Soil Organic Matter Accumulation Research Articles

Microbial carbon use efficiency promotes global soil carbon storage

Soils store more carbon than other terrestrial ecosystems1,2. How soil organic carbon (SOC) forms and persists remains uncertain1,3, which makes it challenging to understand how it will respond to climatic change3,4. It has been suggested that soil microorganisms play an important role in SOC formation, preservation and loss5–7. Although microorganisms affect the accumulation and loss of soil organic matter through many pathways4,6,8–11, microbial carbon use efficiency (CUE) is an integrative metric that can capture the balance of these processes12,13. Although CUE has the potential to act as a predictor of variation in SOC storage, the role of CUE in SOC persistence remains unresolved7,14,15. Here we examine the relationship between CUE and the preservation of SOC, and interactions with climate, vegetation and edaphic properties, using a combination of global-scale datasets, a microbial-process explicit model, data assimilation, deep learning and meta-analysis. We find that CUE is at least four times as important as other evaluated factors, such as carbon input, decomposition or vertical transport, in determining SOC storage and its spatial variation across the globe. In addition, CUE shows a positive correlation with SOC content. Our findings point to microbial CUE as a major determinant of global SOC storage. Understanding the microbial processes underlying CUE and their environmental dependence may help the prediction of SOC feedback to a changing climate.

Pedogenesis at the coastal arid-hyperarid transition deduced from a Late Quaternary chronosequence at Paposo, Atacama Desert

Under hyperarid climate conditions, pedogenesis is driven by the atmospheric deposition and subsequent accumulation of easily to moderately soluble salts forming extreme types of Aridisols. In contrast, the processes and timescales of soil formation in coastal desert environments are as yet not well understood. Therefore, a soil chronosequence at the arid-hyperarid transition in the south-central coastal Atacama Desert is investigated. We measured physicochemical soil parameters of shallow soil profiles on four generations of a multi-stage alluvial fan system, assisted by micromorphological analysis, allowing to deduce the soil-forming processes. We further established a geochronological framework by applying 10Be cosmogenic nuclide exposure dating on the abandoned surface generations, which allowed to infer the timescales for soil formation. The results indicate initial yet clearly identifiable pedogenesis occurring since MIS 5e–c. Along the Late Quaternary chronosequence, physicochemical soil properties show decreasing trends with growing age for the median grain size, salinity, long-term pH development, and CaCO3 contents. Contrarily, organic carbon, the ratio of organic to total phosphorus, the redness, and the contents of total and poorly crystalline pedogenic iron oxides tend to increase with age. This provides evidence for soil formation under an arid to hyperarid coastal climate characterized by (i) redistribution of salts by leaching causing topsoil desalinization; (ii) decalcification coupled with (iii) dealkalinization in totally decalcified horizons; (iv) accumulation of soil organic matter; (v) initial rubification through formation of pedogenic iron oxides (i.e. hematite); and (vi) initial loamification that, in turn, might have impeding effects on the translocation of soil constituents on timescales larger than 105 a. Furthermore, in situ pedogenesis might be superimposed considerably by aeolian dust influx. At Atacama’s south-central coast, the state of pedogenic alteration scales with the cumulative precipitation received throughout the entire Late Quaternary, yet evolved strongest between MIS5 and the MIS4/3-transition.

Distribution of Mercury in Drained Peatlands as the Effect of Secondary Transformation of Soil Organic Matter

