Soil Decomposition Research Articles

Stronger negative priming effect and lower basal respiration rates in nutrient-poor as compared to nutrient-rich forestry-drained peatland.

Land-use changes, e.g., forestry drainage, modify the characteristics of peatland soil and affect the peatland carbon (C) balance. Peat soil nutrient status, related mainly to the original peatland type, also has an impact on the C balance after drainage, as observed earlier at the ecosystem scale for two forestry-drained sites in Southern Finland. Here the aim was to compare the soil CO2 fluxes from the two sites, nutrient-poor and nutirent-rich forestry-drained peatlands, and study the effect of plant photosynthates on the decomposition of peat C. Therefore, the respiration rates and priming effect (PE) of peat soils with variable nutrient status were examined in the laboratory. Half of the samples were labelled with 13 C-glucose to study the effect of fresh C addition on the soil decomposition. The 13 CO2 -samples were analysed with isotope ratio mass spectrometry. A two-pool mixing model was applied to separate the soil- and sugar-derived respirations and to determine the PE. The nutrient-rich peat soil respired generally more than the nutrient-poor peat. A negative PE was observed in both peat soils, suggesting that the addition of fresh C did not increase the soil decomposition, but on the contrary decreased it. The negative PE was significantly more pronounced in nutrient-poor peat soil than in the nutrient-rich peat treatments, suggesting that the higher nutrient availability suppresses the negative PE. These results imply that microbes prefer utilizing fresh C instead of old C in the short term and that the peat decomposition is suppressed in the presence of fresh C inputs from vegetation at forestry-drained peatlands. These effects are even stronger in peat soils with less nutrients available. Ecosystem scale and soil process models could be improved with the help of these results.

Maize-potato residue mixing in agricultural soils enhances residue decomposition and stable carbon content by modifying the potential keystone microbial taxa

Microbe-regulated organic residue decomposition is a central hub of carbon (C) cycling in ecosystems. However, little is known about the changes in organic C composition and its microbial mechanisms during mixed crop residue decomposition in agroecosystems. We conducted a field litterbag experiment to explore the changes in organic C chemical structure and their associations with microbial communities during mixed (1:1 maize:potato residues based on dry matter mass) and single-species residue decomposition in agricultural soils. Compared with single-species residues, mixed residues exhibited a positive non-additive effect, specifically higher mass loss, and more recalcitrant organic C composition. Structural equation modelling combined with network analysis suggested that residues mixing modified bacterial keystone taxa, augmented the activity of C-degrading enzymes such as β-glucosidase, and increased stable C content during mixed residues decomposition. Thus, this study highlights the potential advantages of applying residue mixtures to agri-cropping soils to increase the relative amount of persistent aromatic compounds derived from their decomposition and the importance of bacterial keystone taxa during residue decomposition.

Response of Cellulose Decomposition and Nodulation in Soils Amended with Biochar for Peri-Urban Agriculture

Peri-urban agriculture is becoming a potential step to promote sustainable and environmental food production systems. Our aim was to study the effect of biochar application at various rates on faba bean growth, cellulose decomposition, nodulation, and selected enzyme activities associated with carbon cycling in clay and sandy soils collected from peri-urban agricultural areas near the city of El-Minia, Egypt. To achieve this aim, incubation and pot experiments were conducted under controlled greenhouse conditions using clay and sandy soil. Among the studied treatments, using biochar at the rate of 3 kg/sq·m was the most effective soil amendment followed by biochar at the rate of 2 kg/sq·m. At 60 days of incubation, the count of cellulose-decomposing microorganisms reached a high level in both clay and sandy soil, and then decreased after 90 days, regardless of the biochar rate. The response of the cellulose-decomposer ratio (Fcd/Bcd) was positively correlated with biochar rates and incubation time. The obtained results showed significant increases in fresh and dry weight in clay soil compared to sandy soil. In any case, the use of biochar as a soil amendment enhanced soil health, soil microbial communities, and increased cellulose-decomposing microorganisms, thus improving faba bean nodulation and growth.

