Papers by Maxim Dorodnikov
The application of stable isotopes is an approach to identify pathways of methanogenesis, methane... more The application of stable isotopes is an approach to identify pathways of methanogenesis, methane (CH4) oxidation and transport in peatlands. We measured the stable C isotopic characteristics (δ13C) of CH4 in peat profiles under hummocks, lawns and hollows of a Finnish mire to study the patterns of CH4 turnover. Porewater CH4 concentrations ([CH4]; at 0.5-2 m) increased with depth in all microforms. Emissions of CH4 from hummocks were the lowest, and increased with the increasing water saturated zone, being ~10 times higher at hollows. Thus, the microtopography of the peatland did not affect the porewater [CH4] in the water saturated part of the peat profile, but the CH4 emissions were affected due to differences in the oxidative potential of the microforms. There was a decrease in δ13C-CH4 with depth at all microforms indicating dominance of CO2-reduction over acetate cleavage pathway of methanogenesis at deep peat layers. However, estimated potential portions of transported CH4 comprised 50-70% of the δ13C-CH4 enrichment on microforms at the 0.5 m depth, hereby masking the acetate cleavage pathway of methanogenesis. Stable C composition (δ13C) of CH4 proved to be a suitable (but not sufficient) tool to differentiate between types of methanogenesis in continuously water-saturated layers under microforms of a peatland. Combined flux-based and multi-isotopic approaches are needed to better understand the CH4 turnover process.
Plant-mediated methane (CH4) transport and the contribution of recent photosynthates to methanoge... more Plant-mediated methane (CH4) transport and the contribution of recent photosynthates to methanogenesis were studied on two dominating vascular plant species – Eriophorum vaginatum and Scheuchzeria palustris – at three types of microrelief forms (hummocks – E. hummocks, lawns – E. lawns and hollows – S. hollows) of a boreal natural minerogenic, oligotrophic fen in Eastern Finland. 14C-pulse labeling of mesocosms with shoots isolated from entire belowground peat under controlled conditions allowed estimation of plant-mediated CH4 flux and contribution of recent (14C) photosynthates to total CH4. The results showed (i) CH4 flux increased in the order E. hummocks ≤ E. lawns < S. hollows corresponding to the increasing water table level at the relief microforms as adjusted to field conditions. (ii) Plant-mediated CH4 flux accounted for 38, 38 and 51% of total CH4 at E. hummocks, E. lawns and S. hollows, respectively. (iii) Contribution of recent photosynthates to methanogenesis accounted for 0.03 % for E. hummocks, 0.06 % for E. lawns and 0.13 % for S. hollows of assimilated 14C. Thus, microsites with S. palustris were characterized by higher rates of transported CH4 from the peat column to the atmosphere when compared to E. vaginatum of drier lawns and hummocks. Contribution of recent photosynthates to methanogenesis was dependent on the plant biomass within-species level (E. vaginatum at hummocks and lawns) but was not observed between species: smaller S. palustris had higher flux of 14CH4 as compared to larger E. vaginatum. Therefore, for the assessment of CH4 dynamics over meso- and macroscale as well as for the implication and development of the modeling of CH4 fluxes, it is necessary to account for plant species-specific differences in CH4 production, consumption and transport and the attribution of those species to topographic forms of microrelief.