Peat organic soils play a major role in the accumulation of soil organic matter (SOM) and the mercury (Hg) cycle. Large mercury resources in peatlands can be a source of methylmercury for many decades and centuries, even if deposition is significantly reduced. The organic matter of peatland soils drained for agricultural use is subject to secondary transformation, which may affect the accumulation and resources of mercury. The aim of our work is to assess the secondary transformation of organic matter in the soils of drained peatlands of the temperate climate zone and to examine whether it affects mercury resources and profile distribution in organic soils. Field research was conducted in peatlands located in eastern Poland. In the present study, evaluation of secondary transformations occurring after drainage was based on observations of soil morphological characteristics, physical and chemical properties as well as fractional composition of organic matter of the identified soil horizons (to depth 70 cm). Standard cold vapor atomic absorption spectrometry (CV-AAS) was used to measure the total mercury content. In our research, we found a significant effect of the secondary transformation of organic matter occurring in drained peatlands of the temperate climate zone on the total mercury content and stock in soils. The highest content and differentiation of mercury occurred in murshic horizons (up to a maximum depth of 43 cm). The average mercury content of the distinguished soil horizons is grouped in the following series (in μg kg−1): M1 (212.0) > M2 (182.8) > M3 (126.3) > Pt (84.9). The mercury stock, up to a depth of 70 cm in the tested soils, ranged from 17.5 to 39.6 mg m−2. As much as 82.2% of soil mercury was found in the upper murshic horizons. We found strong correlations between soil properties characteristically variable in the secondary transformation process and total mercury content. The increased content of humic substances in murshic horizons caused a significant increase in the total mercury content. Our research is of great importance for soil monitoring, as the amount of determined mercury was greatly influenced by the depth of sampling (up to 25 cm). The results of the research should be taken into account when planning the restoration of peatlands of the temperate climate zone. There is a potential risk that elevated mercury concentrations in the upper murshic horizons may be a source of methylmercury for a long period of time. In peat soils with a high concentration of mercury, the risk of contamination with this toxic metal should be determined before re-irrigation.

Long-term (>90 years) wastewater irrigation effect on the pore characteristics and stability of soil aggregates

Wastewater (WW) agricultural irrigation is becoming a common practice as an alternative to water scarcity. However, WW irrigation may affect the soil structure at different hierarchical levels. This issue was tackled by evaluating the long-term (>90 years) WW irrigation effects on soil structure. Samples of Ap and Ah horizons from eight rainfed and eight WW-irrigated plots were collected for physicochemical characterization. Undisturbed samples were analyzed for aggregate stability, and the pore space of small macroaggregates (0.5–1 mm) from Ah horizons of three rainfed and three WW-irrigated plots was analyzed by x-ray microtomography. Long-term WW-irrigated plots had higher contents of C (Ap = 2.54%; Ah = 1.64%) and N (Ap = 0.24%; Ah = 0.16%) compared to rainfed soils, as well as higher aggregates stability (mean weight diameter = 23.6 mm, p = 0.001). However, soil organic matter accumulation was not the main driver of the higher aggregate stability in WW-irrigated soils (Spearman correlation coefficients of 0.467 and 0.476 for organic C and total N, respectively). It was proposed that a combination of factors including SOM and easily degradable OM (C/N = 2.10) input from WW was the reason for this higher stability. The results did not allow one to conclude on the long-term effect of WW irrigation on the microstructural pore space because the scatter in the data of the rainfed samples was high. Considering a higher number of samples may address this problem. Nevertheless, the findings of this research improve our understanding of the effects of WW irrigation on soil structure and provide a better assessment of the benefits and risks associated with this practice.

Consistent microbial and nutrient resource island patterns during monsoon rain in a Chihuahuan Desert bajada shrubland

AbstractIn dryland soils, spatiotemporal variation in surface soils (0–10 cm) plays an important role in the function of the “critical zone” that extends from canopy to groundwater. Understanding connections between soil microbes and biogeochemical cycling in surface soils requires repeated multivariate measurements of nutrients, microbial abundance, and microbial function. We examined these processes in resource islands and interspaces over a two‐month period at a Chihuahuan Desert bajada shrubland site. We collected soil in Prosopis glandulosa (honey mesquite), Larrea tridentata (creosote bush), and unvegetated (interspace) areas to measure soil nutrient concentrations, microbial biomass, and potential soil enzyme activity. We monitored the dynamics of these belowground processes as soil conditions dried and then rewetted due to rainfall. Most measured variables, including inorganic nutrients, microbial biomass, and soil enzyme activities, were greater under shrubs during both wet and dry periods, with the highest magnitudes under mesquite followed by creosote bush and then interspace. One exception was nitrate, which was highly variable and did not show resource island patterns. Temporally, rainfall pulses were associated with substantial changes in soil nutrient concentrations, though resource island patterns remained consistent during all phases of the soil moisture pulse. Microbial biomass was more consistent than nutrients, decreasing only when soils were driest. Potential enzyme activities were even more consistent and did not decline in dry periods, potentially helping to stimulate observed pulses in CO2 efflux following rain events observed at a co‐located eddy flux tower. These results indicate a critical zone with organic matter cycling patterns consistently elevated in shrub resource islands (which varied by shrub species), high decomposition potential that limits soil organic matter accumulation across the landscape, and nitrate fluxes that are decoupled from the organic matter pathways.

