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Kyungmin Kim
Department of Plant Soil and Microbial Sciences, Michigan State University, East Lansing, USA

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Preprint content
Published: 04 March 2021
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High temporal and spatial variability of nitrous oxide (N2O) emission from soils has been a challenge for the systematic prediction of global climate change. It is attributed to multiple hotspots occurring simultaneously and affecting the N dynamics cumulatively on an ecosystem scale. Understanding the mechanisms and contributing factors of N2O emission in single hotspots is a prerequisite to overcoming this problem.

We investigated the decomposing switchgrass roots as N2O hotspots, using isotope dual-labeling (15N and 13C) and zymography. Our main objectives were i) to quantify the contribution of decomposing roots to N2O emission along with the N contents in the soil (total, organic, and inorganic N) and microbial pools, and ii) to differentiate the extracellular enzyme activity in decomposing roots from the bulk soil, and test if the ‘spatially differentiated’ hotspot enzyme activity indeed related to ‘isotopically differentiated’ hotspot N2O emissions. We treated the soils of the same origin to have different moisture contents (40% and 70% water-filled pore space, WFPS) and pore size distributions (dominant pores of >30 Ø and < 10 mm Ø, referred to as coarse and fine soil), to evaluate how these variables change the contribution of decomposing roots to the N2O production.

Our results showed that up to 0.4 % of the root driven N can be emitted as N2O gas, only within 21 days of the decomposition. Approximately 21 ~35% of root N was transformed to dissolved organic N, while less than 1 % of the root N remained as ammonium (NH4+) and nitrate (NO3-) during the incubation. Decreasing NH4+ and increasing NO3- suggested nitrification. Surprisingly, both inorganic and organic N content was greater in coarse soil, which likely led to intense hotspots of enzyme activity and N2O emission. However, there was no difference in microbial biomass between the soil materials. Higher chitinase activity and relatively large pores in coarse soils suggest that the fungal activity was higher in coarse soils compared to the fine soils. Root chitinase activity was positively correlated with the root driven N2O emission rate (p< 0.01, R2=0.22), supporting that the microbial hotspot formed near the root is the hotspots of N2O emission.

Our study showed that the intensity of root driven N2O hotspots can highly depend on the soil physical characteristics, being mediated by decomposed substances, and enzyme activity. Tracking the fate of N during the plant root decomposition can provide a new perspective on the strategies to minimize N2O emissions in bioenergy systems.

ACS Style

Kyungmin Kim; Jenie Gil; Nathaniel Ostrom; Hasand Gandhi; Maxwell Oerther; Yakov Kuzyakov; Andrey Guber; Alexandra Kravchenko. Decomposing in-situ grown switchgrass roots as hotspots of microbial activity and N2O emission: the combination of dual-isotope labeling and zymography. 2021, 1 .

AMA Style

Kyungmin Kim, Jenie Gil, Nathaniel Ostrom, Hasand Gandhi, Maxwell Oerther, Yakov Kuzyakov, Andrey Guber, Alexandra Kravchenko. Decomposing in-situ grown switchgrass roots as hotspots of microbial activity and N2O emission: the combination of dual-isotope labeling and zymography. . 2021; ():1.

Chicago/Turabian Style

Kyungmin Kim; Jenie Gil; Nathaniel Ostrom; Hasand Gandhi; Maxwell Oerther; Yakov Kuzyakov; Andrey Guber; Alexandra Kravchenko. 2021. "Decomposing in-situ grown switchgrass roots as hotspots of microbial activity and N2O emission: the combination of dual-isotope labeling and zymography." , no. : 1.

Preprint content
Published: 04 March 2021
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An understanding of the drivers of hotspot/hot moments of N2O production is required to better constrain the global N2O budget and to plan the mitigation strategies. Hot spots are areas with very high N2O emission rates relative to the surrounding area, while hot moments are short periods of time with very high emission rates. As the decomposition of fresh organic matter is transitory in nature, it may have a strong influence on hotspot and hot moment N2O production. Roots are well known to be hotspots for microbial activity but roots direct contribution to N2O production and emissions in soil remain poorly understood.

In this study, we evaluated the role of root decomposition on N2O production and emissions, as a function of soil pore size and water content. We hypothesized that (i) the greatest N2O emissions will be observed from root decomposition in the soil dominated by large (>30 µm Ø) pores due to their high connectivity and (ii) enhanced N2O production by denitrification will be observed due to local anaerobic conditions, generated by O2 consumption by decomposers.