Solid tailings after supercritical CO<sub>2</sub> extraction of lignocellulosic biomass as a source of quality biochar for energetic use and as soil improvement

Lignocellulosic biomass is a rich source of bioactive compounds that are extracted industrially from different parts of the plant. The extraction process generates residues that can contain from 75% to 95% of the raw material depending on the species. Among the many potential products of post-extraction residue’ processing there is biochar. The research objective was: i) to evaluate the parameters of biochars derived from post-extraction bark, wood and bark and wood of four lignocellulosic species; and ii) to discuss the parameters in the context of biochar functionality as an energy carrier and soil improver. The residues were subjected to pyrolysis at the three temperatures 170, 270, and 370°C, which correspond to the initiation of carbonization, and two biochars that differ in the decomposition rates of hemicelluloses, cellulose and lignin. On average, biochars had a high energy value owing to the increased content of the total and fixed carbon and calorific value by 77.0-78.4% DM, 64.6-66.7% DM and 25.8-30.1 MJ kg–1, respectively. The higher quantity of ash after processing of bark residues than wood residues implicates a lower energy value but at the same time the ash obtained is a better source of mineral compounds in the context of soil fertilization. Concerning the use of biochar as a soil improver, the biochars demonstrated lower H/C and O/C molar ratios, that indicate raised stability and resistance to the geochemical decomposition in soil. It was proven that the bark-based biochars had much higher concentrations of micro- and macronutrients as well as a higher pH, while processed wood fractions resulted in higher concentrations of total carbon and fixed carbon in biochar. The research results suggest that lignocellulose biomass extraction residues can serve as a valuable input material for production of biochar.

Porewater constituents inhibit microbially mediated greenhouse gas production (GHG) and regulate the response of soil organic matter decomposition to warming in anoxic peat from a Sphagnum-dominated bog.

Northern peatlands store approximately one-third of terrestrial soil carbon. Climate warming is expected to stimulate the microbially mediated degradation of peat soil organic matter (SOM), leading to increasing greenhouse gas (GHG; carbon dioxide, CO2; methane, CH4) production and emission. Porewater dissolved organic matter (DOM) plays a key role in SOM decomposition; however, the mechanisms controlling SOM decomposition and its response to warming remain unclear. The temperature dependence of GHG production and microbial community dynamics were investigated in anoxic peat from a Sphagnum-dominated peatland. In this study, peat decomposition, which was quantified by GHG production and carbon substrate utilization is limited by terminal electron acceptors (TEA) and DOM, and these controls of microbially mediated SOM degradation are temperature-dependent. Elevated temperature led to a slight decrease in microbial diversity, and stimulated the growth of specific methanotrophic and syntrophic taxa. These results confirm that DOM is a major driver of decomposition in peatland soils contains inhibitory compounds, but the inhibitory effect is alleviated by warming.

Decomposition of green tea and rooibos tea across three monospecific temperate forests: Effect of litter type and tree species

We studied the effect of different forest covers on carbon (C) and nitrogen (N) dynamics of two standardised litters during decomposition in soil. For this purpose, commercially available bags containing green tea or rooibos tea were incubated in close monospecific stands of Fagus sylvatica, Pseudotsuga menziesii, and Quercus cerris, in the Apennines range, Italy, and then analysed at different intervals for up to two years. We also investigated the fate of various C functional groups in both types of litter under beech by nuclear magnetic resonance spectroscopy. After two years of incubation, green tea had not changed its original C/N ratio of 10, while rooibos tea had nearly halved its original value of 45, because of different C and N dynamics. Both litters progressively lost C, about fifty per cent of the initial content in the case of rooibos tea, and a little more for green tea, most of the loss occurring in the first three months. In terms of N, green tea behaved as for C, while rooibos tea in the early stage lost part of its N stock, fully recovering it by the end of the first year. Under beech, both litters showed a preferential loss in carbohydrates during the first trimester of incubation and, consequently, an indirect enrichment in lipids. Later on, the relative contribution of the various C forms remained practically constant.Our results overall support that the decay rate and compositional changes of litter depend strongly on the litter type and little on the tree cover of the soil in which the litter is incubated.

