Forest Soil Organic Carbon Research Articles

Simulating Impacts of Increased Nitrogen Deposition on the Content of Active Organic Carbon in Forest Soils Along the Urban-Rural Gradient

Simulating Impacts of Increased Nitrogen Deposition on the Content of Active Organic Carbon in Forest Soils Along the Urban-Rural Gradient

Climate-Sensitive Spatial Variability of Soil Organic Carbon in Multiple Forests, Central China

Climate-Sensitive Spatial Variability of Soil Organic Carbon in Multiple Forests, Central China

湘西石漠化区3种造林模式土壤真菌群落结构差异

PDF HTML阅读 XML下载 导出引用 引用提醒 湘西石漠化区3种造林模式土壤真菌群落结构差异 DOI: 10.5846/stxb202008072061 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 中央级科研院所基本科研业务费重点项目（CAFYBB2019SZ003）；中南林业科技大学研究生科技创新基金（CX20192026） Differences of soil fungal community structure under three afforestation modes in rocky desertification region of Western Hunan Province Author: Affiliation: Fund Project: “Degradation mechanism and restoration technology of typical forests in South China 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:湘西石漠化地区是我国生态系统脆弱而又敏感的区域，土壤微生物在维持石漠化区森林生态系统结构和功能稳定中发挥重要作用。选取石漠化地区立地条件相同的32年生的马尾松纯林、光皮桦纯林及马尾松-光皮桦混交林为研究对象，以立地条件相似的未造林荒地演变成的灌草群落作为对照，比较分析石漠化地区不同造林模式对土壤真菌群落结构和多样性的影响及其主要驱动因素。采用Illumina HiSeq第二代高通量测序技术，分析了3种森林土壤真菌群落组成及多样性。结果表明，不同造林模式下土壤真菌优势类群不同，光皮桦、马尾松-光皮桦混交林以及石漠化灌草地土壤真菌优势门均为子囊菌门（Ascomycota），且在石漠化灌草地相对丰度最大，为64.0%；马尾松则以担子菌门（Basidiomycota）为优势类群，其相对丰度占57.9%。混交林土壤真菌物种总数和Shannon指数显著高于马尾松和光皮桦林地，整体上真菌群落多样性表现为：未造林灌草地 > 混交林 > 马尾松林 > 光皮桦林。与未造林灌草地相比，马尾松-光皮桦混交林和光皮桦纯林显著提升了土壤有机碳（SOC）和全氮（TN）含量。Mantel test检验结果显示，真菌群落结构与全磷（TP）、有机碳（SOC）、铵态氮（NH4+-N）、硝态氮（NO3--N）、全氮（TN）、pH和含水量（SWC）具有显著相关性（P<0.05），其中土壤SOC、TN、pH值对真菌群落结构影响最大。冗余分析（RDA）结果发现，子囊菌（Ascomycota）与pH、TP、SOC、TN、AP、NO3--N含量均呈正相关；担子菌门（Basidiomycota）和被孢霉门（Mortierellomycota）主要与NH4+-N成正相关，与pH、TP、SOC、TN、AP、NO3--N呈负相，而罗氏菌门（Rozellomycota）与SWC呈正相关（P<0.05）。综上，相比针叶纯林，石漠化地区针阔混交林能通过增加土壤SOC、TN而显著提高真菌群落多样性，促进土壤肥力状况的提升。此研究结果可以为石漠化区人工植被恢复以及土壤肥力管理提供依据。 Abstract:Rocky desertification area in Western Hunan province is a fragile and sensitive area of ecosystem in China. Soil microorganisms play an important role in maintaining the stability of forest ecosystem structure and function in rocky desertification area. Thirty two year-old pure Pinus massoniana forest, pure Betula luminifera forest and mixed Pinus massoniana and Betula luminifera forest in rocky desertification area with the same site conditions were selected as the research objects. The non-forested shrub grassland with the similar site conditions was taken as the control to compare and analyze the influence of different afforestation modes on soil fungal community structure and diversity and their main driving factors. The composition and diversity of soil fungal communities in three forests were analyzed by Illumina HiSeq second-generation high-throughput sequencing technology. The results showed that the dominant groups of soil fungi were different under different afforestation modes. The dominant phylum of soil fungi in Betula luminifera, mixed forest and non-forested shrub grassland were Ascomycota, and the relative abundance was the largest in non-forested shrub grassland, which was 64.0%. Basidiomycota was the dominant group in Pinus massoniana, its relative abundance accounted for 57.9%. The total number of soil fungal species and Shannon index of mixed forest were significantly higher than those of Pinus massoniana and Betula luminifera forest. On the whole, the diversity of fungal community was as follows:non-forested shrub grassland > mixed forest > Pinus massoniana forest > Betula luminifera forest. The contents of soil organic carbon (SOC) and total nitrogen (TN) in the mixed forest and Betula luminifera pure forest were significantly higher than those in non-forested shrub grassland. Mantel test showed that fungal community structure was significantly correlated with total phosphorus (TP), SOC, ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N), TN, pH and water content (SWC) (P<0.05). Soil SOC, TN and pH had the greatest impact on fungal community structure. Redundancy analysis (RDA) showed Ascomycetes were positively correlated with pH, TP, SOC, TN, AP and NO3--N content; Basidiomycetes and Mortierella were mainly positively correlated with NH4+-N, and negatively correlated with pH, TP, SOC, TN, AP and NO3--N. There was a positive correlation between Rozellomycota and SWC. In conclusion, compared with pure coniferous forest, coniferous and broad-leaved mixed forest in rocky desertification area can significantly improve the diversity of fungal community by increasing soil SOC and TN, and promote the improvement of soil fertility. The results can provide basis for artificial vegetation restoration and soil fertility management in rocky desertification area. 参考文献 相似文献 引证文献

