Carbon dioxide (CO2) efflux from soil (or soil respiration, SR) is one of the most important yet variable characteristics of soil. When evaluating large areas, CO2 efflux modeling serves as a viable alternative to direct measurements. This research aims to identify site-specific differences and their effects on empirical CO2 efflux modeling. The experimental data from 25 years of field observations were utilized to identify the optimal site- and weather-specific models, parameterized for normal, wet, and dry years, for the forest and grassland ecosystems located on similar Entic Podzols (Arenic) in the same bioclimatic coniferous–deciduous forest zone. The following parameters were considered in the examined models: mean monthly soil or air temperatures (Tsoil and Tair), amount of precipitation during the current (P) and the previous (PP) months, and the storage of soil organic carbon (SOC) in the top 20 cm of soil. The weighted non-linear regression method was employed to estimate the model parameters for the normal, wet, and dry years. To increase the magnitude of the model resolutions, we controlled the slope and intercept of the linear model comparison between the measured and modeled data through the change in R0—CO2 efflux at Tsoil = 0 °C. The mean bias error (MBE), root-mean-square error (RMSE), and determination coefficient (R2) were employed to assess the quality of the model’s performance. The measured Tsoil, Tair, and P, as well as the litter (for forest) or sod (for grassland) horizon (modeled by the Soil SCLmate Statistical Simulator (SCLISS)), and soil temperatures (Tlit_m, Tsoil_m) and moistures (Mlit_m, Msoil_m), were used for SR simulation. For the CO2 efflux in the forest ecosystem with the lower SOC availability for mineralization, the direct Tsoil and Tair measurements in combination with SOC storage provided better parameterization for the empirical TPPC model. For the CO2 efflux in the grassland ecosystem with the high SOC availability for mineralization, the temperature became the governing factor, and the TPPrh model provided better performance over all the considered models. The model’s performance was the best for the wet years, and the worst for the dry years for both ecosystems. For forest ecosystems, the model performance for average precipitation years was equivalent to that in wet years. For grassland ecosystems, however, the model performance was equivalent to that in dry years due to differing exposure and hydrothermal regimes. The wet-year R0 obtained for both forest and grassland ecosystems differed from the normal- and dry-year values. The measured SR values relevant for the R0 estimations distribute along the precipitation range for the forest and along the temperature range for the grassland. The SCLISS-modeled Tlit_m and Mlit_m provide good alternatives to direct atmospheric measurements, and can be used as initial temperature and moisture data for CO2 efflux modeling when direct soil and moisture observations are not available on site.

Mycorrhizal symbiosis has been the focus of research for more than a century due to the positive effect of fungi on the growth of the majority of woody plants. The extramatrical mycelium (EMM) of ectomycorrhiza (EMR) accounts for up to one-third of the total soil microbial biomass, whereas litter from this short-living pool accounts for 60% of the total litterfall mass in forest ecosystems. The functioning of EMR improves the nitrogen (N) nutrition of trees and thus contributes to the carbon (C) balance of forest soils. The model presented here is an attempt to describe these EMR functions quantitatively. It calculates the growth of EMM and the subsequent “mining” of additional nitrogen from recalcitrant soil organic matter (SOM) for EMR growth, with the associated formation of “dissolved soil carbon”. The decomposition of EMM litter is carried out by all organisms in the soil food webs, forming available NH4+ in the first phase and then solid-phase by-products (excretes) as a new labile SOM pool. These substances are the feedback that determines the positive role of EMR symbiosis for forest vegetation. A sensitivity analysis revealed a leading role of the C:N ratio of biotic components in the dynamics of EMM. The model validation showed a satisfactory agreement between simulated and observed data in relation to EMM respiration in larch forest plantations of different ages. Model testing within the EFIMOD3 model system allowed a quantitative assessment of the contribution of different components to forest soil and ecosystem respiration. The validation and testing of this model demonstrated the adequacy of the theoretical background used in this model, with a fast EMM decomposition cycle by all soil biota of the food webs and without direct resource exchange between plants and fungi.

