Does the addition of labile substrate destabilise old soil organic matter?

Abstract

Input of organic matter to soil may stimulate microbial activity and alter soil carbon storage by modifying the mineralization of native soil organic carbon (SOC). Assessing the age of SOC affected by the altered mineralization is a major challenge as the destabilisation of old SOC would be much more damageable for the overall carbon budget than the mobilization of recent SOC. Here, we investigated the microbial populations sequentially activated after the addition of a labile substrate. We questioned whether they have distinct metabolic potential and we characterised the age of the native SOC they primed. We used soils from Congolese Eucalyptus plantations that were previously under savannah and which old and recent SOC exhibited different ?13C. Soils were amended with glucose, in an amount sufficient to induce microbe growth, and incubated for one week. The ?13C of respired CO2 was continuously recorded using a tuneable diode laser spectrometer (TDLS). The combination of two glucose treatments with different ?13C signatures allowed partitioning the various sources of CO2 over time (recent SOC, old SOC and glucose). This was combined with phospholipids fatty acids (PLFA) analyses and potential metabolic activities measurements after 40 h and seven days of incubation. A peak of glucose mineralization occurred after 17 h of incubation. Before this peak (Stage 1), some specific communities with a strong feeding preference for recent SOC were activated. After the glucose peak (Stage 2), over-mineralization of native SOC occurred for some days. The recent C3 SOC was first preferentially used (Stage 3), while the old C4 SOC was destabilised in a later stage (Stage 4). Metabolic functions and composition of microbial communities also differed between Stages 3 and 4. Microbial populations collected at Stage 4 were slower compared to Stage 3, but more efficient in decomposing nutrient-containing substrates. Gram negative bacteria (16:1w7c and 18:1w7c) were stimulated at Stage 3 only, while Gram negative bacteria (cy17:0) were stimulated at both Stages 3 and 4. Our results demonstrated that the input of labile substrate alters the microbial community composition, potential metabolic activities, and the SOC pools utilisation. They pointed out the necessity to assess the age of destabilised SOC when investigating the impact of priming on carbon storage in soil. (Résumé d'auteur

Bacterial community structure in maize stubble-amended soils with different moisture levels estimated by bar-coded pyrosequencing

“…Microbial communities appear as a largely dormant population with an enormous richness of species and an ability to survive hard times (e.g., drought and oligotrophy) (Jenkinson and Ladd, 1981). The entrance of easily mobilizable organic substrates into the soil can temporarily activate diverse microbial populations (Kuzyakov, 2010), and the activity of these activated populations decays quickly when the energy provided by the added substrates is insufficient to synthesize enzymes and to grow (Derrien et al, 2014). Therefore, DOC brought by the stubble promotes a priming effect that triggers the bacterial populations that are dormant and potentially active.…”

“…Desiccated crop straw consists of cellulose, lignin, crude protein, low molecular carbohydrates, inorganic salts, etc. When crop straw is returned into the fields, it will be decomposed by soil microflora, which makes an important contribution to biogeochemical cycling of C and nitrogen (N) (Wakelin et al, 2007), and the maintenance of soil fertility (Derrien et al, 2014).…”

Effects of plant-derived dissolved organic matter (DOM) on soil CO2 and N2O emissions and soil carbon and nitrogen sequestrations

“…Several studies reported that the addition of labile substrates could trigger dormant and potential active microorganisms, alter microbial community composition and potential metabolic activities, accelerate the turnover of SOC (Derrien et al, 2014;Fontaine et al, 2003;Fontaine et al, 2004a;2004b;Kuzyakov, 2010;Liang et al, 1996;Paterson and Sim, 2013) and induce a negative C balance (Liang et al, 1996;Fontaine et al, 2004aFontaine et al, , 2004b. Application of DOM led to 198% and 133% SOC priming effects in PDOM and PDOM + N treatments, relative to the control soil.…”

“…The litter-derived soluble organic carbon accounts for 5-15% of the total C content, which corresponds to 5-25% of the litter biomass (Cleveland et al, 2004). The plant-derived DOM represents a major source of soil DOM (Kalbitz et al, 2000), while adding this kind of soluble organic matter to soil may lead to an increase in microbial activity and subsequently accelerate the turnover of SOC through priming effect (PE) (Derrien et al, 2014;Fontaine et al, 2004;Kuzyakov et al, 2000;Paterson and Sim, 2013). The PE is generally neglected in soil C balance calculation because it is commonly accepted that the PE is temporary leading to small soil C losses (Kuzyakov et al, 2000).…”

An assessment of factors controlling N2O and CO2 emissions from crop residues using different measurement approaches

“…In particular, the GHG emission from the soil is mediated by soil porosity (Killham et al 1993), pH (Mørkved et al 2006), organic C and N content (Hayakawa et al 2009), microbial community (Graf et al 2016), texture (Chen et al 2013), soil temperature (Kesik et al 2006) and moisture content, all of which regulate gas production processes and emission (Skiba and Ball 2002;Rees et al 2013). Moreover, crop residue addition to the soil can also indirectly affect GHG emissions, providing a source of readily available C and N in the soil, stimulating microbial activity (Aulakh et al 2001;Huang et al 2004), promoting the decomposition of native SOC and altering soil aeration, water holding capacity, oxidation and denitrification processes in the soil (Fontaine et al 2004;Derrien et al 2014).…”