Microbial necromass under global change and implications for soil organic matter.

Microbial necromass is an important source and component of soil organic matter (SOM), especially within the most stable pools. Global change factors such as anthropogenic nitrogen (N), phosphorus (P), and potassium (K) inputs, climate warming, elevated atmospheric carbon dioxide (eCO2 ), and periodic precipitation reduction (drought) strongly affect soil microorganisms and consequently, influence microbial necromass formation. The impacts of these global change factors on microbial necromass are poorly understood despite their critical role in the cycling and sequestration of soil carbon (C) and nutrients. Here, we conducted a meta-analysis to reveal general patterns of the effects of nutrient addition, warming, eCO2 , and drought on amino sugars (biomarkers of microbial necromass) in soils under croplands, forests, and grasslands. Nitrogen addition combined with P and K increased the content of fungal (+21%), bacterial (+22%), and total amino sugars (+9%), consequently leading to increased SOM formation. Nitrogen addition alone increased solely bacterial necromass (+10%) because the decrease of N limitation stimulated bacterial more than fungal growth. Warming increased bacterial necromass, because bacteria have competitive advantages at high temperatures compared to fungi. Other global change factors (P and NP addition, eCO2 , and drought) had minor effects on microbial necromass because of: (i) compensation of the impacts by opposite processes, and (ii) the short duration of experiments compared to the slow microbial necromass turnover. Future studies should focus on: (i) the stronger response of bacterial necromass to N addition and warming compared to that of fungi, and (ii) the increased microbial necromass contribution to SOM accumulation and stability under NPK fertilization, and thereby for negative feedback to climate warming.

Estimation of Carbon Stocks and Stabilization Rates of Organic Matter in Soils of the «Ladoga» Carbon Monitoring Site

The establishment of a network of monitoring sites (term in Russian—«carbon polygons») for monitoring climatic processes as well as the emission and deposition of carbon compounds in various ecosystems is one of the priority tasks in the field of climate and biosphere conservation in the world. This paper presents the results of the study of the soil sections of the «Ladoga» carbon monitoring site. Folic Podzol (Arenic) and Fibric Histosol were considered. These soils are widely represented in the southern taiga subzone and can be used as benchmark monitoring soil sections. As a result of the analysis of chemical parameters, it was revealed that Fibric Histosol and Folic Podzol (Arenic) are characterized by an acidic reaction of pH, pronounced podsolization, and peat accumulation. Fibric Histosol stores a significant amount of soil organic matter (SOM) up to 42.95 kgC/m2. In the analysis of the molecular composition of humic acids (HAs) extracted from the studied soils, it was found that HAs from Fibric Histosol were characterized by a relatively high content of aromatic structural fragments (27–41%), while in Folic Podzol (Arenic), aliphatic structural fragments prevailed (up to 70%). The increase of aromatic structural fragments in the HAs composition indicates the stabilization and conservation of SOM. The creation of a monitoring network will make it possible to identify the main trends of SOM accumulation, determine the conditions under which accumulation occurs, and calculate its contribution to climate change on the planet.