The results of forest simulation modeling of the dynamics of carbon pools and fluxes in forest ecosystems under different forest management scenarios are considered using the example of the Dankovsky forestry district (south of the Moscow oblast, subzone of coniferous-broadleaved mixed forests). The impact of changes in forest management practices such as the reserve regime, the reduction in the proportion of forest lands as a result of residential development, and zoning of the territory with an emphasis on increasing the recreational use of forests on the carbon balance is analyzed. In computational experiments, a set of Russian models is used: the FORRUS-S dynamic model of a forest stand, the Romul_Hum model of soil organic matter dynamics, and the SCLISS model of the hydrothermal regime of soils. Calculations are performed for a time period of 100 years at the forestry unit level, and they are also aggregated at the level of the entire forestry district. The diversity of types of forest growth conditions (FGCs), together with the species diversity and the initial different ages of stands, determine significant variations in the calculated indicators of forest stand production and the quantity and quality of plant litter entering the soil. For all cases, model estimates of changes in carbon reserves occurred in the forest stands within the initial 40–60 years with a subsequent decrease in the calculated values. Under the conservation scenario, an increase in the organic substance reserves in forest litter and soil is observed: for FGCs C2 and C3, an increase of over 100 years was approximately 5–10 kg m–2; for the remaining FGCs, it is at the level of 2–3 kg m–2 in terms of carbon. Under the economic use scenarios, a comparative “levelling” of forestry district area towards the lower end of the spectrum is shown in terms of soil carbon reserves. The maximum ecosystem carbon stock is calculated for FGC C2 and C3, and the minimum is for A5 and C4. Depending on the scenario, over 100 years, the total net absorption of carbon by the forests of the Dankovsky forestry district (with a total area of forested land of 6836 ha) is estimated within the range of 0.15–0.57 Tg.

The goal of this work is to analyze the dynamics of soil organic matter (SOM) in arable soils of Yamal using computational experiments with the ROMUL model. Soil temperature and moisture dynamics were simulated using the SCLISS model. The Yamal experimental station was organized in 1932. The soil is Plaggic Podzol. The thickness of humus horizon (PY) is 30 cm. Pools, kg/m2: SOM – 9.32 and 13.75; N – 0.46 and 0.66 for 0–20 and 0–30 cm respectively. Background: soddy-green-moss tundra near Salekhard. Soil: Folic Podzol: litter (O, 2 cm) and humus-accumulative (AY, 4 cm) and illuvial ferruginous (BF, 6 cm) horizons. Pools, kg/m2: SOM – 1.38 and 2.69, N – 0.03 and 0.18 for 0–2 and 2–6 cm respectively. The quantity and quality of background fall was estimated according to literature data. Clarification of the amount of fall was carried out by the method of inverse problem solving (spin-up). Peat application was simulated: starting application in the dose of 12 kg/m2 and maintenance (every 6 years) in doses 4, 8 and 12 kg/m2, N 1%. Application of mineral fertilizers, 2 variants: a) N 4 g/m2 (40 kg/ha) in peatting years and b) application of the same dose of nitrogen every year. The duration of computational experiments is 30 and 90 years. Computational experiments showed that after the starting peatting of Folic Podzol at the rate of 12 kg/m2 after 30 years, only 15% of the applied detritus remained. Maintenance peatting of 8–12 kg/m2 leads to an increase in SOM pool to 20–30 kg/m2 and excessive accumulation of detritus. Application of 4 kg/m2 of peat once every 6 years for 90 years shows the dynamics of SOM pools from Folic Podzol to Plaggic Podzol which is confirmed by field survey data. Application of mineral nitrogen (4 g/m2) once every 6 years does not affect SOM pools. Annual application of mineral N (4 g/m2) increases SOM pools due to intensified humification. This fact requires experimental verification.