Soil Organic Carbon in Forest and Other Land Use Types at Bengkulu City, Indonesia

Conversion of natural forest into agricultural land uses has decreased soil organic carbon (SOC) and increased carbon emission into the atmosphere, but proper management of agricultural land can sequester carbon from the atmosphere and increase the SOC. This study was conducted to estimate the SOC content and storage in a forest, agroforestry land, oil palm plantation, and agricultural experimental field and to analyze the correlation between the SOC and other soil characteristics at Bengkulu City, Indonesia. Soil were sampled from the following depths: 0–10 cm, 10–20 cm, and 20–30 cm. The biomass of litter and ground cover was also sampled. This study found that the forest had the highest average SOC content from the three depths, and 0–30 cm depth SOC storage, while the agroforestry system had the lowest of both SOC content and storage. The 0–10 cm depth had the highest SOC content and storage, while the 20–30 cm depth had the lowest of both variables. The SOC was positively correlated with litter biomass, field capacity, exchangeable potassium, cation exchange capacity, and negatively correlated with bulk density and exchangeable calcium, but not correlated with total nitrogen and available phosphorus. High litter biomass input is the key to the maintenance of high SOC.

Decreased Soil Organic Carbon under Litter Input in Three Subalpine Forests

Soil organic carbon (SOC) is the largest terrestrial organic carbon pool. Plant litter is an important source of SOC, but the knowledge gap between SOC fractions and plant litter input remains inconsistent. Here, a litter input control experiment was conducted at three subalpine forest types (coniferous forest, mixed forest, and broadleaved forest). We assessed the variations of total organic C, active organic C (easily oxidizable C, labile organic C), recalcitrant organic C, and microbial biomass C under litter input or removal. The results showed that soil total organic C decreased greatly under litter input. It was mainly caused by the change of easily oxidizable C and labile C, while the influence of recalcitrant C was small. At the same time, this effect varied among different forest types. Among them, the effect of litter input on SOC was weak and slow in the coniferous forest with low-quality litter input, while a quick effect was observed in the mixed and broadleaved forests with high-quality litter input. Microbial biomass C declined under litter input in most cases, and its variation was strongly controlled by soil temperature and freeze-thaw events. Overall, our results provide new evidence that forest type would strongly control SOC dynamics, in concert with litter quality shifts, with potential consequences for long-term C sequestration. We highlighted that litter input could reduce microbial biomass carbon which might limit the native SOC decomposition, but the loss of active C ultimately changed the SOC in the subalpine forests. It suggested that the interaction of multiple mechanisms should be considered in the study of SOC in this region.