The Effects of Natural Humus Material Amendment on Soil Organic Matter and Integrated Fertility in the Black Soil of Northeast China: Preliminary Results

The input of exogenous organic materials is an effective way to improve soil organic matter (SOM) content in cropland. The exploration of the impact of new organic materials such as woody peat on black soil fertility can provide an important reference for preventing the degradation of black soil in Northeast China. In this study, the effects of adding woody peat to SOM and the soil-integrated fertility of black cropland were studied by seven treatments (no organic matter addition, CK; crop straw returning, SR; decomposed straw addition, DS; organic manure addition, OM; 6 t/ha woody peat addition, LWP; 10.5 t/ha natural humus material addition, MWP; and 15 t/ha natural humus material addition, HWP). The results show that natural humus material additions (LWP, MWP, and HWP treatments) could significantly increase SOM (increased by 4.79~9.41 g/kg), labile SOM (increased by 2.49~4.52 g/kg), and recalcitrant SOM (increased by 2.13~6.39 g/kg) components, respectively. For comparison, traditional organic material inputs (SR, DS, and OM treatments) had no significant effect on SOM but induced an increase in the labile SOM component in the following year. This study also found that natural humus material additions could improve soil-integrated fertility in a year term, especially in promoting SOM accumulation. However, organic manure amendment showed both the advantage of increasing soil fertility slightly and the disadvantage of increasing soil salt sharply. In conclusion, compared with traditional exogenous organic materials, the natural humus material amendment technique can rapidly increase the total SOM quantity and its different stability components and has a great effect in improving the integrated fertility of black soil. Thus, it is of significance to further study the potential of natural humus material amendment in the fertility of black soil in future.

Nitrogen addition mediates monospecific and mixed litter decomposition in a boreal peatland

Litter decomposition is a key determinant of soil organic matter accumulation in boreal peatlands. Climate warming and atmospheric nitrogen (N) deposition have recently increased N availability in boreal peatlands. However, how increased N availability alters decomposition dynamics of plant litter is uncertain in these ecosystems, especially for litter mixtures. Here, we collected fresh litter of four common species (Betula fruticosa, Ledum palustre, Eriophorum vaginatum, and Sphagnum palustre) in a poor fen of northeast China, and established an N addition (6 g N m−2 year−1) experiment to assess the effect of increased N availability on monospecific and mixed litter decomposition in the hummocks and hollows after one and three years of decomposition. In both hummocks and hollows, N addition increased mass loss of four monospecific litter after one year of decomposition but only accelerated litter decomposition of E. vaginatum and S. palustre with low litter quality after three years of decomposition. Moreover, N addition effects on monospecific litter decomposition were negatively related to monospecific litter decomposition in the absence of N addition. Irrespective of decomposition position, additive effects were more frequent than synergistic effects during decomposition of litter mixtures. In addition, N addition generally changed synergistic effects to additive effects after one and three years of decomposition, and such changing trends were stronger in hummocks than in hollows. These observations suggest that litter quality mediates N addition effects on monospecific litter decomposition, and highlight that increased N availability will alter mixed litter decomposition by reducing synergistic effects in boreal peatlands.

The influence of inherent soil factors and agricultural management on soil organic matter

AbstractThe accumulation of soil organic matter (SOM) is vital to the agronomic and environmental functioning of agroecosystems, yet the relative influence of inherent soil properties and agricultural management practices on SOM dynamics are not often addressed in individual studies. Using a network of 218 operating farm fields across Wisconsin and southern Minnesota, USA, this research employs single variable analysis (ANOVA and regression) and regression tree analysis to assess the effects of soil properties (texture, drainage class, and pH) and management variables related to crop rotation, tillage, cover cropping, and manure application on SOM, as well as total organic carbon (TOC) and total nitrogen (TN) in the upper 15 cm. Single variable analysis revealed that greater SOM, TOC, and TN were associated with poorly drained soil, tile‐drained fields, high clay content soil, and high biomass crop rotations. SOM and TOC were strongly related (R2 = 0.71), but different regression trees were produced; SOM was most influenced by clay content, while TOC was most influenced by drainage class. Future assessment for the building of SOM or TOC should be conducted with drainage and texture class categories and on a regional basis, given that these factors influence the practices that occur within landscapes. A rapid building of datasets through unstructured sampling, including an abundance of metadata, should be a research priority in agricultural science to identify practices to build SOM on a regional basis.

