Bradford Mark A.

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Mark A.

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  • Preprint
    Decreased mass specific respiration under experimental warming is robust to the microbial biomass method employed
    ( 2009-05) Bradford, Mark A. ; Wallenstein, Matthew D. ; Allison, Steven D. ; Treseder, Kathleen K. ; Frey, Serita D. ; Watts, Brian W. ; Davies, Christian A. ; Maddox, Thomas R. ; Melillo, Jerry M. ; Mohan, Jacqueline E. ; Reynolds, James F.
    Hartley et al. question whether reduction in Rmass, under experimental warming, arises because of the biomass method. We show the method they treat as independent yields the same result. We describe why the substrate-depletion hypothesis cannot alone explain observed responses, and urge caution in the interpretation of the seasonal data.
  • Preprint
    Animating the carbon cycle
    ( 2013-08) Schmitz, Oswald J. ; Raymond, Peter A. ; Estes, James A. ; Kurz, Werner A. ; Holtgrieve, Gordon W. ; Ritchie, Mark E. ; Schindler, Daniel E. ; Spivak, Amanda C. ; Wilson, Rod W. ; Bradford, Mark A. ; Christensen, Villy ; Deegan, Linda A. ; Smetacek, Victor ; Vanni, Michael J. ; Wilmers, Christopher C.
    Understanding the biogeochemical processes regulating carbon cycling is central to mitigating atmospheric CO2 emissions. The role of living organisms has been accounted for, but the focus has traditionally been on contributions of plants and microbes. We develop the case that fully “animating” the carbon cycle requires broader consideration of the functional role of animals in mediating biogeochemical processes and quantification of their effects on carbon storage and exchange among terrestrial and aquatic reservoirs and the atmosphere. To encourage more hypothesis-driven experimental research that quantifies animal effects we discuss the mechanisms by which animals may affect carbon exchanges and storage within and among ecosystems and the atmosphere. We illustrate how those mechanisms lead to multiplier effects whose magnitudes may rival those of more traditional carbon storage and exchange rate estimates currently used in the carbon budget. Many animal species are already directly managed. Thus improved quantitative understanding of their influence on carbon budgets may create opportunity for management and policy to identify and implement new options for mitigating CO2 release at regional scales.
  • Preprint
    Thermal adaptation of soil microbial respiration to elevated temperature
    ( 2008-07-22) Bradford, Mark A. ; Davies, Christian A. ; Frey, Serita D. ; Maddox, Thomas R. ; Melillo, Jerry M. ; Mohan, Jacqueline E. ; Reynolds, James F. ; Treseder, Kathleen K. ; Wallenstein, Matthew D.
    In the short-term heterotrophic soil respiration is strongly and positively related to temperature. In the long-term its response to temperature is uncertain. One reason for this is because in field experiments increases in respiration due to warming are relatively short-lived. The explanations proposed for this ephemeral response include depletion of fast-cycling, soil carbon pools and thermal adaptation of microbial respiration. Using a >15 year soil warming experiment in a mid-latitude forest, we show that the apparent ‘acclimation’ of soil respiration at the ecosystem scale results from combined effects of reductions in soil carbon pools and microbial biomass, and thermal adaptation of microbial respiration. Mass specific respiration rates were lower when seasonal temperatures were higher, suggesting that rate reductions under experimental warming likely occurred through temperature-induced changes in the microbial community. Our results imply that stimulatory effects of global temperature rise on soil respiration rates may be lower than currently predicted.