Indicators Of Organic Matter Quality Research Articles

Evidence linking calcium to increased organo-mineral association in soils

Geochemical indicators are emerging as important predictors of soil organic carbon (SOC) dynamics, but evidence concerning the role of calcium (Ca) is scarce. This study investigates the role of Ca prevalence in SOC accumulation by comparing otherwise similar sites with (CaCO3-bearing) or without carbonates (CaCO3-free). We measured the SOC content and indicators of organic matter quality (C stable isotope composition, expressed as δ13C values, and thermal stability) in bulk soil samples. We then used sequential sonication and density fractionation (DF) to separate two occluded pools from free and mineral-associated SOC. The SOC content, mass, and δ13C values were determined in all the fractions. X-ray photoelectron spectroscopy was used to investigate the surface chemistry of selected fractions. Our hypothesis was that occlusion would be more prevalent at the CaCO3-bearing site due to the influence of Ca on aggregation, inhibiting oxidative transformation, and preserving lower δ13C values. Bulk SOC content was twice as high in the CaCO3-bearing profiles, which also had lower bulk δ13C values, and more occluded SOC. Yet, contrary to our hypothesis, occlusion only accounted for a small proportion of total SOC (< 10%). Instead, it was the heavy fraction (HF), containing mineral-associated organic C, which accounted for the majority of total SOC and for the lower bulk δ13C values. Overall, an increased Ca prevalence was associated with a near-doubling of mineral-associated SOC content. Future investigations should now aim to isolate Ca-mediated complexation processes that increase organo-mineral association and preserve organic matter with lower δ13C values.

Relative Contributions of DNRA and Denitrification to Nitrate Reduction in Thalassia testudinum Seagrass Beds in Coastal Florida (USA)

Seagrass beds are vulnerable to eutrophication (nutrient loading) and declining worldwide. To quantify the fate of nitrogen (N) inputs, intact sediment cores were incubated in a continuous-flow system with 15N enrichments to compare N consumption and efflux pathways within and near seagrass (Thalassia testudinum) beds in St. Joseph Bay, Florida. Sediment oxygen demand and total ammonium (NH4+) efflux were greater (p < 0.001) in vegetated versus unvegetated sediments, suggesting that seagrasses enhance organic matter remineralization. Denitrification rates were 2–20× greater than estimates of potential dissimilatory nitrate reduction to ammonium (DNRA). The effect of vegetation on denitrification rates was inconsistent. Direct denitrification of overlying water nitrate and N fixation rates were low, suggesting tight coupling between remineralization, nitrification, and denitrification. DNRA rates were lower than denitrification and consistently greater in vegetated sediments. DNRA rate measurements are conservative if sediment cation exchange decreases the fraction of 15NH4+ reaching overlying water, especially in vegetated sediments, where rates of nitrate-induced ammonium fluxes were observed. Coupled nitrification-denitrification was the major N loss pathway in this system, as evidenced by the lack of 15N-labeled N2 production in isotope-enriched cores. Using measured sediment oxygen demand and NH4+ fluxes as an indicator of organic matter quality and quantity, these results are consistent with previous work showing that labile organic matter helps regulate the balance between N removal and internal recycling pathways in seagrass systems, which has implications for coastal management strategies to address eutrophication.

Effects of peat drainage on labile organic carbon and water repellency in NE Poland

Hot and cold water-extractable organic carbon (HWC and CWC, respectively) fractions, as good indicators of organic matter quality, as well as water repellency (WDPT test) and state of secondary humification were analyzed in topsoil samples of peatland drained for agricultural purposes 160 years ago. The examined sites (drained and used as grassland) at the peatland had been affected by the moorsh-forming process. During this process, intense mineralization and secondary humification of organic matter took place. The state of transformation of organic soils varied from weak to complete degradation. The HWC contents ranged between 2.623 and 3.572 g kg-1 in field-moist samples and 3.999 and 6.074 g kg-1 in air-dried soil samples. The CWC contents were generally lower than HWC and ranged between 0.411 and 0.535 g kg-1 in field-moist samples and 0.696 and 0.939 g kg-1 in air-dried soil samples. The examined soils were extremely water repellent when dried. The measures of transformation of peat after drainage and WDPT were not significantly correlated, but a tendency for higher values of water repellency at the site regarded as degraded was noted. Deep drainage caused an increase of HWC fraction, which in light of the moorsh-forming process should be regarded as negative. The topsoil of the peatland became dry and resistant to rewetting. However, when the ground water level is maintained at not deeper than 0.50 m, the changes in peat matter do not lead to degradation. HWC is a good measure to show differences occurring within the ecosystem. Given its correlation with state of transformation (W1 index) and water repellency (WDPT test), HWC is a good measurement of peat quality. HWC and WDPT measurements may be helpful in determining degradation of peat soil after drainage.