Soil organic matter in temperate forest-grassland systems: A case study from the Southern Cis-Ural, Russia

Understanding the dynamics of SOM in different land use types is critical for effective land management and climate mitigation strategies. In this study, we investigated the differences in soil organic matter (SOM) content between forest and grassland landscapes in the mountainous zone of Republic of Bashkortostan, Russia. We collected soil samples from multiple locations under both land use types and analysed them for SOM content using standard laboratory techniques. The results showed that the SOM content varied from 2.2 to 15.3% under forest landscape with an average of 6.7% and was characterized by high variability (51.8%). The SOM concentrations under grassland ranged from 2.1 to 6.5% with an average of 3.2%, while the coefficient of variation was 31.8%. According to the classification, the average SOM value in forest soils was classified as “high”, while in grassland soils it was classified as “low”. Overall, the variability in SOM content within forested landscapes can be influenced by a range of factors, including topography, erosion, and redeposition of soil. These factors contributed to the complex patterns of SOM accumulation and decomposition observed in forest soils, and should be considered when evaluating the potential impacts of land use change on SOM. Our study highlights the importance of understanding the factors that influence SOM content in soils, and the need for careful management of land use systems to maintain or enhance soil fertility and productivity.

Sugarcane straw management by inoculation of microbial consortia and its impact on short-term N source and amelioration of ratoon sugarcane yield

ABSTRACT The objectives of this study was to assess the effect of the inoculation of sugarcane straw with an artificial microbial consortium (MC) on soil mineral N, soil organic matter (SOM), sugarcane straw decomposition, hydrolytic enzyme activities (β-glucosidase, urease), oxidative enzyme activities (phenoloxidase, peroxidase), nutrient uptake and ratoon cane yield. The experiment consisted of two field experiments, i.e. the experiment I field was sandy soil, and the experiment II field was sandy loam soil in Khon Kaen Province. After planted cane harvest, there were three treatments, namely, burn (B), incorporation (I) and I+ MC treatments. Experiment II consisted of three treatments, namely, B, mulch (M) and M+ MC treatments. Sugarcane straw was applied at a rate of 6.25 tons ha−1. The results revealed that sugarcane straw management by inoculation of microbial consortia had a higher soil mineral N content than that of other treatments, improved the straw decomposition, hydrolytic and oxidative enzyme activities, SOM accumulation (7.60, 20.58 g kg−1 respectively), yield (49.47, 131.51 ton ha−1 respectively), nutrient uptake and nutrient use efficiency of ratoon cane. Thus, sugarcane straw management by inoculation of microbial consortia becomes a short-term N source and a potential application to enhance decomposition leading to increased ratoon cane yield.

Pedodiversity and Organic Matter Stock of Soils Developed on Sandstone Formations in the Northern Apennines (Italy)

Pedodiversity is considered the cornerstone of biodiversity. This work aimed to (1) assess pedodiversity according to vegetation, topographic factors, and lithology and to (2) identify the major soil-forming factors on soil organic matter (SOM) stock at a 0–30 cm depth. These goals were reached using data from 147 georeferenced soil profiles distributed along 400–1000 m (≤1000) and 1000–2134 m (>1000) altitudinal gradients in the northern part of the Apennine chain in Italy. Soils showed mainly weak or incipient development (i.e., Entisols and Inceptisols), which could be attributed to sand-based lithology, high slope gradients, and low SOM accumulation rates, which promote soil erosion processes. However, higher pedodiversity was observed at >1000 m than at ≤1000 m, likely due to the higher vegetation cover diversity and climate variability; Spodosols and Mollisols were also found. A greater SOM stock was found at >1000 than ≤1000 m, and vegetation seemed to not affect SOM amounts, suggesting a greater influence of climate on SOM content compared to vegetation. Considering ecosystem conservation, the observed spatial pedodiversity could be considered a critical basis for the protection of soil resources and pedodiversity itself in mountain regions.

