Responses of soil respiration to elevated CO2, air warming, and changing soil water availability in a model old‐field grassland

Responses of soil respiration to atmospheric and climatic change will have profound impacts on ecosystem and global C cycling in the future. This study was conducted to examine effects on soil respiration of the concurrent driving factors of elevated atmospheric CO2 concentration, rising temperature, and changing precipitation in a constructed old-field grassland in eastern Tennessee, USA. Model ecosystems of seven old-field species in 12 open-top chambers (4 m in diameter) were treated with two CO2 (ambient and ambient plus 300 ppm) and two temperature (ambient and ambient plus 3 C) levels. Two split plots with each chamber were assigned with high and low soil moisture levels. During the 19-month experimental period from June 2003 to December 2004, higher CO2 concentration and soil water availability significantly increased mean soil respiration by 35.8% and 15.7%, respectively. The effects of air warming on soil respiration varied seasonally from small reductions to significant increases to no response, and there was no significant main effect. In the wet side of elevated CO2 chambers, air warming consistently caused increases in soil respiration, whereas in other three combinations of CO2 and water treatments, warming tended to decrease soil respiration over the growing season but increase it overmore » the winter. There were no interactive effects on soil respiration among any two or three treatment factors irrespective of testing time period. Temperature sensitivity of soil respiration was reduced by air warming, lower in the wet than the dry side, and not affected by CO2 treatment. Variations of soil respiration responses with soil temperature and soil moisture ranges could be primarily attributable to the seasonal dynamics of plant growth and its responses to the three treatments. Using a conceptual model to interpret the significant relationships of treatment-induced changes in soil respiration with changes in soil temperature and moisture observed in this study, we conclude that elevated CO2, air warming, and changing soil water availability had both direct and indirect effects on soil respiration via changes in the three controlling factors: soil temperature, soil moisture, and C substrate. Our results demonstrate that the response of soil respiration to climatic warming should not be represented in models as a simple temperature response function. A more mechanistic understanding of the direct and indirect impacts of concurrent global change drivers on soil respiration is needed to facilitate the interpretation and projection of ecosystem and global C cycling in response to atmospheric and climate change.« less

[1]  Markus Reichstein,et al.  Modeling temporal and large‐scale spatial variability of soil respiration from soil water availability, temperature and vegetation productivity indices , 2003 .

[2]  E. Rasmussen,et al.  A most beautiful polar low. A case study of a polar low development in the Bear Island region , 1992 .

[3]  Eric A. Davidson,et al.  Biogeochemistry: Soil warming and organic carbon content , 2000, Nature.

[4]  C. Potter,et al.  Interannual variability in global soil respiration, 1980–94 , 2002 .

[5]  Yiqi Luo,et al.  Response of soil CO2 efflux to water manipulation in a tallgrass prairie ecosystem , 2002, Plant and Soil.

[6]  R. Norby,et al.  Temperature‐controlled open‐top chambers for global change research , 1997 .

[7]  J. Raich,et al.  Vegetation and soil respiration: Correlations and controls , 2000 .

[8]  Yiqi Luo,et al.  Acclimatization of soil respiration to warming in a tall grass prairie , 2001, Nature.

[9]  Mark G Tjoelker,et al.  Thermal acclimation and the dynamic response of plant respiration to temperature. , 2003, Trends in plant science.

[10]  Yiqi Luo,et al.  Net ecosystem carbon exchange in two experimental grassland ecosystems , 2004 .

[11]  E. Davidson,et al.  Soil water content and temperature as independent or confounded factors controlling soil respiration in a temperate mixed hardwood forest , 1998 .

[12]  A. Knapp,et al.  Biomass production and species composition change in a tallgrass prairie ecosystem after long‐term exposure to elevated atmospheric CO2 , 1999 .

[13]  I. Impens,et al.  Free Air Temperature Increase (FATI): a new tool to study global warming effects on plants in the field , 1996 .

[14]  R. Ceulemans,et al.  End-of-season effects of elevated temperature on ecophysiological processes of grassland species at different species richness levels , 2006 .

[15]  E. Davidson,et al.  Temperature sensitivity of soil carbon decomposition and feedbacks to climate change , 2006, Nature.

[16]  N. Buchmann,et al.  Large-scale forest girdling shows that current photosynthesis drives soil respiration , 2001, Nature.

[17]  S. Trumbore.  Carbon respired by terrestrial ecosystems – recent progress and challenges , 2006 .

[18]  M. Kirschbaum,et al.  Will changes in soil organic carbon act as a positive or negative feedback on global warming? , 2000 .