Temporal soil carbon and nitrogen accumulation after land use change from paddy rice to upland sugarcane cropping in Thailand

In this study it was hypothesized that accelerated soil organic carbon (SOC) mineralization caused by land use change (LUC) from lowland (paddy rice) to upland (sugarcane) cropping could be compensated for by increased inputs of new sugarcane biomass-derived C and N. We used the 13C natural abundance of SOC to follow dynamics of “old” rice-derived and “new” sugarcane-derived SOC after LUC. C and N dynamics in the top 100 cm soil layer as well as annual C and N inputs from plant biomass (residues, roots) and N input from chemical fertilizer were analysed using samples from farmers' fields: monocrop paddy rice cultivated for >40 years and sugarcane with 6, 13 and 17 years cropping after conversion from rice. LUC increased inputs of C and N by 91–141% and 39–48%, respectively, considering plant-derived biomass and applied chemical fertilizer. This resulted in temporal accumulation of total soil C and N stocks. Partitioning of soil C sources based on 13C measurements showed that the fraction of rice-derived C comprised 65% of the total that corresponded to a decrease of rice-derived C from 58.9 to 38.8 Mg C ha−1 after 17 years of LUC. Total content of sugarcane-derived C along the soil profile increased with time. Accumulation of new sugarcane-derived C in the soil was slower over time than decomposition of rice-derived soil C in upper and deeper soil layers. Our research revealed a fundamental understanding of the transient C accumulation potential of agricultural soils after LUC from anaerobic to aerobic cropping.

Characterization of physicochemical parameters and bacterial diversity of composted organic food wastes in Dubai

Composting favours recycling organic waste and producing an end product with high bioenergy potential and significant nutritional value for the soil. Analysing composted organic waste prepared in Dubai, a region with a desertic climate and a unique environment is essential since environmental conditions can greatly affect the physicochemical and biological soil properties and no studies in the Gulf region have been published yet on that process. This study analysed twelve different compost samples prepared in well ventilated wooden chambers, using home-generated organic wastes following the hot aerobic composting method for a duration of three months. The physicochemical parameters, measured at the end of the study, revealed that organic matter, electrical conductivity and pH were within the standard ranges while moisture content was low. Concerning macronutrients, most of the samples were within the standard range for carbon, potassium and sodium, while they were poor in phosphorous and nitrogen. Metagenomic analysis with Illumina MiSeq revealed the abundance of Firmicutes (30.35%), followed by Bacteroidota (26.69%), Proteobacteria (21.47%), and Actinobacteriota (11.17%). The phylum Planctomycetota, solely detected in compost and known to have a significant impact on soil ecosystem and decomposition of organic matter, was reported at a relatively significant level (2.35%). The Clostridia class, efficient in degrading cellulose, was described at high levels compared to other studies. The composting project succeeded in generating a healthy soil but lengthening the duration will allow the samples to fully decompose and therefore increase the total available nitrogen and phosphorus to meet the criteria of a typical mature compost. Various microbial consortia helped in the decomposition process. The qualitative information collected in this study will help in improving the composting technology to favour its utilization by a larger public in the Gulf region.

The footprint of large wildfires on the multifunctionality of fire-prone pine ecosystems is driven by the interaction of fire regime attributes

BackgroundMediterranean ecosystems dominated by Pinus pinaster Ait. (maritime pine) are subject to a shift from fuel-limited to drought-driven fire regimes, characterized by an increasing wildfire extent, recurrence, and severity. Previous studies have not addressed the interacting effects of fire recurrence and severity on the ecosystem multifunctionality (EMF) of maritime pine forests, although complex relationships between such fire regime attributes are expected. Here, we evaluated the medium-term effects of fire recurrence and severity on the EMF response of unmanaged, native pine ecosystems dominated by Pinus pinaster in the western Mediterranean Basin. We considered four key ecosystem functions computed from functional indicators (carbon regulation, decomposition, soil fertility, and plant production), which were pooled into an EMF construct. The fire regime effects on the trade-offs and synergies between the considered ecosystem functions were also analyzed.ResultsMultiple ecosystem functions responded differentially to fire recurrence and severity. Fire recurrence had a strong effect on soil fertility, decomposition, and plant production functions. No significant effects of fire severity on any of the individual functions were detected. However, both fire regime attributes interacted to determine soil fertility and decomposition functions, suggesting that their performance is only impaired by fire severity when fire recurrence is low. The differing responses to the fire regime attributes among ecosystem functions fostered a significant EMF response to fire severity and its interaction with fire recurrence, indicating that the effect of fire severity on EMF was stronger under low fire recurrence scenarios, even when relationships between individual functions and fire severity were weak. Fire recurrence caused significant trade-offs between functions to emerge. However, these trade-offs were not strong enough to differ significantly from the intrinsic trade-offs (i.e., regardless of the fire regime) of maritime pine ecosystems.ConclusionsOur results indicated the need to use an integrative approach to assess the response of ecosystem functioning to the fire regime in maritime pine ecosystems. Adaptive management responses are necessary towards the minimization of repeated burnings and the reduction of the fuel load in unmanaged maritime pine stands of the western Mediterranean Basin with similar characteristics to those analyzed in this study.