Organic and inorganic matter in Louisiana coastal waters: Vermilion, Atchafalaya, Terrebonne, Barataria, and Mississippi regions

Chromophoric dissolved organic matter (CDOM) spectral absorption, dissolved organic carbon (DOC) concentration, and the particulate fraction of inorganic (PIM) and organic matter (POM) were measured in Louisiana coastal waters at Vermilion, Atchafalaya, Terrebonne, Barataria, and Mississippi River locations, in 2007–2008. The range of CDOM was 0.092m−1 at Barataria in June 2008 to 11.225m−1 at Mississippi in February 2008. An indicator of organic matter quality was predicted by the spectral slope of absorption coefficients from 350 to 412nm which was between 0.0087m−1 at Mississippi in May 2008 and 0.0261m−1 at Barataria in June 2008. CDOM was the dominant component of light attenuation at Terrebonne and Barataria. Detritus and CDOM were the primary components of light attenuation at Vermilion, Atchafalaya, and Mississippi. DOC ranged between 65 and 1235μM. PIM ranged between 1.1 and 426.3mgL−1 and POM was between 0.3 and 49.6mgL−1.

Soil Quality and Tree Growth in Plantations of Forest and Agricultural Origin

Soil organic matter loss and increased soil compaction have been identified as the factors most likely to directly impact tree growth in managed forests. We compared the soil quality of plantations established on former agricultural lands (n = 20) with plantations established following clear cutting of native forests (n = 20). Half of the plantations had been planted with jack pine (Pinus banksiana Lamb.) and half with white spruce [Picea glauca (Moench) Voss], 9 to 27 yr before the study. The old field plantations had lower (at 0–10 and 10–20 cm) mineral soil macroporosity and higher field capacity than forest plantations, indicating more severe soil compaction. The old field plantations, however, also had higher soil C content, raising the permanent wilting point and canceling compaction effects on the available water holding capacity. An indicator of organic matter quality, namely the potential net mineralization per unit of soil Kjeldahl N, was lower in the old fields. Species also affected soil quality indicators—with lower values of macroporosity and higher values of field capacity observed under white spruce. Despite significant differences in soil conditions, no significant effect (P &lt; 0.05) of plantation origin on tree growth could be found. Old fields can support productive plantations of both species.

Distribution of living benthic foraminifera in relation with environmental variables within the Aiguillon cove (Atlantic coast, France): improving knowledge for paleoecological interpretation

Abstract Search for bioindicators in marine environments has provided new tools for monitoring global and local natural changes. Among these tools, benthic foraminifera play a central role. More accurate paleogeographical and paleoecological reconstructions become possible on the basis of the ecology of recent foraminifera. Nevertheless, factors acting on foraminiferal assemblages are still partially understood. The aim of this study is to correlate the distribution patterns of living (stained) benthic foraminifera with environmental variables such as tidal elevation, interstitial pore water salinity, organic matter content of the sediment, pheopigments, chlorophyll a, carbonate contents and grain size distribution of the sediment from 86 samples collected in the Aiguillon cove (France). In this paralic environment, sediment grain size, salinity and tidal elevation are fundamental factors that drive the distribution of the most abundant species i.e. Brizalina variabilis, Cribroelphidium excavatum and Haynesina germanica. Organic matter also influences the distribution patterns of benthic foraminifera: the relative abundance of Ammonia tepida is typically favored by an increase of total organic matter food resources. Chlorophyll a and pheopigments, as indicators of organic matter quality however may not be limiting in the proportion present in the Aiguillon cove. Carbonate proportions do not limit benthic foraminifera of the Aiguillon cove essentially with carbonaceous shells.

