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

• Published in: The New phytologist 2010-12, Vol.188 (4), p.1055-1064
• Main Authors: de Graaff, Marie-Anne, Classen, Aimee T., Castro, Hector F., Schadt, Christopher W.
• Format: Article
• Language: English
• Subjects: ABUNDANCE; Acid soils; BACTERIA; Bacteria - drug effects; Bacteria - genetics; BASIC BIOLOGICAL SCIENCES; Biodegradation, Environmental - drug effects; CARBON; Carbon - metabolism; Carbon - pharmacology; CARBON DIOXIDE; Carbon Dioxide - metabolism; carbon‐13; Cell Respiration - drug effects; Community composition; DECOMPOSITION; ENVIRONMENTAL SCIENCES; Exudates; Exudation; FUNGI; Fungi - drug effects; Fungi - genetics; Gene Dosage - drug effects; GENES; INCUBATION; Incubation period; Low concentrations; Microbial activity; Microbiomes; Microorganisms; Nucleotide sequence; Panicum - cytology; Panicum - drug effects; Panicum - metabolism; PCR; Plant communities; Plant residues; POLYMERASE CHAIN REACTION; priming; qPCR; Relative abundance; RESIDUES; RESPIRATION; root exudation; rRNA; Soil; Soil - analysis; Soil amendment; Soil biochemistry; Soil biology; Soil composition; Soil ecology; Soil fungi; Soil Microbiology; Soil microorganisms; Soil respiration; Soil water; SOILS
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.2010.03427.x

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.