SOM Quality Research Articles

Spatial and temporal variability of organic matter sources and food web structure across benthic habitats in a low diversity system (southern Baltic Sea)

Understanding the effects of basal resources on the functioning of coastal ecosystems is of great interest in ecology since the different composition and availability of food sources directly affect trophic pathways and energy flow in systems. In this study, we determined which basal resources fuel the food webs of four benthic communities from different habitats in the shallow, low diversity Puck Lagoon (Gulf of Gdańsk, southern Baltic Sea) over a full seasonal cycle. Using δ13C and δ15N values, the relative contribution of various potential carbon sources to the diets of dominant consumers were estimated with a mixing model in R (SIAR). The organic matter pool assimilated by macrofauna included primarily suspended particulate matter (SPOM), phytoplankton, and sediment detritus (SOM) that contained degraded vascular plants and macroalgae in areas with high vegetative biomass. Benthic invertebrates fed mostly on food sources available in their habitats and had species-specific carbon and nitrogen isotope compositions. On sediments with little vegetation, two separate trophic pathways included SPOM, phytoplankton, and suspension feeders, while SOM supported deposit feeders and omnivores in a sheltered environment close to a river mouth. On sediments dominated by Stuckenia, SOM and macroalgae supported the benthic food web that was dominated by opportunistic and tolerant omnivores and herbivores. In contrast, the large biomass of benthic vegetation and high SOM quality on Chara/Cladophora sediment induced high trophic diversity with two main trophic pathways, SPOM and phytoplankton supported suspension feeders, and macroalgae and epiphytes promoted grazers and omnivores. Vascular plants were found not to have been consumed by benthic invertebrates or fishes, but they provided suitable substrata for the macroalgae that developed on their blades and roots.

Issues in Using Self-Organizing Maps in Human Movement and Sport Science

Abstract Self-Organizing Maps (SOMs) are steadily more integrated as data-analysis tools in human movement and sport science. One of the issues limiting researchers’ confidence in their applications and conclusions concerns the (arbitrary) selection of training parameters, their effect on the quality of the SOM and the sensitivity of any subsequent analyses. In this paper, we demonstrate how quality and sensitivity may be examined to increase the validity of SOM-based data-analysis. For this purpose, we use two related data sets where the research question concerns coordination variability in a volleyball spike. SOMs are an attractive tool for analysing this problem because of their ability to reduce the highdimensional time series to a two-dimensional problem while preserving the topological, non-linear relations in the original data. In a first step, we systematically search the SOM parameter space for a set of options that produces significantly lower continuity, accuracy and combined map errors and we discuss the sensitivity of SOM-based analyses of coordination variability to changes in training parameters. In a second step, we further investigate the effect of using different numbers of trials and variables on the SOM quality and sensitivity. These sensitivity analyses are able to validate the conclusions from statistical tests. Using this type of analysis can guide researchers to select SOM parameters that optimally represent their data and to examine how they affect the subsequent analyses. This may also enforce confidence in any conclusions that are drawn from studies using SOMs and enhance their integration in human movement and sport science.

Laboratory Assessment of Forest Soil Respiration Affected by Wildfires under Various Environments of Russia

Pyrogenic carbon emission rates were estimated in the soils of three natural zones in Russia: forest-tundra, south-taiga, and forest-steppe. Postfire soils were found to be characterized by essential losses of soil C due to the combustion fire effect. Soils lost 3 or 5 parts of initial carbon content and showed an essential decrease in the C/N ratio during the fire effect. The pH values increased due to soil enrichment by ash during the fire events. CO2 emission rates were highest in natural soil samples, because the amount of organic matter affected by mineralization in those soils was higher than in natural ones. Simultaneously, the total values of mineralized carbon were higher in postfire soils because the SOM quality and composition were altered due to the fire effect. The only exception was in forest-tundra soils, where a high portion of dissolved organic compounds was released during the surface fire. The quality of initial SOM and intensity of the wildfire play the most important roles in the fate of SOM in postfire environments. Further study of CO2 emissions is needed to better characterize postfire SOM dynamics and develop an approach to model this process.