National-scale 3D mapping of soil organic carbon in a Japanese forest considering microtopography and tephra deposition

Geographic information on soil organic carbon (SOC) is important for climate change research and understanding the global carbon cycle. At present, this information is limited for forest soils in mountainous regions that have complex topographies and are affected by tephra deposition. This study predicted the SOC concentration (OC), bulk density (BD), apparent rock coarse fraction (CF), and SOC stock (OCS) at 0–5, 5–15, and 15–30 cm in the soil horizon for the forested areas (ca. 230 000 km2) of Japan. This was carried out with a 10 m grid resolution using a digital soil mapping (DSM) approach. To determine the appropriate spatial prediction model, we evaluated the accuracy of a two dimensional approach for ordinary kriging (OK) and regression kriging (RK), and a three dimensional approach for random forest model (RF). The RF was based on topography, climate and vegetation factors (RFenv), distance and direction from 152 volcanos (RFenv+vol), distance from survey points (RFenv+sp); these factors were also combined (RFall) as explanatory attributes. The results demonstrated an improvement in the average root mean square errors (RMSEs) of RFenv+vol, RFenv+sp, and RFall by approximately 12%, 14%, 5%, and 21% for OC, BD, CF, and OCS using 10-fold cross-validation on a site-by-site basis, respectively, compared with OK. Based on the relatively small difference in improvement among RFenv+vol, RFenv+sp, and RFall (<0.5%), and the considerably high computational cost of RFenv+sp and RFall, RFenv+vol was considered as the appropriate model for the area. The R2 of RFenv+vol was calculated at 0.59, 0.44, 0.30, and 0.38 in OC, BD, CF, and OCS, respectively, using 10-fold cross validation on a site-by-site basis. The predicted map by RFenv+vol accurately reproduced the large spatial variation in OCS at small watershed, regional, and national scales; this have been derived from the effect of microtopography, tephra deposition, and the gradient of temperature with latitude, respectively. A larger OCS was predicted to accumulate on the ridges, highland slopes, near volcanos, and higher latitudes than at other areas. The mean OCS was estimated to be 7.6 kg·m−2 for a soil depth of 0–30 cm in Japanese forests. The results also suggest that the fine-scale three dimensional random forest approach using the distances from volcanoes showed promise for regional-scale OCS prediction. This approach was considered particularly effective in hills and mountainous areas that are strongly exposed to tephra deposition, this includes the Pacific Rim regions and other volcanic countries.

The magnitude and causes of edge effects on soil organic carbon stocks within and across urban to rural forest patches

Landscape fragmentation has created large areas of forest edge. Understanding how soil organic carbon (SOC) stocks within forest edges respond to fragmentation is essential to assess carbon budgets; however, the causes and magnitude of edge effects on SOC stocks have been poorly characterized. Here, we quantify the edge effects on SOC stocks within and across urban to rural forest patches from three fragmented urban forests to a large patch of rural forest. The SOC stocks within 20 m of the rural forest edge (1.86kgCm−2) is on average 80% lower than the interiors of rural forest (10.47kgCm−2). We found that biotic factors, including annual litterfall mass (R2 > 0.94), peak leaf area index (R2 > 0.92), and fine-root mass density (R2 > 0.77), explained the spatial variation in SOC stocks within the rural forest. In urban forests, human activities at forest edges led to contrasting edge effects on SOC stocks, for instance, the SOC stocks at the east edges (4.74 kgC m−2) were 56% greater than at the west edges (3.03 kgC m−2) explained by the adjacent land uses (e.g., paved roads vs. non-paved soils) and in-situ litterfall management. We also found significant differences in summer soil temperature (ΔTS > 2.8 °C) and soil moisture (ΔVWC > 0.05 m3 m−3) between the east and west forest edges. Our results reveal that the factors responsible for the edge effects on SOC stocks in rural forests are biotic factors, while heterogeneous human activities at the local scale lead to complex edge effects on urban forest SOC stocks.

Potential relationships of selected abiotic variables, chemical elements and stand characteristics with soil organic carbon in spruce and beech stands

