Soil Carbon Retention Research Articles

Defining a core microbial necrobiome associated with decomposing fungal necromass.

Despite growing interest in fungal necromass decomposition due to its importance in soil carbon retention, whether a consistent group of microorganisms is associated with decomposing necromass remains unresolved. Here we synthesize knowledge on the composition of the bacterial and fungal communities present on decomposing fungal necromass from a variety of fungal species, geographic locations, habitats, and incubation times. We found that there is a core group of both bacterial and fungal genera (i.e. a core fungal necrobiome), although the specific size of the core depended on definition. Based on a metric that included both microbial frequency and abundance, we demonstrate that the core is taxonomically and functionally diverse, including bacterial copiotrophs and oligotrophs as well as fungal saprotrophs, ectomycorrhizal fungi, and both fungal and animal parasites. We also show that the composition of the core necrobiome is notably dynamic over time, with many core bacterial and fungal genera having specific associations with the early, middle, or late stages of necromass decomposition. While this study establishes the existence of a core fungal necrobiome, we advocate that profiling the composition of fungal necromass decomposer communities in tropical environments and other terrestrial biomes beyond forests is needed to fill key knowledge gaps regarding the global nature of the fungal necrobiome.

Response of Forest Ecosystems to Decreasing Atmospheric Nitrogen Deposition

Nitrogen deposition has serious consequences to global change. Excessive nitrogen deposition leads to nitrogen saturation in forests, resulting in soil acidification, nitrate leaching, an increase in nitrous oxide emissions, and a decrease in plant species diversity and vegetation productivity. Under the reduction of atmospheric nitrogen deposition in Europe, North America, and China, summarizing the response of forests to decreasing nitrogen deposition can not only improve the knowledge framework of the impact of nitrogen deposition on forests, but also evaluate the effects of emission abatement actions, as well as provide scientific basis for future air pollution control. This study reviewed the response of soil, surface water, nitrogen cycle, and vegetation of temperate forests in Europe and North America and subtropical forests in southwest China to the reduction in atmospheric nitrogen pollution gases and thus nitrogen deposition. The soil water nitrogen concentration responded rapidly to the nitrogen deposition reduction, although the trend was inconsistent. The soil acidification and nitrogen cycles showed a delayed response of recovery from high nitrogen deposition. The nitrogen mineralization and immobilization, soil carbon retention, and net primary production might take decades to respond to the nitrogen deposition reduction. However, the soil inorganic nitrogen pool and nitrogen leaching decreased with the decline in nitrogen deposition, although a one-or two-year lag existed. The surface water nitrogen concentration was closely related to nitrogen status in forests. After the nitrogen deposition decreased, the nitrogen leaching and thus the surface water nitrogen concentration decreased in the areas with historically high nitrogen deposition. However, the low surface water nitrogen concentration in the nitrogen-limited forests was not significantly affected by the nitrogen deposition changes. The recovery of surface water acidification was affected by soil sulfur desorption/mineralization and nitrification/denitrification. The foliar nitrogen concentration decreased with the decline in nitrogen deposition. The nitrogen-saturated forests and regional surface water in southwest China showed a recovery trend from high nitrogen deposition, as a consequence of the implementation of the Total Emissions Control of Air Pollutants and later the Action Plan of Air Pollution Prevention and Control.

Lower microbial carbon use efficiency reduces cellulose-derived carbon retention in soils amended with compost versus mineral fertilizers

Cellulose decomposition is a key process in soil carbon (C) cycling due to the high abundance of cellulose in plant biomass. Microbial functional groups that sequester C from cellulose, and the accumulation of cellulose C in soil aggregates, remains debated. We hypothesized that cellulose derived 13C would be more efficiently converted into soil organic C by microorganisms, and retained in soil subjected to long-term application of compost. In this study, soil sampled from a long-term (27 years) field experiment with application of compost (Compost), NPK fertilizers (NPK) and without fertilizers (control), was incubated with 13C-cellulose for 120 days. The cellulose 13C content, microbial community structure (lipid biomarkers) and microbial 13C use efficiency (CUE) were measured. The incorporation of 13C into large macroaggregates (>2000 μm), small macroaggregates (250–2000 μm), microaggregates (53–250 μm), and silt + clay fraction (<53 μm) was analyzed to elucidate cellulose 13C sequestration process in aggregates. In contrast to our initial hypothesis, 13C remaining in soil after 120 days of incubation was maximal in unfertilized soil (25%) and minimal in Compost soil (17%). Compost soil had higher abundance of fungi and especially fast-growing bacteria (Gram-negative (G–) bacteria) than NPK and control soils. This accelerated decomposition and lowered CUE of 13C, therefore reducing the amount of 13C remaining in the Compost soil. In contrast, in the other soils, the lower fungal abundance reduced cellulose decomposition, which in turn contributed to growth of Gram-positive (G+) bacteria characterized by larger CUE than G– bacteria. This increased the ratio of G+/G– bacteria, resulting in larger CUE and more 13C remaining in NPK and control soils. Cellulose-derived 13C content decreased in small macroaggregates and microaggregates for all three soils, and in silt + clay fraction for the Compost soil; meanwhile, cellulose-derived 13C content increased in the silt + clay fraction for NPK and control soils from day 14 onwards. The ratios of 13C content in small macroaggregates and microaggregates to that in silt + clay fraction were higher in NPK and unfertilized soils than in Compost soil during the incubation. This indicated that less 13C was redistributed from large aggregates to silt + clay fraction in Compost soil. Overall, cellulose was more rapidly decomposed and incorporated into aggregates in organic C-rich soil, but their transformation efficiency into soil organic C was lower than in organic C-poor soil.