Soil organic matter quality and composition in a postfire Scotch pine forest in Tolyatti, Samara region

Evaluation of humus accumulation and humification rates was conducted on soils affected by surface and crown fires during 2010 forest fires near Tolyatti (Samara region, Russia). Three key soil plots were studied for estimating SOM quality changes under the forest fire effect. Total carbon and nitrogen content, as well as Сhumic acids/Cfulvic acids (Cha/Cfa) ratios, were estimated to evaluate the dynamics of soil recovery. Humic acid powders were extracted from soils and analyzed by elemental composition and 13C-NMR spectroscopy to assess changes in structure and composition. The data indicate that the burning of a forest floor and humic horizon led to humus losses and decreases in total carbon stocks and content. As a result of the fires, the content of humic acids in the pyrogenic horizon increased. Greater increases in the degree of organic matter humification were observed for surface fires than for crown fires. Fire also lead to the formation of humic acids with an increased proportion of aromatic compounds than in control soils, which indicates the degradation of carboxylic and aliphatic groups of molecules under the burning effect. This corresponds well with the decrease of the proportion of hydrogen when comparing the elemental composition of burned soil with that of mature soil.

Effects on the composition and structural properties of the humified organic matter of soil in sugarcane strawburning: A chronosequence study in the Brazilian Cerrado of Goiás State

The heating of soil organic matter after burning events can significantly change the composition and structure of humified organic matter. The impact of burning on the amount and quality of SOM depends on fire intensity, recurrence, the type of vegetation, soil texture and the local climate. The present study identified the composition and structural properties of humic acids (HA) extracted from a sandy loam textured Latossolo Vermelho (Oxisol) managed with the pre-harvest burning of sugarcane straw for chronosequences of 1, 5, 10 and 20 years in Rio Verde, Goiás (GO). Soil samples were collected at depths of 0–0.05, 0.05–0.10, 0.10–0.20 and 0.20–0.30m. To obtain a reference of natural conditions, soil was also sampled in adjacent areas covered with native vegetation and Pasture grass. The HA samples from soil under different burning conditions and areas (Cerrado and Pasture grass) were analyzed using chemical-spectroscopic characterization and the chemiometric technique. The greatest modifications in HA composition after burning occurred in the most superficial soil layers. At a depth of 0.0–0.05m, the main changes observed were a decrease in mean C and N levels and enrichment in O, irrespective of the length of time that burning practices had been adopted. Additionally, in the most superficial layer, the ultraviolet-visible spectroscopy assay showed that burning enhanced the aromatic properties (<E4/E6) of HA, and FTIR spectroscopy coupled with PCA confirmed that the top soil layer shows higher variations in the functional groups as a function of burning. The PCA analysis of 13C NMR spectra also showed that stronger aromatic properties were found in the most superficial layer, and the PCA of FTIR spectra reinforced the result by grouping HAs in these layers and thereby indicated that the most intense changes occurred in the 0.0–0.05m layer. The most intense disturbances produced by sugarcane burning on the composition and structure of humified organic matter occurred in the most superficial layer. The combined use of the methods adopted was efficient and, along with the chemiometric techniques, consisted of useful tools that can support the development of procedures to study phenomena such as burning.

Soil organic matter in crop rotations under no-till

ABSTRACT Soil organic matter conservation, paramount in tropical agriculture, is affected by the composition of cultivated plant species and the input of dry matter and nitrogen into the system. However, SOM development in tropical soils managed under no-till in the long term is not well understood. The objective of this study was to evaluate SOM concentration and quality as a result of crop rotations under NT in two soils in Botucatu, Brazil, over a 10-year experimental period (2003–2012). Crop rotations including grasses and a legume grown in the fall/winter and spring were conducted for seven years in a clay Rhodic Hapludox. In a clay Typic Rhodudalf, crop rotations were compared with a fallow/chiseled treatment for 10 years. The cash crop was soybean grown every year in the summer. In both experiments, SOM lability was affected mainly by the spring crops. The absence of spring cover crops in chiseled treatments resulted in less total organic carbon in the 0.0–0.10 m soil depth. Soil concentration of TOC and its fractions were higher under crop rotations with higher nitrogen input, especially where sunn hemp was grown in spring. The strongest effects occurred in the Typic Rhodudalf, probably as a result of its higher clay content and the longer period under crop rotation. Under NT, the increase in labile and stable SOM is limited by the lack of cover crops in the spring or N availability. However, SOM humification degree is decreased with higher C input. These results highlight the importance of the use of cover crops and nitrogen inputs in soil conservation strategies and the sustainability of agricultural systems in the tropics.