Substâncias húmicas, atividade microbiana e carbono orgânico lábil em agregados de um Latossolo Vermelho distrófico sob duas coberturas vegetais

A matéria orgânica (MO) constitui um atributo indicativo da qualidade do solo. O conhecimento de seus distintos componentes, explicando a influência que as práticas de manejo exercem sobre a MO e a agregação dos solos, é de grande importância para a sustentabilidade dos sistemas agrícolas. Neste trabalho, avaliaram-se as substâncias húmicas, a atividade microbiana e o C orgânico lábil em agregados de um Latossolo Vermelho distrófico de Minas Gerais sob vegetação natural de Cerradão e sob cultivo convencional com milho durante 30 anos. Para isso, foram retiradas amostras de solo nas profundidades de 5-10 e 15-20 cm em quatro pontos diferentes. Após coletado, o material foi seco ao ar e fracionado, por via seca, nas classes de agregados de: 4,75-2,0; 2,0-1,0; 1,0-0,5; 0,5-0,25; 0,25-0,105; e &lt; 0,105 mm de diâmetro. Nesses materiais determinaram-se o C orgânico das frações ácidos fúlvicos (AF), ácidos húmicos (AH) e huminas (HUM) e o C orgânico lábil (COL) utilizando KMnO4 15,6 e 33,0 mmol L-1. Os materiais foram ainda submetidos a um ensaio de respirometria, em que os valores da produção de CO2 foram ajustados a equações logísticas [Y = a/1 + e-(b + cx)], estimando-se o tempo necessário para atingir metade da produção máxima de CO2 (t1/2). Os resultados mostraram que, em média, os agregados do solo sob cultivo apresentaram maiores teores de C orgânico da fração AH e de COL determinado com KMnO4 33,0 mmol L-1. Para as frações AF e HUM e o COL determinado com KMnO4 15,6 mmol L-1, esse comportamento foi observado somente na profundidade de 15-20 cm. Nos agregados do solo sob Cerradão, verificou-se maior produção de CO2. Os agregados de menor tamanho tenderam a apresentar maiores teores de C orgânico das frações AF e AH e do COL, além de serem responsáveis pela maior produção de CO2, constituindo-se em sítios favoráveis tanto para o estoque de MO, em decorrência da proteção física e química, quanto para sua mineralização, dada a ação preferencial dos microrganismos nesses locais. Os coeficientes da equação logística (a, b, c) e o t1/2 se mostraram importantes indicadores de qualidade da MO do solo em distintos manejos e, conseqüentemente, de sua labilidade.

Can the Biochemical Features and Histology of Wheat Residues Explain their Decomposition in Soil?

The biochemical characteristics or quality of crop residues is an important factor governing soil residue decomposition. To improve C and N biotransformation models the process underlying this decomposition needs to be better understood and new quality criteria found to describe it. The aims of this explorative study were to (i) improve our understanding of residue decomposition from detailed studies of cell wall biochemical compositions and tissue architecture (ii) find new ways of exploring generic indicators of organic matter quality. To do this, the cell wall composition and tissue architecture of wheat leaves, internodes and roots, before and after their incorporation into soil were determined. Results showed that leaves which were poorly lignified decomposed faster in soil than internodes and roots. Cellulose was the most degraded polysaccharide irrespective of wheat residue. However, cellulose was much more degraded in the case of leaves as compared to internodes and roots. Leaves also presented a highly condensed lignin structure and the extent to which uncondensed leaf lignin was affected by soil decomposition suggests that the contribution of leaf lignin to C mineralization during incubation was very low. Roots which contained similar amounts of lignin than the internodes decomposed more slowly. Roots were enriched in phenolic acids, and more particularly p-coumaric acid (pCA) and presented a more condensed lignin structure than internodes. Phenolic acids are involved in the formation of lignin–polysaccharide complexes known to be recalcitrant to enzymatic attack. Microscopic investigations confirmed that the vessels were the most resistant tissues to decomposition in soil and this could be related either to their lignin content or to the quality of this lignin (condensed-like type lignin). Therefore, cell wall biochemical analyses have revealed that phenolic acids, which in their esterified form represent only 0.1–1% of plant dry matter, have cross link functions within the cell walls that could be of major interest in estimating soil residue degradability. Lignin quality (monomers, level of condensation) was another crucial criterion that could explain why residues with similar amounts of lignin decomposed at different rates in soil (roots vs. aerial parts). Visualization of residue cell walls before and after decomposition in soil underlined the interest of a microscopic approach coupled with image analysis. This study, corroborated by the extensive literature on forage digestibility, confirmed that the proportions of vascular tissue and sclerenchyma cells in plant material are determinant factors affecting plant degradability. In the future, classification of plant material based on these criteria could lead to the definition of new quality parameters for models of C and N biotransformation in soil.