Biogeosciences Discussions, 2011
Contribution of recent photosynthates to methanogenesis and plant-mediated methane (CH 4 ) transp... more Contribution of recent photosynthates to methanogenesis and plant-mediated methane (CH 4 ) transport were studied on two dominating vascular plant species -Eriophorum vaginatum and Scheuchzeria palustris -at three microform types (hummocks, lawns and hollows) of a boreal natural minerogenic, oligotrophic fen in Eastern Finland. Mea-5 surements of total CH 4 flux, isolation of shoots from entire peat and 14 C-pulse labeling of mesocosms under controlled conditions allowed estimation of plant-mediated CH 4 flux and contribution of recent ( 14 C) photosynthates to total CH 4 . The obtained results
Increased root exudation under elevated atmospheric CO 2 and the contrasting environments in soil... more Increased root exudation under elevated atmospheric CO 2 and the contrasting environments in soil macro-and microaggregates could affect microbial growth strategies. We investigated the effect of elevated CO 2 on the contribution of fast-(r-strategists) and slow-growing (K-strategists) microorganisms in soil macroand microaggregates. We fractionated the bulk soil from the ambient and elevated (for 5 years) CO 2 treatments of FACE-Hohenheim (Stuttgart) into large macro-(4 2 mm), small macro-(0.25-2.00 mm), and microaggregates (o 0.25 mm) using 'optimal moist' sieving. Microbial biomass (C mic ), the maximum specific growth rate (m), growing microbial biomass (GMB) and lagperiod (t lag ) were estimated by the kinetics of CO 2 emission from bulk soil and aggregates amended with glucose and nutrients. Although C org and C mic were unaffected by elevated CO 2 , m values were significantly higher under elevated than ambient CO 2 for bulk soil, small macroaggregates, and microaggregates. Substrate-induced respiratory response increased with decreasing aggregate size under both CO 2 treatments. Based on changes in m, GMB and lag period, we conclude that elevated atmospheric CO 2 stimulated the r-selected microorganisms, especially in soil microaggregates. Such an increase in r-selected microorganisms indicates acceleration of available C mineralization in soil, which may counterbalance the additional C input by roots in soils in a future elevated atmospheric CO 2 environment.
Soil Biology and Biochemistry, 2011
Turnover of C and N in an arable soil under Free Air Carbon Dioxide (FACE) experiment was studied... more Turnover of C and N in an arable soil under Free Air Carbon Dioxide (FACE) experiment was studied by the use of 13 C natural abundance and 15 N-labeled fertilizers. Wheat was kept four growing seasons under ambient and elevated CO 2 concentrations and fertilized for three growing seasons. Density fractionation of soil organic matter (SOM) allowed to track 13 C and 15 N in free particulate organic matter (fPOM; <1.6 g cm À3 ), particulate organic matter occluded within aggregates with two densities (oPOM 1.6, oPOM 1.6e2.0 g cm À3 ), and in mineral-associated organic matter (>2.0 g cm À3 ) fractions. Elevated CO 2 and N fertilization did not significantly affect C and N contents in the bulk soil. Calculated mean residence time (MRT) of C and N revealed the qualitative differences of SOM density fractions: (i) the shortest MRT C and MRT N in fPOM confirmed high availability of this fraction to decomposition. Larger C/N ratio of fPOM under elevated vs. ambient CO 2 indicated an increasing recalcitrance of FACE-derived plant residues. (ii) There was no difference in MRT of C and N between lighter and heavier oPOMs probably due to short turnover time of soil aggregates which led to oPOM mixing. The increase of MRT C and MRT N in both oPOMs during the experiment confirmed the progressive degradation of organic material within aggregates. (iii) Constant turnover rates of C in the mineral fraction neither confirmed nor rejected the assumed stabilization of SOM to take place in the mineral fraction. Moreover, a trend of decreasing of C and N amounts in the Min fraction throughout the experiment was especially pronounced for C under elevated CO 2 . Hence, along with the progressive increase of C FACE in the Min fraction the overall losses of C under elevated CO 2 may occur at the expense of older "pre-FACE" C.
