Invasive perennial forb effects on gross soil nitrogen cycling and nitrous oxide fluxes depend on phenology.

Invasive plants can increase soil nitrogen (N) pools and accelerate soil N cycling rates, but their effect on gross N cycling and nitrous oxide (N2 O) emissions has rarely been studied. We hypothesized that perennial pepperweed (Lepidium latifolium) invasion would increase rates of N cycling and gaseous N loss, thereby depleting ecosystem N and causing a negative feedback on invasion. We measured a suite of gross N cycling rates and net N2 O fluxes in invaded and uninvaded areas of an annual grassland in the Sacramento-San Joaquin River Delta region of northern California. During the growing season, pepperweed-invaded soils had lower microbial biomass N, gross N mineralization, dissimilatory nitrate reduction to ammonium (DNRA), and denitrification-derived net N2 O fluxes (P < 0.02 for all). During pepperweed dormancy, gross N mineralization, DNRA, and denitrification-derived net N2 O fluxes were stimulated in pepperweed-invaded plots, presumably by N-rich litter inputs and decreased competition between microbes and plants for N (P < 0.04 for all). Soil organic carbon and total N concentrations, which reflect pepperweed effects integrated over longer time scales, were lower in pepperweed-invaded soils (P < 0.001 and P = 0.04, respectively). Overall, pepperweed invasion had a net negative effect on ecosystem N status, depleting soil total N to potentially cause a negative feedback to invasion in the long term

Organic matter compositions and loadings in soils and sediments along the Fly River, Papua New Guinea

The compositions and loadings of organic matter in soils and sediments from a diverse range of environments along the Fly River system were determined to investigate carbon transport and sequestration in this region. Soil horizons from highland sites representative of upland sources have organic carbon contents (%OC) that range from 0.3 to 25 wt%, carbon:nitrogen ratios(OC/N) that range from 7 to 25 mol/mol, highly negative stable carbon isotopic compositions (δ¹³C[subscript org] -25 ‰) and non-woody vegetation biomarkers (cinnamyl phenols and cutin acids) more abundant relative to upper floodplain sites. Soils developed on relict Pleistocene floodplain terraces, which are typically not flooded and receive little sediment from the river, were characterized by low %OC contents ( -21 ‰) and low LP concentrations (~ 3 mg/100 mg OC). These relict floodplain soils contain modern carbon that reflects primarily local (C₃ or C₄) vegetation sources. Total suspended solids collected along the river varied widely in overall concentrations (1 > TSS > 9,000 mg/L), %OC contents (0.1 to 60 wt%), OC/N ratios (7 to 17 mol/mol) and δ¹³C[subscript org] signatures (-26 to -32 ‰). These compositions reflect a mixture of C₃ vascular plants and freshwater algae. However, little of this algal production appears to be preserved in floodplain soils. A comparison of organic carbon loadings of active floodplain soils (0.2 and 0.5 mg C/m²) with previous studies of actively depositing sediments in the adjacent delta-clinoform system (0.4 to 0.7 mg C/m²) indicates that Fly River floodplain sediments are less effective at sequestering organic carbon than deltaic sediments. Furthermore, relict Pleistocene floodplain sites with low or negligible modern sediment accumulation rates display significantly lower loadings (0.1 to 0.2 mg C/m²). This deficit in organic carbon likely reflects mineralization of sedimentary organic carbon during long term oxidative weathering, further reducing floodplain carbon storage

The North American tree-ring fire-scar network

Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree-ring fire scars provide valuable perspectives on fire regimes, including centuries-long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree-ring fire-scar network (NAFSN), which contains 2562 sites, >37,000 fire-scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000-m elevation and across a range of topographic settings that vary by ecoregion. Multiple regions are densely sampled (e.g., >1000 fire-scarred trees), enabling new spatial analyses such as reconstructions of area burned. To demonstrate the potential of the network, we compared the climate space of the NAFSN to those of modern fires and forests; the NAFSN spans a climate space largely representative of the forested areas in North America, with notable gaps in warmer tropical climates. Modern fires are burning in similar climate spaces as historical fires, but disproportionately in warmer regions compared to the historical record, possibly related to under-sampling of warm subtropical forests or supporting observations of changing fire regimes. The historical influence of Indigenous and non-Indigenous human land use on fire regimes varies in space and time. A 20th century fire deficit associated with human activities is evident in many regions, yet fire regimes characterized by frequent surface fires are still active in some areas (e.g., Mexico and the southeastern United States). These analyses provide a foundation and framework for future studies using the hundreds of thousands of annually- to sub-annually-resolved tree-ring records of fire spanning centuries, which will further advance our understanding of the interactions among fire, climate, topography, vegetation, and humans across North America

Invasive perennial forb effects on gross soil nitrogen cycling and nitrous oxide fluxes depend on phenology.

