Pore size effect on soil carbon dynamics during decomposition of switchgrass

2020 ◽  
Author(s):  
Kyungmin Kim ◽  
Andrey Guber ◽  
Alexandra Kravchenko
Keyword(s):  
Microbial Biomass ◽  
Pore Size ◽  
Microbial Activity ◽  
Priming Effect ◽  
Pore Space ◽  
Phenol Oxidase ◽  
Physical Factors ◽  
Soil System ◽  
Soil C ◽  
C Cycle

<p>Soil pore size distribution (PSD) regulates oxygen diffusion and transport of water/mineralized nutrients. Microbial activity, which drives the carbon (C) cycle in the soil system, can react to these physical factors regulated by PSD. In this study, we investigated the contribution of PSD to C-related microbial activity during the switchgrass decomposition. We used two types of soils, which have controlled PSD (dominant pore size of < 10um and > 30 um). 13C labeled switchgrass leaf and root were incorporated into different PSD of soils and incubated for 21 days under 50% water-filled pore space. During the incubation, microbial activity was assessed with several indicators. i) Fate and transport of mineralized switchgrass, ii) Priming effect, iii) Spatial distribution of b-glucosidase and phenol oxidase, and iv) Microbial biomass. Our preliminary results showed that CO2 emission from switchgrass leaf was greater in the soil dominated by < 10 um pores. Higher b -glucosidase activity and mineralized C from switchgrass leaf supported greater C-related activity in such soil. However, interestingly, we observed a greater priming effect in the soil dominated by > 30 um pores. Due to the less mineralization and transport of switchgrass-derived C in such pores, enzymes targeting more complex substrate could be more active in such soil stimulating mineralization of native soil C. Our full results of phenol oxidase, microbial biomass, and more detailed analysis on 13C and C dynamics will help understanding how PSD can affect biochemical reactions in plant decomposition system.</p>

Anaerobic Digestate Fraction and Nutrient Stoichiometry Significantly Influence the Carbon Cycle in Grassland Soils

2020 ◽  
Author(s):  
Marta Cattin ◽  
Marc Stutter ◽  
Alfonso Lag-Brotons ◽  
Phil Wadley ◽  
Kirk T. Semple ◽  
...  
Keyword(s):  
Microbial Biomass ◽  
Soil Ph ◽  
Soil Nutrient ◽  
Nutrient Status ◽  
Microbial Biomass C ◽  
Grassland Soils ◽  
Soil Nutrient Status ◽  
Soil C ◽  
C Cycle ◽  
Soil C Cycle

<p>The application of digestate from anaerobic digestion to grassland soils is of growing interest as an agricultural practice. However, significant uncertainties surrounding the potential impacts of digestate application on processes associated with the soil microbial community remain, particularly for processes governing Carbon Use Efficiency (CUE) and the broader soil C cycle. In this research, we examined how the C:N stoichiometry of digestate and the nutrient status of soil influenced the impact of digestate application on the soil C cycle.  </p><p>Three fractions of digestate (whole [WD], solid [SD] and liquid [LD]), spanning a range of C:N, were each applied to two soils of contrasting starting nutrient status (high and low) and compared to unamended controls (Ctr). Two short-term incubations, each lasting seven days, were undertaken. In the first, applications of WD, SD and LD each achieved the same total N input to soils. In the second, digestate applications were adjusted to provide consistent total C input to soils. In each incubation, CO<sub>2</sub>-C efflux, microbial biomass C (C<sub>micro</sub>) and pH were determined.  </p><p>In each of the two incubations, the application of digestate significantly increased cumulative CO<sub>2</sub>-C efflux compared to control soils. However, the precise effect of digestate application varied between the two incubations and with both soil nutrient status and digestate fraction. Microbial biomass C was largely unchanged by the treatments in both incubations. During the first incubation, soil pH decreased substantially following each digestate treatment in both soil types. A similar pattern was observed within the second incubation in the high nutrient soil. However, in contrast, soil pH increased substantially following LD and WD application to the low nutrient soil in the second incubation. Varying CUE responses are likely to be observed following the application of digestate to agricultural soils, dependent on digestate fraction, C:N ratio of the digestate, and the initial soil nutrient status. Therefore, digestate application rates and soil management must be carefully planned in order to avoid adverse impacts of digestate application to land. </p><p> </p>

scholarly journals Synthetic Constraint of Soil C Dynamics Using 50 Years of 14C and Net Primary Production (NPP) in a New Zealand Grassland Site

