Publications

Shallow thermokarst lakes are important sources of greenhouse gases (GHGs) such as methane (CH4 ) and carbon dioxide (CO2 ) resulting from continuous permafrost thawing due to global warming. Concentrations of GHGs dissolved in water typically increase with decreasing lake size due to coastal abrasion and organic matter delivery. We hypothesized that (i) CH4 oxidation depends on the natural oxygenation gradient in the lake water and sediments and increases with lake size because of stronger wind-induced water mixing; (ii) CO2 production increases with decreasing lake size, following the dissolved organic matter gradient; and (iii) both processes are more intensive in the upper than deeper sediments due to the in situ gradients of oxygen (O2 ) and bioavailable carbon. We estimated aerobic CH4 oxidation potentials and CO2 production based on the injection of 13 C-labeled CH4 in the 0-10 cm and 10-20 cm sediment depths of small (~300 m2 ), medium (~3000 m2 ), and large (~106 m2 ) shallow thermokarst lakes in the West Siberian Lowland. The CO2 production was 1.4-3.5 times stronger in the upper sediments than in the 10-20 cm depth and increased from large (158 ± 18 nmol CO2 g-1 sediment d.w. h-1 ) to medium and small (192 ± 17 nmol CO2 g-1 h-1 ) lakes. Methane oxidation in the upper sediments was similar in all lakes, while at depth, large lakes had 14- and 74-fold faster oxidation rates (5.1 ± 0.5 nmol CH4 -derived CO2 g-1 h-1 ) than small and medium lakes, respectively. This was attributed to the higher O2 concentration in large lakes due to the more intense wind-induced water turbulence and mixing than in smaller lakes. From a global perspective, the CH4 oxidation potential confirms the key role of thermokarst lakes as an important hotspot for GHG emissions, which increase with the decreasing lake size.

Intensive crop production systems worldwide, particularly in China, rely heavily on nitrogen (N) fertilization, but left more than 50% of fertilizer N in the environment. Nitrogen (over) fertilization and atmospheric N deposition induce soil acidification, which is neutralized by soil inorganic carbon (SIC; carbonates), and carbon dioxide (CO2 ) is released to the atmosphere. For the first time, the loss of SIC stocks in response to N-induced soil acidification was estimated for Chinese croplands from 1980 to 2020 and forecasts were made up to 2100. The SIC stocks in croplands in 1980 were 2.16 Pg C (16.3 Mg C/ha) in the upper 40 cm, 7% (0.15 Pg C; 1.1 Mg C/ha) of which were lost from 1980 to 2020. During these 40 years, 7 million ha of cropland has become carbonate free. Another 37% of the SIC stocks may be lost up to 2100 in China, leaving 30 million ha of cropland (37.8%) without carbonates if N fertilization follows the business-as-usual (BAU) scenario. Compared to the BAU scenario, the reduction in N input by 15%-30% after 2020 (scenarios S1 and S2) will decrease carbonate dissolution by 18%-41%. If N input remains constant as noted in 2020 (S3) or decreases by 1% annually (S4), a reduction of up to 52%-67% in carbonate dissolution is expected compared to the BAU scenario. The presence of CaCO3 in the soil is important for various processes including acidity buffering, aggregate formation and stabilization, organic matter stabilization, microbial and enzyme activities, nutrient cycling and availability, and water permeability and plant productivity. Therefore, optimizing N fertilization and improving N-use efficiency are important for decreasing SIC losses from acidification. N application should be strictly calculated based on crop demand, and any overfertilization should be avoided to prevent environmental problems and soil fertility decline associated with CaCO3 losses.

The soil organic carbon (SOC) pool is larger than the combined carbon stock in the world’s vegetation and the earth’s atmosphere. Carbon (C) exchanges between soil and atmosphere are quantitatively relevant for the terrestrial C cycle. Soil microbes regulate soil C dynamics through the transformation of plant-derived C, assimilation of C resources to build up their biomass, and decomposition of soil organic matter. The efficiencies of these processes are critical determinants of net ecosystem C storage. Though there is a continuing and growing interest in elucidating the underlying microbial mechanisms driving soil C transformation, stabilization, and release processes, there are still challenges in manipulating the soil microbial community for C storage. For example, identifying major players in C storage and decomposition; determining the genetic basis of the mechanisms involved in C sequestration; understanding complex interactions between soil physicochemical properties, plants and soil microbes over large spatial and temporal scales; and incorporating microbial community patterns and process rates into ecosystem models.<br/><br/>This research topic aims to increase our understanding of the role of microorganisms in soil organic C storage and mobilization processes, as well as to improve our capabilities in developing and evaluating cost-effective microbial strategies for carbon sequestration and anthropogenic carbon dioxide (CO2) emissions mitigation, ultimately assi...