Invasive plants can increase soil nitrogen (N) pools and accelerate soil N cycling rates, but their effect on gross N cycling and nitrous oxide (N2 O) emissions has rarely been studied. We hypothesized that perennial pepperweed (Lepidium latifolium) invasion would increase rates of N cycling and gaseous N loss, thereby depleting ecosystem N and causing a negative feedback on invasion. We measured a suite of gross N cycling rates and net N2 O fluxes in invaded and uninvaded areas of an annual grassland in the Sacramento-San Joaquin River Delta region of northern California. During the growing season, pepperweed-invaded soils had lower microbial biomass N, gross N mineralization, dissimilatory nitrate reduction to ammonium (DNRA), and denitrification-derived net N2 O fluxes (P < 0.02 for all). During pepperweed dormancy, gross N mineralization, DNRA, and denitrification-derived net N2 O fluxes were stimulated in pepperweed-invaded plots, presumably by N-rich litter inputs and decreased competition between microbes and plants for N (P < 0.04 for all). Soil organic carbon and total N concentrations, which reflect pepperweed effects integrated over longer time scales, were lower in pepperweed-invaded soils (P < 0.001 and P = 0.04, respectively). Overall, pepperweed invasion had a net negative effect on ecosystem N status, depleting soil total N to potentially cause a negative feedback to invasion in the long term

GoniMiguelCEOASOrganicMatterCompositions(Tables1-5).pdf

The compositions and loadings of organic matter in soils and sediments from a diverse range of environments along the Fly River system were determined to investigate carbon transport and sequestration in this region. Soil horizons from highland sites representative of upland sources have organic carbon contents (%OC) that range from 0.3 to 25 wt%, carbon:nitrogen ratios(OC/N) that range from 7 to 25 mol/mol, highly negative stable carbon isotopic compositions (δ¹³C[subscript org] -25 ‰) and non-woody vegetation biomarkers (cinnamyl phenols and cutin acids) more abundant relative to upper floodplain sites. Soils developed on relict Pleistocene floodplain terraces, which are typically not flooded and receive little sediment from the river, were characterized by low %OC contents ( -21 ‰) and low LP concentrations (~ 3 mg/100 mg OC). These relict floodplain soils contain modern carbon that reflects primarily local (C₃ or C₄) vegetation sources. Total suspended solids collected along the river varied widely in overall concentrations (1 > TSS > 9,000 mg/L), %OC contents (0.1 to 60 wt%), OC/N ratios (7 to 17 mol/mol) and δ¹³C[subscript org] signatures (-26 to -32 ‰). These compositions reflect a mixture of C₃ vascular plants and freshwater algae. However, little of this algal production appears to be preserved in floodplain soils. A comparison of organic carbon loadings of active floodplain soils (0.2 and 0.5 mg C/m²) with previous studies of actively depositing sediments in the adjacent delta-clinoform system (0.4 to 0.7 mg C/m²) indicates that Fly River floodplain sediments are less effective at sequestering organic carbon than deltaic sediments. Furthermore, relict Pleistocene floodplain sites with low or negligible modern sediment accumulation rates display significantly lower loadings (0.1 to 0.2 mg C/m²). This deficit in organic carbon likely reflects mineralization of sedimentary organic carbon during long term oxidative weathering, further reducing floodplain carbon storage

GoniMiguelCEOASOrganicMatterCompositions(ElectronicAnnexI).pdf

The compositions and loadings of organic matter in soils and sediments from a diverse range of environments along the Fly River system were determined to investigate carbon transport and sequestration in this region. Soil horizons from highland sites representative of upland sources have organic carbon contents (%OC) that range from 0.3 to 25 wt%, carbon:nitrogen ratios(OC/N) that range from 7 to 25 mol/mol, highly negative stable carbon isotopic compositions (δ¹³C[subscript org] -25 ‰) and non-woody vegetation biomarkers (cinnamyl phenols and cutin acids) more abundant relative to upper floodplain sites. Soils developed on relict Pleistocene floodplain terraces, which are typically not flooded and receive little sediment from the river, were characterized by low %OC contents ( -21 ‰) and low LP concentrations (~ 3 mg/100 mg OC). These relict floodplain soils contain modern carbon that reflects primarily local (C₃ or C₄) vegetation sources. Total suspended solids collected along the river varied widely in overall concentrations (1 > TSS > 9,000 mg/L), %OC contents (0.1 to 60 wt%), OC/N ratios (7 to 17 mol/mol) and δ¹³C[subscript org] signatures (-26 to -32 ‰). These compositions reflect a mixture of C₃ vascular plants and freshwater algae. However, little of this algal production appears to be preserved in floodplain soils. A comparison of organic carbon loadings of active floodplain soils (0.2 and 0.5 mg C/m²) with previous studies of actively depositing sediments in the adjacent delta-clinoform system (0.4 to 0.7 mg C/m²) indicates that Fly River floodplain sediments are less effective at sequestering organic carbon than deltaic sediments. Furthermore, relict Pleistocene floodplain sites with low or negligible modern sediment accumulation rates display significantly lower loadings (0.1 to 0.2 mg C/m²). This deficit in organic carbon likely reflects mineralization of sedimentary organic carbon during long term oxidative weathering, further reducing floodplain carbon storage