Organic matter characteristics under native forest, long-term pasture, and recent conversion to Eucalyptus plantations in Western Australia: microbial biomass, soil respiration, and permanganate oxidation

The influence of land-use management on Walkley-Black soil carbon (C) concentration, 3 concentrations of permanganate oxidisable C (33, 167, and 333 mm), microbial biomass, and soil respiration in a laboratory incubation was tested in surface soil from 10 sites in south-western Australia. The sites ranged in total C concentration from 1.9 to 8.3%, and represented a broad climatic and soil-type distribution across south-western Australia. At each of the sites, 0-10 cm soil was collected from plots in pasture (20-71 years old), Eucalyptus globulus plantation (7-10 years old, established on ex-pasture), and native vegetation. Soil profiles and position in the landscape for each of the land-use types were matched as closely as possible at each site to minimise influences other than land use. Total C was highly correlated with clay content. Land use caused no significant change in the relationship between total C and soil texture, and land use had little effect on total C concentration. Permanganate-oxidisable C was highly correlated with Walkley-Black organic C (R2�&amp;gt;�0.90) for all 3 concentrations that were investigated. Only the most dilute concentration of permanganate-oxidisable C (33 mm) was sensitive enough to detect small changes in soil organic matter with land use (P = 0.045). Microbial biomass and respiration at 25 kPa matric potential moisture content and 35°C temperature were used as biological indicators of soil organic matter lability. Cumulative respired C was more sensitive to land use than Walkley-Black organic C, with lower respiration in native soils compared with managed soils with low C concentrations, but higher than the managed soils at sites with high C concentrations. Microbial biomass was not significantly affected by land use. Microbial biomass and cumulative respired C were strongly influenced by soil texture, with the microbial quotient (proportion of microbial biomass in total carbon) and the proportion of total C respired significantly lower in soils with higher silt and clay contents. Land use had no significant effect on these relationships. Overall, land use caused only minor differences in the biological and chemical indicators of organic matter quality across a broad range of sites in south-western Australia.

Labile organic matter as an indicator of organic matter quality in arable and pastoral soils in New Zealand

Labile organic matter fractions (light fraction C, microbial biomass C and water-soluble organic matter) were extracted from two soils (Lismore silt loam and Temuka clay loam) varying in cropping history from long-term (>9 yr) arable cropping to long-term (>9 yr) pasture in the Canterbury region of New Zealand. With increasing periods under pasture, soil organic C content increased and the amounts of labile organic matter extracted increased (microbial biomass C, 1.0–2.2% of organic C; light fraction, 1.8–4.6% organic C and water-soluble C, 0.7–1.2% organic C). Labile organic matter was more closely correlated with previous cropping history ( R=0.89–0.96) than with soil organic C content ( R=0.81–0.82). Alternating these soils under rotations of 2–5 yr of pasture followed by 2–5 yr arable resulted in soil organic C remaining unchanged while labile organic matter increased under pasture and declined under the arable phase. The three indices of labile organic matter were closely correlated suggesting they are interrelated properties. In the Lismore soil the mean proportion of total soil organic C, N and P present in water-soluble form differed widely being 0.28, 0.18 and 0.03% respectively for field-moist samples. This presumably reflects differences in chemical nature, solubility, biodegradability and affinity for soil colloids of soil organic C, N and P compounds. Water-soluble organic C, N and P was much greater when extracted from air-dried than field-moist soils and this difference was proportionately greater for soils with higher total soil organic matter contents. Water-soluble organic matter in air-dried soils was thought to have originated from soil solution, from lysed desiccated microbial cells and from labile humic material. It was concluded that inclusion of grazed pastures in a cropping system maintains labile organic C in higher amounts than is possible under annual cropping.

Spatial and Temporal Variability of Extractable Lipids as Influenced by Cropping History

Tillage and crop rotations may alter soil organic matter (SOM) content and quality. Organic matter content can be satisfactorily assessed by determining total organic matter and C content, but easily obtainable, reliable, and highly sensitive indicators of its quality are still lacking to assess its biological, chemical, and physical functions. The spatial and temporal distributions of diethyl ether–(DEE) and chloroform‐(CHCl3) extractable lipids and gravimetric DEE/CHCl3 and CHCl3/total extractable lipids (TEL) ratios were evaluated as indicators of organic matter quality in two soils of Agri‐Food Canada cropping system fields situated in Qu e ´ bec. Diethyl ether and TEL were significantly (P ≤ 0.001) more abundant under perennial than annual crops, indicating that the perennial crops were better suppliers of easily biodegradable organic matter. Chloroform‐extractable lipids remained relatively constant under both crop rotations, indicating that soil biochemical inertness was relatively the same. Spatial and temporal distributions of these indicators of soil organic matter quality closely correlated with total organic C and clay contents. The DEE/CHCl3 and CHCl3/TEL ratios proposed for assessing organic matter quality were very sensitive (P ≤ 0.01) in detecting changes in SOM status resulting from crop rotations and tillage practices.