Kinetic Properties of Microbial Exoenzymes Vary With Soil Depth but Have Similar Temperature Sensitivities Through the Soil Profile

Current knowledge of the mechanisms driving soil organic matter (SOM) turnover and responses to warming is mainly limited to surface soils, although over 50% of global soil carbon is contained in subsoils. Deep soils have different physicochemical properties, nutrient inputs, and microbiomes, which may harbor distinct functional traits and lead to different SOM dynamics and temperature responses. We hypothesized that kinetic and thermal properties of soil exoenzymes, which mediate SOM depolymerization, vary with soil depth, reflecting microbial adaptation to distinct substrate and temperature regimes. We determined the Michaelis-Menten (MM) kinetics of three ubiquitous enzymes involved in carbon (C), nitrogen (N) and phosphorus (P) acquisition at six soil depths down to 90 cm at a temperate forest, and their temperature sensitivity based on Arrhenius/Q10 and Macromolecular Rate Theory (MMRT) models over six temperatures between 4–50°C. Maximal enzyme velocity (Vmax) decreased strongly with depth for all enzymes, both on a dry soil mass and a microbial biomass C basis, whereas their affinities increased, indicating adaptation to lower substrate availability. Surprisingly, microbial biomass-specific catalytic efficiencies also decreased with depth, except for the P-acquiring enzyme, indicating distinct nutrient demands at depth relative to microbial abundance. These results suggested that deep soil microbiomes encode enzymes with intrinsically lower turnover and/or produce less enzymes per cell, reflecting distinct life strategies. The relative kinetics between different enzymes also varied with depth, suggesting an increase in relative P demand with depth, or that phosphatases may be involved in C acquisition. Vmax and catalytic efficiency increased consistently with temperature for all enzymes, leading to overall higher SOM-decomposition potential, but enzyme temperature sensitivity was similar at all depths and between enzymes, based on both Arrhenius/Q10 and MMRT models. In a few cases, however, temperature affected differently the kinetic properties of distinct enzymes at discrete depths, suggesting that it may alter the relative depolymerization of different compounds. We show that soil exoenzyme kinetics may reflect intrinsic traits of microbiomes adapted to distinct soil depths, although their temperature sensitivity is remarkably uniform. These results improve our understanding of critical mechanisms underlying SOM dynamics and responses to changing temperatures through the soil profile.

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Kinetic Properties of Microbial Exoenzymes Vary with Soil Depth but Have Similar Temperature Sensitivities Through the Soil Profile

10.1101/2021.07.02.450965 ◽

2021 ◽

Author(s):

Ricardo J Eloy Alves ◽

Ileana A Callejas ◽

Gianna L Marschmann ◽

Maria Mooshammer ◽

Hans W Singh ◽

...

Keyword(s):

