Soil Oxygen Content Research Articles

Variation of Soil Microbial Population in Different Soil Horizons

Large diversity of micro flora and fauna are found in soil horizons. Microbial population in soil are determined by various factor such as soil depth, organic matter, porosity, oxygen and carbon dioxide concentration, soil PH, etc. Factors that influence microorganism role in nutrient building and cycling in soil and organic matter decomposition are of unique interest. Microorganisms decompose organic matter, detoxifying the toxic substance, fixing the nitrogen, transformation of nitrogen, phosphorous, potassium and other secondary & micro nutrients are the major biochemical activities performed by microbes in soil. Low population of microorganism is found in the compact soil, soil with low organic matter percentage and on deeper strata of soil. So, this paper was reviewed to explore major factors that influence soil microbial population and its role in soil productivity. This was already established fact but main aim of this paper is to collect related information and conclude the future research prospects to strengthen the microorganism role in soil productivity and factor that influence growth of microorganism.

Investigation of agar as a soil analogue for corrosion studies

Solid agar based gels have been investigated as an electrolyte system for the electrochemical study of soil corrosion, specifically microbiologically influenced corrosion (MIC) in soil. Traditional techniques for studying corrosion in soil include solutions and soil samples; however these systems do not reliably simulate the physico‐chemical properties of soil. Soils are complex environments with three phases critical to corrosion (solid‐soil, liquid‐water and gas‐oxygen). Therefore there is a need for a system which replicates and considers this complex environment and its effects on corrosion processes, while reducing inconsistencies and variations associated with moisture and oxygen content in soil. Open circuit potential (OCP) and potentiodynamic scans (PDS) were conducted on carbon steel exposed to solid agar electrolyte with varying oxygen concentrations. Results were analysed using Tafel extrapolation, consistency in anodic‐cathodic trends and optical microscopy of the exposed regions. For the conditions tested, a cathodic shift was seen with the observed corrosion potentials being notably lower than the measured OCPs. Consistency in the anodic‐cathodic trends of the PDS was observed with minimal oxygen conditions. Overall, an agar based gel system has potential as an electrolyte for soil based MIC studies, especially as an analogue for moist clay soils.

Biology and control of Pectobacterium in potato

Pectobacterium species cause soft rot, blackleg, and stem rot in potato and a wide range of other vegetable crops and ornamental plants. Diseases caused by Pectobacterium are controlled mainly through use of healthy planting material, sanitation and copper sprays. Environmental factors, such as temperature, moisture and soil oxygen concentration, have a large effect on development of diseases caused by Pectobacterium and disease incidence can be unpredictable. The pathogen is spread by various mechanisms including water, seed, equipment and insects. Little is understood about plant resistance to soft rot bacterial pathogens and no commercial potato cultivars are resistant to soft rot, although some have tolerance and some wild potato species are resistant. Pectobacterium is a diverse genus, with multiple species capable of infecting potato. Multiple Pectobacterium species may be found in the same field and even on the same plant. Pectobacterium strains vary in aggressiveness and the virulence genes they encode but there are many commonalities across the genus. Over the past decade, genomic studies have provided new insights into Pectobacterium biology. For example, some Pectobacterium strains may elicit plant cell death to promote disease in leaves. Strains of the pathogen also produce an orange pigment and volatile compounds that increase virulence and that may act as insect kairomones. Recent work with a supervised machine learning program has identified several novel target genes likely to contribute to plant-microbe interactions, suggesting that there is still much to learn about how soft rot bacteria cause disease.

Microbially mediated nitrogen retention and loss in a salt marsh soil

Salt marshes currently play an important role as filters for upslope nitrogen (N) inputs. This could change in the future with sea level rise, warming and eutrophication, which are expected to favor monocultures over diverse plant communities. We explored patterns in gross N cycling, dissimilatory nitrate (NO3−) reduction to ammonium (NH4+) (DNRA), and denitrification in a salt marsh soil under two typical redox conditions (aerobic and anaerobic), and in soils under plant communities manipulated to simulate potential future composition (forb and graminoid monocultures). Natural salt marsh soils exhibited high potential gross N mineralization rates, averaging 50.4 ± 5.7 μg N g−1 d−1 under aerobic conditions; rates declined to 23.6 ± 3.4 μg N g−1 d−1 under an N2 headspace. Microbial NH4+ uptake and gross nitrification together accounted for only 14 % of gross N mineralization. Nitrogen retention via DNRA and microbial uptake greatly exceeded N losses via denitrification. Gross nitrification rates were greater in the forb and graminoid monocultures than in the control. This effect may be mediated by the lower plant biomass in the monocultures than in the control, which may have reduced competition between plants and nitrifiers for NH4+. Soil NO3− concentrations and net nitrous oxide (N2O) fluxes were greatest for the forb monoculture, likely due to higher soil oxygen (O2) concentrations in these plots. Our results suggest that salt marsh soils with a diverse plant community have high potential rates of N mineralization and microbial N retention, and the establishment of forb monocultures could lead to greater ecosystem N losses.