To evaluate the role of root decomposition on N2O production we used soil microcosms cultivated with switchgrass (Panicum virgatum L. variety Cave-in-rock). From the same composite soil samples we created two soil materials with contrasting pore architectures, namely soil with prevalence of large pores (≥ 35 μm Ø) and small pores (≤ 10 μm Ø). After four months of growing in a greenhouse, plants were cut and soil microcosms with roots were incubated in the dark at room T for 21 days, at two contrasting soil moisture conditions: 40% and 70% water filled pore space (WFPS). Gas headspace samples were collected at different time points during incubation for N2O and CO2 concentration analysis and isotopic characterization of N2O (δ15Nbulk, site preference (SP), and δ18O).

The daily emissions of N2O and CO2 from soil microcosms with grown roots showed the same trend during the incubation period and were significantly higher compared to soil microcosms without roots (control) (p < 0.05). Microcosm with large pores soil had significantly higher N2O flux rates compared to the microcosms with small pore soil for both soil moisture treatments (p < 0.001). The relationship between SP  and δ18O (isotope mapping) indicated that heterotrophic bacterial denitrification strongly dominated N2O production between day 1 to 7 of the incubation (≥ 97%) and N2O reduction was higher during this period (40 – 60%) in soil microcosms with both pore size and moisture treatment. Later on, N2O reduction decreased (1 – 35%) while the share of nitrification/fungal sources increased for soil microcosms with large pores.

Our results indicated that decomposing roots acted as hotspots enhancing N2O emissions and N2O hotspots occurring during root decomposition are strongly influenced by soil pore architecture. While differences in soil pore architecture did not cause differences in N2O production process at the initial phase of decomposition, it might influence the relative contribution of N2O microbial production pathways in later stage of decomposition.

ACS Style

Jenie Gil; Kyungmin Kim; Hasand Gandhi; Maxwell Oerther; Nathaniel Ostrom; Alexandra Kravchenko. The influence of root decomposition on N2O fluxes and N2O microbial production pathways in soil with contrasting pore characteristics. 2021, 1 .

AMA Style

Jenie Gil, Kyungmin Kim, Hasand Gandhi, Maxwell Oerther, Nathaniel Ostrom, Alexandra Kravchenko. The influence of root decomposition on N2O fluxes and N2O microbial production pathways in soil with contrasting pore characteristics. . 2021; ():1.

Chicago/Turabian Style

Jenie Gil; Kyungmin Kim; Hasand Gandhi; Maxwell Oerther; Nathaniel Ostrom; Alexandra Kravchenko. 2021. "The influence of root decomposition on N2O fluxes and N2O microbial production pathways in soil with contrasting pore characteristics." , no. : 1.

Regular article
Published: 11 February 2021 in Plant and Soil
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Plant residues decomposing within the soil matrix are known to serve as hotspots of N2O production. However, the lack of technical tools for microscale in-situ N2O measurements limits understanding of hotspot functioning. Our aim was to assess performance of microsensor technology for evaluating the temporal patterns of N2O production in immediate vicinity to decomposing plant residues. We incorporated intact switchgrass leaves and roots into soil matrix and monitored O2 depletion and N2O production using electrochemical microsensors along with N2O emission from the soil. We also measured residue’s water absorption and b-glucosidase activity on the surface of the residue - the characteristics related to microenvironmental conditions and biological activity near the residue. N2O production in the vicinity of switchgrass residues began within 0–12 h after the wetting, reached peak at ~0.6 day and decreased by day 2. N2O was higher near leaf than near root residues due to greater leaf N contents and water absorption by the leaves. However, N2O production near the roots started sooner than near the leaves, in part due to high initial enzyme levels on root surfaces. Electrochemical microsensor is a useful tool for in-situ micro-scale N2O monitoring in immediate vicinity of soil incorporated plant residues. Monitoring provided valuable information on N2O production near leaves and roots, its temporal dynamic, and the factors affecting it. The N2O production from residues measured by microsensors was consistent with the N2O emission from the whole soil, demonstrating the validity of the microsensors for N2O hotspot studies.

ACS Style

Kyungmin Kim; Turgut Kutlu; Alexandra Kravchenko; Andrey Guber. Dynamics of N2O in vicinity of plant residues: a microsensor approach. Plant and Soil 2021, 462, 331 -347.

AMA Style

Kyungmin Kim, Turgut Kutlu, Alexandra Kravchenko, Andrey Guber. Dynamics of N2O in vicinity of plant residues: a microsensor approach. Plant and Soil. 2021; 462 (1-2):331-347.