Wildfire‐induced alterations of topsoil organic matter and their recovery in Mediterranean eucalypt stands detected with biogeochemical markers

SummaryThis study addressed fire‐induced changes in topsoil organic matter (SOM) from a eucalypt plantation in Portugal over 2 years by using three complementary biogeochemical techniques: elemental analysis, analysis of biomarkers from the total extractable lipids (TLE) and solid state 13C nuclear magnetic resonance (NMR) spectroscopy. Direct wildfire effects included a marked decrease in soil total organic carbon (TOC) and total nitrogen (TN) content. However, both contents seem to have recovered during the 2 years. Fire also substantially reduced the TLE, producing noticeable changes in its composition. These included the thermal breakdown and cracking of n‐alkyl compounds. Ratios of short‐to‐long n‐alkanes and n‐fatty acid methyl esters (FAMEs) increased and typical carbon number predominance indices for n‐alkanes (odd‐to‐even) and n‐FAMEs (even‐to‐odd) were altered. Furthermore, the relative abundances of certain markers that are plant‐species specific were modified, especially by decreasing terpenoids such as epiglobulol, ledol and globulol, which are characteristic of Eucalyptus globulus. Other differences observed in the burnt soil were the appearance of levoglucosan, a typical marker for the thermal alteration of polysaccharides, larger relative abundances of lignin‐derived compounds (vanillin and methoxyphenols) and the presence of N‐heteroaromatic structures, which suggested the accumulation of ‘black nitrogen’. The 13C NMR spectra indicated that the wildfire produced a considerable increase in the aromaticity and aromatic condensation of the topsoil SOM. This was reflected in a broadening of the signal of aromatic compounds at the expense of O‐alkyl and alkyl‐C compounds. The continuation of these differences in SOM quality during the 2‐year study suggested a slow recovery of soil properties, possibly influenced by a limited recovery of the vegetation after the fire combined with the fire‐enhanced losses of soil.

Small variations of soil properties control fire-induced water repellency .

Fire induced soil water repellency (WR) is controlled by many different factors (temperature reached, amount and type of fuel, etc.). Soil properties may determine the occurrence and intensity of this property in burned soils. The objectives of this paper are to make advances in the study of soil properties as key factors controlling the behaviour of fire-induced WR, and to study the impact of pre-fire SOM content and SOM quality in fire-induced soil WR. In this research, experimental laboratory burnings were carried out using soil samples from different sites with different lithologies, soil types and plant species. Soil samples taken from the same site differ only in quantity and quality of soil organic matter, as they were collected from under different plant species. All soil samples were heated in a muffle furnace at 200, 250, 300 and 350 ºC without the addition of any fuel load. WR was measured using the water drop penetration time test (WDPT). The results showed significant differences between soil types and plant species, indicating that small differences in soil properties may act as key factors controlling the development and persistence of WR reached, with burned soil samples ranging from wettable to extremely water repellent. The main soil property controlling the response was texture, specifically sand content. The quality of organic matter was also observed to have an effect, since soil samples from the same site with similar organic matter contents, but taken from beneath different plant species, showed different WR values after burning.

Use of thermal analysis and solid-state 13C CP-MAS NMR spectroscopy to diagnose organic matter quality in relation to burn severity in Atlantic soils

Wildfire has highly variable effects on soil, and different conservation strategies are required to address different levels of soil degradation. Rapid diagnosis of soil burn severity is required to enable the design of emergency post-fire rehabilitation treatments. This study evaluated whether visually different levels of soil burn severity (SBS) reflect changes in SOM quality. Five areas recently affected by wildfires were selected for study in a fire-prone environment in an Atlantic area of Southern Europe (NW Spain). Soil organic carbon (SOC) concentration and quality of mineral soil samples (0–5cm depth) were analyzed after the fires, in relation to three visually different levels of soil burn severity (SBS): control (unburned), moderate (bare soil and soil structure unaffected) and high (bare soil and surface soil structure and color altered). The samples were collected along sampling transects, to control the spatial variability. SOM quality was characterized by 13C CP-MAS NMR spectroscopy and differential scanning calorimetry (DSC). Although large reductions in SOC concentration were found in both moderate and SBS (up to 70%), important effects on SOM quality were associated only with high SBS. NMR analysis revealed these changes as losses of O-alkyl, alkyl and carboxylic structures (variable in the different soils studied) and increased values of the aromatic structures (up to 50%). The DSC analysis revealed decreased combustion heat released up to 375°C, and increased T50 (the temperature at which 50% of the energy stored in SOM is released). Relationships between thermal properties and chemical-shift regions in the NMR helped provide a better understanding of SOM thermal properties. Discriminant analysis, using the SBS levels as classification factors, revealed that thermal parameters reliably distinguished the three visually recognized levels and correctly classified 86% of the samples. Visual classification of SBS levels could therefore be used to characterize SOM changes on the basis of SOM thermal and chemical properties.