Soil inorganic carbon (SIC) contributes up to half to the soil carbon (C) stock globally and is especially crucial in arid and semi-arid zones. Widespread soil acidification due to fertilization neutralize carbonates getting an irrecoverable net source of CO2 out of SIC. Nevertheless, SIC is generally neglected as a CO2 source and disregarded in the C balance between soil and atmosphere. A 40-year fertilization field experiment provides an excellent option to investigate the influences of mineral and organic fertilizers on carbonate-derived CO2 efflux by partitioning CO2 sources using the δ13C signature. Although 40 years of mineral fertilizers caused soil acidification and SIC neutralization, SIC-derived CO2 was comparable with that from the control soils. This could be explained by that mineral fertilizer decreased soil-derived CO2 production and the partial pressure of soil CO2, which led to the weak reduction of SIC dissolution in the long term. Thus, the annual contribution of SIC-derived CO2 to total CO2 under long-term mineral fertilization may look as of minor importance. Organic fertilizers (manure, straw) reduced the proportional contribution of SIC-derived CO₂ by 16–42 % relative to controls, despite elevating total CO₂ emissions by 5.4–9.1 Mg C ha⁻¹ yr⁻¹. This divergence stems from Ca²⁺ inputs during organic matter decomposition, which catalyzed CO₂ reprecipitation as pedogenic carbonates, decoupling dissolution from atmospheric release. Crucially, manure amendments achieved net soil C sequestration (0.47 Mg C ha⁻¹ yr⁻¹). In contrast, straw-induced SIC losses (2.0 Mg C ha⁻¹ over 40 years) negated 52 % of SOC gains, yielding marginal net sequestration (2.4 ± 1.7 Mg C ha⁻¹). These results underscore the imperative to evaluate SIC-SOC interactions when assessing the climate efficiency of organic management. SIC-derived CO₂ efflux fluctuated seasonally, peaking during the flowering phase (19–35 % of total emissions), then declining by 5.0–9.7 %. This temporal decoupling highlights rhizosphere activity as a key regulator of SIC. Ignoring SIC contributions led to a 35 % overestimation of heterotrophic respiration in total CO₂ efflux, illustrating systemic biases in current C models. Our findings advocate for manure-based management to maximize C sequestration not as SOC but as SIC and to minimize CO2 emissions from SIC, a dual strategy to reconcile agricultural productivity with climate resilience in semi-arid regions.

Spatial heterogeneity of soil bacterial community depends on scales.The fine-scale spatial heterogeneity of bacterial community composition and functions remains unknown.We analyzed the main driving factors of fine-scale spatial patterns of soil bacterial community composition and carbon metabolic functions across a 30 m × 40 m plot within a Korean pine forest by combining Illumina 16S rRNA sequencing with Biolog Ecoplates based on 53 soil samples.Clear spatial patterns in bacterial community composition and metabolic functions were observed in the forest soil.The bacterial community composition and metabolic functions both showed distance-decay of similarity within a distance of meters.Structural equation model analysis revealed that environmental variables and geographic distance together explained 37.9% and 63.1% of community and metabolic functions, respectively.Among all environmental factors, soil organic carbon (SOC) and root biomass emerged as the most important drivers of the bacterial community structure.In contrast, soil pH explained the largest variance in metabolic functions.Root biomass explained the second-largest variance in soil bacterial community composition, but root traits made no difference in metabolic functions variance.These results allow us to better understand the mechanisms controlling belowground diversity and plant-microbe interactions in forest ecosystems.