Fluxes of CO2, N2O and CH4 by 222Rn and chamber methods in cold-temperate grassland soil, northern Japan

This study conducted flux measurements of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4), estimated by 222Rn (Radon) and chamber methods in a cold-temperate northern Japanese grassland soil during summer and winter seasons. Our research aims to compare these fluxes of CO2, N2O and CH4 calculated by 222Rn and static chamber methods, and to understand the responses of fluxes by 222Rn and chamber methods to temperature. 222Rn fluxes ranged from 0.0046 to 0.0157 Bq m2 s−1, and the average was 0.0068 ± 0.0013 Bq m2 s−1 on sandy soil (> 50% sand). The average diffusion coefficients for CO2, N2O and CH4 calculated using the 222Rn method were 0.049 ± 0.008 cm2 s−1, 0.023 ± 0.005 cm2 s−1 and 0.054 ± 0.008 cm2 s−1, respectively, reflecting seasonality. CO2, N2O and CH4 flux measurements from the 222Rn method were in good agreement with those of the static chamber method, within the observed range of error, suggesting a high correlation coefficient of > 89% between the methods. Also, the temperatures of air and soil at 5-cm depth played a significant role in determining the fluxes of CO2 and CH4 measured by the 222Rn and chamber methods; meanwhile, the N2O flux displayed an inverse exponential relation to temperature. This suggests that N2O flux may be regulated by other factors such as soil water content and soil oxygen concentration. The contribution of winter fluxes of CO2, N2O and CH4 corresponded to 9, 51 and 3% of the annual fluxes of CO2, N2O and CH4, respectively, reflecting higher winter N2O production due to the constraint of oxygen in soil.

New insights into how increases in fertility improve the growth of rice at the seedling stage in red soil regions of subtropical China.

The differences in rhizosphere nitrification activities between high- and low- fertility soils appear to be related to differences in dissolved oxygen concentrations in the soil, implying a relationship to differences in the radial oxygen loss (ROL) of rice roots in these soils. A miniaturised Clark-type oxygen microelectrode system was used to determine rice root ROL and the rhizosphere oxygen profile, and rhizosphere nitrification activity was studied using a short-term nitrification activity assay. Rice planting significantly altered the oxygen cycling in the water-soil system due to rice root ROL. Although the oxygen content in control high-fertility soil (without rice plants) was lower than that in control low-fertility soil, high rice root ROL significantly improved the rhizosphere oxygen concentration in the high-fertility soil. High soil fertility improved the rice root growth and root porosity as well as rice root ROL, resulting in enhanced rhizosphere nitrification. High fertility also increased the content of nitrification-induced nitrate in the rhizosphere, resulting in enhanced ammonium uptake and assimilation in the rice. Although high ammonium pools in the high-fertility soil increased rhizosphere nitrification, rice root ROL might also contribute to rhizosphere nitrification improvement. This study provides new insights into the reasons that an increase in soil fertility may enhance the growth of rice. Our results suggest that an amendment of the fertiliser used in nutrient- and nitrification-poor paddy soils in the red soil regions of China may significantly promote rice growth and rice N nutrition.

The Influence of Soil Moisture, Temperature and Oxygen on the Oxic Decay of Organic Archaeological Deposits

The sensitivity of organic‐rich archaeological layers at Bryggen in Bergen, Norway, to changes in soil temperatures, water contents and oxygen concentrations is investigated. This is done by linking measurements of oxic decay at varying temperatures and water contents with on‐site monitoring data using a one‐pool decomposition model. The results show that the model can be used to elucidate the current in situ decay and to evaluate where and when the decay takes place. Future investigations need to include long‐term incubation experiments and decay studies at zero or very low oxygen contents in order to improve the robustness of predictions.

