assimilated fertilizer N to shoots.”
e1“Lolium perenne sward”
Claim · model-written summary
Elevated carbon dioxide slowed the nitrogen cycle at ambient temperature.
- Taxon
- Lolium perenneLolium perennee1
- Treatment
- elevated [CO 2 ]e0
- Outcome
- N cyclee0
- Direction
- slowed downe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“at ambient temperature, the N cycle was slowed down under elevated [CO 2 ]”
e1“Lolium perenne sward”
Claim · model-written summary
Slower nitrogen cycling restricted increased aboveground sward production.
- Taxon
- Lolium perenneLolium perennee1
- Outcome
- aboveground production of the grass swarde0
- Qualifier
- N cycle was slowed downe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the N cycle was slowed down under elevated [CO 2 ], which restricted the increase in the aboveground production of the grass sward”
e1“Lolium perenne sward”
Claim · model-written summary
Temperature increase under elevated carbon dioxide improved sward nitrogen nutrition.
- Taxon
- Lolium perenneLolium perennee1
- Treatment
- a temperature increase under elevated [CO 2 ]e0
- Outcome
- N nutrition of the swarde0
- Direction
- improvede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a temperature increase under elevated [CO 2 ] stimulated the soil nitrogen cycle, improved the N nutrition of the sward”
e1“Lolium perenne sward”
The same questions in other papers
co2 · nutrient: content · Lolium perenne (perennial ryegrass)Positive and negative results
1 paper in the same direction as this paper · 2 in the opposite direction
- no effect
- negative
- positive
Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.