Linking above and belowground carbon sequestration, soil organic matter properties, and soil health in Brazilian Atlantic Forest restoration.

Forest restoration mitigates climate change by removing CO2 and storing C in terrestrial ecosystems. However, incomplete information on C storage in restored tropical forests often fails to capture the ecosystem's holistic C dynamics. This study provides an integrated assessment of C storage in above to belowground subsystems, its consequences for greenhouse gas (GHG) fluxes, and the quantity, quality, and origin of soil organic matter (SOM) in restored Atlantic forests in Brazil. Relations between SOM properties and soil health indicators were also explored. We examined two restorations using tree planting ('active restoration'): an 8-year-old forest with green manure and native trees planted in two rounds, and a 15-year-old forest with native-planted trees in one round without green manure. Restorations were compared to reformed pasture and primary forest sites. We measured C storage in soil layers (0-10, 10-20, and 20-30 cm), litter, and plants. GHG emissions were assessed using CH4 and CO2 fluxes. SOM quantity was evaluated using C and N, quality using humification index (HLIFS), and origin using δ13C and δ15N. Nine soil health indicators were interrelated with SOM attributes. The primary forest presented the highest C stocks (107.7 Mg C ha-1), followed by 15- and 8-year-old restorations and pasture with 69.8, 55.5, and 41.8 Mg C ha-1, respectively. Soil C stocks from restorations and pasture were 20% lower than primary forest. However, 8- and 15-year-old restorations stored 12.3 and 28.3 Mg ha-1 more aboveground C than pasture. The younger forest had δ13C and δ15N values of 2.1 and 1.7‰, respectively, lower than the 15-year-old forest, indicating more C derived from C3 plants and biological N fixation. Both restorations and pasture had at least 34% higher HLIFS in deeper soil layers (10-30 cm) than primary forest, indicating a lack of labile SOM. Native and 15-year-old forests exhibited higher soil methane influx (141.1 and 61.9 µg m-2 h-1). Forests outperformed pasture in most soil health indicators, with 69% of their variance explained by SOM properties. However, SOM quantity and quality regeneration in both restorations approached the pristine forest state only in the top 10 cm layer, while deeper soil retained agricultural degradation legacies. In conclusion, active restoration of the Atlantic Forest is a superior approach compared to pasture reform for GHG mitigation. Nonetheless, the development of restoration techniques to facilitate labile C input into deeper soil layers (>10 cm) is needed to further improve soil multifunctionality and long-term C storage.

Soil carbon stock and humification in pastures under different levels of intensification in Brazil

Intensive management of tropical pastures has shown potential for greenhouse gas (GHG) mitigation due to high forage production and C accumulation in the soil. This study aimed to evaluate different pasture management options in relation to their effect on soil C stocks and soil organic matter (SOM) humification. Pastures in four beef cattle production systems were assessed: intensive and irrigated pasture with high stocking rate (IHS); dryland pasture with high stocking rate (DHS); dryland pasture with moderate stocking rate (DMS); degraded pasture (DP). The soil under the native forest was also evaluated and soil carbon stocks from the 0-100 and 0-30 cm layers were assessed. Carbon stocks (0-100 cm) ranged from 99.88 to 142.33 Mg ha1 in DP and DMS, respectively and were, respectively, 14 % and 24 % higher compared to the soil under the forest and indicate the capacity of adequately managed tropical pastures to mitigate GHG emissions from livestock production. Humification indexes indicated the presence of more labile C in pastures with greater C accumulation (DHS and DMS), mainly in the upper soil layers, indicating recent C accumulation resulting from correct management. However, more labile C can be easily lost to the atmosphere as CO2, depending on pasture management. Low C stocks associated with high humification indexes are characteristics of DP in which significant amounts of SOM are lost. It is necessary to develop technologies to improve C sequestration in IHS and results indicate the importance of quantifying C stocks in association with C stability.(AU)

Soil carbon stock and humification in pastures under different levels of intensification in Brazil