地下水位制御システム（FOEAS）設工ほ場における設定水位が秋まきキャベツの生育に及ぼす影響

地下水位制御システム（FOEAS：Farm-Oriented Enhancing Aquatic System）を施工した水田転換畑において，設定した地下水位が土壌水分量，気相の酸素濃度，秋まきキャベツの生育に及ぼす影響を評価した．地下水位を-30 cmに設定した高水位区，-60 cmに設定した低水位区を設けた．低水位区では高水位区よりも高い土壌水分吸引圧で推移したが，それは最大約40 kPaまでの緩やかな増加であった．両区とも，降水量に応じて地下水位が上昇した．降雨による土壌水分量の増加と地下水位の上昇に伴って気相率だけでなく作土の酸素濃度が低下し，特に高水位区では生育後期にしばしば0％まで低下した．冬季には，高水位区において土壌水分が高く維持された結果，低水位区よりもやや鉛直投影面積が大きかったが，後期には生育が抑制され，最終的な結球重は低水位区の約60％と小さかった．従って，FOEASが施工された水田転換畑において地下水位を高く一定に設定することは，湿害の危険性を増し，キャベツ収量を低下させる可能性が高いと考えられた．

Preliminary study of N<sub>2</sub>O emission and denitrification at early exposure period in Pengxi River drawdown area, Three Gorges Reservoir

Soil N2O emission and denitrification in the wetland( water level drawdown) area of reservoirs are critical pathways in the N biogeochemistry cycles. The intact soil core-acetylene inhibition technique was applied to investigate the N2 O emission and denitrification rates on grass land,cultivated area and background group in Lake Gaoyang drawdown area of Pengxi River,a tributary in the Three Gorges Reservoir,from March to April in 2013. Environmental impact factors,e. g. p H,oxidation-reduction potential,temperature,organic matter,total nitrogen,ammonium nitrogen,nitrate nitrogen and water-filled pore space,were measured simultaneously. The grass land had a mean N2 O emission rate of 9. 88 ± 6. 49 g N /( ha·d),and a mean denitrification rate of 58. 94 ± 52. 84 g N /( ha·d). The mean N2 O emission rate and denitrification rate of cultivated area were 7. 71 ± 4. 44 g N /( ha·d) and 30. 70 ± 25. 68 g N/( ha·d),respectively. The difference of N2 O emission rate in different land use types was significant. The N2 O emission and denitrification processes were greatly affected by the soil oxygen content,water content and nitrogen content of soils. An increase in soil oxygen content stimulated the N2 O emission in grass area and inhibited the denitrification process in a certain extent. Larger water content in the cultivated area,comparing with that in the grass area,probably lead to a smaller N2 O emission rate. Soil nitrogen content had a positive relationship with the decline of denitrification rate in the drawdown area.

Responses of the soil nematode community to management of hybrid napiergrass: The trade-off between positive and negative effects

An orthogonal experiment (form L16(45)) was used to investigate how the soil nematode community (density, diversity, and faunal structure) and soil health were affected by hybrid napiergrass management. The experiment included four levels of the each of the following main factors: nitrogen fertilization, cutting frequency, cutting intensity, and irrigation. The soil nematode community was affected more by nitrogen fertilization and irrigation than by cutting frequency and cutting intensity. Hybrid napiergrass develops a large root system and the carbon stored in the roots might have buffered any adverse effects of cutting on soil nematodes in the present study. The responses to fertilization indicated that fertilization had both positive and negative effects on the soil community and that the net effect depended on the level of fertilization. Additional water applied in irrigation was detrimental to soil nematode communities in that it might reduce the oxygen content of soil and also increases the potential for the leaching of nutrients from soil. Additionally, we suggest that moderate N fertilization (460kgha−1yr−1), moderate irrigation (one time yr−1 during the dry season), and cutting (three times per year at 20cm height) will maintain soil health and provide substantial hybrid napiergrass yields.

Increased root zone oxygen by a capillary barrier is beneficial to bell pepper irrigated with brackish water in an arid region

Limitations to growth and biomass production are expected under high (>30°C) soil temperatures due to low soil oxygen levels and insufficient oxygen transport to roots. These limitations will be exacerbated when irrigation with brackish water dictates large amounts of water application for leaching salts. We hypothesized that the introduction of an artificial capillary barrier (CB), in the form of a gravel layer at the lower root-zone boundary, can increase yields of irrigated horticultural crops due to better soil aeration and improved oxygen supply to roots. The specific objectives of the study were (1) to isolate scenarios where insufficient oxygen concentrations may limit pepper plant growth, (2) to measure oxygen concentrations in media under varied scenarios of CB placement below the active root zone and (3) to understand the environmental factors leading to sub-optimum oxygen concentrations in horticultural soils in a desert environment where supra-optimal soil temperatures are prevalent. At high root-zone temperatures oxygen flux to the roots was lower than the potential uptake rate and therefore soil oxygen concentrations were sub-optimal. These conditions led to reduced plant biomass and fruit yield. Fruit yield was found to decrease by 1% for every soil oxygen concentration decrease of 700ppm. In a fine textured Reg soil, allowing roots to penetrate into the capillary barrier gravel layer increased oxygen concentration in the root zone by 5% and improved biomass and fruit yield by 16% and 18%, respectively.