Thermal Properties ◽

Microbial Biomass ◽

Temperature Sensitivity ◽

Soil Profile ◽

Soil Depth ◽

Coniferous Forest ◽

Rate Theory ◽

Kinetic Properties ◽

Dependent Manner ◽

Nutrient Inputs

Current knowledge of the mechanisms and responses of soil organic matter (SOM) turnover to warming is mainly limited to surface soils, although over 50% of global soil carbon is contained in subsoils. Deep soils have different physicochemical properties, nutrient inputs and microbiomes, which may harbor distinct functional traits and lead to different SOM dynamics and temperature responses. We hypothesized that kinetic and thermal properties of microbial exoenzymes, which mediate SOM depolymerization, vary with soil depth, reflecting microbial adaptation to distinct substrate and temperature regimes. We determined the Michaelis-Menten (MM) kinetics of three ubiquitous enzymes involved in carbon (C), nitrogen (N) and phosphorus (P) acquisition at six soil depths down to 90 cm at a temperate coniferous forest, and their temperature sensitivity based on Arrhenius and Macromolecular Rate Theory (MMRT) models over six temperatures between 4-50°C. Maximal enzyme velocity (Vmax) decreased strongly with depth for all enzymes, both on a dry soil mass and a microbial biomass C basis, whereas their affinities increased, indicating adaptation to lower substrate availability. Surprisingly, microbial biomass-specific catalytic efficiencies also decreased with depth, except for the P-acquiring enzyme, indicating distinct nutrient demands at depth relative to microbial abundance. These results indicated that deep soil microbiomes encode enzymes with intrinsically lower turnover and/or produce less enzymes per cell, likely reflecting distinct life strategies. The relative kinetics between different enzymes also varied with depth, suggesting an increase in relative P demand with depth, or that phosphatases may be involved in C acquisition. Warming consistently led to increased Vmax and catalytic efficiency of all enzymes, and thus to overall higher SOM-decomposition potential, but enzyme temperature sensitivity was similar through the soil profile based on both Arrhenius/Q10 and MMRT models. Nevertheless, temperature directly affected the kinetic properties of different enzyme types in a depth-dependent manner, and thus the relative depolymerization potential of different compounds. Our results indicate that kinetic and thermal properties of exoenzymes are intrinsic traits of soil microbiomes adapted to distinct physicochemical conditions associated with different soil depths, and improve our conceptual understanding of critical mechanisms underlying SOM dynamics and responses to warming through the soil profile.

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Effective remediation of diazinon from spent sheep dip wash by disposal on land

Australian Journal of Experimental Agriculture ◽

10.1071/ea05361 ◽

2007 ◽

Vol 47 (1) ◽

pp. 13 ◽

Cited By ~ 5

Author(s):

G. W. Levot

Keyword(s):

Soil Profile ◽

Soil Depth ◽

Disposal Site ◽

Deep Soil ◽

Limit Of Quantification ◽

Entire Volume ◽

South Wales ◽

Run Off ◽

Australian Wool ◽

Pre Treatment

Spent sheep dip wash (about 3500 L) containing 59 mg diazinon/L was evenly distributed onto a 450-m2 grassed, soil-bunded, sloping site near Cumnock in central New South Wales, Australia. The entire volume was contained within the bunded area but surface run-off created ponding in the lowest corner of the site. The mean concentration within the top 7 cm of soil was 2.32 mg/kg a day after application. By day 14, this had dropped to 0.4 mg/kg and by day 56, was below the limit of quantification (0.1 mg/kg). The half-life of diazinon in soil was estimated to be 7 days. Residues in the next 7 cm of soil depth were much lower and were below the limit of quantification in all samples collected at day 28 or later. This suggests that vertical leaching of diazinon within the soil profile did not occur despite more than 95 mm of rain during the trial interval. Throughout the 56-day trial interval, diazinon concentrations in the top 7 cm of soil 3 m downhill of the lowest corner of the dip disposal site were unchanged from background pre-treatment levels. No diazinon was detected in samples at 7–14 cm depth in the soil profile in this area. With neither vertical nor lateral movement of diazinon away from the initial treatment zone, we consider the disposal of spent diazinon sheep dips as described here, to be an acceptable and convenient option for Australian wool producers and dipping contractors. Suitable dip disposal sites should be situated away from sensitive locations in areas that have good grass cover over deep soil and that are contained by an effective bund. Stock and other animals should be excluded from these sensitive locations.

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Soil depth gradients in microbial growth kinetics under deeply- vs. shallow-rooted plants

10.1101/2021.04.26.441349 ◽

2021 ◽

Author(s):

Kyungjin Min ◽

Eric Slessarev ◽

Megan Patricia Kan ◽

Karis Mcfarlane ◽

Erik Oerter ◽

...