Plant and Soil, 2007
CO 2 applied for Free-Air CO 2 Enrichment (FACE) experiments is strongly depleted in 13 C and thu... more CO 2 applied for Free-Air CO 2 Enrichment (FACE) experiments is strongly depleted in 13 C and thus provides an opportunity to study C turnover in soil organic matter (SOM) based on its δ 13 C value. Simultaneous use of 15 N labeled fertilizers allows N turnover to be studied. Various SOM fractionation approaches (fractionation by density, particle size, chemical extractability etc.) have been applied to estimate C and N turnover rates in SOM pools. The thermal stability of SOM coupled with C and N isotopic analyses has never been studied in experiments with FACE. We tested the hypothesis that the mean residence time (MRT) of SOM pools is inversely proportional to its thermal stability. Soil samples from FACE plots under ambient (380 ppm) and elevated CO 2 (540 ppm; for 3 years) treatments were analyzed by thermogravimetry coupled with differential scanning calorimetry (TG-DSC). Based on differential weight losses (TG) and energy release or consumption (DSC), five SOM pools were distinguished. Soil samples were heated up to the respective temperature and the remaining soil was analyzed for δ 13 C and δ 15 N by IRMS. Energy consumption and mass losses in the temperature range 20-200°C were mainly connected with water volatilization. The maximum weight losses occurred from 200-310°C. This pool contained the largest amount of carbon: 61% of the total soil organic carbon in soil under ambient treatment and 63% in soil under elevated CO 2 , respectively. δ 13 C values of SOM pools under elevated CO 2 treatment showed an increase from −34.3‰ of the pool decomposed between 20-200°C to −18.1‰ above 480°C. The incorporation of new C and N into SOM pools was not inversely proportional to its thermal stability. SOM pools that decomposed between 20-200 and 200-310°C contained 2 and 3% of the new C, with a MRT of 149 and 92 years, respectively. The pool decomposed between 310-400°C contained the largest proportion of new C (22%), with a MRT of 12 years. The amount of fertilizer-derived N after 2 years of application in ambient and elevated CO 2 treatments was not significantly different in SOM pools decomposed up Plant Soil : [15][16][17][18][19][20][21][22][23][24][25][26][27][28] to 480°C having MRT of about 60 years. In contrast, the pool decomposed above 480°C contained only 0.5% of new N, with a MRT of more than 400 years in soils under both treatments. Thus, the separation of SOM based on its thermal stability was not sufficient to reveal pools with contrasting turnover rates of C and N.
Isotopes in Environmental and Health Studies, 2008
2008)'Thermal stability of soil organic matter pools and their turnover times calculated by 13 C ... more 2008)'Thermal stability of soil organic matter pools and their turnover times calculated by 13 C under elevated CO 2 and two levels of N fertilisation',Isotopes in Environmental and Health Studies,44:4,[365][366][367][368][369][370][371][372][373][374][375][376] To link to this Article:
Global Change Biology, 2010
Increasing the belowground translocation of assimilated carbon by plants grown under elevated CO ... more Increasing the belowground translocation of assimilated carbon by plants grown under elevated CO 2 can cause a shift in the structure and activity of the microbial community responsible for the turnover of organic matter in soil. We investigated the long-term effect of elevated CO 2 in the atmosphere on microbial biomass and specific growth rates in root-free and rhizosphere soil. The experiments were conducted under two free air carbon dioxide enrichment (FACE) systems: in Hohenheim and Braunschweig, as well as in the intensively managed forest mesocosm of the Biosphere 2 Laboratory (B2L) in Oracle, AZ. Specific microbial growth rates (l) were determined using the substrateinduced respiration response after glucose and/or yeast extract addition to the soil. For B2L and both FACE systems, up to 58% higher l were observed under elevated vs. ambient CO 2 , depending on site, plant species and N fertilization. The l-values increased linearly with atmospheric CO 2 concentration at all three sites. The effect of elevated CO 2 on rhizosphere microorganisms was plant dependent and increased for: Brassica napus 5 Triticum aestivumoBeta vulgarisoPopulus deltoides. N deficiency affected microbial growth rates directly (N limitation) and indirectly (changing the quantity of fine roots). So, 50% decrease in N fertilization caused the overall increase or decrease of microbial growth rates depending on plant species. The l-value increase was lower for microorganisms growing on yeast extract then for those growing on glucose, i.e. the effect of elevated CO 2 was smoothed on rich vs. simple substrate. So, the r/K strategies ratio can be better revealed by studying growth on simple (glucose) than on rich substrate mixtures (yeast extract). Our results clearly showed that the functional characteristics of the soil microbial community (i.e. specific growth rates) rather than total microbial biomass amount are sensitive to increased atmospheric CO 2 . We conclude that the more abundant available organics released by roots at elevated CO 2 altered the ecological strategy of the soil microbial community specifically a shift to a higher contribution of fast-growing r-selected species was observed. These changes in functional structure of the soil microbial community may counterbalance higher C input into the soil under elevated atmospheric CO 2 concentration.