Intensive management of tropical pastures has shown potential for greenhouse gas (GHG) mitigation due to high forage production and C accumulation in the soil. This study aimed to evaluate different pasture management options in relation to their effect on soil C stocks and soil organic matter (SOM) humification. Pastures in four beef cattle production systems were assessed: intensive and irrigated pasture with high stocking rate (IHS); dryland pasture with high stocking rate (DHS); dryland pasture with moderate stocking rate (DMS); degraded pasture (DP). The soil under the native forest was also evaluated and soil carbon stocks from the 0-100 and 0-30 cm layers were assessed. Carbon stocks (0-100 cm) ranged from 99.88 to 142.33 Mg ha1 in DP and DMS, respectively and were, respectively, 14 % and 24 % higher compared to the soil under the forest and indicate the capacity of adequately managed tropical pastures to mitigate GHG emissions from livestock production. Humification indexes indicated the presence of more labile C in pastures with greater C accumulation (DHS and DMS), mainly in the upper soil layers, indicating recent C accumulation resulting from correct management. However, more labile C can be easily lost to the atmosphere as CO2, depending on pasture management. Low C stocks associated with high humification indexes are characteristics of DP in which significant amounts of SOM are lost. It is necessary to develop technologies to improve C sequestration in IHS and results indicate the importance of quantifying C stocks in association with C stability.

Humification process in different kinds of organic residue by composting and vermicomposting: have microbioreactors really accelerated the process?

The organic matter existing in nature presents as a complex system of various substances. The humic fraction refers to the humic substances (HS) and consists of humic acids (HA), fulvic acids (FA), and humins, according to solubility in aqueous solution. The physical and chemical characteristics of HA, FA, and humins depend on many factors, among which is the type of original organic material. Two processes for the stabilization of organic materials are known worldwide: composting and vermicomposting. Cattle manure, rice straw, sugarcane bagasse, and vegetable wastes from leaves were the organic residues chosen for the composting and vermicomposting processes. In this study, the differences between the HS extracted from such composted and vermicomposted residues were evaluated. The so-extracted HS were evaluated by spectroscopy in the regions of infrared and ultraviolet-visible, and pyrolysis coupled with gas chromatography with mass spectrometric detection is applied. Thus, we expect that the results obtained here indicate which of the two processes is more efficient in the biotransformation of organic residues in a short period with respect to the HS content. It was also observed that the basic units of the humic fractions generated (although they presented different degrees of maturation) are the same. Altogether, the data reported here bring to light that the structures of the HS are very similar, differing in quantities. These results can still be extrapolated to several other raw materials, since the most variable organic matrices were used here to allow this data extrapolation. In addition, the process seems to lead to the formation of more aliphatic substances, counterpoising what is found in the literature.

Humic fractions of forest, pasture and maize crop soils resulting from microbial activity.

Humic substances result from the degradation of biopolymers of organic residues in the soil due to microbial activity. The objective of this study was to evaluate the influence of three different ecosystems: forest, pasture and maize crop on the formation of soil humic substances relating to their biological and chemical attributes. Microbial biomass carbon (MBC), microbial respiratory activity, nitrification potential, total organic carbon, soluble carbon, humic and fulvic acid fractions and the rate and degree of humification were determined. Organic carbon and soluble carbon contents decreased in the order: forest > pasture > maize; humic and fulvic acids decreased in the order forest > pasture = maize. The MBC and respiratory activity were not influenced by the ecosystems; however, the nitrification potential was higher in the forest than in other soils. The rate and degree of humification were higher in maize soil indicating greater humification of organic matter in this system. All attributes studied decreased significantly with increasing soil depth, with the exception of the rate and degree of humification. Significant and positive correlations were found between humic and fulvic acids contents with MBC, microbial respiration and nitrification potential, suggesting the microbial influence on the differential formation of humic substances of the different ecosystems.

