Microbial competition for nitrogen and carbon is as intense in the subsoil as in the topsoil

Jones, Davey L.; Magthab, Ebtsam; Gleeson, Deirdre; Hill, Paul W.; Sánchez‐Rodríguez, Antonio Rafael; Roberts, Paula; Ge, Tida; Murphy, Daniel V.

doi:10.1016/j.soilbio.2017.10.024

Cited by 136 publications

(74 citation statements)

References 85 publications

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“…Apart from these cases, effects of cropping system on biochemical variables were minimal, suggesting that the greater delivery of root C in the four-year systems was accompanied by a proportional increase in microbial processing throughout the profile. This finding supports recent observations of high C turnover in both topsoils and subsoils when organic substrate is added (Jones et al, 2018).…”

Section: Values (Supplementarysupporting

confidence: 92%

Whole-profile soil organic matter content, composition, and stability under cropping systems that differ in belowground inputs

Poffenbarger

Olk

Cambardella

et al. 2020

Agriculture, Ecosystems & Environment

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Subsoils have been identified as a potential carbon sink because they typically have low soil organic carbon (SOC) concentrations and high SOC stability. One proposed strategy to increase SOC stocks is to enhance C inputs to the subsoil by increasing crop rotation diversity with deep-rooted perennial crops. Using three long-term field trials in Iowa (study durations of 60, 35, and 12 years), we examined the effects of contrasting cropping systems [maize (Zea mays L.)-soybean (Glycine max (L.) Merr) (= two-year system) vs. maize-soybean-oat (Avena sativa L.)/alfalfa (Medicago sativa L.)-alfalfa or maize-maize-oat/ alfalfa-alfalfa (= four-year system)] on above-and below-ground C inputs, as well as the content, biochemical composition, and distribution of SOC among physical fractions differing in stability to 90 cm depth. Average annual total C inputs were similar in the two-year and four-year systems, but the proportion of C delivered belowground was 20-35 % greater in the four-year system. Despite the long duration of these studies, the effect of cropping system on SOC content to 90 cm was inconsistent across trials, ranging from −7 % to +16 % in the four-year relative to the two-year system. At the one site where SOC was significantly greater in the four-year system, the effect of cropping system on SOC content was observed in surface and subsoil layers rather than limited to the subsoil (i.e., below 30 cm).Cropping system had minimal effects on biochemical indicators of plant-derived organic matter or on the proportions of SOC in labile particulate organic matter versus stable mineral-associated organic matter. We conclude that adoption of cropping systems with enhanced belowground C inputs may increase total profile SOC, but the effect is minimal and inconsistent; furthermore, it has minor impact on the vertical distribution, biochemical composition, and stability of SOC in Mollisols of the Midwest U.S.Subsoils have been identified as a potential carbon sink because they typically have low soil organic carbon (SOC) concentrations and high SOC stability. One proposed strategy to increase SOC stocks is to enhance C inputs to the subsoil by increasing crop rotation diversity with deep-rooted perennial crops. Using three longterm field trials in Iowa (study durations of 60, 35, and 12 years), we examined the effects of contrasting cropping systems [maize (Zea mays L.)-soybean (Glycine max (L.) Merr) (= two-year system) vs. maize-soybeanoat (Avena sativa L.)/alfalfa (Medicago sativa L.)-alfalfa or maize-maize-oat/alfalfa-alfalfa (= four-year system)] on above-and below-ground C inputs, as well as the content, biochemical composition, and distribution of SOC among physical fractions differing in stability to 90 cm depth. Average annual total C inputs were similar in the two-year and four-year systems, but the proportion of C delivered belowground was 20-35 % greater in the fouryear system. Despite the long duration of these studies, the effect of cropping system on SOC content to 90 cm was inconsistent across trials...

