Soil organic carbon accrual due to more efficient microbial utilization of plant inputs at greater long-term soil moisture

Journal Article · Sat Apr 30 00:00:00 EDT 2022 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/j.gca.2022.04.028· OSTI ID:1977157

Shabtai, Itamar A. ^[1]; Das, Srabani ^[2]; Inagaki, Thiago M. ^[3]; Azimzadeh, Behrooz ^[4]; Richards, Brian ^[4]; Martínez, Carmen Enid ^[4]; Kögel-Knabner, Ingrid ^[3]; Lehmann, Johannes ^[4]

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1. Cornell University, Ithaca, NY (United States); OSTI
2. The Ohio State University, Columbus, OH (United States)
3. Technical University of Munich (Germany)
4. Cornell University, Ithaca, NY (United States)

High long-term soil moisture may either stimulate or inhibit soil organic carbon (SOC) losses through changes to mineral and chemical composition, and resultant organo-mineral interactions. Yet, the trade-off between mineralization and accrual of SOC under long-term variation in unsaturated soil moisture remains uncertain. We tested the underexplored relationships between long-term soil moisture and organo-mineral chemical composition and its implications for SOC persistence in an experimental field in New York, USA, with differences in long-term mean soil volumetric water content (0–0.15 m depth) ranging from 0.40 to 0.63 (v/v) during the growing season. Long-term soil moisture across 20 subplots on four fallow plots were positively correlated with SOC (R² = 0.23; P = 0.019, n = 20), mineral-associated organic matter (MAOM) content (g fraction/g soil) (R² = 0.44; P = 0.001; n = 20) and occluded particulate organic matter (oPOM) content (R² = 0.18; P = 0.033; n = 20). Higher long-term soil moisture was associated with a decrease in the relative content of sodium pyrophosphate extractable Fe (R² = 0.33; P < 0.005; n = 20), an increase in sodium dithionite extractable Fe (R² = 0.44; P < 0.001; n = 20), and an increase in SOC retention by non-crystalline Al pools (R² = 0.51; P = 0.0002 for sodium pyrophosphate extracts, R² = 0.41; P = 0.0014 for hydroxylamine hydrochloride extracts; n = 20 for both). Increasing long-term soil moisture was associated with a four-fold increase in microbial biomass C (per unit SOC) and lower metabolic quotient (R² = 0.56, P < 0.001). MAOM fractions of high-moisture soils had lower C:N (from C:N 9.5 to 9.0, R² = 0.27, P = 0.011, n = 20). Consistent with decreasing C:N, increasing decomposition with increasing moisture was reflected by a 15% and 10% greater proportion of oxidized carboxylic-C to aromatic-C and O-alkyl C, respectively, as measured with ¹³C NMR, and a more pronounced FTIR signature of N-containing proteinaceous compounds in high-moisture MAOM fractions, indicative of microbial metabolites and transformation products. A partial least squares regression showed that SOC content increased with greater long-term moisture (P = 0.019), pyrophosphate-extractable Al (P = 0.0001), and exchangeable Ca (P = 0.013). Here our results show that higher long-term soil moisture resulted in SOC accrual by enhancing conversion of plant inputs into microbial biomass that interacts with reactive minerals.

• Research Organization: Cornell University, Ithaca, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER); United States – Israel Binational Agricultural Research and Development Fund (BARD); US Department of Agriculture (USDA)
• Grant/Contract Number: SC0016364
• OSTI ID: 1977157
• Alternate ID(s): OSTI ID: 1867949
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: C Vol. 327; ISSN 0016-7037
• Publisher: Elsevier; The Geochemical Society; The Meteoritical Society
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
long-term soil moisture
metabolic quotient
microbial carbon cycling
organo-mineral interactions
soil organic carbon