Proteomic evaluation of the biodegradation of wool fabrics in experimental burials

Woollen textiles recovered from archaeological excavations are usually fragile, discoloured, mineralised, or highly biodeteriorated fragmentary remains. The nature and extent of preservation is highly dependent on the site of burial and factors such as soil composition, pH, temperature, oxygen content, and contact with a wood coffin or metals. Understanding the particular biodegradation in archaeological sites is important for biomolecular studies of textiles, and to assist in the conservation of these finds. Wool fabrics dyed and buried for up to 8 yr in bog-type soils in Denmark (Lejre) and Norway (Rørmyra), and in marine sediments in Sweden (Marstrand) were evaluated by proteomics analysis. Wool degradation was found to occur through a range of differing mechanisms, mainly due to the complex nature of wool itself with its many families of proteins (keratin and keratin-associated proteins) and structures. Microbial activity was a large contributory factor to the physical deterioration of the wool fabrics at Lejre and Marstrand, and might result in faster loss of keratin-associated proteins over keratins. Additional hydrolysis took place at Marstrand, influenced by the environmental conditions of the sediment, and in particular the alkaline pH, contributing to the degradation of keratins. However, cross-linking was associated with the long-term preservation of the fabrics at Rørmyra, where pH, temperature, and vegetative composition of the bog prevented microbial activity, and sphagnum moss might preserve wool by binding with keratins.

Waterlogging in Australian agricultural landscapes: a review of plant responses and crop models

This review summarises reported observations of the effects of waterlogging on agricultural production in Australia and briefly discusses potential remediation strategies. Inconsistencies are demonstrated in the current indicators used for assessment of waterlogging potential across agricultural landscapes as well as in parameters measured in waterlogging studies. It is suggested that predictions of waterlogging potential for landscapes should be based on a minimum dataset that includes pedological, topographical, and climate data for the defined area, as well as observations of plant morphological appearance and visible surface water. The review also summarises the effects of low oxygen concentration in soil on rhizosphere processes, and discusses evidence for direct effects on plant physiology of reductions in soil oxygen caused by waterlogging. Finally, the review describes current crop growth, water use, and yield simulation models used in Australia (SWAGMAN, DRAINMOD, and APSIM) that incorporate waterlogging stress. It is suggested that there is scope for modifications to these models based on recent improved understanding of plant physiological responses to waterlogging and on further research. The review concludes that improvements in modelling waterlogging outcomes to assist growth and yield predictions should ultimately enhance management capacity for growers.

When Wet Gets Wetter: Decoupling of Moisture, Redox Biogeochemistry, and Greenhouse Gas Fluxes in a Humid Tropical Forest Soil

Upland humid tropical forest soils are often characterized by fluctuating redox dynamics that vary temporally and spatially across the landscape. An increase in the frequency and intensity of rainfall events with climate change is likely to affect soil redox reactions that control the production and emissions of greenhouse gases. We used a 24-day rainfall manipulation experiment to evaluate temporal and spatial trends of surface soil (0‐20 cm) redox-active chemical species and greenhouse gas fluxes in the Luquillo Experimental Forest, Puerto Rico. Treatments consisted of a high rainfall simulation (60 mm day -1 ), afl uctuating rainfall regime, and a control. Water addition generated high temporal and spatial variation in soil moisture (0.3‐0.6 m 3 m -3 ), but had no significant effect on soil oxygen (O2) concentrations. Extractable nitrate (NO3 - ) concentrations decreased with daily water additions and reduced iron (Fe(II)) concentrations increased towards the end of the experiment. Overall, redox indicators displayed a weak, non-deterministic, nonlinear relationship with soil moisture. High concentrations of Fe(II) and manganese (Mn) were present even where moisture was relatively low, and net Mn reduction occurred in all plots including controls. Mean CO2 fluxes were best explained by soil C concentrations and a composite redox indicator, and not water addition. Several plots were CH4 sources irrespective of water addition, whereas other plots oscillated between weak CH4 sources and sinks. Fluxes of N2 Ow ere highest in control plots and were consistently low in water-addition plots. Together, these data suggest (1) a relative decoupling between soil moisture and redox processes at our spatial and temporal scales of measurement, (2) the co-occurrence of aerobic and anaerobic biogeochemical processes in well-drained surface soils, and (3) an absence of threshold effects from sustained precipitation on redox reactions over the scale of weeks. Our data suggest a need to re-evaluate representations of moisture in biogeochemical models.

