Labile soil carbon inputs mediate the soil microbial community composition and plant residue decomposition rates

Abstract

Summary Root carbon (C) inputs may regulate decomposition rates in soil, and in this study we ask: how do labile C inputs regulate decomposition of plant residues, and soil microbial communities? In a 14 d laboratory incubation, we added C compounds often found in root exudates in seven different concentrations (0, 0.7, 1.4, 3.6, 7.2, 14.4 and 21.7 mg C g−1 soil) to soils amended with and without 13C‐labeled plant residue. We measured CO2 respiration and shifts in relative fungal and bacterial rRNA gene copy numbers using quantitative polymerase chain reaction (qPCR). Increased labile C input enhanced total C respiration, but only addition of C at low concentrations (0.7 mg C g−1) stimulated plant residue decomposition (+2%). Intermediate concentrations (1.4, 3.6 mg C g−1) had no impact on plant residue decomposition, while greater concentrations of C (> 7.2 mg C g−1) reduced decomposition (−50%). Concurrently, high exudate concentrations (> 3.6 mg C g−1) increased fungal and bacterial gene copy numbers, whereas low exudate concentrations (< 3.6 mg C g−1) increased metabolic activity rather than gene copy numbers. These results underscore that labile soil C inputs can regulate decomposition of more recalcitrant soil C by controlling the activity and relative abundance of fungi and bacteria.

Microbial community structure mediates response of soil C decomposition to litter addition and warming

“…2). Soil priming has been attributed to the activity of certain microbes (particularly fungi) more than others (De Graaff et al, 2010;Fontaine et al, 2011;Garcia-Pausas and Paterson, 2011;Paterson and Sim, 2013), although gram-positive bacteria have also been implicated (Bird et al, 2011). We did not find evidence for fungi mediating changes in priming with litter addition or temperature in this study, but we did observe significant changes in microbial community structure with temperature, particularly a consistent increase in soil-utilizing gram-positive bacteria (Fig.…”

“…However, whether changes in litter decomposition will ultimately impact downstream soil-C dynamics is uncertain (Kemmitt et al, 2008;Schimel and Schaeffer, 2012;Cleveland et al, 2014). Priming, the increased loss of soil-C due to the addition of labile substrates, has also been related to changes in microbial community structure (Fontaine et al, 2003;De Graaff et al, 2010;Blagodatskaya et al, 2014), and provides a link between the quantity or quality of more thermodynamically labile inputs and the potential destabilization of soil carbon (Guenet et al, 2012;Wild et al, 2014).…”

Linking soil bacterial biodiversity and soil carbon stability

“…With this approach, any evolved CO 2 carrying the 13 C signature of the added glucose is considered respiration of glucose, including 13 C-labeled biomass and metabolites derived from prior glucose additions. Thus, this approach quantifies priming as the oxidation of SOC present at the beginning of the experiment, consistent with many other studies of priming (Cheng et al, 2003;De Graaff et al, 2010). In a parallel incubation for dual-stable isotope probing, the repeated-pulse samples received unlabeled glucose (500 mg C-glucose per gram soil) for 6 weeks while the non-amended and singlepulse samples received sterile deionized water.…”

Agricultural Management and Labile Carbon Additions Affect Soil Microbial Community Structure and Interact with Carbon and Nitrogen Cycling

“…5, Tables 1 and 2). Organic management practices have been shown previously to increase the rate of soil processes without causing increases in microbial biomass [8,10,21,24,55,60]. Other studies have also similarly shown that when exposed to small additions of carbon substrate the rate of microbial processes can increase without a change in standing biomass [24,55].…”

“…Since heterotrophic soil microbes are most commonly limited by carbon availability, increases of easily used carbon substrates can lead to rapid increases in microbial biomass and decomposition of more recalcitrant SOM [23][24][25]. This increased rate of decomposition, also known as the priming effect, can also increase N mineralized from recalcitrant organic matter [26].…”