Keyword(s):

Microbial Biomass ◽

Growth Kinetics ◽

Microbial Growth ◽

Growth Parameters ◽

Soil Depth ◽

Rooting Depth ◽

Deep Soil ◽

Switch Grass ◽

Microbial Growth Kinetics ◽

Deep Soils

Climate-smart land management practices that replace shallow-rooted annual crop systems with deeply-rooted perennial plants can contribute to soil carbon sequestration. However, deep soil carbon accrual may be influenced by active microbial biomass and their capacity to assimilate fresh carbon at depth. Incorporating active microbial biomass, dormancy and growth in models can improve our ability to predict the capacity of soil to store carbon. But, so far, the microbial parameters that are needed for such modeling are poorly constrained, especially in deep soil layers. Here, we investigated whether a change in crop rooting depth affects microbial growth kinetics in deep soils compared to surface soils. We used a lab incubation experiment and growth kinetics model to estimate how microbial parameters vary along 240 cm of soil depth in profiles under shallow- (soy) and deeply-rooted plants (switch grass) 11 years after plant cover conversion. We also assessed resource origin and availability (total organic carbon, 14C, dissolved organic carbon, specific UV absorbance, total nitrogen, total dissolved nitrogen) along the soil profiles to examine associations between soil chemical and biological parameters. Even though root biomass was higher and rooting depth was deeper under switch grass than soy, resource availability and microbial growth parameters were generally similar between vegetation types. Instead, depth significantly influenced soil chemical and biological parameters. For example, resource availability, and total and relative active microbial biomass decreased with soil depth. Decreases in the relative active microbial biomass coincided with increased lag time (response time to external carbon inputs) along the soil profiles. Even at a depth of 210-240 cm, microbial communities were activated to grow by added resources within a day. Maximum specific growth rate decreased to a depth of 90 cm and then remained consistent in deeper layers. Our findings show that > 10 years of vegetation and rooting depth changes may not be long enough to alter microbial growth parameters, and suggest that at least a portion of the microbial community in deep soils can grow rapidly in response to added resources. Our study determined microbial growth parameters that can be used in models to simulate carbon dynamics in deep soil layers.

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Soil carbon sequestration by three perennial legume pastures is greater in deeper soil layers than in the surface soil

Biogeosciences ◽

10.5194/bg-13-527-2016 ◽

2016 ◽

Vol 13 (2) ◽

pp. 527-534 ◽

Cited By ~ 21

Author(s):

X.-K. Guan ◽

N. C. Turner ◽

L. Song ◽

Y.-J. Gu ◽

T.-C. Wang ◽

...

Keyword(s):

Carbon Sequestration ◽

Soil Carbon ◽

Soil Profile ◽

Soil Depth ◽

Arable Land ◽

Growth Period ◽

Bare Soil ◽

Soil Carbon Sequestration ◽

Deep Soil ◽

Perennial Legume

Abstract. Soil organic carbon (SOC) plays a vital role as both a sink for and source of atmospheric carbon. Revegetation of degraded arable land in China is expected to increase soil carbon sequestration, but the role of perennial legumes on soil carbon stocks in semiarid areas has not been quantified. In this study, we assessed the effect of alfalfa (Medicago sativa L.) and two locally adapted forage legumes, bush clover (Lespedeza davurica S.) and milk vetch (Astragalus adsurgens Pall.) on the SOC concentration and SOC stock accumulated annually over a 2 m soil profile. The results showed that the concentration of SOC in the bare soil decreased slightly over the 7 years, while 7 years of legume growth substantially increased the concentration of SOC over the 0–2.0 m soil depth. Over the 7-year growth period the SOC stocks increased by 24.1, 19.9 and 14.6 Mg C ha−1 under the alfalfa, bush clover and milk vetch stands, respectively, and decreased by 4.2 Mg C ha−1 in the bare soil. The sequestration of SOC in the 1–2 m depth of the soil accounted for 79, 68 and 74 % of the SOC sequestered in the 2 m deep soil profile under alfalfa, bush clover and milk vetch, respectively. Conversion of arable land to perennial legume pasture resulted in a significant increase in SOC, particularly at soil depths below 1 m.