Effects of waterlogging on growth, porosity and radial oxygen loss of three tree species

Aims Flooding reduces soil oxygen content, and leads to oxygen deprivation in the root system of plants. Since oxygen is essential for mitochondrial respiration, this process cannot be maintained under anoxic conditions and must be replaced by other pathways. Our objective was to understand flooding adaptation mechanisms of baldcy- press (Taxodium distichum), Chinese tallow tree (Sapium sebiferum) and pecan (Carya illinoensis) under water- logged conditions. Methods One-year seedlings of baldcypress, Chinese tallow tree and pecan were grown in pots, and three treat- ments were implemented: CK (control, common soil water content), WA (waterlogging, water level equal with soil surface) and FL (flooding, water level 8 cm above soil surface). Treatments lasted 65 days, and indexes of growth, porosity and root oxygen consumption were determined at different times after treatment. Important findings We found that WA and FL treatments inhibited growth of both Chinese tallow tree and pe- can,but biomass and biomass increment of baldcypress increased under WA condition, indicating that baldcypress was more tolerant to flooding. Root/shoot ratio of the three tree species increased significantly under WA and FL treatments, which was primarily due to the decrease of stem and leaf biomass. WA and FL treatments also stimu- lated aerenchyma formation in the roots, stems and leaves of the three tree species, thereby the porosity in the roots, stems and leaves of the three tree species increased significantly under WA and FL conditions. The aeren- chyma formation and increased porosity enhanced O2 diffusion to roots and rhizosphere. Our results indicate that baldcypress, Chinese tallow tree and pecan exhibit several adaptive mechanisms in response to waterlogging, in- cluding formation of new roots, aerenchyma formation, increased porosity of the roots, stems and leaves, and in- creased O2 release into the rhizosphere.

Soil and plant responses to controlled traffic farming in Switzerland

A long-term tillage experiment in Tänikon, Switzerland showed that compared to ploughed plots, untilled plots developed a compact soil structure with decreased porosity and a trend towards lower oxygen concentration in the soil air. All these factors resulted in lower plant yields. To investigate the influence of wheeling on these plots, the shallow-tilled plots were converted to controlled traffic farming (CTF) with no-tillage in 2008. The hypothesis is that a sustainable improvement in soil structure and plant development is achievable in areas with no traffic. In a field trial with four repeated blocks, ‘CTF no-tillage’ was compared with ‘random trafficked mouldboard ploughing’ and ‘random trafficked no-tillage’. The crop rotation was winter wheat – winter barley – meadow, established on luvisol (23% clay, 34% silt, 42% sand) with an annual rainfall of 1190mm and an average annual temperature of 8.4 °C. An intensive monitoring programme was set up for various parameters: Soil-surface-level changes, penetration resistance, macropore volume, soil-air composition, matric potential, volumetric soil-water content, emergence rate, intermediate harvests and harvest yield. Results for 2008 to 2011 show that traffic has a clearly negative impact on soil structure in all variants, even when wheelings are done with low tyre-inflation pressure. Traffic-induced soil-surface-level changes were small, but nonetheless affected the soil’s physical parameters. Soil penetration resistance is higher and soil oxygen content after precipitations lower in the trafficked areas than in traffic-free zones. Yield effects were not as pronounced as in other published field trials. CTF and no-tillage achieved approximately the same yield levels, but routine ploughing resulted in the highest yields. CTF leads to a certain improvement in the soil structure, but the plant response showed that more improvement is necessary to optimise yields.

Soil oxygen affects denitrification

Rates of denitrification, the metabolic process by which bacteria produce nitrogen (N2) gas, are variable and difficult to measure in ecosystems. Burgin and Groffman sought to learn more about the influence of soil oxygen, which is not often measured, on the denitrification process in wetlands. They collected samples and measured soil oxygen concentration in a riparian zone in Millbrook, N. Y. The site included a wet zone close to a stream and a drier zone slightly farther from the stream.