GoniMiguelCEOASOrganicMatterCompositions(Figures1-12).pdf

The compositions and loadings of organic matter in soils and sediments from a diverse range of environments along the Fly River system were determined to investigate carbon transport and sequestration in this region. Soil horizons from highland sites representative of upland sources have organic carbon contents (%OC) that range from 0.3 to 25 wt%, carbon:nitrogen ratios(OC/N) that range from 7 to 25 mol/mol, highly negative stable carbon isotopic compositions (δ¹³C[subscript org] -25 ‰) and non-woody vegetation biomarkers (cinnamyl phenols and cutin acids) more abundant relative to upper floodplain sites. Soils developed on relict Pleistocene floodplain terraces, which are typically not flooded and receive little sediment from the river, were characterized by low %OC contents ( -21 ‰) and low LP concentrations (~ 3 mg/100 mg OC). These relict floodplain soils contain modern carbon that reflects primarily local (C₃ or C₄) vegetation sources. Total suspended solids collected along the river varied widely in overall concentrations (1 > TSS > 9,000 mg/L), %OC contents (0.1 to 60 wt%), OC/N ratios (7 to 17 mol/mol) and δ¹³C[subscript org] signatures (-26 to -32 ‰). These compositions reflect a mixture of C₃ vascular plants and freshwater algae. However, little of this algal production appears to be preserved in floodplain soils. A comparison of organic carbon loadings of active floodplain soils (0.2 and 0.5 mg C/m²) with previous studies of actively depositing sediments in the adjacent delta-clinoform system (0.4 to 0.7 mg C/m²) indicates that Fly River floodplain sediments are less effective at sequestering organic carbon than deltaic sediments. Furthermore, relict Pleistocene floodplain sites with low or negligible modern sediment accumulation rates display significantly lower loadings (0.1 to 0.2 mg C/m²). This deficit in organic carbon likely reflects mineralization of sedimentary organic carbon during long term oxidative weathering, further reducing floodplain carbon storage

GoniMiguelCEOASOrganicMatterCompositions.pdf

The compositions and loadings of organic matter in soils and sediments from a diverse range of environments along the Fly River system were determined to investigate carbon transport and sequestration in this region. Soil horizons from highland sites representative of upland sources have organic carbon contents (%OC) that range from 0.3 to 25 wt%, carbon:nitrogen ratios(OC/N) that range from 7 to 25 mol/mol, highly negative stable carbon isotopic compositions (δ¹³C[subscript org] -25 ‰) and non-woody vegetation biomarkers (cinnamyl phenols and cutin acids) more abundant relative to upper floodplain sites. Soils developed on relict Pleistocene floodplain terraces, which are typically not flooded and receive little sediment from the river, were characterized by low %OC contents ( -21 ‰) and low LP concentrations (~ 3 mg/100 mg OC). These relict floodplain soils contain modern carbon that reflects primarily local (C₃ or C₄) vegetation sources. Total suspended solids collected along the river varied widely in overall concentrations (1 > TSS > 9,000 mg/L), %OC contents (0.1 to 60 wt%), OC/N ratios (7 to 17 mol/mol) and δ¹³C[subscript org] signatures (-26 to -32 ‰). These compositions reflect a mixture of C₃ vascular plants and freshwater algae. However, little of this algal production appears to be preserved in floodplain soils. A comparison of organic carbon loadings of active floodplain soils (0.2 and 0.5 mg C/m²) with previous studies of actively depositing sediments in the adjacent delta-clinoform system (0.4 to 0.7 mg C/m²) indicates that Fly River floodplain sediments are less effective at sequestering organic carbon than deltaic sediments. Furthermore, relict Pleistocene floodplain sites with low or negligible modern sediment accumulation rates display significantly lower loadings (0.1 to 0.2 mg C/m²). This deficit in organic carbon likely reflects mineralization of sedimentary organic carbon during long term oxidative weathering, further reducing floodplain carbon storage

Indexing Permafrost Soil Organic Matter Degradation Using High-Resolution Mass Spectrometry

<div><p>Microbial degradation of soil organic matter (SOM) is a key process for terrestrial carbon cycling, although the molecular details of these transformations remain unclear. This study reports the application of ultrahigh resolution mass spectrometry to profile the molecular composition of SOM and its degradation during a simulated warming experiment. A soil sample, collected near Barrow, Alaska, USA, was subjected to a 40-day incubation under anoxic conditions and analyzed before and after the incubation to determine changes of SOM composition. A CHO index based on molecular C, H, and O data was utilized to codify SOM components according to their observed degradation potentials. Compounds with a CHO index score between –1 and 0 in a water-soluble fraction (WSF) demonstrated high degradation potential, with a highest shift of CHO index occurred in the N-containing group of compounds, while similar stoichiometries in a base-soluble fraction (BSF) did not. Additionally, compared with the classical H:C vs O:C van Krevelen diagram, CHO index allowed for direct visualization of the distribution of heteroatoms such as N in the identified SOM compounds. We demonstrate that CHO index is useful not only in characterizing arctic SOM at the molecular level but also enabling quantitative description of SOM degradation, thereby facilitating incorporation of the high resolution MS datasets to future mechanistic models of SOM degradation and prediction of greenhouse gas emissions.</p></div