Carbon input to soil may decrease soil carbon content

Abstract

It is commonly predicted that the intensity of primary production and soil carbon (C) content are positively linked. Paradoxically, many long-term field observations show that although plant litter is incorporated to soil in large quantities, soil C content does not necessarily increase. These results suggest that a negative relationship between C input and soil C conservation exists. Here, we demonstrate in controlled conditions that the supply of fresh C may accelerate the decomposition of soil C and induce a negative C balance. We show that soil C losses increase when soil microbes are nutrient limited. Results highlight the need for a better understanding of microbial mechanisms involved in the complex relationship between C input and soil C sequestration. We conclude that energy available to soil microbes and microbial competition are important determinants of soil C decomposition.

Priming and microbial nutrient limitation in lowland tropical forest soils of contrasting fertility

“…The rapid priming (the peak in primed-CO 2 occurred before the peak in sucrose derived-CO 2 ) due to microbial nutrient demand as indicated by our data is consistent with some studies of temperate soils (Zyakun and Dilly 2005;Blagodatskaya et al 2007;Nottingham et al 2009), but at odds with others that do not predict such rapid priming (Fontaine et al 2004) or an increased production of extracellular enzymes (De Nobili et al 2001). This suggests that different mechanisms may apply in different soils on different time scales.…”

“…Inputs of labile organic compounds to soil can stimulate microbial mineralization of pre-existing organic matter through 'priming effects' (Fontaine et al 2004). Priming effects have the potential to feedback positively on climate change by contributing an additional source of atmospheric CO 2 .…”

“…According to this theory, the soil C-specialists increase in abundance by utilizing some of the new labile C and persist to degrade stable soil C when the labile C becomes diminished (Fontaine et al 2003). Supporting evidence for this mechanism is provided by studies that measured prolonged priming after supply of added labile C is exhausted (Fontaine et al 2004), and priming alongside an increased dominance of the microbial community by fungi (Carney et al 2007).…”

“…Priming due to increased abundance of recalcitrant-C degrading microorganisms can be identified by a shift in microbial community composition (e.g. increase in fungal:bacterial ratios; Carney et al 2007), prolonged priming following the exhaustion of the added substrate, and greater priming in low fertility soils (Fontaine et al 2003(Fontaine et al , 2004.…”

Using experimental manipulation to assess the roles of leaf litter in the functioning of forest ecosystems

“…Greater Oi and Oe horizons could increase the incorporation of dissolved and particulate organic matter into the mineral soil. Increased litter inputs may also cause the 'priming effect ' (sensu Fontaine et al, 2004), the increased decomposition of older organic matter with increasing fresh organic matter inputs. Litter addition studies also provide an excellent opportunity to assess some of the effects of increasing primary production in forests and therefore improve predictions of the effects of elevated CO 2 levels in forest ecosystems.…”