Radiocarbon ◽  
2013 ◽  
Vol 55 (2) ◽  
pp. 1071-1076 ◽  
Author(s):  
W Troy Baisden ◽  
E D Keller
Keyword(s):  
Time Series ◽  
New Zealand ◽  
Net Primary Productivity ◽  
Net Primary Production ◽  
Turnover Rates ◽  
Full Data ◽  
Soil System ◽  
Soil C ◽  
Plant Soil ◽  
C Cycle

Time-series radiocarbon measurements have substantial ability to constrain the size and residence time of the soil C pools commonly represented in ecosystem models. 14C remains unique in its ability to constrain the size and turnover rate of the large stabilized soil C pool with roughly decadal residence times. The Judgeford soil, near Wellington, New Zealand, provides a detailed 11-point 14C time series enabling observation of the incorporation and loss of bomb 14C in surface soil from 1959–2002. Calculations of the flow of C through the plant-soil system can be improved further by combining the known constraints of net primary productivity (NPP) and 14C-derived C turnover. We show the Biome-BGC model provides good estimates of NPP for the Judgeford site and estimates NPP from 1956–2010. Synthesis of NPP and 14C data allows parameters associated with the rapid turnover “active” soil C pool to be estimated. This step is important because it demonstrates that NPP and 14C can provide full data-based constraint of pool sizes and turnover rates for the 3 pools of soil C used in nearly all ecosystem and global C-cycle models.

scholarly journals Microbial biomass and activity in litter during the initial development of pure and mixed plantations of Eucalyptus grandis and Acacia mangium

2013 ◽  
Vol 37 (1) ◽  
pp. 76-85 ◽  
Author(s):  
Daniel Bini ◽  
Aline Fernandes Figueiredo ◽  
Mylenne Cacciolari Pinheiro da Silva ◽  
Rafael Leandro de Figueiredo Vasconcellos ◽  
Elke Jurandy Bran Nogueira Cardoso
Keyword(s):  
Microbial Biomass ◽  
Microbial Activity ◽  
Eucalyptus Grandis ◽  
Acacia Mangium ◽  
Soil Nutrient ◽  
Microbial Biomass C ◽  
Senescent Leaf ◽  
Soil C ◽  
Nutrient Contents ◽  
Leaf Drop

Studies on microbial activity and biomass in forestry plantations often overlook the role of litter, typically focusing instead on soil nutrient contents to explain plant and microorganism development. However, since the litter is a significant source of recycled nutrients that affect nutrient dynamics in the soil, litter composition may be more strongly correlated with forest growth and development than soil nutrient contents. This study aimed to test this hypothesis by examining correlations between soil C, N, and P; litter C, N, P, lignin content, and polyphenol content; and microbial biomass and activity in pure and mixed second-rotation plantations of Eucalyptus grandis and Acacia mangium before and after senescent leaf drop. The numbers of cultivable fungi and bacteria were also estimated. All properties were correlated with litter C, N, P, lignin and polyphenols, and with soil C and N. We found higher microbial activity (CO2 evolution) in litter than in soil. In the E. grandis monoculture before senescent leaf drop, microbial biomass C was 46 % higher in litter than in soil. After leaf drop, this difference decreased to 16 %. In A. mangium plantations, however, microbial biomass C was lower in litter than in soil both before and after leaf drop. Microbial biomass N of litter was approximately 94 % greater than that of the soil in summer and winter in all plantations. The number of cultivable fungi and bacteria increased after leaf drop, especially so in the litter. Fungi were also more abundant in the E. grandis litter. In general, the A. mangium monoculture was associated with higher levels of litter lignin and N, especially after leaf drop. In contrast, the polyphenol and C levels in E. grandis monoculture litter were higher after leaf drop. These properties were negatively correlated with total soil C and N. Litter in the mixed stands had lower C:N and C:P ratios and higher N, P, and C levels in the microbial biomass. This suggests more effective nutrient cycling in mixed plantations in the long term, greater stimulation of microbial activity in litter and soil, and a more sustainable system in general.