Linking bacterial life strategies with soil organic matter accrual by karst vegetation restoration

Vegetation restoration affects belowground microbial diversity and trait-based life strategies, as well as soil organic matter (SOM) accumulation. Despite the growing focus on microbial diversity, the relationship between SOM accrual and life strategies following vegetation restoration remains unclear. We used three independent but complementary approaches to relate six soil parameters to SOM accrual and further connected them with microbial diversity and life strategies. Sites with two vegetation restoration strategies (after 15 years of vegetation recovery): i) actively planted forests and ii) passive naturally regenerating forests, were compared with croplands and established 60-year-old secondary forests. Data from seven sites along a large climatic gradient (Δ temperature >9 °C) in subtropical karst regions showed that the average index of SOM accrual increased by 47% in plantations and by 60% in natural regeneration forests compared to that in croplands, but remained lower than that of secondary forests. Related soil parameters (water holding capacity, organic carbon and total nitrogen contents, and bacterial and fungal biomasses) were comparable. Compared to croplands, vegetation restoration decreased the sensitivity of the soil parameters to climate warming. Vegetation restoration reduced bacterial diversity and shifted the community towards K-strategy, as evidenced by i) lower 16S rRNA operon copy number and ii) higher ratios of phyla classified a priori as oligotrophic versus copiotrophic bacteria. These changes were mainly attributed to the decline in labile nutrient content and increase in carbon stability in calcium-rich karst soils after vegetation restoration. Bacterial diversity was negatively associated with SOM accrual at low levels of functioning, whereas the prevalence of K-strategists showed a strong positive association with it, especially at near-peak capacity. Consequently, i) bacterial rather than fungal diversity and life strategies are associated with SOM accrual, and ii) linking bacterial life strategies with SOM accrual is important to deepen the understanding of soil-microbial interactions.

The Influence of Plantation on Soil Carbon and Nutrients: Focusing on Tibetan Artificial Forests

As terrestrial ecosystem carbon (C) sinks, plantation ecosystems play essential roles in species diversity protection, resource supply and climate change. Artificial afforestation is of great important in improving the ecological condition, economic development and production in Tibet. Forests can improve soil property changes, yet the understanding of how plantations influence soil C and nutrient conditions in Tibet is still insufficient. This review combines with previous studies to explore the characteristics of soil nutrients, involving nitrogen (N) and phosphorus (P) on Tibetan poplar plantations. Generally, plantations have better abilities in improving the soil C and N cycles, and enhancing the soil stability. In this review, we further analyze the factors, including the modality of land-use, afforested period, tree species, climate factors and soil properties, which may affect the soil C and nutrients. (1) The patterns of land-use affect the accumulation of soil organic matter, thus influence the accumulation of soil C and nutrients; (2) Soil C and N increase with the years of artificial forests, while soil P is on the contrary; (3) The effects of different tree species on soil C and nutrients vary widely; (4) In terms of climate, the C sink of Tibetan plantation soil is most likely to be affected by precipitation, while the nutrient is more likely to be influenced by temperature; (5) Among soil properties, the most related factor to C is soil texture. Furthermore, our review pointed out that future research on soil ecological functions should be focused on soil microbes on Tibet plantation. At the end, we concluded three major challenges for the future research. Therefore, this review contributes to a better understand the effects of plantation on soil C and nutrients on the Tibetan Plateau.