Chicago/Turabian Style

Kyungmin Kim; Turgut Kutlu; Alexandra Kravchenko; Andrey Guber. 2021. "Dynamics of N2O in vicinity of plant residues: a microsensor approach." Plant and Soil 462, no. 1-2: 331-347.

Journal article
Published: 13 June 2020 in Geoderma
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The “sponge effect”, or water absorption by incorporated plant leaf residues, was recently identified as one of the mechanisms that drives activity in microbial hotspots. We explored the presence of the sponge effect in plant root residues, and its role in root decomposition and associated N2O and CO2 emissions. Young soybean (Glycine max) plants were grown in microcosms with two soil materials dominated by (i) large (>30 μm Ø) and (ii) small (<10 μm Ø) pores. After termination, the microcosms with the decomposing roots were incubated at 50% and 75% water-filled pore space (WFPS) soil moisture levels. Root decomposition, water absorption by the decomposing roots, and water redistribution were quantified using X-ray computed micro-tomography (μCT), including dual-energy scanning. The results demonstrated occurrence of the sponge effect in young, in-situ grown soybean roots and sharp gradients in the distribution of the added liquid within ~150 µm distance from the decomposing roots. At 50% WFPS the large pore soil emitted 185% more N2O than the small pore soil; and, during the first 5 days of incubation, more N2O than the large pore soil at 75% WFPS. This finding indicates that the decomposing roots acted as hotspots of N2O production, potentially due to sponge effect and associated anoxic conditions. Our study suggests that the interactions between pore characteristics and soil moisture can play a significant role in defining the contribution of detritusphere, specifically, decomposing young roots, to soil biogeochemical processes, including microbial activity and denitrification dynamics.

ACS Style

Kyungmin Kim; Andrey Guber; Mark Rivers; Alexandra Kravchenko. Contribution of decomposing plant roots to N2O emissions by water absorption. Geoderma 2020, 375, 114506 .

AMA Style

Kyungmin Kim, Andrey Guber, Mark Rivers, Alexandra Kravchenko. Contribution of decomposing plant roots to N2O emissions by water absorption. Geoderma. 2020; 375 ():114506.

Chicago/Turabian Style

Kyungmin Kim; Andrey Guber; Mark Rivers; Alexandra Kravchenko. 2020. "Contribution of decomposing plant roots to N2O emissions by water absorption." Geoderma 375, no. : 114506.

Preprint content
Published: 11 March 2020
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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.

ACS Style

Kyungmin Kim; Andrey Guber; Alexandra Kravchenko. Pore size effect on soil carbon dynamics during decomposition of switchgrass. 2020, 1 .

AMA Style

Kyungmin Kim, Andrey Guber, Alexandra Kravchenko. Pore size effect on soil carbon dynamics during decomposition of switchgrass. . 2020; ():1.

Chicago/Turabian Style

Kyungmin Kim; Andrey Guber; Alexandra Kravchenko. 2020. "Pore size effect on soil carbon dynamics during decomposition of switchgrass." , no. : 1.

Journal article
Published: 04 February 2020 in Chemosphere
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Leaching of toxic metallic elements (Cu, Zn, As, Cd, and Pb) from two solid mine wastes was characterized under different drying treatments. During 14 batch decant-refill leaching steps, samples were intermittently dried four times in 40 °C oven or −20 °C freezer. For all leachates, the pH, pE, Fe2+/Fe3+, and SO42− were analyzed. The parameters of the two-site model (kfast, kslow, and ffast) and labile fractions (F1 + F2) were determined. High levels of toxic metallic elements were determined in waste samples; however, their leaching was limited, as evidenced by the magnitudes of F1 + F2, ffast, and kslow. Leachate solutions were acidic, at pH 3–4, and oxic, at 150 mV < Eh 300 < mV, thus having negligible Fe2+. Leachate concentrations of toxic metallic elements increased (4–58%) after drying at 40 °C and were strongly correlated (r2 = 0.780) with those of sulfate in liquid phase. The mass of element elution was in the order of 40 °C drying > −20 °C drying ≥ continuous wetting. Results indicate that the element leachability is increased through drying events and the leachate concentration is associated with the dissolution reaction of sulfur-bearing minerals. Frequent occurrence of prolonged droughts along with high temperatures over the mine waste disposal site, can enhance the leaching potential of toxic metallic elements.

ACS Style

Hyunwoo Bang; Juhee Kim; Kyungmin Kim; Seunghun Hyun. Effect of drying treatment on the leachability of metallic elements from weathered solid mine wastes. Chemosphere 2020, 248, 126111 .

AMA Style

Hyunwoo Bang, Juhee Kim, Kyungmin Kim, Seunghun Hyun. Effect of drying treatment on the leachability of metallic elements from weathered solid mine wastes. Chemosphere. 2020; 248 ():126111.