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Changes in microbial biomass and structural stability at the surface of a duplex soil under direct drilling and stubble retention in north-eastern Victoria

Soil Research ◽

10.1071/sr9920493 ◽

1992 ◽

Vol 30 (4) ◽

pp. 493 ◽

Cited By ~ 29

Author(s):

MR Carter ◽

PM Mele

Keyword(s):

Microbial Biomass ◽

Soil Depth ◽

Cropping Systems ◽

Aggregate Stability ◽

Microbial Biomass C ◽

Organic C ◽

Stubble Retention ◽

C And N ◽

Direct Drilling ◽

Wet Sieving

Changes and relationships for organic C, microbial biomass C and N, and soil structural stability indices were determined at the soil surface after 10 years of direct drilling stubble retained (DDR) and stubble burnt (DDB), and cultivation with stubble burnt (CCB) for cropping systems on a sandy clay loam, duplex soil (calcic luvisol) in south-eastern Australia. Direct drilling caused a slight but significant increase in soil organic C at the 0-25 mm soil depth compared to the cultivated treatment. Microbial biomass C and N increases over the 0-100 mm soil depths were seasonal and generally greater for the DDR in comparison with DDB and CCB systems. Use of short duration wet sieving for the 0-25 mm soil depth showed a significant increase in aggregate stability for the DDR, especially for 2-10 mm sized aggregates, compared with the other tillage treatments. Such differences were reduced by standard wet sieving or use of a dispersion test illustrating the fragile nature of these unstable aggregates developed under cropping systems. Soil structural indices (water stable aggregates >2.00 mm, and >0.25 mm; mean weight diameter) were weakly correlated with increases in microbial biomass (r = 0.45, P < 0.01) and to total organic C (r = 0.35, P < 0.05). For these tillage systems, microbial biomass tended to be a poor predictor of changes in soil organic C. Overall, the long term effect of direct drilling and stubble retention in these cropping systems provided only relatively minor increases in organic C and, consequently, aggregate stability.

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Variation in soil microbial biomass in the dry tropics: impact of land-use change

Soil Research ◽

10.1071/sr13265 ◽

2014 ◽

Vol 52 (3) ◽

pp. 299 ◽

Cited By ~ 5

Author(s):

Mahesh Kumar Singh ◽

Nandita Ghoshal

Keyword(s):

Land Use ◽

Microbial Biomass ◽

Soil Microbial Biomass ◽

Soil Depth ◽

Natural Forest ◽

Microbial Biomass C ◽

Soil Microbial Biomass C ◽

Soil Microbial ◽

Land Use Types ◽

C And N

The impact of land-use change on soil microbial biomass carbon (C) and nitrogen (N) was studied through two annual cycles involving natural forest, degraded forest, agroecosystem and Jatropha curcas plantation. Soil microbial biomass C and N, soil moisture content and soil temperature were analysed at upper (0–10 cm), middle (10–20 cm) and lower (20–30 cm) soil depths during the rainy, winter and summer seasons. The levels of microbial biomass C and N were highest in the natural forest, followed in decreasing order by Jatropha curcas plantation, degraded forest and the agroecosystem. The highest level of soil microbial biomass C and N was observed during summer, decreasing through winter to the minimum during the rainy season. Soil microbial biomass C and N decreased with increasing soil depth for all land-use types, and for all seasons. Seasonal variation in soil microbial biomass was better correlated with the soil moisture content than with soil temperature. The microbial biomass C/N ratio increased with the soil depth for all land-use types, indicating changes in the microbial community with soil depth. It is concluded that the change in land-use pattern, from natural forest to other ecosystems, results in a considerable decrease in soil microbial biomass C and N. Jatropha plantation may be an alternative for the restoration of degraded lands in the dry tropics.