Mycorrhizal symbiosis has been the focus of research for more than a century due to the positive effect of fungi on the growth of the majority of woody plants. Extramatrical mycelium (EMM) of ectomycorrhiza (EMR) reaches one third of the total soil microbial biomass, and litter from this short-living pool represents 60% of the total litterfall mass in forest ecosystems. The functioning of EMR improves the nitrogen nutrition of trees and thus contributes to the carbon balance of forest soils. The model presented here is an attempt to describe these EMR functions quantitatively. It calculates the growth of EMM, and the subsequent “mining” of additional nitrogen from recalcitrant soil organic matter (SOM) for EMR growth, with the associated formation of “dissolved soil carbon”. The decomposition of EMM litter is carried out by all organisms in the soil food webs, forming available NH4+ in the first phase, and then solid-phase by-products (excretes) as a new labile SOM pool. These substances are the feedback that determines the positive role of the EMR symbiosis for forest vegetation. The sensitivity analysis revealed a leading role of the C:N ratio of biotic components in the dynamics of EMM. The model validation showed a satisfactory agreement between simulated and observed data in relation to EMM respiration in larch forest plantations of different ages. The model testing within the EFIMOD3 model system allowed a quantitative evaluation of the contribution of different components in forest soil and ecosystem respiration. The validation and testing of this model demonstrated the adequacy of the theoretical background used in this model, with a fast EMM decomposition cycle by all soil biota of food webs, and without direct resource exchange between plants and fungi.

Many problems of modern forest ecology require analysis of the conjugated dynamics of processes occurring at different spatio-temporal scales of the functioning of plant communities and soils resulted from their interaction under the influence of all edaphic and anthropogenic factors. Mathematical models can be an effective tool for such analysis. The aim of this study is to present the implementation of new model system that makes it possible to reproduce in simulation experiments the spatial structure of forest phytocenoses formed by tree and grass-shrub layers, as well as associated heterogeneity of soil conditions and the diversity of ecological niches at different hierarchical levels. To determine the required level of detail of the spatial heterogeneity of forest biogeocenoses related to the processes of their multi-scale functioning, experimental studies were carried out on permanent sampling plots in the Prioksko-Terrasny State Natural Biosphere Reserve and in the «Kaluzhskie Zaseki» State Nature Reserve. The spatial structure of communities and related heterogeneity of ecological conditions were studied using traditional soil and geobotanical, as well as modern instrumental methods. The obtained data were used to construct the algorithms and to estimate the parameters of different blocks of the new system of models. The implementation of a spatially-explicit process-based system of models has shown its ability to reproduce the dynamics of forest ecosystems, taking into account the species composition and spatial structure of different layers of vegetation and the associated patchiness of soil conditions. Due to a wide range of interrelated ecosystem characteristics implemented in the system of models it is possible to simulate productivity, biological turnover of C and N, and the dynamics of forest ecosystems, taking into account their typical spatial structure at different scales. This improves understanding of ecosystem processes and their contribution to maintaining the sustainable functioning of forests, which can be used for predictive assessments of the efficiency of forest management techniques and in solving other forestry and environmental problems.

The activity of CO2 efflux, N2 fixation, and denitrification, as well as the physiological state of the community of microorganisms-destructors were assessed depending on the decay stage of the coarse woody debris (CWD) in the incubation experiments with the coarse woody debris of Norway spruce (Picea abies L.) and podzolic soil (Retisol). The coarse woody debris and soil were sampled at the experimental sites of the Central Forest State Reserve (Tver Region, Russia). Maximal CO2 emissions caused by CWD decomposition was associated with the decay stages III and IV. Also, the latter two showed maximal values of such sound indices of microbial activity as substrate induced respiration (SIR, 50 μg С–СО2/(g h)), percentage of easily decomposable С in organic matter (А1, 66%) and metabolic quotient qCO2 (0.78). Unlike the СО2 emission, maximal activity of N2 fixation was at the earlier decay stage II. The values of N2 fixation and denitrification activities indicate a gradual and complicatedly regulated transition process from the properties of bacterial and fungal communities of CDW to those in the soil during stages II, III and IV. The dramatic, more than 3-fold decrease was found only for C : N in CWD during the stages III–IV transition. СО2 emission at the stage V increased dramatically. Nevertheless, the CWD organic matter even at this latest decay stage had lower sustainability than organic matter of podzolic soil.