Humic fractions of forest, pasture and maize crop soils resulting from microbial activity

Humic substances result from the degradation of biopolymers of organic residues in the soil due to microbial activity. The objective of this study was to evaluate the influence of three different ecosystems: forest, pasture and maize crop on the formation of soil humic substances relating to their biological and chemical attributes. Microbial biomass carbon (MBC), microbial respiratory activity, nitrification potential, total organic carbon, soluble carbon, humic and fulvic acid fractions and the rate and degree of humification were determined. Organic carbon and soluble carbon contents decreased in the order: forest > pasture > maize; humic and fulvic acids decreased in the order forest > pasture=maize. The MBC and respiratory activity were not influenced by the ecosystems; however, the nitrification potential was higher in the forest than in other soils. The rate and degree of humification were higher in maize soil indicating greater humification of organic matter in this system. All attributes studied decreased significantly with increasing soil depth, with the exception of the rate and degree of humification. Significant and positive correlations were found between humic and fulvic acids contents with MBC, microbial respiration and nitrification potential, suggesting the microbial influence on the differential formation of humic substances of the different ecosystems.

Humic fractions of forest, pasture and maize crop soils resulting from microbial activity

Humic substances result from the degradation of biopolymers of organic residues in the soil due to microbial activity. The objective of this study was to evaluate the influence of three different ecosystems: forest, pasture and maize crop on the formation of soil humic substances relating to their biological and chemical attributes. Microbial biomass carbon (MBC), microbial respiratory activity, nitrification potential, total organic carbon, soluble carbon, humic and fulvic acid fractions and the rate and degree of humification were determined. Organic carbon and soluble carbon contents decreased in the order: forest > pasture > maize; humic and fulvic acids decreased in the order forest > pasture=maize. The MBC and respiratory activity were not influenced by the ecosystems; however, the nitrification potential was higher in the forest than in other soils. The rate and degree of humification were higher in maize soil indicating greater humification of organic matter in this system. All attributes studied decreased significantly with increasing soil depth, with the exception of the rate and degree of humification. Significant and positive correlations were found between humic and fulvic acids contents with MBC, microbial respiration and nitrification potential, suggesting the microbial influence on the differential formation of humic substances of the different ecosystems.

Adsorption, immobilization and activity of cellulase in soil: the impacts of maize straw and its humification

The present work aimed to study some aspects of sorption and immobilization of cellulase molecules on soil components by the analysis of the reactions of cellulase in a soil treated with different levels of maize residue and incubated for 90 days. The analysis of variance showed that the effects of the treatments of maize straw, incubation time and their interaction on cellulase adsorption, desorption and immobilization were statistically significant. The adsorption and immobilization capacities of soil by application of maize straw increased significantly. However they decreased with decreasing the soil organic matter (SOM) after 45 days of incubation. The desorption of adsorbed cellulase molecules from the soil by washing with distilled water depended on the SOM contents and its humification. The binding strength of cellulase molecule with fresh miaze straw was significantly stronger than that with humified maize straw. The immobilized cellulase activity, particularly its specific activity increased significantly by increasing the OC contents in the soil treated with maize straw.

Pinus afforestation in South Brazilian highlands: soil chemical attributes and organic matter composition

In the last three decades, exotic tree species are being introduced in the natural pastures of the highlands located at the northeastern part of Rio Grande do Sul State (RS), Brazil. This alteration of land use may impart drastic changes in the soil attributes. In this context, this work aimed to evaluate the impact of Pinus taeda afforestation on soil chemical attributes and organic matter (SOM) composition in Leptosols from Campos de Cima da Serra, RS. Soil samples under eight year old (Pi8) and 30 year old (Pi30) Pinus plantations and under native pasture (NP) were studied. Contents of exchangeable cations and of micronutrients and soil pH were determined. The SOM composition was investigated by means of elemental analyses and FTIR spectroscopy. The soil under pasture had a higher content of nutrients and of SOM in comparison to Pinus soils, reflecting the higher input and decomposition rate of the below ground added residue in the grassland environment. The SOM in pasture soils showed a higher content of carbohydrate and of structures derived from microbial metabolism. Besides the depletion of nutrients and of SOM, Pinus afforestation affected the SOM quality: following afforestation, the proportion of chemically recalcitrant structures and of carboxylic groups increased, whereas N-containing groups decreased.

