Bahn Michael

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Bahn
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Michael
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  • Article
    Looking deeper into the soil : biophysical controls and seasonal lags of soil CO2 production and efflux
    (Ecological Society of America, 2010-09) Vargas, Rodrigo ; Baldocchi, Dennis D. ; Allen, Michael F. ; Bahn, Michael ; Black, T. Andrew ; Collins, Scott L. ; Yuste, Jorge Curiel ; Hirano, Takashi ; Jassal, Rachhpal S. ; Pumpanen, Jukka ; Tang, Jianwu
    We seek to understand how biophysical factors such as soil temperature (Ts), soil moisture (θ), and gross primary production (GPP) influence CO2 fluxes across terrestrial ecosystems. Recent advancements in automated measurements and remote-sensing approaches have provided time series in which lags and relationships among variables can be explored. The purpose of this study is to present new applications of continuous measurements of soil CO2 efflux (F0) and soil CO2 concentrations measurements. Here we explore how variation in Ts, θ, and GPP (derived from NASA's moderate-resolution imaging spectroradiometer [MODIS]) influence F0 and soil CO2 production (Ps). We focused on seasonal variation and used continuous measurements at a daily timescale across four vegetation types at 13 study sites to quantify: (1) differences in seasonal lags between soil CO2 fluxes and Ts, θ, and GPP and (2) interactions and relationships between CO2 fluxes with Ts, θ, and GPP. Mean annual Ts did not explain annual F0 and Ps among vegetation types, but GPP explained 73% and 30% of the variation, respectively. We found evidence that lags between soil CO2 fluxes and Ts or GPP provide insights into the role of plant phenology and information relevant about possible timing of controls of autotrophic and heterotrophic processes. The influences of biophysical factors that regulate daily F0 and Ps are different among vegetation types, but GPP is a dominant variable for explaining soil CO2 fluxes. The emergence of long-term automated soil CO2 flux measurement networks provides a unique opportunity for extended investigations into F0 and Ps processes in the near future.
  • Article
    Soil respiration at mean annual temperature predicts annual total across vegetation types and biomes
    (Copernicus Publications on behalf of the European Geosciences Union, 2010-07-09) Bahn, Michael ; Reichstein, M. ; Davidson, Eric A. ; Grunzweig, J. ; Jung, M. ; Carbone, M. S. ; Epron, D. ; Misson, L. ; Nouvellon, Y. ; Roupsard, O. ; Savage, K. ; Trumbore, Susan E. ; Gimeno, C. ; Curiel Yuste, J. ; Tang, Jianwu ; Vargas, Rodrigo ; Janssens, Ivan A.
    Soil respiration (SR) constitutes the largest flux of CO2 from terrestrial ecosystems to the atmosphere. However, there still exist considerable uncertainties as to its actual magnitude, as well as its spatial and interannual variability. Based on a reanalysis and synthesis of 80 site-years for 57 forests, plantations, savannas, shrublands and grasslands from boreal to tropical climates we present evidence that total annual SR is closely related to SR at mean annual soil temperature (SRMAT), irrespective of the type of ecosystem and biome. This is theoretically expected for non water-limited ecosystems within most of the globally occurring range of annual temperature variability and sensitivity (Q10). We further show that for seasonally dry sites where annual precipitation (P) is lower than potential evapotranspiration (PET), annual SR can be predicted from wet season SRMAT corrected for a factor related to P/PET. Our finding indicates that it can be sufficient to measure SRMAT for obtaining a well constrained estimate of its annual total. This should substantially increase our capacity for assessing the spatial distribution of soil CO2 emissions across ecosystems, landscapes and regions, and thereby contribute to improving the spatial resolution of a major component of the global carbon cycle.