Metagenomics reveals the effect of long-term fertilization on carbon cycle in the maize rhizosphere.

Long-term fertilization can result in the changes in carbon (C) cycle in the maize rhizosphere soil. However, there have been few reports on the impacts of microbial regulatory mechanisms on the C cycle in soil. In the study, we analyzed the response of functional genes that regulate the C fixation, decomposition and methane (CH4) metabolism in maize rhizosphere soil to different fertilization treatments using metagenomics analysis. As the dominant C fixation pathway in maize rhizosphere soil, the abundance of the functional genes regulating the reductive citrate cycle (rTCA cycle) including korA, korB, and IHD1 was higher under the chemical nitrogen (N) fertilizer treatments [nitrogen fertilizer (N), compound chemical fertilization (NPK), the combination of compound chemical fertilizer with maize straw (NPKS)] than maize straw return treatments [maize straw return (S), the combination of phosphorus and potassium fertilizer with maize straw (PKS)]. The NPK treatment decreased the abundance of functional genes involved in 3-hydroxypropionate bicycle (3-HP cycle; porA, porB, and porD), which was one of the major C fixation pathways in soil aside from dicarboxylate-hydroxybutyrate (DC/4-HB cycle) and Calvin cycle. The abundance of functional genes related to C degradation was higher in S, PKS and NPKS treatments than N and NPK treatments, and chemical N fertilizer application had a significant effect on C degradation. The dominant Methanaogenesis pathway in maize rhizosphere soil, used acetate as a substrate, and was significantly promoted under chemical N fertilizer application. The functional genes that were related to CH4 oxidation (i.e., pmoA and pmoB) were reduced under N and NPK treatments. Moreover, soil chemical properties had a significant impact on the functional genes related to C fixation and degradation, with SOC (r2 = 0.79) and NO3--N (r2 = 0.63) being the main regulators. These results implied that N fertilization rather than maize straw return had a greater influence on the C cycle in maize rhizosphere soil.

Fe(III) stabilizing soil organic matter and reducing methane emissions in paddy fields under varying flooding conditions

The role of iron (Fe) in soil organic matter (SOM) stabilization and decomposition in paddy soils has recently gained attention, but the underlying mechanisms during flooding and drying periods remain elusive. As the depth water layer is maintained in the fallow season, there will be more soluble Fe than during the wet and drainage seasons and the availability of oxygen (O2) will be different. To assess the influence of soluble Fe on SOM mineralization during flooding, an incubation experiment was designed under oxic and anoxic flooding conditions, with and without Fe(III) addition. The results showed that Fe(III) addition significantly (p < 0.05) decreased SOM mineralization by 14.4 % under oxic flooding conditions over 16 days. Under anoxic flooding incubation, Fe(III) addition significantly (p < 0.05) decreased 10.8 % SOM decomposition, mainly by 43.6 % methane (CH4) emission, while no difference in carbon dioxide (CO2) emission was noticed. These findings suggest that implementing appropriate water management strategies in paddy soils, considering the roles of Fe under both oxic and anoxic flooding conditions, can contribute to SOM preservation and mitigation of CH4 emissions.