Climate and geology overwrite land use effects on soil organic nitrogen cycling on a continental scale

Abstract. Soil fertility and plant productivity are globally constrained by N availability. Proteins are the largest N reservoir in soils, and the cleavage of proteins into small peptides and amino acids has been shown to be the rate-limiting step in the terrestrial N cycle. However, we are still lacking a profound understanding of the environmental controls of this process. Here we show that integrated effects of climate and soil geochemistry drive protein cleavage across large scales. We measured gross protein depolymerization rates in mineral and organic soils sampled across a 4000 km long European transect covering a wide range of climates, geologies and land uses. Based on structural equation models we identified that soil organic N cycling was strongly controlled by substrate availability, e.g., by soil protein content. Soil geochemistry was a secondary predictor, by controlling protein stabilization mechanisms and protein availability. Precipitation was identified as the main climatic control on protein depolymerization, by affecting soil weathering and soil organic matter accumulation. In contrast, land use was a poor predictor of protein depolymerization. Our results highlight the need to consider geology and precipitation effects on soil geochemistry when estimating and predicting soil N cycling at large scales.

Habitat-specific responses of soil organic matter decomposition to Spartina alterniflora invasion along China's coast.

Plant invasions cause a fundamental change in soil organic matter (SOM) turnover. Disentangling the biogeographic patterns and key drivers of SOM decomposition and its temperature sensitivity (Q10 ) under plant invasion is a prerequisite for making projections of global carbon feedback. We collected soil samples along China's coast across saltmarshes to mangrove ecosystems invaded by the smooth cordgrass (Spartina alterniflora Loisel.). Microcosm experiments were carried out to determine the patterns of SOM decomposition and its thermal response. Soil microbial biomass and communities were also characterized accordingly. SOM decomposition constant dramatically decreased along the mean annual temperature gradient, whereas the cordgrass invasion retarded this change (significantly reduced slope, p < 0.05). The response of Q10 to invasion and the soil microbial quotient peaked at midlatitude saltmarshes, which can be explained by microbial metabolism strategies. Climatic variables showed strong negative controls on the Q10 , whereas dissolved carbon fraction exerted a positive influence on its spatial variance. Higher microbial diversity appeared to weaken the temperature-related response of SOM decomposition, with apparent benefits for carbon sequestration. Inconsistent responses to invasion were exhibited among habitat types, with SOM accumulation in saltmarshes but carbon loss in mangroves, which were explained, at least in part, by the SOM decomposition patterns under invasion. This study elucidates the geographic pattern of SOM decomposition and its temperature sensitivity in coastal ecosystems and underlines the importance of interactions between climate, soil, and microbiota for stabilizing SOM under plant invasion.

Soil Carbon and Nitrogen Stocks under Agrosilvopastoral Systems with Different Arrangements in a Transition Area between Cerrado and Caatinga Biomes in Brazil

Production systems that promote the accumulation of soil organic matter (SOM) must be implemented to maintain the sustainability of agriculture, livestock, and forestry. Since increases in MOS content contribute to improving the chemical, physical, and biological quality of the soil, as well as helping to reduce carbon emissions to mitigate climate change. Therefore, the objective of this study was to evaluate soil organic carbon (SOC) and nitrogen (N) stocks after the implementation of agrosilvopastoral (ASP) systems in a Cerrado-Caatinga transition zone in Brazil. Native vegetation of Cerrado-Caatinga (NV), regenerating stratum of Cerrado-Caatinga (RS), two arrangements of ASP systems cultivating Cenchrus ciliaris L. intercropped with Eucalyptus camaldulensis Dehnh. × Eucalyptus tereticornis Sm. hybrid (ASP1 and ASP2), and intercropped with Eucalyptus urophylla S.T. Blake × Eucalyptus grandis W. Mill ex Maiden hybrid (ASP3 and ASP4) were evaluated. Soil C and N stocks and the C content in the humic fractions of SOM were evaluated at 0–10, 10–20, and 20–30 cm soil depths. The introduction of ASP2, ASP3, and ASP4 systems in an area previously occupied by low productivity pasture increased and restored SOC stocks to levels found in NV, at a depth of 0–30 cm. N stocks were higher in ASP systems, regardless of the arrangement studied. As a result, the ASP systems provided accumulations that ranged from 1.0 to 4.31 Mg SOC ha−1 yr−1 and from 0.33 to 0.36 Mg N ha−1 yr−1. The carbon contents in humic fractions remained higher in NV. The hierarchical grouping and principal component analysis showed that the implementation of the ASP systems was efficient in increasing soil C and N stocks over time. In conclusion, the present study identified that integrated production systems can support land use intensification strategies based on sustainable and low-carbon agriculture in a transition area between the Cerrado and Caatinga biomes in Brazil.