The relationships between the rhizosphere factor Rf values for a number of indices of soil biological activity, allocation in soil horizons, and bacterial community structure in the rhizosphere and the bulk soil of Retisol under spruce trees (Picea abies L.) have been studied in the Central Forest Nature Reserve (Tver oblast, Russia). The Rf expressed as the ratios of soil characteristics in the rhizosphere to those in the bulk soil are determined for the basic indices of microbial respiration, biomass, and available nutrient pools in the humus-accumulative AEL (3–15 cm) and eluvial EL (15–46 cm) horizons. The most prominent rhizosphere effect (Rf > 1.6) is observed for microbial biomass, basal respiration, and the turnover rate of soil organic matter (SOM). The Rf value for the SOM turnover rate in AEL horizon is approximately 1.5, reaching as high as 6 in the EL horizon. The rhizosphere demonstrated a higher microbial diversity with a significant contribution of both gram-positive and gram-negative bacteria, including representatives of Acidobacteria, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Solibacteres, and Spartobacteria. The gram-positive orders Bacillales and Clostridiales are prevalent in the bulk soil, with the relative contributions of over 80 and 50

The activity of CO2 efflux, N2 fixation, and denitrification, as well as the physiological state of the community of microorganisms-destructors were assessed depending on the decay stage of the coarse woody debris (CWD) in the incubation experiments with the coarse woody debris of Norway spruce (Picea abies L.) and podzolic soil (Retisol). The coarse woody debris and soil were sampled at the experimental sites of the Central Forest State Reserve (Tver Region, Russia). Maximal CO2 emissions caused by CWD decomposition was associated with the decay stages III and IV. Also, the latter two showed maximal values of such sound indices of microbial activity as substrate induced respiration (SIR, 50 μg С–СО2/(g h)), percentage of easily decomposable С in organic matter (А1, 66%) and metabolic quotient qCO2 (0.78). Unlike the СО2 emission, maximal activity of N2 fixation was at the earlier decay stage II. The values of N2 fixation and denitrification activities indicate a gradual and complicatedly regulated transition process from the properties of bacterial and fungal communities of CDW to those in the soil during stages II, III and IV. The dramatic, more than 3-fold decrease was found only for C : N in CWD during the stages III–IV transition. СО2 emission at the stage V increased dramatically. Nevertheless, the CWD organic matter even at this latest decay stage had lower sustainability than organic matter of podzolic soil.

The paper considers the results of calculations of the heterotrophic (HR) and total soil respiration for Entic Carbic Podzol under a coniferous-broad-leaved forest in the South of the Moscow region (54.89° N, 37.56° E), performed using the soil model Romul_Hum and a new version of the system of models EFIMOD3. The results of soil respiration modeling had a good correlation with the field measurement data. The Romul_Hum model simulates better the intensity of HR of the studied soil in wet than in dry years when it lightly overestimates the HR values. In the spatially detailed modeling of heterotrophic and root respiration using the EFIMOD3, the variability of carbon pools and fluxes associated with the distribution of the litterfall and hydrothermal conditions under the forest canopy was taken into account. The data obtained show that the intensity of HR at the beginning and middle of the growing season differs by about a factor of two, and HR values between different parts of the simulation site at the same time differ by more than 3.5 times. Spatial and temporal variability of the soil respiration affects the accuracy of estimates of C stocks in forest ecosystems. The used models are effective tools to analyze changes in soil carbon stocks, soil respiration, and carbon sink estimation in forest ecosystems, including tasks of forest management.