Viruses are the most abundant biological entities in the world, but their ecological functions in soil are virtually unknown. We hypothesized that greater abundance of T4-like phages will increase bacterial death and thereby suppress soil organic carbon (SOC) mineralization. A range of phage and bacterial abundances were established in sterilized soil by reinoculation with 10–3 and 10–6 dilutions of suspensions of unsterilized soil. The total and viable 16S rRNA gene abundance (a universal marker for bacteria) was measured by qPCR to determine bacterial abundance, with propidium monoazide (PMA) preapplication to eliminate DNA from non-viable cells. Abundance of the g23 marker gene was used to quantify T4-like phages. A close negative correlation between g23 abundance and viable 16S rRNA gene abundance was observed. High abundance of g23 led to lower viable ratios for bacteria, which suggested that phages drove microbial necromass production. The CO2 efflux from soil increased with bacterial abundance but decreased with higher abundance of T4-like phages. Elimination of extracellular DNA by PMA strengthened the relationship between CO2 efflux and bacterial abundance, suggesting that SOC mineralization by bacteria is strongly reduced by the T4-like phages. A random forest model revealed that abundance of T4-like phages and the abundance ratio of T4-like phages to bacteria are better predictors of SOC mineralization (measured as CO2 efflux) than bacterial abundance. Our study provides experimental evidence of phages' role in organic matter turnover in soil: they can retard SOC decomposition but accelerate bacterial turnover.

Biochar (BC) application to soil is a method of long-term carbon (C) sequestration in croplands. Along with contribution to climate change mitigation, agronomic benefits of biochar are widely accepted. Amelioration and nutritive benefits of biochar are mainly attributed to high applications rates, which may not be viable for farmers. We suggest a new approach: band application, which implements biochar in modern intensive crop rotations and optimizes both C and nutrients cycles (i.e. phosphorus (P)). As maize is globally one of the most widely planted crops, corncobs (CC) may be utilized for BC production. Corncob biochar (CC BC) may be implemented into the farming practice as suspension with liquid phosphorus solution jointly applied in band in the close proximity to seeds. We conducted an incubation experiment to evaluate the short-term effects (within 32 days) of corncob biochar and inorganic P application on P availability and microbial activity in a loamy Luvisol. Corncobs were pyrolyzed to biochar (350oC; 0.2-0.3oC s-1), grinded (&lt;200 &amp;#181;m), suspended and mixed with phosphate solution (as monopotassium phosphate). We compared liquid phosphorus (P) and joint P and BC application (BC+P) to control (water). The application rates were: 30 kg ha-1 P (200 mg kg-1 P) and 300 kg ha-1 BC (0.2% w/w). Soil was sampled on day 7, 14, and 32 to measure pH, available P, enzyme kinetics, microbial biomass C, N, and P. Despite the alkaline pH of BC (pH 8.7), application of BC+P and P decreased soil pH (5.6-5.7) compared to soil in control (5.8). Acidifying effect of suspensions was attributed to used phosphate source and may differ for others. BC+P did not alter soil P availability compared to solely P applied. Thus, dynamics of soil available P within 32 days was mainly attributed to soil processes but not the BC effect. Higher basal respiration in amended soil compared to control within first 7 days indicates that physiological status of microorganisms was affected by P and BC+P application. But this was independent on changes in microbial biomass C and dissolved organic C. Microbial biomass-specific activity of beta-glucosidase and leucine aminopeptidase (but not acid phosphatase) in BC+P soil were lower compared to only P application, that may be caused by adsorbing properties of BC. The application BC+P increased the catalytic efficiency (Ka) of all enzymes compared to only P, which indicates the positive effect of biochar on enzymatic efficiency of soil. Sole P application resulted in acceleration of P immobilization on day 32, as microbial molar C:N:P ratio for only P (18:2:1) differed from control and BC+P (35:3:1 and 36:4:1, accordingly). Principal Component Analysis revealed that BC+P treatment differed from the control and solely P applied at all time points. To conclude, joint application of corncob biochar suspension and phosphorus solution may not only increase soil P availability, but prevent high P immobilization by microorganisms and facilitate higher enzyme efficiency to potentially increase nutrient availability for seedlings in the application bands.