Effects of landscape restoration on migration of lead and cadmium at an abandoned mine site

Abandoned lead and zinc (Pb/Zn) mining wastes represent a serious environmental hazard because heavy metals (e.g., Pb and Cd) are continuously released into the environment, threatening ecological and human health. This study was devoted to investigate the stability of Pb and Cd in the soil at an abandoned Pb/Zn mine site after landscape restoration by five-year monitoring. Chemical extraction was applied to measure the distribution of metals. The results showed that the bioavailability of Pb and Cd in soil increased, during the accumulation of soil organic matter of about seven g/kg, and that the soil pH value decreased from 4.82 to 4.44. Soil organic matter and soil pH significantly affected the distribution of metals. Long-term afforestation can lead to continuous soil acidification. There was a significant negative correlation between the carbonate-bound state distribution and soil pH. With the decrease in pH, the decomposition of carbonates was promoted, and relative abundances of Pb and Cd in the distribution associated with the fulvic and humic complex of organic matter increased by 0.54% and 3.17%, respectively. Pb and Cd showed different migration behavior in pine. Compared with Cd, Pb was more concentrated in roots. These results have important implications for the long-term sustainable management of forests formed by the phytostabilization of contaminated soil.

Soil organic matter accumulation before, during, and after the last glacial maximum in Byers Peninsula, Maritime Antarctica

Organic matter is incorporated into soil by biological activity, and its preservation depends on composition and organic-mineral interactions. Frost activity, dry and cold climate, and glacial retreat-advance dynamics complexify soil organic matter storage in Antarctica. Byers Peninsula is the largest ice-free area in Antarctica and hosts a high diversity of vegetable and animal species. We hypothesize that (i) the SOM in the Byers Peninsula may reveal a distinct composition due to the antiquity of the ice-free areas not entirely obliterated by the advancing glaciers during the LGM; and (ii) the advancing ice caps at Byers allowed the accumulation of organic carbon at sheltered points of the Peninsula. Thus, the objectives of this work were: i) to characterize physically and chemically selected soils at Byers Peninsula, with emphasis on organic C and N stocks in different soil types, and ii) SOM dating of representative soil profiles. Thirteen soil profiles were dug, described, and classified. The plant species present at each site were identified. Chemical and physical attributes were determined. The C and N contents, δ13C and δ15N ratio isotopes were determined in the SOM physical size-fractionated particles. The C and N stocks were calculated for each SOM fraction. The deepest horizon of six soil profiles were dated by the 14C method.. Soils from Byers Peninsula showed a diverse and varied biochemical nature of SOM, resulting in varying content of C and N. The δ13C weighted mean of the SOM reflects the dominant vegetation type present in each sampling location, except for pre-Holocene soils and soils influenced by ornithogenesis. The highest organic C and N pools were recorded at subsurface horizons and attributed to the organo-mineral association fraction in upper platforms. For all soil groups, there was a significant overlap of δ13C and enrichment of δ15N in all fractions of SOM, requiring the combination of these two signatures to identify possible sources of contribution to SOM in this environment. The oldest soils, subjected to early-mid Holocene uplift, revealed an endolithic signature of pre-LGM age, the first recorded in Maritime Antarctica to this day. This first pre-LGM SOC record can indicate the initial modern colonization of Maritime Antarctica and suggests that ice caps advance during LGM was limited. Soils formed during and after the LGM in low platforms have a lacustrine signature indicating an influence of snowmelt, ice thawing, and permafrost degradation in selecting hygrophilous species. Soils formed in raised beaches have the lowest organic C and N stocks, and the isotopic composition of SOM indicates ancient ornithogenic influence.