Increasing attention is given to carbon sequestration in forest soil with regard to climate change and the mitigation of its impacts; therefore, it is very important to know which parameters and variables could influence carbon sequestration and throw light on their relationships. The aim of this study is to assess the role of abiotic variables, chemical elements and stand parameters in soil carbon sequestration, and clarify which of these could affect soil organic carbon (SOC) content in the surface mineral horizon in Norway spruce and European beech stands in Czech Republic. We analyzed 81 monitoring plots within pure and mixed stands of spruce and beech with different degrees of forest naturalness. In each monitoring plot, SOC content, chemical elements (content of bound forms of oxides: tFe, tAl, tCa, tMg, tK, tMn, tP, tN) and related variables (BS, pH, C/N) were measured. The effect of these variables, including abiotic variables (elevation, temperature, precipitation, duration of growing season and soil group) on SOC content was tested, and differences between represented stands (natural vs. unnatural, pure vs. mixed, spruce vs. beech) were analyzed. The results showed that elevation has a positive relationship to SOC content. Of the studied chemical elements and related variables, only tN content was significantly related to SOC content. A positive relationship was also demonstrated between forest naturalness and SOC content. The highest SOC and tN contents were observed in pure natural Norway spruce stands, which likely play a very important role in SOC sequestration. In the context of the current issue of unnatural Norway spruce stands in the Czech Republic, a higher SOC content was found in mixed natural European beech stands than in either pure or mixed unnatural Norway spruce stands. Therefore, replacing the unnatural Norway spruce stands in the study area with mixed natural European beech stands could represent a viable alternative to current forest management in terms of soil carbon sequestration, especially in the context of global climate change and spruce dieback.

Variations in Soil Organic Carbon Stocks under Different Land-Use Categories in Subtropical Ecosystems of Kashmir

Abstract Quantification of soil organic carbon (SOC) stocks in different land uses holds vital significance because of its implications regarding carbon sequestration as the largest terrestrial carbon pool. The current study was conducted to quantify and compare SOC stocks in forest land, agricultural land, and barren land-use categories in the subtropical ecosystems of the Himalayan foothills in Kashmir. Results showed the highest SOC value in the forest soil (75 ± 11.1 Mg C ha−1) followed by agricultural soil (58 ± 7.0 Mg C ha−1) and barren land (44 ± 6.5 Mg C ha−1). SOC stocks in different land uses showed broad variations with values as high as 106 ± 11.3 Mg C ha−1 (forest soils) and as low as 14.1 ± 7.1 Mg C ha−1 (barren land). The forest SOC values responded significantly to species composition with the highest values in Pinus roxburghii Sarg. pure stands as compared with broad leaved forests. Multivariate ordination analyses revealed that the variations in SOC stocks were significantly correlated with vegetation type, altitude, and soil bulk density. The study has identified anthropogenic disturbances as a major factor deteriorating local SOC stocks and recommends immediate soil restoration efforts to enhance the ecological significance of soils as vital regional carbon sinks.

Factors controlling soil organic carbon stocks in hardwood floodplain forests of the lower middle Elbe River

We assessed key relationships of soil organic carbon (SOC) stocks to hydromorphic features, soil texture, C/N ratio, pH, and forest age in hardwood floodplain forests. Floodplain ecosystems play a significant role in the global carbon cycle, particularly due to their SOC storage potential. Interactions between heterogeneous micro-relief and anthropogenically affected vegetation and the hydrologic situation of floodplains make predicting SOC stocks difficult without field validation. Especially within hardwood floodplain forests, the controlling factors for SOC storage remain understudied, whereas these floodplain types can be the largest reservoir for carbon and have a substantial SOC sequestration potential. To determine the controlling factors for SOC storage, we selected 38 hardwood floodplain forest and 11 floodplain grasslands of the lower middle Elbe River and categorized them according to vegetation type (grassland, young forest, or old forest) and hydrologic situation (low-lying or high elevated and active or former floodplain). Profile SOC stocks were determined to a depth of 1 m, and topsoil SOC stocks were related to vegetation and soil characteristics, particularly pedological traits (e.g., hydromorphic features).Forest SOC stocks ranged between 99 and 149 t ha−1. SOC stocks decreased with depth throughout all categories and were unaffected by vegetation type within the same hydrologic situation. Vegetation parameters such as age, basal area, or leaf litter carbon stock had no direct effect on SOC stocks. An active connection to the river had the strongest effect on SOC stocks, with former floodplain sites storing 33% less SOC than the active sites. Within the active floodplains, low sites stored 50% more SOC than high sites. This effect was mainly controlled by relief-affected features such as flooding duration and fine texture, which also were the strongest univariate predictors for SOC stocks (R2 = 0.39 and 0.63). A multiple linear regression showed that fine texture, pH, C/N ratio and forest age can be used to explain 86% of variance in SOC stocks.We conclude that proxies for relief and sedimentation (i.e., hydromorphic features, flooding duration, soil texture, C/N ratio, and pH) are the strongest factors controlling SOC stocks in hardwood floodplain forests. Both can be related to allochthonous carbon inputs, increasing SOC stabilization through the accumulation of fine soil particles, and decreasing aerobic carbon mineralization potential through oxygen scarcity, while vegetation plays only a subordinate role.