Nas três últimas décadas, o cultivo de espécies exóticas vem sendo introduzido nas áreas de pastagem de solos de altitude localizados na região nordeste do Estado do rio Grande do Sul. Essa alteração de uso do solo pode causar mudanças drásticas nos atributos do solo. Avaliou-se o impacto do florestamento com Pinus Taeda nos atributos químicos e na composição da matéria orgânica (MOS) de Neossolos Litólicos dos Campos de Cima da Serra, RS. Foram estudadas amostras de solo sob plantação de Pinus há oito (Pi8) e há 30 anos (Pi30) e sob pastagem natural (NP), sendo determinados os teores de cátions trocáveis e de micronutrientes e o pH do solo. A composição da MOS foi investigada por análise elementar e espectroscopia de FTIR. O solo sob pastagem apresentou maior teor de nutrientes e de MOS comparativamente aos solos sob Pinus, refletindo a maior taxa de decomposição de resíduos subsuperficiais em ambiente de campo. A MOS apresentou maior proporção de carboidratos e de estruturas de origem microbiana nos solos sob pastagem natural. Além da depleção de nutrientes e de MOS, florestamento com Pinus afetou a qualidade da MOS: ao longo do tempo a proporção de estruturas quimicamente recalcitrantes e de grupos carboxílicos aumentou, enquanto a de grupos nitrogenados diminuiu.

Pinus afforestation in South Brazilian highlands: soil chemical attributes and organic matter composition

In the last three decades, exotic tree species are being introduced in the natural pastures of the highlands located at the northeastern part of Rio Grande do Sul State (RS), Brazil. This alteration of land use may impart drastic changes in the soil attributes. In this context, this work aimed to evaluate the impact of Pinus taeda afforestation on soil chemical attributes and organic matter (SOM) composition in Leptosols from Campos de Cima da Serra, RS. Soil samples under eight year old (Pi8) and 30 year old (Pi30) Pinus plantations and under native pasture (NP) were studied. Contents of exchangeable cations and of micronutrients and soil pH were determined. The SOM composition was investigated by means of elemental analyses and FTIR spectroscopy. The soil under pasture had a higher content of nutrients and of SOM in comparison to Pinus soils, reflecting the higher input and decomposition rate of the below ground added residue in the grassland environment. The SOM in pasture soils showed a higher content of carbohydrate and of structures derived from microbial metabolism. Besides the depletion of nutrients and of SOM, Pinus afforestation affected the SOM quality: following afforestation, the proportion of chemically recalcitrant structures and of carboxylic groups increased, whereas N-containing groups decreased.

Nas três últimas décadas, o cultivo de espécies exóticas vem sendo introduzido nas áreas de pastagem de solos de altitude localizados na região nordeste do Estado do rio Grande do Sul. Essa alteração de uso do solo pode causar mudanças drásticas nos atributos do solo. Avaliou-se o impacto do florestamento com Pinus Taeda nos atributos químicos e na composição da matéria orgânica (MOS) de Neossolos Litólicos dos Campos de Cima da Serra, RS. Foram estudadas amostras de solo sob plantação de Pinus há oito (Pi8) e há 30 anos (Pi30) e sob pastagem natural (NP), sendo determinados os teores de cátions trocáveis e de micronutrientes e o pH do solo. A composição da MOS foi investigada por análise elementar e espectroscopia de FTIR. O solo sob pastagem apresentou maior teor de nutrientes e de MOS comparativamente aos solos sob Pinus, refletindo a maior taxa de decomposição de resíduos subsuperficiais em ambiente de campo. A MOS apresentou maior proporção de carboidratos e de estruturas de origem microbiana nos solos sob pastagem natural. Além da depleção de nutrientes e de MOS, florestamento com Pinus afetou a qualidade da MOS: ao longo do tempo a proporção de estruturas quimicamente recalcitrantes e de grupos carboxílicos aumentou, enquanto a de grupos nitrogenados diminuiu.