Suchergebnisse

The response of mineral-stabilized soil organic carbon (SOC) to environmental change is a source of uncertainty in the understanding of SOC cycling. Fluctuating wet-dry cycles and associated redox changes in otherwise well-drained soils may drive mineral dissolution, organic carbon (OC) mobilization, and subsequent OC mineralization. However, the extent to which rapid fluctuations between water-saturated and unsaturated conditions (i.e., flashy conditions) result in long-term changes in mineral composition and organo-mineral interactions is not well understood. In this study, the effect of variable saturation frequency on soil mineral composition, mineral-associated OC, and OC mineralizability was tested using selective dissolution, bulk spectroscopy, microscale imaging, and aerobic-anaerobic incubation experiments. Previous water table fluctuation measurements and diagnostic profile characteristics at Hubbard Brook Experimental Forest (NH) were used to identify soils with high, medium, and low saturation frequency regimes (defined by historical water table cycling frequency; i.e., water table presence and recession in the upper B horizon). We found the amount of OC released during extractions targeting non-crystalline minerals was of similar magnitude as extracted iron (Fe) in lower saturation frequency soils. However, the magnitude of extracted OC was 2.5 times greater than Fe but more similar to extractable aluminum (Al) in higher saturation frequency soils. Bulk soil Fe was spatially more strongly correlated to soil organic matter (SOM) in lower saturation frequency soils (Spearman Rank r(s) = 0.62, p < 0.005), whereas strong correlations between Al and SOM were observed in higher saturation frequency soils (r(s) = 0.88, p < 0.005) using nanoscale secondary ion mass spectrometry (NanoSIMS) imaging. Characterization of bulk soil Fe with X-ray absorption spectroscopy showed 1.2-fold greater Fe(II) and 1-fold lower contribution of Fe-organic bonding in soils with high saturation frequency. Fe(III) interactions with carboxylic and aromatic C were identified with C-13 nuclear magnetic resonance (NMR) spectroscopy Fe(III) interference experiments. Additionally, carboxylic acid enrichment in high saturation frequency soils quantified by C K-edge X-ray absorption spectroscopy point towards the role of carboxylic functional groups in Al-organic in addition to Fe-organic interactions. In our incubation experiments, a doubling in short-term CO2 evolution (per unit total soil C) was detected for high relative to low saturation frequency soils. Further, an order of magnitude increase in CO2 evolution (per unit water-extractable OC) following anaerobic incubation was only detected in high saturation frequency soils. The observed shift towards Al-dominated SOC interactions and higher OC mineralizability highlights the need to describe C stabilization in soils with flashy wet-dry cycling separately from soils with low saturation frequency or persistent saturation. ; NSF IGERT in Cross-Scale Biogeochemistry and Climate at Cornell University (NSF)National Science Foundation (NSF) [1069193]; Institute for Advanced Study (IAS) from the Technical University of Munich (TUM); Andrew W. Mellon Foundation; Cornell College of Agriculture and Life Sciences Alumni Foundation, USA; National Science FoundationNational Science Foundation (NSF) [DMR-1332208]; Canada Foundation for InnovationCanada Foundation for InnovationCGIAR; Natural Sciences and Engineering Research Council of CanadaNatural Sciences and Engineering Research Council of Canada (NSERC)CGIAR; University of Saskatchewan; Government of Saskatchewan; Western Economic Diversification Canada; National Research Council Canada; Canadian Institutes of Health Research, CanadaCanadian Institutes of Health Research (CIHR) ; Funding for this study was provided by the NSF IGERT in Cross-Scale Biogeochemistry and Climate at Cornell University (NSF Award #1069193) and the Institute for Advanced Study (IAS) from the Technical University of Munich (TUM) through the Hans-Fisher Senior Fellowship. Additional research funds were provided by the Andrew W. Mellon Foundation and the Cornell College of Agriculture and Life Sciences Alumni Foundation, USA. Hubbard Brook Experimental Forest is operated and maintained by the US Forest Service, Northern Research Station, Newtown Square, PA, USA. This work uses research conducted at the Cornell High Energy Synchrotron Source (CHESS) which is supported by the National Science Foundation under award DMR-1332208. Research was performed at the Canadian Light Source (CLS), which is supported by the Canada Foundation for Innovation, Natural Sciences and Engineering Research Council of Canada, the University of Saskatchewan, the Government of Saskatchewan, Western Economic Diversification Canada, the National Research Council Canada, and the Canadian Institutes of Health Research, Canada. The authors thank Dr. Rong Huang of CHESS, Dr. Tom Regier of CLS, Kelly Hanley and Akio Enders of Cornell University for technical assistance; Dr. Carmen Hoschen, Johann Lugmeier and Dr. Carsten Mueller of the Technical University of Munich for their support with the NanoSIMS measurements; Dr. Carmen Enid Martinez' research group for providing iron XAS standard materials; Dr. Linda Pardo, Stephanie Duston, Brittany LeBeau, and Johali Sotelo for soil sample collection and field characterization; and the referees for their invaluable insights. ; Public domain authored by a U.S. government employee