Distinct storage mechanisms of soil organic carbon in coniferous forest and evergreen broadleaf forest in tropical China

The impact of human activities on soil carbon (C) storage in tropical forests has aroused wide concern during the past decades, because these ecosystems play a key role in ameliorating global climate change. However, there remain uncertainties about how land-use history alters soil organic carbon (SOC) stability and storage in different forests. In this study, we measured the C content and mass distributions of soil aggregates, density fractions, mineral-bound C and microbial biomass C in the organic horizon, 0-10 cm and 10-20 cm soil layers in coniferous forest and evergreen broadleaf forest at Dinghushan Biosphere Reserve in tropical China. The broadleaf forest had larger SOC stocks than the coniferous forest, but the proportion of SOC stored in different density fractions at 0-10 cm soils was similar between forest types, while a greater proportion of SOC was stored in microaggregates in the coniferous forest. Most of the SOC was held as light fraction C in the organic horizon in the coniferous forest, whereas the concentrations of mineral-bound C were higher in the broadleaf forest. These findings indicate clear differences in the protection of SOC between broadleaf and coniferous forests growing on the same soil type. We propose that historic conversion of broadleaf forest to coniferous forest has reduced soil C sequestration capacity by altering the diversity and quality of plant inputs to the soil, which in turn affected macroaggregate formation, soil chemical properties and microbial biomass. Our results thus demonstrate that changes in forest tree species composition could have long-lasting effects on soil structure and carbon storage, providing crucial evidence for policy decisions on forest carbon sink management.

Silvicultural Interventions Drive the Changes in Soil Organic Carbon in Romanian Forests According to Two Model Simulations

We investigated the effects of forest management on the carbon (C) dynamics in Romanian forest soils, using two model simulations: CBM-CFS3 and Yasso15. Default parametrization of the models and harmonized litterfall simulated by CBM provided satisfactory results when compared to observed data from National Forest Inventory (NFI). We explored a stratification approach to investigate the improvement of soil C prediction. For stratification on forest types only, the NRMSE (i.e., normalized RMSE of simulated vs. NFI) was approximately 26%, for both models; the NRMSE values reduced to 13% when stratification was done based on climate only. Assuming the continuation of the current forest management practices for a period of 50 years, both models simulated a very small C sink during simulation period (0.05 MgC ha−1 yr−1). Yet, a change towards extensive forest management practices would yield a constant, minor accumulation of soil C, while more intensive practices would yield a constant, minor loss of soil C. For the maximum wood supply scenario (entire volume increment is removed by silvicultural interventions during the simulated period) Yasso15 resulted in larger emissions (−0.3 MgC ha−1 yr−1) than CBM (−0.1 MgC ha−1 yr−1). Under ‘no interventions’ scenario, both models simulated a stable accumulation of C which was, nevertheless, larger in Yasso15 (0.35 MgC ha−1 yr−1) compared to CBM-CSF (0.18 MgC ha−1 yr−1). The simulation of C stock change showed a strong “start-up” effect during the first decade of the simulation, for both models, explained by the difference in litterfall applied to each scenario compared to the spinoff scenario. Stratification at regional scale based on climate and forest types, represented a reasonable spatial stratification, that improved the prediction of soil C stock and stock change.

Land use and management effects on soil carbon in U.S. Lake States, with emphasis on forestry, fire, and reforestation.

There is growing need to quantify and communicate how land use and management activities influence soil organic carbon (SOC) at scales relevant to, and in the tangible control of landowners and forest managers. The continued proliferation of publications and growth of data sets, data synthesis and meta-analysis approaches allows the application of powerful tools to such questions at ever finer scales. In this analysis, we combined a literature review and effect-size meta-analysis with two large, independent, observational databases to assess how land use and management impact SOC stocks, primarily with regards to forest land uses. We performed this work for the (Great Lakes) U.S. Lake States, which comprise 6% of the land area, but 7% of the forest and 9% of the forest SOC in the United States, as the second in a series of ecoregional SOC assessments. Most importantly, our analysis indicates that natural factors, such as soil texture and parent material, exert more control over SOC stocks than land use or management. With that for context, our analysis also indicates which natural factors most influence management impacts on SOC storage. We report an overall trend of significantly diminished topsoil SOC stocks with harvesting, consistent across all three data sets, while also demonstrating how certain sites and soils diverge from this pattern, including some that show opposite trends. Impacts of fire grossly mirror those of harvesting, with declines near the top of the profile, but potential gains at depth and no net change when considering the whole profile. Land use changes showing significant SOC impacts are limited to reforestation on barren mining substrates (large and variable gains) and conversion of native forest to cultivation (losses). We describe patterns within the observational data that reveal the physical basis for preferential land use, e.g., cultivation of soils with the most favorable physical properties, and forest plantation establishment on the most marginal soils, and use these patterns to identify management opportunities and considerations. We also qualify our results with ratings of confidence, based on their degree of support across approaches, and offer concise, defensible tactics for adapting management operations to site-specific criteria and SOC vulnerability.