Impact of Agricultural Practices and their Management Techniques on Soil Carbon Sequestration: A Review

Carbon emissions through various sources possess a great threat to the environment. An increase in carbon concentration in the atmosphere resulted in increased temperature. Escalating warmness in the environment started melting of glaciers, day by day water level in oceans also increasing at an alarming rate. Forests, oceans and agricultural soils act as a sink for atmospheric carbon. Sinking sites help in making the balance of various gases in the atmosphere. Managing agricultural soils provides a good opportunity for more carbon storage. Adoption of conservation tillage, incorporation or on surface management of crop residue and balanced fertilization helps in reducing carbon removal from soil. More organic matter means more humus formation and more carbon retention in soil. Such management practices not only boost soil carbon-storing capacity but also increase soil fertility through hiking nutrient availability to plants and microbial populations in the soil. Higher plant growth results in more assimilation of CO2 in the photosynthesis process.

Long-term fertilisation strategies and form affect nutrient budgets and soil test values, soil carbon retention and crop yield resilience

The aim of this study was to evaluate the effects of long-term mineral and organic fertilisation on crop performance and soil fertility. The Long-Term Nutrient Depletion Trial (Denmark) was used to analyse changes in concentrations of Olsen-P, exchangeable potassium (K) and soil carbon (C). Yield responses (2010–2016) were evaluated making use of an early-season temperature model, fertilisation practices were evaluated by nutrient budgets, and nitrogen use efficiency by calculation of apparent recovery (ANR) in subplots receiving mineral N. Olsen-P (r2 = 0.68, P < 0.001) and exchangeable K (r2 = 0.86, P < 0.001) were correlated with the nutrient budgets. Soil C concentrations increased from 10.0 g kg−1 (1995) to between 11.1–14.6 g kg−1 (2016), with the greatest accumulation under slurry applications (P < 0.05, equalling 17–47% retention of slurry-C inputs). Relative yield responses of spring barley were associated with early season cold stress, but the model was not applicable to other crops. Increases of ANR in response to long-term phosphorus (P) applications were not significant. Balanced fertilisation is an effective way to maintain nutrient availability, and to ensure high and stable crop productivity and efficient use of nutrients. Direct C inputs from animal slurry are a major driver for increases of soil C concentrations.

The effect of C:N ratios on the fate of carbon from straw and green manure in soil

SummaryStraw and green manures are among the most important soil amendments used worldwide to provide agricultural soil with organic matter (OM). The reported improvement in soil organic matter content varies greatly; therefore, there is a need for mechanistic approaches to evaluate substrate turnover in the soil. This study compares the results of a field and an incubation experiment to follow the fate of carbon from organic fertilizers in soil as a function of the C:N ratio of the amendments. The amendments were straw (small‐N, Hordeum vulgare L.; large‐N, Pisum sativum L.) or green manure (Sinapis alba (M)) with additional organic or mineral fertilizers to alter the C:N ratio of the soil–substrate mixture. In the 100‐day field study, C respiration was measured at defined intervals at three locations with different soil types (Luvisol, Fluvisol and Arenosol). In the incubation experiment, C changes over 300 days were quantified based on the measurement of C respiration and C amounts in the soil–substrate mixture at the start and end of the experiment. Furthermore, microbial biomass was quantified at the end of the experiment to enable an assessment of microbial C‐use efficiency. In the field experiment, a significant correlation between N supply and C fate occurred at one site only (Luvisol) where retention of C from organic substrates was larger with increased N supply. In the incubation experiment, N supply and C fate were correlated significantly for both soils under study (Arenosol and Fluvisol). Furthermore, C‐use efficiency was positively correlated with C retention from organic inputs to the Fluvisol in the incubation experiment, whereas the opposite situation occurred with the Arenosol. This indicated that C retention from organic inputs was not dependent on carbon‐use efficiency by the microbial community under these conditions. We conclude that stoichiometric implications apply to carbon retention in soil that depend on N availability for soil microbes. In the early stages of organic matter turnover, the outcome of N availability might be concealed by the effect of chemical recalcitrance of the substrates. The length of this phase will depend on environmental conditions for microbial activity. The effect of the C:N ratio on the fate of C from organic amendments must be considered in the assessment of C management strategies in arable farming.Highlights Organic inputs to soil with a large C:N ratio lose more C in turnover than amendments with a small C:N ratio. Retention of C from organic amendments in soil appears to depend on microbial C-use efficiency and availability of nitrogen. The soil type and related environmental conditions affect CUE and the magnitude of C retention. Negative correlation between C:N ratio of organic amendments and C fate in soil must be considered in carbon management strategies.

