Abstract
Abstract Ecosystem carbon use efficiency (CUE) is a key indicator of an ecosystem's capacity to function as a carbon sink. While previous studies have predominantly focused on how climate and resource availability affect CUE through physiological processes during the growing season, the role of canopy structure in regulating carbon and energy exchange, especially its interactions with winter climate processes and nitrogen use efficiency (NUE) in shaping ecosystem CUE in semi‐arid grasslands, remains insufficiently understood. Here, we conducted a 5‐year snow manipulation experiment in a temperate grassland to investigate the effects of deepened snow on ecosystem CUE. We measured ecosystem carbon fluxes, soil nitrogen concentration, species biomass, plants' nitrogen concentration, canopy height and cover and species composition. We found that deepened snow increased soil nitrogen availability, while the concurrent rise in soil moisture facilitated nutrient acquisition and utilization. Together, these changes supported greater biomass accumulation per unit of nitrogen uptake, thereby enhancing NUE. In addition, deepened snow favoured the dominance of C3 grasses, which generally exhibit higher NUE and greater height than C3 forbs, providing a second pathway that further elevated community‐level NUE. The enhanced NUE, through both physiological efficiency and compositional shifts, promoted biomass production and facilitated the development of larger canopy volumes. Larger canopy volumes under deepened snow increased gross primary production through improved light interception, while the associated increase in autotrophic maintenance respiration was moderated by higher NUE. Besides, denser canopies reduced understorey temperatures throughout the day, particularly at night, thereby suppressing heterotrophic respiration. Ultimately, deepened snow increased ecosystem CUE by enhancing carbon uptake while limiting respiratory carbon losses. Synthesis . These findings demonstrated the crucial role of biophysical processes associated with canopy structure and NUE in regulating ecosystem CUE, which has been largely overlooked in previous studies. We also highlight the importance of winter processes in shaping carbon sequestration dynamics and their potential to modulate future grassland responses to climate change.
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Claims 13
Claim · model-written summary
Deepened snow increased soil nitrogen availability.
- Taxon
- temperate grasslandt0
- Treatment
- deepened snowe0
- Outcome
- soil nitrogen availabilitye0
- Direction
- increasede0
Not reportedComparator
Verbatim
e0“deepened snow increased soil nitrogen availability”
t0“temperate grassland”
Claim · model-written summary
Deepened snow raised soil moisture.
Not reportedComparator
Verbatim
e0“the concurrent rise in soil moisture facilitated nutrient acquisition and utilization”
e1“deepened snow increased soil nitrogen availability”
t0“temperate grassland”
Claim · model-written summary
Greater soil moisture facilitated nutrient acquisition and utilization.
Verbatim
e0“the concurrent rise in soil moisture facilitated nutrient acquisition and utilization”
e1“deepened snow increased soil nitrogen availability”
t0“temperate grassland”
Claim · model-written summary
Deepened snow increased biomass accumulated per unit nitrogen uptake and NUE.
- Taxon
- temperate grasslandt0
- Treatment
- deepened snowe1
- Outcome
- biomass accumulation per unit of nitrogen uptakee0
- Direction
- greatere0
Not reportedComparator
Verbatim
e0“Together, these changes supported greater biomass accumulation per unit of nitrogen uptake, thereby enhancing NUE.”
e1“deepened snow increased soil nitrogen availability”
t0“temperate grassland”
Claim · model-written summary
Deepened snow favored C3 grass dominance.
Not reportedComparator
Verbatim
e0“deepened snow favoured the dominance of C3 grasses”
Claim · model-written summary
C3 grasses had generally higher NUE and height than C3 forbs.
Verbatim
e0“C3 grasses, which generally exhibit higher NUE and greater height than C3 forbs”
Claim · model-written summary
Enhanced NUE promoted biomass production.
Verbatim
e0“The enhanced NUE, through both physiological efficiency and compositional shifts, promoted biomass production”
t0“temperate grassland”
Claim · model-written summary
Enhanced NUE supported larger canopy volumes.
Verbatim
e0“The enhanced NUE, through both physiological efficiency and compositional shifts, promoted biomass production and facilitated the development of larger canopy volumes.”
t0“temperate grassland”
Claim · model-written summary
Larger canopy volumes increased gross primary production through light interception.
Verbatim
e0“Larger canopy volumes under deepened snow increased gross primary production through improved light interception”
t0“temperate grassland”
Claim · model-written summary
Higher NUE moderated the associated increase in autotrophic maintenance respiration.
Verbatim
e0“the associated increase in autotrophic maintenance respiration was moderated by higher NUE”
t0“temperate grassland”
Claim · model-written summary
Denser canopies reduced understorey temperatures, especially at night.
Verbatim
e0“denser canopies reduced understorey temperatures throughout the day, particularly at night”
t0“temperate grassland”
Claim · model-written summary
Denser canopies suppressed heterotrophic respiration via cooling.
Verbatim
e0“denser canopies reduced understorey temperatures throughout the day, particularly at night, thereby suppressing heterotrophic respiration”
t0“temperate grassland”
Claim · model-written summary
Deepened snow increased ecosystem carbon use efficiency.
Not reportedComparator
Verbatim
e0“deepened snow increased ecosystem CUE by enhancing carbon uptake while limiting respiratory carbon losses”
t0“temperate grassland”