The values of heterotrophic (HR) and total soil respiration for the Entic Carbic Podzol under a coniferous–broadleaved forest in the south of Moscow oblast (54.89° N, 37.56° E) calculated using the Romul_Hum model and a new version of the EFIMOD3 system of models are reported. The results of soil respiration modeling correlate well with the field measurement data. The Romul_Hum model better simulates the HR intensity of the studied soil in wet years as compared with dry years, when it somewhat overestimates the HR values. The spatially explicit modeling of HR and root respiration using EFIMOD3 takes into account the variation of carbon pools and fluxes associated with the distribution of the plant litterfall and hydrothermal conditions under the forest canopy. The results show that the HR intensity differs approximately twofold in early and middle growing season, and the HR values in individual parts of the simulation site at the same dates differ more than 3.5-fold. The spatial and temporal variation of soil respiration influences the accuracy of estimates for the carbon budget in forest ecosystems. The used models are efficient tools for analyzing the changes in carbon stocks and soil respiration and estimating carbon sink in forest ecosystems, including the tasks related to forest management.

The activities of CO2 emission, N2 fixation, and denitrification, as well as the physiological state of the community of microbial decomposers are assessed at different stages of decay of coarse woody debris (CWD) in the incubation experiments with the Norway spruce (Picea abies L.) and the humus horizon of podzolic soil (Retisol). The CWD of five decomposition stages and soil are sampled at the experimental plots of the Central Forest State Reserve (Tver oblast, Russia). The maximum CO2 emissions are associated with CWD decay stages III and IV. In addition, characteristic of these stages are the maximum values of the important indices of CWD and soil microbial activity, such as the substrate-induced respiration (SIR, 50 µg C–CO2/(g h), share of easily decomposable С in organic matter (A1, 66

The relationships between the rhizosphere effects, allocation in soil horizons and bacterial community structure in the rhizosphere and the bulk soil of Retisol under spruce trees (Tver region, Russia) were studied. The rhizosphere factors (Rf) expressed as ratios of soil characteristics in the rhizosphere to that in the bulk soil were determined for the basic indices of microbial respiration, biomass and available nutrients pools in the top AEL (3–15 cm) and deep EL horizons (15–46 cm). The most prominent rhizosphere effects (Rf 1.6) were revealed for microbial biomass C, basal respiration, and SOM turnover rate. Rf value for the SOM turnover rate in humus AEL horizon was approximately 1.5, while in the EL horizon it reached 6. The Rhizosphere had higher microbial diversity, with a significant contribution of both Gram-positive and Gram-negative bacteria, including representatives of Acidobacteria, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Solibacteres and Spartobacteria. The Gram-positive orders Bacillales and Clostridiales predominated in the bulk soil, with the relative contributions of more than 80 and 50% for the AEL and EL horizons, respectively. Based on the number of microbial activity indices with high Rf values (three for the lower EL horizon and only one for the upper humus AEL horizon), the rhizosphere of the lower horizon is probably more pronounced “hot spot” of biological activity than that in the top soil layer.

Investigations into heterogeneity in the spatial distribution of dwarf shrub cenopopulations have proven that the dominance of bilberries (Vaccinium myrtillus L.) and lingonberries (V. vitis-idaea L.) in the groundcover is relevant to environmental factors. The moisture of soils on the strongly expressed microrelief under the same ambient light conditions acts as a limiting factor for the spatial distribution of dwarf shrubs. Bilberries usually occupy a lower and wetter microrelief surface when compared to lingonberries. In addition, melt-water flooding over a long period of 1–2 weeks can cause the death of dwarf shrubs covering the land parcels. In the areas of ecological-niche overlap, dwarf shrubs successfully codominate due to the differences in the morphological and physiological characteristics of these species. It is shown that, in single-story pine forests without any woody undergrowth in southern Moscow region, the light factor has no significant effect on the growth of dwarf shrubs. However, the second layer canopy present in the forest limits the distribution of dwarf shrubs under the spruce and linden tree canopies. Thus, it was shown that photosynthetically active radiation (PAR) transmission factor values less than 7