Soil and plant responses to controlled traffic farming in Switzerland

A long-term tillage experiment in Tanikon, Switzerland showed that compared to ploughed plots, untilled plots developed a compact soil structure with decreased porosity and a trend towards lower oxygen concentration in the soil air. All these factors resulted in lower plant yields. To investigate the influence of wheeling on these plots, the shallow-tilled plots were converted to controlled traffic farming (CTF) with no-tillage in 2008. The hypothesis is that a sustainable improvement in soil structure and plant development is achievable in areas with no traffic. In a field trial with four repeated blocks, ‘CTF no-tillage’ was compared with ‘random trafficked mouldboard ploughing’ and ‘random trafficked no-tillage’. The crop rotation was winter wheat – winter barley – meadow, established on luvisol (23% clay, 34% silt, 42% sand) with an annual rainfall of 1190mm and an average annual temperature of 8.4 °C. An intensive monitoring programme was set up for various parameters: Soil-surface-level changes, penetration resistance, macropore volume, soil-air composition, matric potential, volumetric soil-water content, emergence rate, intermediate harvests and harvest yield. Results for 2008 to 2011 show that traffic has a clearly negative impact on soil structure in all variants, even when wheelings are done with low tyre-inflation pressure. Traffic-induced soil-surface-level changes were small, but nonetheless affected the soil’s physical parameters. Soil penetration resistance is higher and soil oxygen content after precipitations lower in the trafficked areas than in traffic-free zones. Yield effects were not as pronounced as in other published field trials. CTF and no-tillage achieved approximately the same yield levels, but routine ploughing resulted in the highest yields. CTF leads to a certain improvement in the soil structure, but the plant response showed that more improvement is necessary to optimise yields.

Interaction and independence on methane oxidation of landfill cover soil among three impact factors: water, oxygen and ammonium

To understand the influence patterns and interactions of three important environmental factors, i.e. soil water content, oxygen concentration, and ammonium addition, on methane oxidation, the soils from landfill cover layers were incubated under full factorial parameter settings. In addition to the methane oxidation rate, the quantities and community structures of methanotrophs were analyzed to determine the methane oxidation capacity of the soils. Canonical correspondence analysis was utilized to distinguish the important impact factors. Water content was found to be the most important factor influencing the methane oxidation rate and Type II methanotrophs, and the optimum value was 15% (w/w), which induced methane oxidation rates 10- and 6- times greater than those observed at 5% (w/w) and 20% (w/w), respectively. Ambient oxygen conditions were more suitable for methane oxidation than 3% oxygen. The addition of 100 mg-N·kg drysoil −1 of ammonium induced different effects on methane oxidation capacity when conducted at low or high water content. With regard to the methanotrophs, Type II was sensitive to the changes of water content, while Type I was influenced by oxygen content. Furthermore, the methanotrophic acidophile, Verrucomicrobia, was detected in soils with a pH of 4.9, which extended their known living environments.

Temporal Dynamics in Soil Oxygen and Greenhouse Gases in Two Humid Tropical Forests

Soil redox plays a key role in regulating biogeochemical transformations in terrestrial ecosystems, but the temporal and spatial patterns in redox and associated controls within and across ecosystems are poorly understood. Upland humid tropical forest soils may be particularly prone to fluctuating redox as abundant rainfall limits oxygen (O2) diffusion through finely textured soils and high biological activity enhances O2 consumption. We used soil equilibration chambers equipped with automated sensors to determine the temporal variability in soil oxygen concentrations in two humid tropical forests with different climate regimes. We also measured soil trace gases (CO2, N2O, and CH4) as indices of redox-sensitive biogeochemistry. On average, the upper elevation cloud forest had significantly lower O2 concentrations (3.0 ± 0.8%) compared to the lower elevation wet tropical forest (7.9 ± 1.1%). Soil O2 was dynamic, especially in the wet tropical forest, where concentrations changed as much as 10% in a single day. The periodicity in the O2 time series at this site was strongest at 16 day intervals and was associated with the hourly precipitation. Greenhouse gas concentrations differed significantly between sites, but the relationships with soil O2 were consistent: O2 was negatively related to both CO2 and CH4 and positively related to N2O. These results are among the first to quantify the temporal and spatial scale of variability in soil redox in humid tropical forests, and show that the timing of precipitation plays a strong role in biogeochemical cycling on the scale of hours to weeks.