Browsing by Author "Vane, Christopher H."

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    Long-term zero-tillage enhances the protection of soil carbon in tropical agriculture
    (Wiley, 2021-03-27) Cooper, Hannah V.; Sjögersten, Sofie; Lark, Richard M.; Girkin, Nicholas T.; Vane, Christopher H.; Calonego, Juliano C.; Rosolem, Ciro; Mooney, Sacha J.
    Contrasting tillage strategies not only affect the stability and formation of soil aggregates but also modify the concentration and thermostability of soil organic matter associated with soil aggregates. Understanding the thermostability and carbon retention ability of aggregates under different tillage systems is essential to ascertain potential terrestrial carbon storage. We characterised the concentration and thermostability of soil organic carbon (SOC) within various aggregate size classes under both zero and conventional tillage using novel Rock‐Eval pyrolysis. The nature of the pore systems was visualised and quantified by X‐ray Computed Tomography to link soil structure to organic carbon preservation and thermostability. Soil samples were collected from experimental fields in Botucatu, Brazil, which had been under zero‐tillage for 2, 15 and 31 years, along with adjacent fields under conventional tillage. Soils under zero‐tillage significantly increased pore connectivity whilst simultaneously decreasing inter‐aggregate porosity, providing a potential physical mechanism for protection of soil organic carbon in the 0‐20 cm soil layer. Changes in the soil physical characteristics associated with the adoption of zero‐tillage resulted in improved aggregate formation compared to conventionally tilled soils, especially when implemented for at least 15 years. In addition, we identified a chemical change in composition of organic carbon to a more recalcitrant fraction following conversion to zero‐tillage, suggesting aggregates were accumulating rather than mineralising soil organic carbon. These data reveal profound effects of different tillage systems upon soil structural modification, with important implications for the potential of zero‐tillage to increase carbon sequestration compared to conventional tillage.
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    Root oxygen mitigates methane fluxes in tropical peatlands
    (IOP, 2020-05-27) Girkin, Nicholas T.; Vane, Christopher H.; Turner, Benjamin L.; Ostle, Nicholas J.; Sjögersten, Sofie
    Tropical peatlands are a globally important source of methane, a potent greenhouse gas. Vegetation is critical in regulating fluxes, providing a conduit for emissions and regular carbon inputs. However, plant roots also release oxygen, which might mitigate methane efflux through oxidation prior to emission from the peat surface. Here we show, using in situ mesocosms, that root exclusion can reduce methane fluxes by a maximum of 92% depending on species, likely driven by the significant decrease in root inputs of oxygen and changes in the balance of methane transport pathways. Methanotroph abundance decreased with reduced oxygen input, demonstrating a likely mechanism for the observed response. These first methane oxidation estimates for a tropical peatland demonstrate that although plants provide an important pathway for methane loss, this can be balanced by the influence of root oxygen inputs that mitigate peat surface methane emissions.
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    Root oxygen mitigates methane fluxes in tropical peatlands: data
    (Cranfield University, 2021-06-21 13:47) Girkin, Nicholas T.; Vane, Christopher H.; Turner, Benjamin L.; Ostle, Nicholas J.; Sjagersten, Sofie
    Tropical peatlands are a globally important source of methane, a potent greenhouse gas. Vegetation is critical in regulating fluxes, providing a conduit for emissions and regular carbon inputs. However, plant roots also release oxygen, which might mitigate methane efflux through oxidation prior to emission from the peat surface. Here we show, using in situ mesocosms, that root exclusion can reduce methane fluxes by a maximum of 92% depending on species, likely driven by the significant decrease in root inputs of oxygen and changes in the balance of methane transport pathways. Methanotroph abundance decreased with reduced oxygen input, demonstrating a likely mechanism for the observed response. These first methane oxidation estimates for a tropical peatland demonstrate that although plants provide an important pathway for methane loss, this can be balanced by the influence of root oxygen inputs that mitigate peat surface methane emissions. This data includes measurements of methane fluxes, peat organic matter properties as assessed by Rock-Eval pyrolysis, bulk peat properties, and microbial community structure as assessed by phospholipid fatty acid (PLFA) analysis.
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    The temperature dependence of greenhouse gas production from Central African savannah soils
    (Elsevier, 2025-03-01) Girkin, Nicholas T.; Cooper, Hannah V.; Johnston, Alice S.; Ledger, Martha; Niamba, G. R. Mouanda; Vane, Christopher H.; Moss-Hayes, Vicky; Crabtree, Dafydd; Dargie, Greta C.; Vasquez, Saul; Bocko, Yannick; Mampouya Wenina, Emmanuel; Mbemba, Mackline; Boom, Arnoud; Ifo, Suspense Averti; Lewis, Simon L.; Sjögersten, Sofie
    Savannahs cover 20 % of the global land surface, but there have been few studies of greenhouse gas (GHG) dynamics from savannah soils. Here, we assess potential turnover of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from surface (0–10 cm) and subsurface (20–30 cm) soils from two contrasting tropical savannah sites in the Republic of Congo, Central Africa, under dry (40 % water-filled-pore-space, WFPS) and wet (70 % WFPS) conditions. Under baseline conditions (25 °C), we found soils were sources of CO2 and N2O, but a sink for CH4. Assessment of the temperature response of GHG fluxes between 20 and 35 °C revealed variable temperature dependences. That is, CO2 fluxes showed a strong temperature response, whereas the temperature response of N2O fluxes was only significant under dry conditions, and no significant temperature response of CH4 fluxes was observed. The temperature quotient (Q10) of soil respiration increased from 1.58 ± 0.004 to 1.92 ± 0.006 at sites with lower soil organic carbon contents. The relative increase in N2O with CO2 fluxes across temperatures was significantly influenced by moisture conditions at both sites. No temperature or soil moisture response was observed for CH4 fluxes, collectively implying divergent GHG responses to changing climatic conditions. Using Rock-Eval pyrolysis we assessed the organic chemistry of all soil types, which indicated contrasting degrees of stability of carbon sources between sites and with depth which, alongside significant differences in a range of other soil parameters (including organic matter content, total carbon, total nitrogen, electrical conductivity, and pH), may account for site-specific differences in baseline GHG emissions. Taken together, our results are amongst the first measures of GHG temperature sensitivity of tropical savannah soils, and demonstrate that soil CO2 emissions are more sensitive to warming and changes in moisture than the emissions of other GHGs, although relatively low compared to responses reported for soils from other tropical ecosystems. This implies that GHG fluxes form savannah soils in the region may be at least partially resilient to climate-induced soil warming compared to other ecosystems.