scholarly journals Buried Soil Carbon Vulnerability to Decomposition with Landscape Disturbance

2020 ◽  
Author(s):  
Abby McMurtry
Keyword(s):  
Microbial Activity ◽  
Root Exudation ◽  
Root Turnover ◽  
Burial Depth ◽  
Atmospheric Conditions ◽  
Soil C ◽  
Surface Conditions ◽  
Incubation Experiments ◽  
C Cycle ◽  
Buried Layers

Buried layers of ancient soil organic carbon (SOC) can store significant amounts carbon (C). Persistence of this C is favored by burial, which disconnects the soil from atmospheric conditions and limits plant derived C inputs, thus reducing microbial activity. However, erosion exposes buried paleosols to modern surface conditions and results in influx of root-derived C through the processes of root exudation and root turnover. These C inputs stimulate microbial activity and leave paleosol C vulnerable to decomposition. Understanding turnover of ancient soil C is critical for predicting the response of this large C reservoir to environmental change and feedbacks to climate. Yet, the effects of root-derived C inputs on decomposition of buried C is not well established. With this study we aim to quantify how root derived C inputs affect decomposition of paleosol C located along varying degrees of isolation from modern surface conditions, Our field site is located in Wauneta, NE where erosion has brought a Pleistocene era soil -the Brady soil- closer to the surface. We collected Brady soil from 0.2m, 0.4m, and 1.2m below the modern surface, and conducted two controlled laboratory incubations, Soils were amended with (1) a lab synthesized 13C labeled (12 atom% 13C) solution to mimic root exudates (0.3 mg C g-1 soil), and (2) root litter enriched with 92% atom% 13C (0.3mg C g-1 soil), in 30 day, and 240 day laboratory incubation experiments, respectively. We measured 13C-CO2 respiration from airtight microcosms throughout the incubations and used the isotopic label to partition between root derived C and Brady soil C respiration. Our data show that Brady soil C is highly vulnerable to decomposition via soil C priming upon addition of root-derived C regardless of burial depth, indicating that exposure of paleosols to modern surface conditions may result in a positive C cycle feedback to climate.

scholarly journals Microbial carbon recycling – an underestimated process controlling soil carbon dynamics – Part 1: A long-term laboratory incubation experiment

2015 ◽  
Vol 12 (20) ◽  
pp. 5929-5940 ◽  
Author(s):  
A. Basler ◽  
M. Dippold ◽  
M. Helfrich ◽  
J. Dyckmans
Keyword(s):  
Land Use ◽  
Microbial Biomass ◽  
Arable Land ◽  
Isotope Analysis ◽  
Co2 Production ◽  
Incubation Experiment ◽  
Soil C ◽  
C Cycle ◽  
Global Soil ◽  
Silty Loam

Abstract. Independent of its chemical structure carbon (C) persists in soil for several decades, controlled by stabilization and recycling. To disentangle the importance of the two factors on the turnover dynamics of soil sugars, an important compound of soil organic matter (SOM), a 3-year incubation experiment was conducted on a silty loam soil under different types of land use (arable land, grassland and forest) by adding 13C-labelled glucose. The compound-specific isotope analysis of soil sugars was used to examine the dynamics of different sugars during incubation. Sugar dynamics were dominated by a pool of high mean residence times (MRT) indicating that recycling plays an important role for sugars. However, this was not substantially affected by soil C content. Six months after label addition the contribution of the label was much higher for microbial biomass than for CO2 production for all examined land use types, corroborating that substrate recycling was very effective within the microbial biomass. Two different patterns of tracer dynamics could be identified for different sugars: while fucose and mannose showed highest label contribution at the beginning of the incubation with a subsequent slow decline, galactose and rhamnose were characterized by slow label incorporation with subsequently constant levels, which indicates that recycling is dominating the dynamics of these sugars. This may correspond to (a) different microbial growing strategies (r and K-strategist) or (b) location within or outside the cell membrane (lipopolysaccharides vs. exopolysaccharides) and thus be subject of different re-use within the microbial food web. Our results show how the microbial community recycles substrate very effectively and that high losses of substrate only occur during initial stages after substrate addition. This study indicates that recycling is one of the major processes explaining the high MRT observed for many SOM fractions and thus is crucial for understanding the global soil C cycle.