Global Change Biology, 2009
Increased belowground carbon (C) transfer by plant roots at elevated CO 2 may change properties o... more Increased belowground carbon (C) transfer by plant roots at elevated CO 2 may change properties of the microbial community in the rhizosphere. Previous investigations that focused on total soil organic C or total microbial C showed contrasting results: small increase, small decrease or no changes. We evaluated the effect of 5 years of elevated CO 2 (550 ppm) on four extracellular enzymes: b-glucosidase, chitinase, phosphatase, and sulfatase. We expected microorganisms to be differently localized in aggregates of various sizes and, therefore analyzed microbial biomass (C mic by SIR) and enzyme activities in three aggregate-size classes: large macro-(42 mm), small macro-(0.25-2 mm), and microaggregates (o0.25 mm). To estimate the potential enzyme production, we activated microorganisms by substrate (glucose and nutrients) amendment. Although C total and C mic as well as the activities of b-glucosidase, phosphatase, and sulfatase were unaffected in bulk soil and in aggregate-size classes by elevated CO 2 , significant changes were observed in potential enzyme production after substrate amendment. After adding glucose, enzyme activities under elevated CO 2 were 1.2-1.9-fold higher than under ambient CO 2 . This indicates the increased activity of microorganisms, which leads to accelerated C turnover in soil under elevated CO 2 . Significantly higher chitinase activity in bulk soil and in large macroaggregates under elevated CO 2 revealed an increased contribution of fungi to turnover processes. At the same time, less chitinase activity in microaggregates underlined microaggregate stability and the difficulties for fungal hyphae penetrating them. We conclude that quantitative and qualitative changes of C input by plants into the soil at elevated CO 2 affect microbial community functioning, but not its total content. Future studies should therefore focus more on the changes of functions and activities, but less on the pools.
FEMS Microbiology Ecology, 2000
Increased root exudation under elevated atmospheric CO 2 and the contrasting environments in soil... more Increased root exudation under elevated atmospheric CO 2 and the contrasting environments in soil macro-and microaggregates could affect microbial growth strategies. We investigated the effect of elevated CO 2 on the contribution of fast-(r-strategists) and slow-growing (K-strategists) microorganisms in soil macroand microaggregates. We fractionated the bulk soil from the ambient and elevated (for 5 years) CO 2 treatments of FACE-Hohenheim (Stuttgart) into large macro-(4 2 mm), small macro-(0.25-2.00 mm), and microaggregates (o 0.25 mm) using 'optimal moist' sieving. Microbial biomass (C mic ), the maximum specific growth rate (m), growing microbial biomass (GMB) and lagperiod (t lag ) were estimated by the kinetics of CO 2 emission from bulk soil and aggregates amended with glucose and nutrients. Although C org and C mic were unaffected by elevated CO 2 , m values were significantly higher under elevated than ambient CO 2 for bulk soil, small macroaggregates, and microaggregates. Substrate-induced respiratory response increased with decreasing aggregate size under both CO 2 treatments. Based on changes in m, GMB and lag period, we conclude that elevated atmospheric CO 2 stimulated the r-selected microorganisms, especially in soil microaggregates. Such an increase in r-selected microorganisms indicates acceleration of available C mineralization in soil, which may counterbalance the additional C input by roots in soils in a future elevated atmospheric CO 2 environment.