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Dynamics in C, N, and P stoichiometry and microbial biomass following soil depth and vegetation types in low mountain and hill region of China

Scientific Reports ◽

10.1038/s41598-021-99075-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Wenting Jiang ◽

Lei Gong ◽

Lihui Yang ◽

Shuping He ◽

Xiaohu Liu

Keyword(s):

Microbial Biomass ◽

Soil Depth ◽

Ecosystem Functions ◽

Microbial Biomass C ◽

Oak Forest ◽

Vegetation Types ◽

Soil Layers ◽

Soil C ◽

Hill Region ◽

The Vertical Distribution

AbstractChanges in soil carbon (C):nitrogen (N):phosphorus (P) stoichiometry have great significance on understand regulatory mechanism and restoration of ecosystem functions. However, the responses of C, N and P stoichiometry to soil depth and different vegetation types remains elusive. To address this problem, the study aims to explore the effects of soil depth and vegetation types on soil C, N, and P stoichiometry, and their relationships with microbial biomass in low mountain and hill region of China. The results indicated that soil SOC and TN concentrations in oak forest were markedly higher than those in grassland, and the vertical distribution of SOC and TN concentration showed an inverted triangle trend as the soil deepens. However, there was no significant change in soil TP concentration among 0–20 cm, 20–40 cm, and 40–60 cm. Soil C/N among different layers (0–20, 20–40, and 40–60 cm) is narrower fluctuation margin, and its value is basically stable within a certain range (11–14.5). Both soil C/P and N/P showed significant variability in different vegetation types, and soil N/P decreased with soil layers deepen. Both the microbial biomass C (MBC) and N (MBN) showed a decreasing trend with the increase of soil depth, and three soil layers from high to low was: oak forest > pine forest > grassland. Our results will potentially provide useful information for the vegetation restoration and forest management and great significance to enrich the scientific theory of ecological stoichiometry.

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Stratification of microbial biomass C and N and gross N mineralisation with soil depth in two contrasting Western Australian agricultural soils

Soil Research ◽

10.1071/s97045 ◽

1998 ◽

Vol 36 (1) ◽

pp. 45 ◽

Cited By ~ 59

Author(s):

D. V. Murphy ◽

G. P. Sparling ◽

I. R. P. Fillery

Keyword(s):

Microbial Biomass ◽

Soil Depth ◽

Isotopic Dilution ◽

Organic N ◽

Microbial Biomass C ◽

N Mineralisation ◽

Soil Cores ◽

C And N ◽

Intact Soil Cores ◽

Intact Soil

The distribution of microbial biomass C and N and the decline in gross N mineralisation and NH4+ consumption with soil depth was investigated in 2 soils with different soil texture and land use. Soils were from an annual pasture on a loamy sand and from a sandy clay loam previously cropped with wheat. Intact soil cores were collected from the surface 0–10 cm in steel tubes and were sampled in 2·5 cm layers. Disturbed soil down to 50 cm was collected in 10 cm sections using a sand auger. Microbial biomass was estimated by chloroform fumigation and 0·5 M K2SO4 extraction. Microbial biomass C was determined from the flush in ninhydrin-positive compounds, and microbial biomass N from the flush in total soluble N after K2S2O8 oxidation. Gross N mineralisation and NH4+ consumption were estimated by 15N isotopic dilution using 15NH3 gas injection to label the soil 14NH4+ pool with 15N. The pattern of distribution of the microbial biomass and the rate of N transformations were similar for both soils. There was a rapid decline in microbial biomass C and N and gross N mineralisation with soil depth. Approximately 55% of the microbial biomass, 70–88% of gross N mineralisation, and 46–57% of NH4+ consumption was in the surface 0–10 cm in both soils. There was also a stratification of microbial biomass and gross N mineralisation within the 0–10 cm layer of intact soil cores. It was estimated that one-quarter of the total microbial biomass and at least one-half of the total gross N mineralisation within the soil profiles (0–50 cm) was located in the surface 2·5 cm layer. These results demonstrate the importance of the surface soil layer as a major source of microbial activity and inorganic N production. There was a strong correlation between the distribution of microbial biomass and the gross rate of mineralisation of soil organic N within the soil profile.