The effect of earthworms on carbon storage and soil organic matter composition in tropical soil amended with compost and vermicompost

The use of organic matter (OM) amendments is widespread in tropical countries and may be beneficial for soil carbon storage. Interactions between earthworms and OM amendments in tropical soils are largely unknown. The aim of this study was to investigate the effect of bioturbation on the quantity and chemical composition of OM in soil amended with compost and vermicompost. Our approach included comparison of soil samples amended with compost, vermicompost or chemical fertilizers in the presence or absence of earthworms during a one-year greenhouse experiment. The soils were submitted to a regular cultivation cycle. After one year, we analysed bulk samples for soil OM elemental composition and characterised its lignin and non-cellulosic carbohydrate components.Our results showed a decrease of the carbon and nitrogen content in soil amended with chemical fertilizers. Vermicompost amendment led to unchanged OC content, whereas the compost amendment increased the soils OC content compared to initial soil. The addition of earthworms reduced OC and N content in soils with organic amendments. This is in contrast to soil amended with mineral fertilizer only, where the presence of earthworms did not have any effect. Bioturbation influenced the lignin signature of the soils, and to a lesser extent the non-cellulosic carbohydrate signature. In conclusion, compost amendment combined with bioturbation influenced the quality and quantity of SOM and as result carbon storage and its biogeochemical cycling in tropical soils. Implications for soil fertility remain to be elucidated.

The Effects of Snow, Soil Microenvironment, and Soil Organic Matter Quality on N Availability in Three Alaskan Arctic Plant Communities

Climate warming in The Arctic may lead to a shift from graminoid to shrub dominance, which may, in turn, alter the structure and function of the ecosystem through shrub influences on the abiotic and/or biotic controls over biogeochemical cycles of carbon (C) and nitrogen (N). In Arctic tundra, near Toolik Lake, Alaska, we quantified net N-mineralization rates under ambient and manipulated snow treatments at three different plant communities that varied in abundance of deciduous shrubs. Our objective was twofold: (1) to test whether the amount of snow that can accumulate around Arctic deciduous shrubs maintains winter soil temperatures high enough to stimulate microbial activity and increase soil N levels (effect of soil microclimate) and (2) to compare the relative effects of snow versus shrubs on N availability via effects on the main drivers of N-mineralization: SOM quality versus microclimate. Winter snow addition had a positive effect on summer, but not winter, N-mineralization rates. Soil organic matter quality had a nine times larger effect on N-mineralization than did soil microclimate in the summer season and only SOM quality had a detectable effect on N-mineralization in the winter. Here we conclude that on a short time scale, shrub interactions with snow may play a role in increasing plant available N, primarily through effects on the summer soil microenvironment. In addition, differences in SOM quality can drive larger differences in net N-mineralization than changes in soil microclimate of the magnitude of what we saw across our three sites.

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.

Plant cover and epipedon SOM stability as factors affecting brown soil profile development and microbial activity