TransparC2U–A two-pool, pedology oriented forest soil carbon simulation model aimed at user investigations of multiple uncertainties

The dynamic character of forest soil organic carbon (SOC) stocks is demonstrated in the simulation model TransparC2U. The model has up to 10 layers, each with two pools with first order kinetics running for 40 years. The model is aimed at teaching soil science to a broad audience in academia, extension services, secondary schools and public life. The learning objective of the model is to bring about an understanding of SOC dynamics over time, uncertainty, and the complexity of the soil profile with its pedogenesis represented by soil horizons. The user works in an illustrated spreadsheet calculator with options for instant and interactive exploration of the multiple uncertainties and constraints on forest SOC stocks. The user divides the initial SOC stock in each horizon into two pools, Cnew with faster mineralization, and Cold with very slow mineralization, based on their knowledge of horizon designations and stabilization mechanisms.Data from 23 soil Nordic and Baltic forest soil profiles with horizons characterized by chemical and physical properties are available. Site information to the user intended for reflections on choosing parameter values includes soil classification, tree species, climate, stand age, soil nutrient status and properties that govern physical or chemical protection of soil C (extractable phosphorus (P), total nitrogen (N), subsoil clay content and extractable iron (Fe)). Other changeable inputs are the average annual aboveground litter fall, root litter allocation to individual soil horizons as a fraction (%) of aboveground input, and decomposition rates of each pool. The game played aims for preservation of the initial C stock by manual calibration by the user. The sensitivity of the potential C change (dC ±) is tested by changing the parameter values and watching the effects on model results, i.e. C stocks in each horizon over time. The sensitivity analysis can involve the uncertainty of the input, the initial C content in each horizon, the fraction of Cold and the turnover rates that represent heterotrophic respiration.The processes representing C input to deeper horizons (roots and exudates), bioturbation by macrofauna, as well as podzolisation provide optional transfer of C between the forest floor and mineral soil layers when judged appropriate by the user based on the site and stand information.The user may interpret results of the simulation by examining the outputs of total C stock change over 40 years by inspecting total N and P requirements for new litter inputs against potentially available current and future N and P stocks in the soil and the capacity of C binding by subsoil clay and Fe-oxides. It highlights the physical and chemical soil properties required to justify the simulated fate of new and old SOC and the sensitivity of controlling parameters on a decadal timescale to the user.

Impact of European Beech Forest Diversification on Soil Organic Carbon and Total Nitrogen Stocks–A Meta-Analysis

Drought-sensitive European beech forests are increasingly challenged by climate change. Admixing other, preferably more deep-rooting, tree species has been proposed to increase the resilience of beech forests to drought. This diversification of beech forests might also affect soil organic carbon (SOC) and total nitrogen (TN) stocks that are relevant for a wide range of soil functions and ecosystem services, such as water and nutrient retention, filter functions and erosion control. Since information of these effects is scattered, our aim was to synthesize results from studies that compared SOC/TN stocks of beech monocultures with those of beech stands mixed with other tree species as well as monocultures of other tree species. We conducted a meta-analysis including 38 studies with 203, 220, and 160 observations for forest floor (i.e., the organic surface layer), mineral soil (0.5 m depth) and the total soil profile, respectively. Monoculture conifer stands had higher SOC stocks compared to monoculture beech in general, especially in the forest floor (up to 200% in larch forests). In contrast, other broadleaved tree species (oak, ash, lime, maple, hornbeam) showed lower SOC stocks in the forest floor compared to beech, with little impact on total SOC stocks. Comparing mixed beech-conifer stands (average mixing ratio with regard to number of trees 50:50) with beech monocultures revealed significantly higher total SOC stocks of around 9% and a smaller increase in TN stocks of around 4%. This equaled a SOC accrual of 0.1 Mg ha−1 yr−1. In contrast, mixed beech-broadleaved stands did not show significant differences in total SOC stocks. Conifer admixture effects on beech forest SOC were of additive nature. Admixing other tree species to beech monoculture stands was most effective to increase SOC stocks on low carbon soils with a sandy texture and nitrogen limitation (i.e., a high C/N ratio and low nitrogen deposition). We conclude that, with targeted admixture measures of coniferous species, an increase in SOC stocks in beech forests can be achieved as part of the necessary adaptation of beech forests to climate change.