The specific features in the formation of a system of biologically active surface horizons (organoprofile) in the Subantarctic lithozems (Leptosols) are analyzed using mathematical modeling. Simulation experiments involve the ROMUL mathematical model. The working scenarios are compiled taking into account the specific features of the effects of climate, fauna, and vegetation of the coasts of King George Island, archipelago of the South Shetland Islands, West Antarctica. The periodicity of temperature recording (using daily or monthly average values) has little effect on the simulation results. As is shown, different localizations of the litterfall under green mosses and Antarctic hair grass (Deschampsia antarctica) lead to development of the organoprofiles differing in their structure and quality. The enrichment with nitrogen due to the vital activity of penguins increases the litterfall transformation intensity and enhances humification. Note that the results of a medium-term (50-year-long) simulation of the dynamics of organic matter pools in the lithozems with different ornithogenic impacts significantly differ in the case of a change in vegetation type and an increase in the nitrogen concentration in litterfall. Long-term (at constant climate and litterfall) computational experiments have shown that the litter and humus pools under the Subantarctic conditions reach a stable state in 200 and 500 years, respectively. Soil CO2 emission in the simulated ranges of soil forming factors can be regarded as consistent with the results of field measurements if a large part of the gross СО2 flux results from the respiration of vegetation. The compilation of scenarios for simulation experiments has shown that the field information on the pools of surface organic horizon (litter) and their quality for drained Antarctic soils is insufficient. Litter is an important indicator of the actual response of Antarctic soils to the change in soil forming factors and must be taken into account. We invite the international community of the scientists studying the soils of Antarctic to agree on the unification of descriptions of the key sites and calculations of the results of field studies.

Purpose . This study is aimed to develop a model of priming effect (accelerated mineralisation of soil organic matter (SOM)) induced by root exudate input into nitrogen (N) limited rhizosphere soil as a typical case for most terrestrial ecosystems. This ecologically important process in the functioning of the “plant-soil” system was parameterized for temperate and boreal forests. Methods. A model of priming effect has been developed based on the concept of N mining to making up for the N scarcity in exudates by accelerating SOM mineralisation. Lacking N for microbial growth is mined from the SOM mineralisation considering C:N ratio of soil. The model has a built-in food web module, which calculates soil fauna feeding on microorganisms, the release of by-products of faunal metabolism and mineral N used for root uptake. Results . The model verification demonstrated the similar order of the priming effect as in the published experiments. Testing at the pedon level revealed a high sensitivity of the model to N content in root exudates. Testing of the model at the ecosystem level revealed that CO 2 emission from the priming can reach 25–30% of CO 2 emission from the whole Ah horizon of forest soil. The same intensities were simulated for the fauna-derived N released within the rhizosphere. Conclusion. The new model reflects important ecological consequences of the main target function of priming effects within the “plant – soil – microorganisms – fauna” system – the microbial acceleration of C and N cycling in the rhizosphere and detritusphere to mobilise mineral N for plants.

The aim of this study was to validate the ROMUL and Romul_Hum simulation models based on the data of long-term measurements of soil respiration performed by the Institute of Physicochemical and Biological Problems in Soil Sciences of the Russian Academy of Sciences in the south of Moscow oblast (54°50′ N, 37°34′ E). We estimated the dynamics of carbon stocks and soil CO 2 emission for three scenarios of plant litterfall compiled with the account of experimental data on the composition and mass of litterfall entering the gray forest soil (Albic Luvisol) under secondary deciduous forest. The calculations of long-term series of temperature and moisture content in the forest litter and upper organo-mineral soil horizons in simulation experiments are based on the real data on air temperature and precipitation for 1973–2016. The correspondence of simulation results to the data of field measurements was better for the Romul_Hum model, which comprises a description of the effects related to the vital activity of soil fauna, leading to the formation of different fractions of soil organic matter. The best correspondence of simulated values of CO 2 emission, carbon stocks, and the C : N ratios in gray forest soil horizons to field data was for the litter scenarios, which excluded the fraction of small branches. The revealed differences between the simulated and real values of soil parameters are explained by specific features of the input and transformation of different litterfall fractions, which are not always taken into account during soil sampling. The results of the study attract the attention to the uncertainties of estimates of carbon budget in forest ecosystems due to the difficulties of accounting both large wood residues (dead tree and coarse branches debris) and smaller wood fractions in the litterfall.