[19]  Michael G. Ryan,et al.  Interpreting, measuring, and modeling soil respiration , 2005 .

[20]  Eric A. Davidson,et al.  On the variability of respiration in terrestrial ecosystems: moving beyond Q 10 , 2006 .

[21]  R. Norby,et al.  Below-ground respiratory responses of sugar maple and red maple saplings to atmospheric CO2 enrichment and elevated air temperature , 1999, Plant and Soil.

[22]  R. B. Jackson,et al.  The fate of carbon in grasslands under carbon dioxide enrichment , 1997, Nature.

[23]  E. Davidson,et al.  Effects of experimental drought on soil respiration and radiocarbon efflux from a temperate forest soil , 2002 .

[24]  M. Kirschbaum,et al.  The temperature dependence of soil organic matter decomposition, and the effect of global warming on soil organic C storage , 1995 .

[25]  H. Rogers,et al.  A field technique for the study of plant responses to elevated carbon dioxide concentrations , 1983 .

[26]  D. E. Schorran,et al.  Impacts of an anomalously warm year on soil CO2 efflux in experimentally manipulated tallgrass prairie ecosystems , 2005 .

[27]  J. Tenhunen,et al.  Does the temperature sensitivity of decomposition of soil organic matter depend upon water content, soil horizon, or incubation time? , 2005 .

[28]  R. Monson,et al.  Differential controls by climate and substrate over the heterotrophic and rhizospheric components of soil respiration , 2006 .

[29]  E. Pendall,et al.  Elevated CO2 stimulates soil respiration in a FACE wheat field , 2001 .

[30]  R. Betts,et al.  Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model , 2000, Nature.

[31]  D. Tingey,et al.  Does soil CO2 efflux acclimatize to elevated temperature and CO2 during long-term treatment of Douglas-fir seedlings? , 2006, The New phytologist.

[32]  J. Berry,et al.  A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species , 1980, Planta.

[33]  Michael G. Ryan,et al.  Evidence that decomposition rates of organic carbon in mineral soil do not vary with temperature , 2000, Nature.

[34]  Michael G. Ryan,et al.  Below-ground process responses to elevated CO2 and temperature: a discussion of observations, measurement methods, and models , 2004 .

[35]  John W. Doran,et al.  Steady‐State Aerobic Microbial Activity as a Function of Soil Water Content , 1990 .

[36]  M. R. Shaw,et al.  Water relations in grassland and desert ecosystems exposed to elevated atmospheric CO2 , 2004, Oecologia.

[37]  J. Lloyd,et al.  On the temperature dependence of soil respiration , 1994 .

[38]  K. Pregitzer,et al.  Elevated atmospheric CO2, fine roots and the response of soil microorganisms: a review and hypothesis , 2000 .

[39]  L. Rustad,et al.  Controls on soil respiration: Implications for climate change , 2000 .

[40]  K. Pilegaard,et al.  Large seasonal changes in Q10 of soil respiration in a beech forest , 2003 .

[41]  Eric A. Davidson,et al.  Effects of soil water content on soil respiration in forests and cattle pastures of eastern Amazonia , 2000 .

[42]  Yiqi Luo,et al.  Substrate regulation of soil respiration in a tallgrass prairie: Results of a clipping and shading experiment , 2003 .

[43]  R. Ceulemans,et al.  Annual Q10 of soil respiration reflects plant phenological patterns as well as temperature sensitivity , 2004 .

[44]  W. Post,et al.  Temperature‐independent diel variation in soil respiration observed from a temperate deciduous forest , 2006 .

[45]  J. Harte,et al.  The effect of experimental ecosystem warming on CO2 fluxes in a montane meadow , 1999 .

[46]  Stephen P. Long,et al.  Modification of the response of photosynthetic productivity to rising temperature by atmospheric CO2 concentrations: Has its importance been underestimated? , 1991 .

[47]  J. Y. King,et al.  Elevated atmospheric CO2 effects and soil water feedbacks on soil respiration components in a Colorado grassland , 2003 .

[48]  J. Lilley,et al.  Productivity of Trifolium subterraneum and Phalaris aquatica under warmer, high CO2 conditions , 2001 .

[49]  Christopher B. Field,et al.  Elevated CO2 increases belowground respiration in California grasslands , 1996, Oecologia.

[50]  R. Norby,et al.  Evaluating ecosystem responses to rising atmospheric CO2 and global warming in a multi‐factor world , 2004 .

[51]  R. B. Jackson,et al.  Gas exchange and photosynthetic acclimation over subambient to elevated CO2 in a C3–C4 grassland , 2001 .