Effect of soil warming and N availability on the fate of recent carbon in subarctic grassland

2020 ◽  
Author(s):  
Kathiravan Meeran ◽  
Niel Verbrigghe ◽  
Lucia Fuchslueger ◽  
Johannes Ingrisch ◽  
Sara Vicca ◽  
...  
Keyword(s):  
Microbial Biomass ◽  
Soil Respiration ◽  
Nitrogen Addition ◽  
Interactive Effects ◽  
N Availability ◽  
Soil Warming ◽  
Soil System ◽  
Soil C ◽  
Microbial C ◽  
The Individual

<p>Climate warming has been suggested to impact high latitude grasslands severely, causing considerable carbon (C) losses from soil. Warming can also stimulate nitrogen (N) turnover, but it is largely unclear whether and how altered N availability impacts soil C dynamics. Even less is known about the individual and interactive effects of warming and N availability on the fate of recently photosynthesized C in soil.  We hypothesized that warming would increase belowground C allocation, while enhanced N availability would decrease it, and that their interactive effects would be additive.</p><p>We studied a subarctic grassland located at a natural geothermal soil warming gradient close to Hveragerði, Iceland, which was established by an earthquake in 2008. We chose 14 plots along the gradient with soil warming temperatures ranging from 0 to 10°C above ambient, and fertilized a subset of plots with 50kg ha<sup>-1</sup> y<sup>-1</sup> of NH<sub>4</sub>NO<sub>3</sub> twice a year prior to the study. We performed <sup>13</sup>CO<sub>2</sub> canopy pulse labeling for an hour and tracked the <sup>13</sup>C pulse through the plant-microbe-soil system and into soil respiration for ten days after labeling.</p><p>Our preliminary results show that at higher temperatures microbial activity increased, causing higher C turnover and a higher respiration of recently assimilated C from the soil. Warming significantly decreased microbial biomass, however, the recent C allocated from roots to microbes increased. This indicates a higher microbial C-limitation and a tighter root-microbe coupling under warming. Nitrogen addition increased the allocation of recent C to roots, microbial biomass, and soil respiration. The effects of N addition and warming were additive with no interaction. Our results indicate that the microbes in warmed soil may not be N limited, but could be C limited and depend more on the supply of recent C from plants. We conclude that in a future climate with warmer soils, more C may be allocated belowground, however, its residence time may decrease.</p>

Understanding the interdependent cycles of soil carbon, nitrogen and phosphorus during soil saturation events 

2021 ◽  
Author(s):  
Hannah Lieberman ◽  
Christian von Sperber ◽  
Maia Rothman ◽  
Cynthia Kallenbach
Keyword(s):  
Soil Moisture ◽  
Microbial Biomass ◽  
Moisture Content ◽  
Soil Carbon ◽  
Microbial Activity ◽  
Soil C ◽  
Flood Duration ◽  
Soil Saturation ◽  
Flood Period ◽  
Soluble C