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Section: Values (Supplementarysupporting

confidence: 92%

Whole-profile soil organic matter content, composition, and stability under cropping systems that differ in belowground inputs

Poffenbarger

Olk

Cambardella

et al. 2020

Agriculture, Ecosystems & Environment

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“…Strong relationships observed between microbial biomass and soil C gains may not be as clear in the subsurface where C inputs and microbial biomass are much lower and impacts of physical processes, such as occlusion and sorption, are more evident. Subsurface losses may be due to soil organic matter degradation from priming (Dignac et al, ) of resource‐limited deep microbial communities and/or low soil moisture conditions decreasing occlusion and adsorption mechanisms (Blankenship & Schimel, ; Jardine, Weber, & McCarthy, ; Jones et al, ); however, more research is needed to elucidate soil C dynamics in this zone. Considering the entire 2 m‐deep soil profile, WCC incorporated without additional nutrient application may have decreased soil C at depths >60 cm, resulting in net declines in soil C across the soil profile in terms of stocks.…”

Section: Discussionmentioning

confidence: 99%

Deep soil inventories reveal that impacts of cover crops and compost on soil carbon sequestration differ in surface and subsurface soils

Tautges

Chiartas

Gaudin

et al. 2019

Global Change Biology

177

111

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Increasing soil organic carbon (SOC) via organic inputs is a key strategy for increasing long‐term soil C storage and improving the climate change mitigation and adaptation potential of agricultural systems. A long‐term trial in California's Mediterranean climate revealed impacts of management on SOC in maize‐tomato and wheat–fallow cropping systems. SOC was measured at the initiation of the experiment and at year 19, at five depth increments down to 2 m, taking into account changes in bulk density. Across the entire 2 m profile, SOC in the wheat–fallow systems did not change with the addition of N fertilizer, winter cover crops (WCC), or irrigation alone and decreased by 5.6% with no inputs. There was some evidence of soil C gains at depth with both N fertilizer and irrigation, though high variation precluded detection of significant changes. In maize‒tomato rotations, SOC increased by 12.6% (21.8 Mg C/ha) with both WCC and composted poultry manure inputs, across the 2 m profile. The addition of WCC to a conventionally managed system increased SOC stocks by 3.5% (1.44 Mg C/ha) in the 0–30 cm layer, but decreased by 10.8% (14.86 Mg C/ha) in the 30–200 cm layer, resulting in overall losses of 13.4 Mg C/ha. If we only measured soil C in the top 30 cm, we would have assumed an increase in total soil C increased with WCC alone, whereas in reality significant losses in SOC occurred when considering the 2 m soil profile. Ignoring the subsoil carbon dynamics in deeper layers of soil fails to recognize potential opportunities for soil C sequestration, and may lead to false conclusions about the impact of management practices on C sequestration.

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“…The biotic and abiotic factors that control SOM decomposition can thus change across ecosystems, over time and between topsoil and subsoil (Rumpel & Kogel‐Knabner, ). These factors include: (a) the state of SOM, that is, whether it is protected in aggregates, associated with minerals or is partially decomposed litter (Six, Conant, Paul, & Paustian, ; von Luetzow et al, ); (b) the abundance, diversity and functional traits of decomposer communities (Ekschmitt et al, ; Fierer, Bradford, & Jackson, ); and (c) the availability of oxygen, water and nutrients (Davidson, Samanta, Caramori, & Savage, ; Jones et al, ).…”

Section: Changing Paradigm Of Som Dynamicsmentioning

confidence: 99%

Zones of influence for soil organic matter dynamics: A conceptual framework for data and models

Cagnarini

Blyth

Emmett

et al. 2019

Global Change Biology

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Microbial competition for nitrogen and carbon is as intense in the subsoil as in the topsoil

Cited by 136 publications

References 85 publications

Whole-profile soil organic matter content, composition, and stability under cropping systems that differ in belowground inputs

Whole-profile soil organic matter content, composition, and stability under cropping systems that differ in belowground inputs

Deep soil inventories reveal that impacts of cover crops and compost on soil carbon sequestration differ in surface and subsurface soils

Zones of influence for soil organic matter dynamics: A conceptual framework for data and models

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