Field inoculation by arbuscular mycorrhizal fungi with contrasting life-history strategies differently affects tomato nutrient uptake and residue decomposition dynamics

PurposePlant microbial biostimulants, such as arbuscular mycorrhizal fungi (AMF), enhance nutrient concentration in fruits, including tomato. However, field studies on tomato AMF inoculation are scarce. AMF species belonging to Gigasporaceae and Glomeraceae families known to vary in life-history strategies may determine differential effects on plant nutrient benefits and residue decomposition. Despite this, the effect of different life-history strategies on nutrient acquisition of tomato fruits has not been investigated yet.MethodsWe studied the effect of inoculation of two tomato varieties with four AMF species belonging to Glomeraceae and Gigasporaceae. Fungal colonization, yield, fruit nutrient concentration, litter decomposition, and bacterial and fungal abundances in soil were assessed in the field under organic agriculture.ResultsOverall Gigasporaceae promoted the concentration of nutrients in tomato fruits compared to Glomeraceae. A variability in AM fungal colonization and fruit nutrient concentration was detected within Glomeraceae. Scutellospora pellucida increased the yield (+ 27%) of var. Rio Grande with respect to Gigaspora gigantea. In var. Rio Grande, inoculation with Funneliformis mosseae did not change litter decomposition as compared to non-inoculated controls, whereas it was lower than in Sclerocystis sinuosa and Gigasporaceae species, which showed the highest decomposition rates. AMF inoculation promoted soil total bacterial and fungal abundance and fungal:bacterial (F:B) ratio compared to controls, and members of Gigasporaceae had the highest F:B ratio.ConclusionThese findings pointed at the inclusion of AM fungal life-history strategy within the selection criteria for the development of biofertilizers able to enhance the nutritional value of vegetables under organic farming systems.

Ratio of In Situ CO2 to CH4 Production and Its Environmental Controls in Polygonal Tundra Soils of Samoylov Island, Northeastern Siberia

AbstractArctic warming causes permafrost thaw and accelerates microbial decomposition of soil organic matter (SOM) to carbon dioxide (CO2) and methane (CH4). The determining factors for the ratio between CO2 and CH4 formation are still not well understood due to scarce in situ measurements, particularly in remote Arctic regions. We quantified the CO2:CH4 ratios of SOM decomposition in wet and dry tundra soils by using CO2 fluxes from clipped plots and in situ CH4 fluxes from vegetated plots. At the water‐saturated site, CO2:CH4 ratios decreased sharply from 95 at beginning of July to about 10 in August and September with a median of 12.2 (7.70–17.1; 25%–75% quartiles) over the whole vegetation period. When considering CH4 oxidation, estimated to reduce in situ CH4 fluxes by 10%–31%, even lower CO2:CH4 ratios were calculated (median 10.9–8.41). Active layer depth and soil temperature were the main factors controlling these ratios. Methane production was associated with subsoil (40 cm) temperature, while heterotrophic respiration was related to topsoil (5 cm) temperatures. As expected, CO2:CH4 ratios were substantially higher at the dry site (median 373, 292–500, 25%–75% quartiles). Both tundra types lost carbon preferentially in form of CO2, and CH4‐C represented only 0.27% of the dry tundra total carbon loss and 6.91% of the wet tundra total carbon loss. The current study demonstrates the dynamic of in situ CO2:CH4 ratios from SOM decomposition and will help improve simulations of future CO2 and CH4 fluxes from thawing tundra soils.

Deforestation for agriculture leads to soil warming and enhanced litter decomposition in subarctic soils

Abstract. The climate-change-induced poleward shift of agriculture could lead to enforced deforestation of subarctic forest. Deforestation alters the microclimate and, thus, soil temperature, which is an important driver of decomposition. The consequences of land-use change on soil temperature and decomposition in temperature-limited ecosystems are not well understood. In this study, we buried tea bags together with soil temperature loggers at two depths (10 and 50 cm) in native subarctic forest soils and adjacent agricultural land in the Yukon Territory, Canada. A total of 37 plots was established on a wide range of different soils and resampled after 2 years to quantify the land-use effect on soil temperature and decomposition of fresh organic matter. Average soil temperature over the whole soil profile was 2.1 ± 1.0 and 2.0 ± 0.8 ∘C higher in cropland and grassland soils compared to forest soils. Cumulative degree days (the annual sum of daily mean temperatures &gt; 0 ∘C) increased significantly by 773 ± 243 (cropland) and 670 ± 285 (grassland). Litter decomposition was enhanced by 2.0 ± 10.4 % and 7.5 ± 8.6 % in cropland topsoil and subsoil compared to forest soils, but no significant difference in decomposition was found between grassland and forest soils. Increased litter decomposition may be attributed not only to increased temperature but also to management effects, such as irrigation of croplands. The results suggest that deforestation-driven temperature changes exceed the soil temperature increase that has already been observed in Canada due to climate change. Deforestation thus amplifies the climate–carbon feedback by increasing soil warming and organic matter decomposition.