<p>With climate change, much of the world will experience devastating shifts in weather patterns like increased flooding, intensifying periods of soil saturation. Soil carbon (C), nitrogen (N) and phosphorus (P) cycles are sensitive to changes in soil saturation, where exchange between the mineral-bound and the soluble bioavailable pools can occur with increases in moisture content. With soil saturation, C, N, and P may be mobilized either through greater diffusion or reduced conditions that cause desorption of mineral-bound C, N and P into their respective soluble pools. De-sorption, resorption and diffusion dynamics of C, N, and P may or may not reflect the stoichiometry of the mineral bound pool. Changes in bioavailable soluble C, N and P that could occur with soil saturation and drying may cause unknown consequences for microbial biomass C:N:P. With increases in soil moisture, simultaneous changes in both substrate stoichiometry and microbial growth may occur that impact microbial biomass stoichiometry.  Such changes in microbial stoichiometry and microbial retention of C, N, and P may affect the post-flood fate of soluble C, N, and P. Understanding how releases in mineral bound C, N and P alter the bioavailable C:N:P and how this in turn impacts microbial activity and accumulation of these substrates can inform predictions of retention or losses of C, N and P following soil saturation events.</p><p>To determine if mineral-bound, soluble and microbial biomass stoichiometry is maintained or altered during and after soil saturation events, we used a laboratory incubation approach with manipulated soil saturation and duration. Soil incubations were maintained at three water-holding capacity (WHC) levels: 20% (control), 50%, (moderate) and 100% (severe). We maintained the moderate and severe water-logging treatments for  0.5 h, 24 h, 1 week, followed by air-drying to 20% WHC to examine the influence of flood duration. To understand the exchanges of C, N and P between different pools during flooding, we compared changes in soluble and mineral bound soil C, N and P and impacts on microbial C, N, and P exo-cellular enzymes, and microbial biomass C:N:P. Preliminary results indicate that greater soil moisture content increases soluble P and that the 24 hour flood period captures shifts in the mineral bound P pool that do not remain for the longer flood period (1 week). Enzyme activity similarly reflects an increase in microbial activity in the soil held at 50% and 100% moisture content for 24 hours. We also discuss how soil moisture levels and flood duration impact soluble and mineral bound C relative to P, and how microbial biomass C:N:P tracks these fractions. By exploring the combined response of mineral-bound and soluble C, N, and P to variation in soil saturation, we can better understand how different flood scenarios will impact soil C, N and P retention.</p>

scholarly journals Phosphorus availability and arbuscular mycorrhizal fungi limit soil C cycling and influence plant responses to elevated CO2 conditions.

2021 ◽  
Author(s):  
Laura Castañeda-Gómez ◽  
Jeff Powell ◽  
Elise Pendall ◽  
Yolima Carrillo
Keyword(s):  
Microbial Biomass ◽  
Plant Growth ◽  
Arbuscular Mycorrhizal ◽  
Am Fungi ◽  
P Availability ◽  
Soil System ◽  
Soil C ◽  
C Cycling ◽  
Soil C Cycling ◽  
Som Decomposition

Enhanced soil organic matter (SOM) decomposition and organic phosphorus (P) cycling may help sustain plant productivity under elevated CO2 (eCO2) and P-limiting conditions. P-acquisition by arbuscular mycorrhizal (AM) fungi and their impacts on SOM decomposition may become even more relevant in these conditions. Yet, experimental evidence of the interactive effect of AM fungi and P availability influencing altered SOM cycling under eCO2 is scarce and the mechanisms of this control are poorly understood. Here, we performed a pot experiment manipulating P availability, AM fungal presence and atmospheric CO2 levels and assessed their impacts on soil C cycling and plant growth. Plants were grown in chambers with a continuous 13C-input that allowed differentiation between plant- and SOM-derived fractions of respired CO2 (R), dissolved organic C (DOC) and microbial biomass (MBC) as relevant C pools in the soil C cycle. We hypothesised that under low P availability, increases in SOM cycling may support sustained plant growth under eCO2 and that AM fungi would intensify this effect. We found the impacts of CO2 enrichment and P availability on soil C cycling were generally independent of each other with higher root biomass and slight increases in soil C cycling under eCO2 occurring regardless of the P treatment. Contrary to our hypotheses, soil C cycling was enhanced with P addition suggesting that low P conditions were limiting soil C cycling. eCO2 conditions increased the fraction of SOM-derived DOC pointing to increased SOM decomposition with eCO2. Finally, AM fungi increased microbial biomass under eCO2 conditions and low-P without enhanced soil C cycling, probably due to competitive interactions with free-living microorganisms over nutrients. Our findings in this plant-soil system suggest that, contrary to what has been reported for N-limited systems, the impacts of eCO2 and P availability on soil C cycling are independent of each other.