This study aimed to evaluate the role of different plant covers on brown soil profile development changing SOM stability in the epipedons. In particular, two brown soils (Eutric Cambisols), located in Monghidoro at the Italian Apennines, were analysed in order to test the hypothesis that plant cover affects the brown soil profile development under eutric qualifier changing SOM stability and soil pH. Also we verified if soil biochemical activities and microbial biomass size could be promoted by factors supporting Eutric Cambisols development. The two soil profiles were formed under coniferous (M con) and beech cover (M beech), respectively; both of them had similar lithology, morphology, exposition, slope and elevation. The development of soil profiles was evaluated by the determination of their physical, chemical and biochemical properties, while SOM stability of the epipedons was assessed through the determination of some properties of humic substances by thermal (TG-DSC) and spectroscopic (FTIR) analysis, humification indexes and eco-physiological indicators such as microbial quotient (C mic:C org) and metabolic quotient (qCO 2). The C org content decreased along both soil profiles. The epipedon of M beech soil was richer in SOM that in turn showed a higher level of humification than M con. The pH value, CEC and the concentrations of all earth-alkaline cations were also higher in M beech than in M con soil profile. Differences in soil reaction and SOM quality seemed to affect weathering process, since the content of all Al forms (amorphous—Alo, crystalline—Ald and linked to SOM—Alp) increased as the soil pH decreased, and the Fe forms increased as the humification level of SOM increased. Nevertheless, the active iron ratio (Feo/Fed) calculated in the two soil profiles did not highlight significant differences between them in terms of podzolitation intensity. The activity of hydrolytic enzymes (β-glucosidase, cellulase and chitinase) was higher in M beech soil than in M con soil profile. The activity of all enzymes, on mass basis, decreased along both soil profiles, while the specific activity (per unit of organic carbon), increased only in the endopedons of M beech. Although biochemical properties were not correlated with physical and chemical properties of soil profile, significant correlations were observed between enzyme activity and the soil organic carbon or nitrogen content. As far as the epipedons SOM quality is concerned, the content of humified C, the microbial biomass carbon (C mic), as well as the C mic:C org were higher in M beech than in M con, whereas the qCO 2 was lower in M beech than in M con. Also the FTIR and TG-DSC analysis showed differences on HAs and FAs hydrophilic character and thermal stability between epipedons of M beech and M con. The SOM quality of epipendon under coniferous resulted in a more recalcitrant and hydrophobic composition than that of epipedon under beech. In conclusion the type of plant cover (coniferous vs. beech-tree) affected the weathering of the pedogenetic substrate changing the SOM properties and soil pH. Even if the beech-tree cover promoted SOM accumulation in soil profile, which represented the organic substrates for microbial biochemical activities, the weathering of soil under coniferous appeared more marked than beech-trees covered soil. Consequently, soil biochemical activity of microbial biomass along soil profile was not promoted by factors supporting weathering processes.

Transformation of buffalo manure by composting or vermicomposting to rehabilitate degraded tropical soils

The addition of composted buffalo manure may lead to qualitative and quantitative improvement of the organic matter content of degraded tropical agricultural soils in Northern Vietnam. The objectives of this study were to follow the biochemical changes occurring during composting of buffalo manure with and without earthworms during 3 months and to study the effect of the end products (compost and vermicompost) on soil biochemical parameters and plant growth after two months of incubation under controlled conditions in an open pot experiment. Our conceptual approach included characterisation of organic matter of the two composts before and after addition to soil by elemental, isotopic analysis and analytical pyrolysis and comparison with conventional fertilisation. We also analysed for lignin content and composition.Our results showed that composting in the presence of earthworms led to stronger transformation of buffalo manure than regular composting. Vermicompost was enriched in N-containing compounds and depleted in polysaccharides. It further contained stronger modified lignin compared to regular compost. In the bulk soil, the amendment of compost and vermicompost led to significant modification of the soil organic matter after 2 months of exposure to natural weather conditions. The lignin component of SOM was unaffected whatever the origin of the organic amendment. Compost and vermicompost amendments both enhanced aggregation and increased the amount of organic matter in water stable aggregates. However, vermicompost is preferable to compost due to its beneficial effect on plant growth, while having similar positive effects on quantity and quality of SOM.

Methods for determination of labile soil organic matter: An overview

Methods for determination of labile soil organic matter: An overviewSoil organic matter (SOM) can be divided into three main pools: labile, stable and inert. Research over recent years has focused on the labile fraction (LF), as it is considered a quickly reactive indicator of soil productivity and health, and important as a supply of energy for soil micro-organisms. A wide spectrum of analytical methods has been used to determine and/or evaluate LF, based on physical, chemical and biochemical principles. The advantages and disadvantages of each technique are explored in this work, but none of the methods can determine LF sufficiently, either because a part of the LF is not involved or because further characterisation is missing. Although analytical methods are widely used to evaluate changes in soil management or organic carbon turnover, the practical question of the quantity and quality of SOM cannot be answered completely. It is also suggested that future research should focus on the interactions among SOM fractions and their better chemical and functional characterisation. It is possible to use a combination of the analytical methods reviewed here in order to accomplish this objective.

