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Title: Reduced diurnal temperature range does not change warming impacts on ecosystem carbon balance of Mediterranean grassland mesocosms

Daily minimum temperature (Tmin) has increased faster than daily maximum temperature (Tmax) in many parts of the world, leading to decreases in diurnal temperature range (DTR). Projections suggest these trends are likely to continue in many regions, particularly northern latitudes and in arid regions. Despite wide speculation that asymmetric warming has different impacts on plant and ecosystem production than equal-night-and-day warming, there has been little direct comparison of these scenarios. Reduced DTR has also been widely misinterpreted as a result of night-only warming, when in fact Tmin occurs near dawn, indicating higher morning as well as night temperatures. We report on the first experiment to examine ecosystem-scale impacts of faster increases in Tmin than Tmax, using precise temperature controls to create realistic diurnal temperature profiles with gradual day-night temperature transitions and elevated early morning as well as night temperatures. Studying a constructed grassland ecosystem containing species native to Oregon, USA, we found the ecosystem lost more carbon at elevated than ambient temperatures, but was unaffected by the 3ºC difference in DTR between symmetric warming (constantly ambient +3.5ºC) and asymmetric warming (dawn Tmin=ambient +5ºC, afternoon Tmax= ambient +2ºC). Reducing DTR had no apparent effect on photosynthesis, likely because temperatures were mostmore » different in the morning and late afternoon when light was low. Respiration was also similar in both warming treatments, because respiration temperature sensitivity was not sufficient to respond to the limited temperature differences between asymmetric and symmetric warming. We concluded that changes in daily mean temperatures, rather than changes in Tmin/Tmax, were sufficient for predicting ecosystem carbon fluxes in this reconstructed Mediterranean grassland system.« less
Authors:
 [1] ;  [2] ;  [2]
  1. Terrestrial Ecosystems Reserach Associates,Corvallis, OR (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. Terrestrial Ecosystems Reserach Associates,Corvallis, OR (United States)
Publication Date:
OSTI Identifier:
1104890
Report Number(s):
DOE-TERA-ER64048-1
Journal ID: ISSN 1354-1013
Grant/Contract Number:
FG02-05ER64048
Type:
Accepted Manuscript
Journal Name:
Global Change Biology
Additional Journal Information:
Journal Volume: 17; Journal Issue: 11; Journal ID: ISSN 1354-1013
Publisher:
Wiley
Research Org:
Terrestrial Ecosystems Reserach Associates,Corvallis, OR (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES DIURNAL TEMPERATURE RANGE; ASYMMETRIC WARMING; RESPIRATION; GRASSLAND; CARBON