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Soil physical and biological properties in an integrated crop-livestock system in the Brazilian Cerrado

Pesquisa Agropecuária Brasileira ◽

10.1590/s0100-204x2018001100006 ◽

2018 ◽

Vol 53 (11) ◽

pp. 1239-1247 ◽

Cited By ~ 1

Author(s):

João de Andrade Bonetti ◽

Helder Barbosa Paulino ◽

Edicarlos Damacena de Souza ◽

Marco Aurélio Carbone Carneiro ◽

Jeander Oliveira Caetano

Keyword(s):

Microbial Biomass ◽

Bulk Density ◽

Microbial Biomass Carbon ◽

Soil Depth ◽

Total Porosity ◽

Soil Bulk Density ◽

Biological Properties ◽

Metabolic Quotient ◽

Microbial Biomass C ◽

Livestock System

Abstract: The objective of this work was to evaluate the soil physical and biological properties in an integrated crop-livestock system (ICLS), with or without cattle grazing, in different seasons. The experiment was carried out in the Cerrado biome, in Brazil, in a Rhodic Eutrudox. The treatments consisted of grazing areas (Urochloa ruziziensis) at 0.25, 0.35, and 0.45 m heights (with soybean cultivation after grazing) and of nongrazed areas. The ICLS had no negative effects on soil bulk density, total porosity, macroporosity, and microporosity. After ICLS implementation, the values of soil bulk density decreased, and those of soil macroporosity increased, in the grazed and nongrazed areas. However, after three years, bulk density and macroporosity were reestablished to values similar to those before ICLS implementation. Soil penetration resistance was higher in the ICLS, mainly at 0.00-0.05 m soil depth. After four years, ICLS promoted the increase of microbial biomass C and N and the reduction of the metabolic quotient. The microbial biomass carbon and the metabolic quotient were related to the weighted mean diameter. ICLS benefits to soil physical and biological properties are associated with adequate ICLS implementation, adequate grazing height (0.35 m), and maintenance of soil cover.

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Characteristics of soil profile CO<sub>2</sub> concentrations in karst areas and their significance for global carbon cycles and climate change

Earth System Dynamics ◽

10.5194/esd-10-525-2019 ◽

2019 ◽

Vol 10 (3) ◽

pp. 525-538

Author(s):

Qiao Chen

Keyword(s):

Soil Ph ◽

Soil Profile ◽

Carbon Sink ◽

Soil Depth ◽

Global Climate ◽

Co2 Concentration ◽

Soil Co2 ◽

Deep Soil ◽

Carbon Cycles ◽

Co2 Concentrations

Abstract. CO2 concentrations of 21 soil profiles were measured in Zhaotong City, Yunnan Province. The varying characteristics of soil profile CO2 concentrations are distinguishable between carbonate and noncarbonate areas. In noncarbonate areas, soil profile CO2 concentrations increase and show significant positive correlations with soil depth. In carbonate areas, however, deep-soil CO2 concentrations decrease and have no significant correlations with soil depth. Soil organic carbon is negatively correlated with soil CO2 concentrations in noncarbonate areas. In carbonate areas, such relationships are not clear. This means that the special geological process in carbonate areas – carbonate corrosion – absorbs part of the deep-soil-profile CO2. Isotope and soil pH data also support such a process. A mathematical model simulating soil profile CO2 concentration was proposed. In noncarbonate areas, the measured and the simulated values are almost equal, while the measured CO2 concentrations of deep soils are less than the simulated in carbonate areas. Such results also indicate the occurrence of carbonate corrosion and the consuming of deep-soil CO2 in carbonate areas. The decreased CO2 concentration was roughly evaluated based on stratigraphic unit and farming activities. Soil pH and the purity of CaCO3 in carbonate bedrock deeply affect the corrosion. The corrosion in carbonate areas decreases deep-soil CO2 greatly (accounting for 5.2 %–66.3 % with average of 36 %) and naturally affects the soil CO2 released into the atmosphere. Knowledge of this process is important for karst carbon cycles and global climate changes and it may be a part of the “missing carbon sink”.

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