A global experiment suggests climate warming will not accelerate litter decomposition in streams but might reduce carbon sequestration

Abstract

The decomposition of plant litter is one of the most important ecosystem processes in the biosphere and is particularly sensitive to climate warming. Aquatic ecosystems are well suited to studying warming effects on decomposition because the otherwise confounding influence of moisture is constant. By using a latitudinal temperature gradient in an unprecedented global experiment in streams, we found that climate warming will likely hasten microbial litter decomposition and produce an equivalent decline in detritivore-mediated decomposition rates. As a result, overall decomposition rates should remain unchanged. Nevertheless, the process would be profoundly altered, because the shift in importance from detritivores to microbes in warm climates would likely increase CO(2) production and decrease the generation and sequestration of recalcitrant organic particles. In view of recent estimates showing that inland waters are a significant component of the global carbon cycle, this implies consequences for global biogeochemistry and a possible positive climate feedback.

Effect of experimental and seasonal warming on litter decomposition in a temperate stream

“…This stimulation was expected since the activities of most temperate fungi and invertebrate species are stimulated by warming within the temperature range observed (Azevedo-Pereira et al 2006;Dang et al 2009;Ferreira and Chauvet 2011a, b). This stimulation is also in agreement with metabolic theory (Brown et al 2004) and with studies where litter was incubated along natural thermal gradients (Irons et al 1994;Fabre and Chauvet 1998;Swan and Palmer 2004;Friberg et al 2009;Boyero et al 2011b). Although an increase in water temperature by 10°C is over that expected for temperate woodland streams solely due to global warming (IPCC (Intergovernmental Panel on Climate Change) 2007; Morrill et al 2005), increases of this magnitude may occur under global-warming scenarios that include removal of riparian vegetation, water abstraction, or warm-water discharge from power plants (Poff and Mathews 1986;Stefan and Sinokrot 1993).…”

“…The relative contributions of microbes and invertebrates to litter decomposition determines the amount of carbon that is mineralized, released into the atmosphere, incorporated into secondary production, and stored in the system for longer periods (Boyero et al 2011b). In this study, invertebrate-driven litter decomposition was more strongly stimulated (*29) over the 10°C temperature gradient than microbial-driven litter decomposition.…”

“…The stimulation of microbial-driven litter decomposition with temperature suggests that the rate of CO 2 release from freshwaters will increase under global warming (Boyero et al 2011b). However, the greater stimulation of invertebrate-driven litter decomposition suggests that a larger fraction of litter carbon might be invested in secondary production and be retained in the system for longer periods than at present, with largely unknown potential consequences for food-web dynamics (O'Connor et al 2009).…”

“…Correlative studies have found a positive relationship between decomposition rates of litter incubated along elevation (Fabre and Chauvet 1998), latitudinal (Irons et al 1994;Boyero et al 2011b), or geothermal gradients (Friberg et al 2009). Studies under different seasonal thermal regimes have also reported faster litter decomposition in warmer seasons (Swan and Palmer 2004;Ferreira et al 2006).…”

“…Studies under different seasonal thermal regimes have also reported faster litter decomposition in warmer seasons (Swan and Palmer 2004;Ferreira et al 2006). However, the relative sensitivity to temperature of microbial-driven and invertebrate-driven litter decomposition has rarely been discussed (but see Irons et al 1994;Friberg et al 2009;Boyero et al 2011b), despite the possibility that the two groups have distinct sensitivities to temperature (Boyero et al 2011b). In this study, we assessed the effects of experimental (*3°C) and seasonal warming (monthly mean temperature: 6-16°C) on oak leaf litter decomposition, and on the relative contributions of microbes and invertebrates to this process, in a small temperate mountain stream.…”