Objectives Carbon (C) content in pools of very young
soils that developed during 45 years from lo... more Objectives Carbon (C) content in pools of very young
soils that developed during 45 years from loess was
analysed in relation to vegetation: deciduous and coniferous forests and cropland. We hypothesised that variations in the amount of particulate organic matter (POM)
can explain the C accumulation and also affects the C
bound to mineral surfaces in soil under various
vegetation.
Methods Soil samples were collected under three vegetation types of a 45-year-old experiment focused on
initialsoildevelopment.Aggregateanddensityfractionations were combined to analyse C accumulation in
large and small macro- and microaggregates as well as
in free and occluded POM and mineral factions.
Results Deciduous forest soil accumulated the highest C
contentinthe0–5cmlayer(43gCkg −1),whereasvalues
in coniferous forest and arable soils were lower (30 and
12 g C kg−1, respectively). The highest portion of C in
arable soil was accumulated in the mineral fraction
(80 %), whereas 50–60 % of the C in forest soils were
in POM. More C was associated with minerals in deciduous forest soil (16 g C kg−1 soil) than under coniferous
forest and arable land (8–10 g C kg −1 soil).
Conclusions Particulateorganic matterexplainsmostof
the differences in organic C accumulation in soils developed during 45 years under the three vegetation
types on identical parent material. The C content of
the mineral soil fraction was controlled by plant cover
and contributed the most to differences in C accumulation in soils developed under similar vegetation type
(forest)
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Papers by Maxim Dorodnikov
soils that developed during 45 years from loess was
analysed in relation to vegetation: deciduous and coniferous forests and cropland. We hypothesised that variations in the amount of particulate organic matter (POM)
can explain the C accumulation and also affects the C
bound to mineral surfaces in soil under various
vegetation.
Methods Soil samples were collected under three vegetation types of a 45-year-old experiment focused on
initialsoildevelopment.Aggregateanddensityfractionations were combined to analyse C accumulation in
large and small macro- and microaggregates as well as
in free and occluded POM and mineral factions.
Results Deciduous forest soil accumulated the highest C
contentinthe0–5cmlayer(43gCkg −1),whereasvalues
in coniferous forest and arable soils were lower (30 and
12 g C kg−1, respectively). The highest portion of C in
arable soil was accumulated in the mineral fraction
(80 %), whereas 50–60 % of the C in forest soils were
in POM. More C was associated with minerals in deciduous forest soil (16 g C kg−1 soil) than under coniferous
forest and arable land (8–10 g C kg −1 soil).
Conclusions Particulateorganic matterexplainsmostof
the differences in organic C accumulation in soils developed during 45 years under the three vegetation
types on identical parent material. The C content of
the mineral soil fraction was controlled by plant cover
and contributed the most to differences in C accumulation in soils developed under similar vegetation type
(forest)
soils that developed during 45 years from loess was
analysed in relation to vegetation: deciduous and coniferous forests and cropland. We hypothesised that variations in the amount of particulate organic matter (POM)
can explain the C accumulation and also affects the C
bound to mineral surfaces in soil under various
vegetation.
Methods Soil samples were collected under three vegetation types of a 45-year-old experiment focused on
initialsoildevelopment.Aggregateanddensityfractionations were combined to analyse C accumulation in
large and small macro- and microaggregates as well as
in free and occluded POM and mineral factions.
Results Deciduous forest soil accumulated the highest C
contentinthe0–5cmlayer(43gCkg −1),whereasvalues
in coniferous forest and arable soils were lower (30 and
12 g C kg−1, respectively). The highest portion of C in
arable soil was accumulated in the mineral fraction
(80 %), whereas 50–60 % of the C in forest soils were
in POM. More C was associated with minerals in deciduous forest soil (16 g C kg−1 soil) than under coniferous
forest and arable land (8–10 g C kg −1 soil).
Conclusions Particulateorganic matterexplainsmostof
the differences in organic C accumulation in soils developed during 45 years under the three vegetation
types on identical parent material. The C content of
the mineral soil fraction was controlled by plant cover
and contributed the most to differences in C accumulation in soils developed under similar vegetation type
(forest)