Forest Soil Organic Carbon Stocks of Tessala Mount in North-West Algeria-Preliminary Estimates

Mountainous forests in Algeria are severely affected by climate change. The degradation is exacerbated by overgrazing, deforestation, and poor land management linked to the harsh topographical conditions of the mountain agrosystem. These conditions have influenced the turnover of the soil organic matter and thus the SOC stocks storage. This study aims to investigate the average of organic carbon stored in forest soils of Tessala Mount in Algeria and to examine the influence of different plant formations alongside with geographical characteristics and soil physicochemical properties on the amount of carbon stored in the soil. We estimated the critical threshold, the saturation point, and the organic carbon deficit of soils. The correlation between geographical characteristics and soil physicochemical properties and soil organic carbon stocks was determined using principal component analysis and other statistical tools. The results of the study show that the organic carbon stock in soils of Tessala Mount area has an average value of 77.4 t ha−1. The maximum average of SOC stocks (121 t ha−1) of 0–30 cm depth was noted under dense matorral of green and kermes oak followed by sparse garrigue with a value of 112 t ha−1. The soil organic carbon stock in Tessala region was positively correlated with coarse silt, elevation, and northern exposure, but negatively with calcium carbonates contents. The current carbon contents of Tessala topsoil are 22 g C kg−1 which is very low and closer to the critical threshold (11 g C kg−1) whose estimate was based on their clay and silt content. The estimated maximum storage capacity is 160 g C kg−1. The preliminary estimate of the forest soils organic carbon stock of Tessala Mount under current natural conditions indicates an alarming situation with a low rate close to the critical threshold, thus exposing this area to further and stronger degradation.

Soil carbon accumulation with increasing temperature under both managed and natural vegetation restoration in calcareous soils

Vegetation restoration has been proposed as an effective strategy for increasing soil organic carbon (SOC) sequestration. However, the responses of SOC to managed and natural vegetation restoration strategies at a large scale are poorly understood due to the varying SOC components and changing climatic conditions. Here, we measured bulk SOC, particulate organic carbon (POC), and mineral-associated organic carbon (MOC) after 15 years of vegetation restoration along an elevation gradient with a corresponding temperature gradient in the calcareous soils of karst region, Southwest China. We compared managed plantation forest and naturally recovered shrubland vegetation restoration strategies, using cropland and mature forest as references. Overall, we found that the SOC and POC densities in both plantation forest and shrubland were significantly higher than in the cropland but lower than in the mature forest. There were no significant differences in the SOC pool between the plantation forest and shrubland. Furthermore, the relative changes in the SOC and POC densities increased with increasing mean annual temperature in the plantation forest and shrubland. Our results showed that both vegetation restoration strategies, characterized by higher soil microbial abundance and exchangeable Ca concentration, were beneficial to POC but not MOC accumulation, and sufficiently compensated SOC decomposition at lower elevation with higher MAT. Our results highlight the potential of both vegetation restoration strategies for promoting SOC accumulation in warmer karst regions and emphasize the necessity to understand soil carbon stabilization mechanisms in calcareous soils.