Physical protection of soil organic matter following mechanized forest operations in Pinus radiata D.Don plantations

Mechanized forest operations have a large impact on soil systems, and may cause disruption of aggregates and exposure of previously protected soil organic matter to microbial attack. In this study, we investigated how C storage, soil structure and unprotected, physically protected and resistant C pools recover 0, 7 and 20 years after mechanical harvesting and site preparation in second rotation Pinus radiata D.Don plantations. We detected differences in dry mean weight diameter (DMWD) of aggregates, with higher DMWD in 0- and 7-year-old pine stands (8.7 and 7.5 mm, respectively) than in 20-year-old stands (4.1 mm). This was attributed to the compaction induced by heavy machinery, as reflected by the positive relationship between DMWD and bulk density ( r = 0.85, P < 0.05). Organic C contents in the top 5 cm were similar 0 and 7 years after disturbance, but were twice as high after 20 years, with mean values of 25, 28 and 52 Mg C ha −1 , respectively. In addition, the resistant C pool was also reduced by up to 7% after clearance. In contrast, unprotected C and physically-protected C were greatest in the youngest stands, indicating that stand establishment and harvesting with heavy machinery may have broken soil aggregates and exposed the previously protected SOM to microbial decomposition and that forest operations may create new mega-aggregates able to protect organic residues. However, the lowest physically-protected C values in 20-year-old pine stands may also be attributed to differences in SOM quality. The alkyl C/O-alkyl C ratios were highest in the oldest stands, indicating that SOM in these stands was more resistant to further decomposition. Mechanized forest operations in radiata pine stands released at least 30 t C ha −1 from the first 5 cm of the soil profile immediately after clearance, caused significant alterations in the soil structure, which lasted for a minimum of seven years, and also reduced the resistant C pool. As the Kyoto Protocol encourages forest management practices that potentially increase carbon sequestration, mechanical harvesting and site preparation in these steep slopes should be reconsidered.

Effect of lithological substrate on microbial biomass and enzyme activity in brown soil profiles in the northern Apennines (Italy)

Abstract The aim of the present study was to investigate the microbial activity along forest brown soil profiles sequence developed on different lithological substrates (carbonate or non-carbonated cement in sandstone formations) at different altitudes. The main question posed was: does carbonate affect the biochemical activity of brown soil profiles at different altitudes? For the purpose of this study, four soil profiles with different amounts and compositions of SOM developed on different lithological substrates were selected: two with carbonate (MB and MZ) and the other two with non-carbonated cement in the sandstone formations (MF1 and MF2). Chemical and biochemical properties of soil were analysed along soil profiles in order to assess the SOM quantity and quality, namely total organic C (Corg), water extractable organic C (WEOC) and humification indices (HI, DH, HR). Microbial biomass (Cmic and Nmic) content, as well as the specific activities of acid phosphatase, β-glucosidase and chitinase enzymes were chosen as indicators of biochemical activity. The soil biochemical properties provided evidence of better conditions for microorganisms in MB than in MF1, MF2 and MZ soil profiles, since patterns of microbial biomass content and activity might be expected in response to the amount and quality of organic substances. The different lithological substrates did not show any clear effect on soil microbial biomass content, since similar values were obtained in MF1, MF2 (with non-carbonated cement) and MZ (with carbonate). However, the specific activities of acid phosphatase (per unit of Corg and per unit of Cmic) were higher in soils with no carbonate (MF1 and MF2) than in soils with carbonate (MB and MZ). In conclusion, the biochemical activity along brown soil profiles was mainly regulated by different soil organic matter content and quality, while the two different lithological substrates (with carbonate or non-carbonated cement in the sandstone formations) did not show any direct effect on microbial biomass and its activity. However, the activity of acid phosphatase per unit of C was particularly enhanced in soil with non-carbonate cement in the sandstone formations.