scholarly journals The undetected loss of aged carbon from boreal mineral soils

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Geert Hensgens ◽  
Hjalmar Laudon ◽  
Mark S. Johnson ◽  
Martin Berggren
Keyword(s):  
Organic Carbon ◽  
Boreal Forest ◽  
Soil C ◽  
Earth Systems ◽  
Nuclear Bomb ◽  
C Cycle ◽  
Water Extractable Organic Carbon ◽  
High Lability ◽  
Mineral Soils ◽  
Terrestrial Biomes

AbstractThe boreal forest is among the largest terrestrial biomes on earth, storing more carbon (C) than the atmosphere. Due to rapid climatic warming and enhanced human development, the boreal region may have begun transitioning from a net C sink to a net source. This raises serious concern that old biogenic soil C can be re-introduced into the modern C cycle in near future. Combining bio-decay experiments, mixing models and the Keeling plot method, we discovered a distinct old pre-bomb organic carbon fraction with high biodegradation rate. In total, 34 ± 12% of water-extractable organic carbon (WEOC) in podzols, one of the dominating boreal soil types, consisted of aged (~ 1000 year) labile C. The omission of this aged (i.e., Δ14C depleted) WEOC fraction in earlier studies is due to the co-occurrence with Δ14C enriched modern C formed following 1950s nuclear bomb testing masking its existence. High lability of aged soil WEOC and masking effects of modern Δ14C enriched C suggests that the risk for mobilization and re-introduction of this ancient C pool into the modern C cycle has gone undetected. Our findings have important implications for earth systems models in terms of climate-carbon feedbacks and the future C balance of the boreal forest.

scholarly journals TIME-INTEGRATED COLLECTION OF CO2 FOR 14C ANALYSIS FROM SOILS

Radiocarbon ◽  
2021 ◽  
pp. 1-17
Author(s):  
Shawn Pedron ◽  
X Xu ◽  
J C Walker ◽  
J C Ferguson ◽  
R G Jespersen ◽  
...  
Keyword(s):  
Soil Temperature ◽  
Molecular Sieve ◽  
Emission Sources ◽  
Soil C ◽  
Silicone Tubing ◽  
2Nd Generation ◽  
C Cycle ◽  
Uptake Rates ◽  
Two Generations ◽  
Cleaning Procedures

ABSTRACT We developed a passive sampler for time-integrated collection and radiocarbon (14C) analysis of soil respiration, a major flux in the global C cycle. It consists of a permanent access well that controls the CO2 uptake rate and an exchangeable molecular sieve CO2 trap. We tested how access well dimensions and environmental conditions affect collected CO2, and optimized cleaning procedures to minimize 14CO2 memory. We also deployed two generations of the sampler in Arctic tundra for up to two years, collecting CO2 over periods of 3 days–2 months, while monitoring soil temperature, volumetric water content, and CO2 concentration. The sampler collects CO2 at a rate proportional to the length of a silicone tubing inlet (7–26 µg CO2-C day-1·m Si-1). With constant sampler dimensions in the field, CO2 recovery is best explained by soil temperature. We retrieved 0.1–5.3 mg C from the 1st and 0.6–13 mg C from the 2nd generation samplers, equivalent to uptake rates of 2–215 (n=17) and 10–247 µg CO2-C day-1 (n=20), respectively. The method blank is 8 ± 6 µg C (mean ± sd, n=8), with a radiocarbon content (fraction modern) ranging from 0.5875–0.6013 (n=2). The sampler enables more continuous investigations of soil C emission sources and is suitable for Arctic environments.

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