Chicago/Turabian Style

Hyunwoo Bang; Juhee Kim; Kyungmin Kim; Seunghun Hyun. 2020. "Effect of drying treatment on the leachability of metallic elements from weathered solid mine wastes." Chemosphere 248, no. : 126111.

Case report
Published: 22 November 2018 in Sustainability
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A common-pool resource (CPR) is a type of good consisting of a natural or human-made resource system. Jeju common ranches are historical CPRs located in Jeju Province where mid-mountainous grassland has been shared for livestock farming by the members of adjacent villages since the 10th century. Because of the recent globalization movement, the number of ranches has decreased from 126 in the 1940s to only 53 in 2015; while the majority of the ranches did not survive the transformation, others have remained active by adopting various solutions. In this study, we analyzed the administrative characteristics of the CPRs to explain their current status (i.e., extinction or continuance as a common property) using logistic regression analysis. From this analysis, four statistically meaningful variables were extracted using a forward stepwise selection method; these include the type of ranch management, ratio of land area to population, number of internal committees in the village, and number of local government grants. These variables correlate well with previously recognized ‘community resilience dimensions’ and can be used to explain the fate of the Jeju common ranches during the study period. This study elucidates what community dimensions should be fortified to promote the resilience of Jeju common ranches in order to effectively cope with the on-going effects of globalization.

ACS Style

Kyungmin Kim; Juhee Kim; Kijong Cho; Jeong-Gyu Kim; Seunghun Hyun. Analysis of the Resilience of Common-Pool Resources during Globalization: The Case of Jeju Common Ranches in Korea. Sustainability 2018, 10, 4346 .

AMA Style

Kyungmin Kim, Juhee Kim, Kijong Cho, Jeong-Gyu Kim, Seunghun Hyun. Analysis of the Resilience of Common-Pool Resources during Globalization: The Case of Jeju Common Ranches in Korea. Sustainability. 2018; 10 (12):4346.

Chicago/Turabian Style

Kyungmin Kim; Juhee Kim; Kijong Cho; Jeong-Gyu Kim; Seunghun Hyun. 2018. "Analysis of the Resilience of Common-Pool Resources during Globalization: The Case of Jeju Common Ranches in Korea." Sustainability 10, no. 12: 4346.

Journal article
Published: 01 September 2018 in Journal of Environmental Management
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Leachate from abandoned mine is frequently enriched with toxic elements but their off-site movement is not well addressed. In this study, the attenuation potential of mine-related metallic elements (Zn, As, and Cd) through downward soil was investigated using batch equilibrium sorption and seepage column studies under simulated leachate composition (single, binary, and ternary solutes in 5-mM CaSO4). In the batch result, the retention of Cd was suppressed by 40–45% in the presence of Zn while the Zn was less affected by Cd. The retention of As increased by 14–25% in the presence of both cations, with a greater effect from Zn. The phenomena were explained by the combined effects of sorption selectivity, the relative element abundance, and the operating sorption mechanism (nonspecific vs. specific). These effects also influenced the effluent element concentrations in the seepage study, as numerically indicated by a two-site model fit and moment analysis (e.g., the peak arrival time and peak concentration). For 500 PV seepage, element retention by the column (Mretention) was strongly correlated (r2 = 0.907) with the sorption constant (Kd∗) during the sorption-dominant stage, but the same correlation was poor (r2 = 0.346) during the depletion-dominant stage, due to the desorption resistance of As compared to Zn and Cd. Therefore, the attenuation of the leaching potential by surrounding soils and the effect of cosolutes dissolved in the leachate phase must be concurrently understood when assessing the off-site leaching of metallic elements from abandoned mine sites.

ACS Style

Kyungmin Kim; Juhee Kim; Seunghun Hyun. Soil attenuation of the leaching potential of mine-related metallic elements (Zn, As, and Cd) under different leachate solute compositions. Journal of Environmental Management 2018, 222, 402 -408.

AMA Style

Kyungmin Kim, Juhee Kim, Seunghun Hyun. Soil attenuation of the leaching potential of mine-related metallic elements (Zn, As, and Cd) under different leachate solute compositions. Journal of Environmental Management. 2018; 222 ():402-408.

Chicago/Turabian Style

Kyungmin Kim; Juhee Kim; Seunghun Hyun. 2018. "Soil attenuation of the leaching potential of mine-related metallic elements (Zn, As, and Cd) under different leachate solute compositions." Journal of Environmental Management 222, no. : 402-408.