Estudo comparativo da matéria orgânica de diferentes classes de solos de altitude do sul do Brasil por técnicas convencionais e espectroscópicas

A região dos Campos de Cima da Serra, RS, apresenta solos com elevados teores de matéria orgânica (MOS), sendo freqüente teores altos de Al trocável. A proposta deste trabalho foi investigar a qualidade da MOS de amostras de camadas superficiais (0 a 10 cm) de oito solos representativos da região (dois Neossolos, dois Gleissolos, três Cambissolos e um Latossolo) sob pastagem nativa, com os seguintes objetivos: avaliar seu comportamento diante da desmineralização da amostra com solução de HF; determinar a sua composição química; e investigar a influência do Al trocável e dos óxidos de Fe na qualidade da MOS. A matéria orgânica foi concentrada com solução de HF 10 cL L-1 e posteriormente avaliada por análise elementar e espectroscopias de FTIR e de RMN 13C CP/MAS. A fração da massa recuperada (5,8 a 10 %) após tratamento com HF correlacionou-se com teor de C original do solo, enquanto a proporção de C recuperado (47 a 86 %) correlacionouse inversamente com o teor de óxidos de Fe. Esse resultado indica que parte da MOS encontra-se associada a esses minerais nesses ambientes. Os teores de estruturas C O-alquil totais (52 a 59 %) foram elevados e os valores de índice I1630/I2920(FTIR) foram baixos, evidenciando baixo grau de decomposição e de humificação da MOS desses solos.

Soil organic matter under different forest types in Southern China

Conversion of native broadleaved forests to pure coniferous plantation is a common management practice driven by an increasing demand for timber production. A study was conducted to evaluate the impact of land-use change from native broadleaved forest to pure coniferous plantation on soil organic matter quantity and quality in San Menjiang Forest, in southern China. Additionally, the potential of hot-water extractable organic matter as an indicator of changes in SOM was also assessed. Significant differences in labile SOM fractions (hot-water extractable organic C and total N, cold-water extractable organic C and total N, and microbial biomass C and N) between pure Cunninghamia lanceolata Hook plantation and native broadleaved forest were tested using ANOVA. The contents of soil organic C, total N, and labile organic matter such as hot-water extractable organic C and total N, cold-water extractable organic C and total N, and microbial biomass was significantly lower in pure C. lanceolata plantation than in native broadleaved forest. The percentage ratios of hot-water extractable organic C and N, cold-water extractable organic C, and microbial biomass C and N to soil organic C or total N were also significantly reduced in C. lanceolata plantation. Hot-water extractable organic C and total N were significantly correlated with cold-water extractable organic C and total N and microbial biomass C and N in both native broadleaved forest and pure coniferous plantation ( r > 0.608, P < 0.01). The correlation coefficients between hot-water extractable organic matter and soil organic C or total N ( r > 0.694, P < 0.01) were higher than that between cold-water extractable organic matter, microbial biomass and soil organic C or total N ( r > 0.525, P < 0.05). Therefore, land-use change from native broadleaved forest to coniferous plantation reduced soil organic matter quantity and quality, and hot-water extractable organic matter can be used as an indicator of changes in SOM quality in forest soils.

Impact of soil organic matter content on Se migration and solid partition

Selenium (Se) is an essential element for life however it becomes rapidly toxic with a safety range extremely narrow. In environment, Se could exists as oxyanions and reacts directly or indirectly with the numerous components of the soil (minerals, organic matter, microorganisms). Understanding its complex behaviour is currently needed to improve risk assessment models. It is commonly admitted that minerals are the main carrier phases of Se in soils, however the role of the organic matter (SOM) is poorly documented and still ambiguous. This study was focused on the impact of SOM on Se solid partition (chemical extractions) and its migration availability. Se sorption tests were performed on 3 grassland soils before and after their SOM have been removed (NaOH and NaOCl washes). The initial amounts of SOM differed between soils from 1.7% (R1) to 7.7% (R3), although they were all constituted by the same mineral background. Removing the SOM had a great impact on Se behaviour leading: (1) to decrease slightly the sorbed Se amount (max. 5%) and (2) to modify severely Se solid partition by increasing the available Se fractions (CaCl2 + K2HPO4) and by decreasing the more stable fractions (NaOH, Na2SO3 and NaOCl) (Fig. 1). Thus, the SOM played a dual role on Se retention: it favoured unsolubilization of an important fraction of Se but it may also limit the extent of this fraction (e.g. aqueous complexation). More, the results obtained with the 3 whole soils suggested that the quality of SOM could play an important role in the Se retention: fresh grass seems to increase sorbed Se and Se is preferentially associated with fulvic acids (fulvic and humic acids separated after NaOH extraction).