Soil organic matter (SOM) decomposition in response to global change represents a critical uncertainty in coupled carbon (C) cycle-climate models. Much of this uncertainty arises from our limited mechanistic knowledge of the effects of organic C input frequency on SOM decomposition. Based on a three-source-partitioning isotopic approach (14C glucose addition to soil continuously labeled by C4 plants over 21 years) and literature review of 86 observations, we assessed the priming of fast- and decadal-SOM decomposition after occasional and frequent (every 12 vs 60 days) labile C input in a grassland soil. Frequent glucose input accelerated SOM decomposition over 200 days, but the occasional input reduced this positive priming by 2.6 times. The positive priming by occasional C input resulted in 139 μg C g−1 soil net C sequestration corresponding to 38% of C input. During the 200 days incubation, the primed fast-cycling C (younger than 21 years) under occasional C addition was 52–94% greater compared with frequent addition. Conversely, the priming of decadal SOM (older than 21 years) by frequent C input was 463 μg C g−1 after the 200 days incubation, which represents 5.3% of the initial decadal-cycling soil C pool. This was 1.5 times higher than by occasional input because of the stronger N mining caused by the continuously high activity of microbial K strategists under frequent C input. Our global scale assessment showed that occasional C input reduces the priming of decadal SOM decomposition by 89–127 Tg per year compared to frequent input and thus, sequestrated an additional 102 Tg C per year. Overall, the vulnerability of decadal SOM to increasing C input frequency thus weakening the C sink of grassland, whilst reduced C input frequency (e.g. by drought) suppresses the SOM priming and reduces the positive feedback of SOM decomposition to global change. This points out the necessity to assess the age of soil C when predicting the consequences of altered soil C input frequency under global change.

Microbial carbon use efficiency (CUE) is a critical parameter that controls carbon storage in soil, but many uncertainties remain concerning adaptations of microbial communities to long-term fertilization that impact CUE. Based on H 2 18 O quantitative stable isotope probing coupled with metagenomic sequencing, we disentangled the roles of active microbial population dynamics and life strategies for CUE in soils after a long-term (35 years) mineral or organic fertilization. We found that the soils rich in organic matter supported high microbial CUE, indicating a more efficient microbial biomass formation and a greater carbon sequestration potential. Organic fertilizers supported active microbial communities characterized by high diversity and a relative increase in net growth rate, as well as an anabolic-biased carbon cycling, which likely explains the observed enhanced CUE. Overall, these results highlight the role of population dynamics and life strategies in understanding and predicting microbial CUE and sequestration in soil. IMPORTANCE Microbial CUE is a major determinant of global soil organic carbon storage. Understanding the microbial processes underlying CUE can help to maintain soil sustainable productivity and mitigate climate change. Our findings indicated that active microbial communities, adapted to long-term organic fertilization, exhibited a relative increase in net growth rate and a preference for anabolic carbon cycling when compared to those subjected to chemical fertilization. These shifts in population dynamics and life strategies led the active microbes to allocate more carbon to biomass production rather than cellular respiration. Consequently, the more fertile soils may harbor a greater microbially mediated carbon sequestration potential. This finding is of great importance for manipulating microorganisms to increase soil C sequestration.

Global warming accelerates soil organic matter (SOM) decomposition with strong feedback to atmospheric CO2. Such an effect should be especially important for no-till agricultural practices, where SOM accumulates in the topsoil as compared with conventional tillage. We incubated soil samples (0–5 cm) at three temperature levels (15, 21 and 27 °C) from long-term till and no-till systems that were in situ warmed and non-warmed to assess the temperature sensitivity of CO2 efflux, labile organic carbon and extracellular enzyme activities. Thermal adaptation to prolonged warming was observed resulting in a lasting effect on SOM decomposition. On average, 26, 14 and 12% more CO2 was emitted at each incubation temperature from the warmed soils compared to the non-warmed soils. The Q 10 value was lower for the warmed than the non-warmed soils. Soil microbial biomass C and dissolved organic C declined with warming. The activities of three extracellular enzymes, β-glucosidase, chitinase, and sulfatase, were higher under warming and no-till as compared to non-warmed and tilled soil. We concluded that the increased SOM decomposition due to the stimulation of microorganisms by warming was long-lasting. Predictions of C accumulation in the topsoil by no-till farming should be taken with caution, as this C pool is especially vulnerable to global warming.