National-scale spectroscopic assessment of soil organic carbon in forests of the Czech Republic

Soil Carbon (C) is central to the functioning of ecosystems and climate change mitigation. It represents the largest terrestrial pool and much of it, is stored in forest soils. Soil Organic Carbon (SOC) in a forest varies not only laterally, but also vertically (i.e., with depth). However, the SOC content of forest soil horizons has not been investigated over large scales, despite its importance for framing our understanding of soil function. Visible–Near Infrared (vis–NIR) reflectance spectroscopy enables rapid and cost-effective examination of forest SOC distribution, both laterally and vertically. This study aims to evaluate the potential of vis–NIR spectroscopy for classifying and predicting the SOC concentration of organic and mineral horizons in forests of the Czech Republic. We investigated 1080 forest sites across the country, each with five soil horizons, representing the Litter (L), Fragmented (F), and Humus (H) organic horizons, as well as the A1 (depth of 2–10 cm) and A2 (depth of 10–40 cm) mineral horizons. We, then, used Support Vector Machines (SVMs) to classify the soil horizons based on their spectra and also to model the SOC concentration of (i) the profile (organic and mineral horizons together), (ii) only the organic horizons, (iii) only the mineral horizons, and (iv) each individual horizon separately. The models were validated using 10-repeated 10-fold cross-validation. Results show that the SVM with radial basis kernel could accurately classify the soil horizons (Correct Classification Rate (CCR) of 70% and Kappa coefficient of 0.63). The SOC model developed for the soil profile performed well (R2 = 0.76 and RMSE = 1.63%). The model of the combined organic horizons was considerably more accurate than that of the combined mineral horizons (R2 = 0.78 and R2 = 0.53, respectively). Estimates of SOC in the individual soil horizons had R2 values greater than 0.63 but those of the F and A1 models were better with R2 > 0.70. The study indicates that vis–NIR spectroscopy can effectively characterize the SOC concentration of the highly variable forest soil horizons in the Czech Republic.

Seasonality, drivers, and isotopic composition of soil CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes from tropical forests of the Congo Basin

Abstract. Soil respiration is an important carbon flux and key process determining the net ecosystem production of terrestrial ecosystems. To address the lack of quantification and understanding of seasonality in soil respiration of tropical forests in the Congo Basin, soil CO2 fluxes and potential controlling factors were measured annually in two dominant forest types (lowland and montane) of the Congo Basin over 2 years at varying temporal resolution. Soil CO2 fluxes from the Congo Basin resulted in 3.45 ± 1.14 and 3.13 ± 1.22 µmol CO2 m−2 s−1 for lowland and montane forests, respectively. Soil CO2 fluxes in montane forest soils showed a clear seasonality with decreasing flux rates during the dry season. Montane forest soil CO2 fluxes were positively correlated with soil moisture, while CO2 fluxes in the lowland forest were not. Smaller differences of δ13C values of leaf litter, soil organic carbon (SOC), and soil CO2 indicated that SOC in lowland forests is more decomposed than in montane forests, suggesting that respiration is controlled by C availability rather than environmental factors. In general, C in montane forests was more enriched in 13C throughout the whole cascade of carbon intake via photosynthesis, litterfall, SOC, and soil CO2 compared to lowland forests, pointing to a more open system. Even though soil CO2 fluxes are similarly high in lowland and montane forests of the Congo Basin, the drivers of them seem to be different, i.e., soil moisture for montane forest and C availability for lowland forest.

A New Approach Using Modeling to Interpret Measured Changes in Soil Organic Carbon in Forests; The Case of a 200 Year Pine Chronosequence on a Podzolic Soil in Scotland

Scotland is continuing to afforest land in order to combat climate change, but the long-term capacity for carbon sequestration in forest soils is still uncertain. Soil organic carbon stock changes were studied in a >120 year-old Scots pine chronosequence and adjacent grassland sites on podzolic soils. Significant differences were observed in the top organic soil horizons, while no changes were noted in the deeper mineral soil horizons. Simulations with the RothC-26.3 model revealed that pine forests could lose a significant amount of soil organic carbon through management operations. The lowest modelled stocks of soil organic carbon were not in the young sites (0-25 years old), but at 43 years since reforestation. Using measured data from our study site, simulations of grassland afforestation suggested that accumulation of organic carbon under forest is mainly in the organic horizons, while the deeper mineral soil horizons are likely to become depleted in soil organic carbon compared to grasslands. Our simulations suggest that afforestation of grasslands would increase overall soil carbon stocks but deplete the more stable carbon pools in the deeper mineral soils, which is not a desirable outcome in the context of climate change. The measurements provide comparative estimates of SOC in grassland and forestry sites at steady state; few studies provide these comparative measures. This study presents a new method for simulating soils that are accumulating carbon using the assumption of steady state with respect to the rate of accumulation. The approach has never been presented before and could have important implications for estimates of impacts of land use and climate change on the large SOC stocks held in highly organic soils. Subsequent simulations provide a new method for interpolating measurements that allow the losses due to management operations to be determined.