Disentangling the mixed effects of soil management on microbial diversity and soil functions: A case study in vineyards

Promoting soil functioning by maintaining soil microbial diversity and activity is central for sustainable agriculture. In viticulture, soil management often includes tillage, which poses a multifaceted disturbance to the soil environment and has direct and indirect effects on soil microbial diversity and soil functioning. However, the challenge of disentangling the effects of different soil management practices on soil microbial diversity and functioning has rarely been addressed. In this study, we investigated the effects of soil management on soil bacterial and fungal diversity as well as soil functions (soil respiration and decomposition) using a balanced experimental design with four soil management types in nine vineyards in Germany. Application of structural equation modelling enabled us to investigate the causal relationships of soil disturbance, vegetation cover, and plant richness on soil properties, microbial diversity, and soil functions. We could show that soil disturbance by tillage increased bacterial diversity but decreased fungal diversity. We identified a positive effect of plant diversity on bacterial diversity. Soil respiration showed a positive response to soil disturbance, while decomposition was negatively affected in highly disturbed soils via mediated effects of vegetation removal. Our results contribute to the understanding of direct and indirect effects of vineyard soil management on soil life and aids designing targeted recommendations for agricultural soil management.

Organic vegetable crop residue decomposition in soils

Soil organic carbon (SOC) is an important property that influences soil chemical, physical, and biochemical processes and is a key indicator of soil health. Rapid decomposition of crop residues incorporated into soil reduces the potential of carbon (C) sequestration in the Southeast United States where SOC is very low rending residue management very critical. We investigated the C contents and the decomposition of cultivars of popular organic vegetable crops [southern pea (Vigna unguiculata), squash (Cucurbita maxima), sweet potato [Ipomoea batatas (L.) Lam] and tomato (Solanum lycopersicum)] in two soils under laboratory conditions. The C contents of the crop residues were determined by using a wet chemistry method. A non-linear regression model was used to determine the potentially mineralizable C (C0) and the first-order rate constant (k) of the decomposition following incubation of soils treated with the vegetable crop residues for 30 days at room temperature. The average C contents varied between 304 and 437 g kg−1. On average, the sweet potato cultivars showed a greater C0 (19.4 g C kg−1) in Cecil soil than in Hartsells soil while tomato cultivars showed the least C0 (15.9 g C kg−1) in Hartsells soil. The k values showed that squash cultivars decomposed faster (0.106 day-1) than any other crop, whereas southern pea cultivars decomposed the least in Cecil and Hartsells soils. Strong relationships between C0, k, and C/N were established. Organic growers are environmentally conscious framers who wants to mitigate the greenhouse effect and global warming by adopting cropping systems that would sequester more C into the soil. Thus, identifying and selecting vegetable crop cultivars that would incorporate more C in soil is of a great interest to them. These findings have potentials of guiding organic growers in selecting crop cultivars that would increase OC sequestration in soils.

Maximum summer temperatures predict the temperature adaptation of Arctic soil bacterial communities

Abstract. Rapid warming of the Arctic terrestrial region has the potential to increase soil decomposition rates and form a carbon-driven feedback to future climate change. For an accurate prediction of the role of soil microbes in these processes, it will be important to understand the temperature responses of soil bacterial communities and implement them into biogeochemical models. The temperature adaptation of soil bacterial communities for a large part of the Arctic region is unknown. We evaluated the current temperature adaption of soil bacterial communities from 12 sampling sites in the sub- to High Arctic region. Temperature adaptation differed substantially between the soil bacterial communities of these sites, with estimates of optimal growth temperature (Topt) ranging between 23.4 ± 0.5 and 34.1 ± 3.7 °C. We evaluated possible statistical models for the prediction of the temperature adaption of soil bacterial communities based on different climate indices derived from soil temperature records or on bacterial community composition data. We found that highest daily average soil temperature was the best predictor for the Topt of the soil bacterial communities, increasing by 0.63 °C °C−1. We found no support for the prediction of temperature adaptation by regression tree analysis based on the relative abundance data of the most common bacterial species. Increasing summer temperatures will likely increase Topt of soil bacterial communities in the Arctic. Incorporating this mechanism into soil biogeochemical models and combining it with projections of soil temperature will help to reduce uncertainty in assessments of the vulnerability of soil carbon stocks in the Arctic.

Decoupling of cellulose decomposition and glucose mineralization in volcanic forest soils

ABSTRACT Decomposition of organic matters in volcanic soils (ando soils) is generally slowed by sorption onto short-range-order minerals, while decomposition of non-charged substrates such as cellulose and glucose is hypothesized to be promoted by high microbial biomass and nitrogen availability, irrespective of short-range-order minerals. To analyze factors regulating decomposition activities of cellulose and glucose, we measured the decomposition rates of cellulose filter papers and the mineralization rates of 14C-labeled glucose in five volcanic soils in Japan. Glucose mineralization activities increased with increasing microbial biomass C and N, while cellulose decomposition activities (standardized with cumulative temperature) were not related to microbial biomass C or N. Cellulose decomposition activities increased with increasing ratio of soil available N relative to microbial biomass N (microbial N availability), while they decreased with decreasing soil pH and with increasing fungal activities. Soils with relatively high soil pH and microbial N availability exhibit the relatively high potentials of cellulose decomposition. Because cellulose decomposition, rather than glucose mineralization, is a rate-limiting step, soil pH and microbial N availability, rather than microbial biomass, could primarily regulate decomposition rates of cellulose and glucose in volcanic soils.

Interactions among science, environmental policy and public perception in a Mississippi River Delta assimilation wetland

In November 2006, the City of Hammond, Louisiana, began discharging secondarily treated, disinfected municipal effluent through a distribution pipeline to a 14,000 ha emergent wetland complex referred to as the East Joyce Wetlands. The primary goals were to improve local water quality by taking effluent that would normally be discharged to local waterways and directing it to wetlands that were hydrologically isolated and degraded by saltwater intrusion. During the 2007 growing season there was robust growth of marsh vegetation with a near doubling of productivity compared to controls, however, during winter 2007 there was a massive decline in vegetation and transition to open water in the 121 ha of wetlands in the direct path of effluent discharge. Herbivory by nutria was found to be the cause of the decline, but not before several other causes were hypothesized and largely accepted by the public, specifically that the cause of the vegetation decline was due to excess nutrients that increased rates of soil decomposition and limited root growth of plants. Studies show these hypotheses were flawed due to scale and methodology issues. Intensive nutria removal began in the spring of 2008 and continued through the winter of 2008–2009, with approximately 2000 nutria killed, and vegetation recovery began during the spring of 2009, which was most pronounced and consistent nearest the discharge pipe. Vegetative cover increased dramatically from the near complete loss after nutria grazing to near 80% by 2015, and wetland recovery has continued to the present.

Carrot genotypes differentially alter soil bacterial communities and decomposition of plant residue in soil

PurposeFarmers need alternative approaches to manage nitrogen (N) that meet crop needs while reducing loss to the environment. Identifying crop genotypes that promote decomposition of organic materials and understanding the potential mechanisms responsible could help address this challenge. Consequently, we aimed to 1) determine whether carrot genotypes differ in their potential to facilitate organic matter decomposition in soil, and 2) identify bacterial taxa that are stimulated by carrot roots, and thus could play a role in these processes.MethodsWe grew five genotypes expected to differ in N use efficiency in a nutrient-poor soil amended with 15 N-enriched corn residue, tracked changes in carbon (C) and N pools, quantified microbial activity and bacterial community composition, and predicted the potential expression of microbial genes involved in soil C and N cycles.ResultsExperimental genotype 8503 had the greatest capacity to promote decomposition of corn residues. This genotype had the highest % of N from the corn residue in its taproots and on average, promoted higher b-glucosidase activity in soils. Distinct bacterial communities from the families Micromonosporaceae, Chromatiaceae, and Rhodospirillaceae were also enriched in the soils of genotypes like 8503 that were most effective in obtaining N from the corn residue, and this was correlated with greater potential expression of genes responsible for β-glucosidase and nitrification activity.ConclusionsCarrot genotypes do differ in their potential to alter soil bacterial communities and stimulate microbially-mediated decomposition of organic materials indicating that it may be possible to begin selecting for this important trait.