Does tree species composition control the soil carbon stocks of the Hyrcanian forest in the Northern Iran? (A case study in Guilan province, Iran)

This work studied the effects of tree species composition on soil carbon storage in five mixed stands dominated by oriental beech and grown in the western Caspian region in Guilan province, called Astara, Asalem, Fuman, Chere and Shenrud. The thickness of the litter layer, soil characteristics, tree composition and percentage of canopy coverage were measured in each stand. Total soil organic carbon differed significantly by stand. Total (organic) carbon stores at Fuman, which had the lowest tree species richness with 2 species and least canopy coverage (75%), were significantly (p <0.05) higher than at other locations. Carbon storage in topsoil (0–10 cm) was significantly lower in Shenrud, which had the highest tree species richness with 5 species and highest canopy coverage (95%). The high percentage of canopy coverage in Shenrud probably limited the conversion of litter to humus. However, in the second soil layer (10–25 cm), Asalem, with high tree species richness and canopy coverage, had the highest carbon storage. This can be explained by the different rooting patterns of different tree species. In the Hyrcanian forest. According to the results, it can be concluded that not only tree composition but also canopy coverage percentage should be taken under consideration to manage soil carbon retention and release.

Potential of Tithonia diversifolia Chimato Composts in Enhancing Soil Carbon Sequestration

Composts have different potentials of sequestering carbon into underground soils. The present study assessed soil carbon sequestration potential of Tithonia diversifolia chimato composts (CC). CC was made by blending Tithonia diversifolia with maize stalks (Td/MS) as follows: 0:100, 20:80, 50:50, 60:40, 80:20 and 100:0. Soil treatments pots were arranged in fully randomized design in which a homogeneous mixture of 1.0 kg of CC and 4 kg of soil was placed in pots. 3 maize seeds were planted per pot and standard agronomical practices were followed till harvesting. Soil organic carbon was determined using standard methods before and after each cropping season. Maximum soil carbon retention was observed in treatments supplemented with chimato composts prepared using Td/MS ratios of 50:50 (89.1%) and 60:40 (92.3%) compared to those 0:100 (20%), 20:80 (23.2%) and 40:60 (10.9%) which experienced greatest soil organic carbon loss. Significant positive correlation was observed (r = 0.996; P < 0.05) between initial T. diversifolia used in making chimato composts and soil organic carbon retention wheras significant negative correlation was observed (r = 0.983) between the same with soil organic carbon losses. The observation is attributable to high levels of maturity and stability of CC prepared with Td/MS = 50:50 and Td/MS = 60:40 such that relatively significant stable C was being oxidized and decomposed to meet microbial and plant N requirements. Considerable nitrogen loss was observed in treatments with chimato composts prepared using Td/MS = 100:0 (58.9%) and Td/MS = 80:20 (47.7%) and maximum nitrogen was retained in supplemented with chimato composts prepared using Td/MS = 50:50 (59.1%) and Td/MS = 60:40 (42.3%). The results suggest CC with Td/MS ? 50:50 and Td/MS ? 60:50 have great potential of combating climate change through sequestration of huge quantities of carbon into underground soil.

Chemical transformations in downed logs and snags of mixed boreal species during decomposition

Snags and downed logs are substantial components of the detrital carbon pool in boreal forests. Effects of their decomposition on chemical and physical characteristics of the forest floor remain relatively unknown. The main objective of this study was to characterize chemical transformations of decaying logs and snags of common tree species in the boreal mixedwood forest. Logs and snags from a wide range of decay classes were sampled and analyzed by solid-state 13C nuclear magnetic resonance spectroscopy and by near-infrared spectroscopy. Little or moderate chemical changes appeared in fresh and moderately decayed snags and logs, but in well-decayed logs, substantial degradation of carbohydrates and increases in lignin concentrations occurred. Deciduous species had initially more carbohydrates than coniferous species, but decomposition narrowed their differences, and in well-decayed logs, species differed mainly in terms of their lignin concentrations. Well-decayed deciduous logs reached very low wood densities, and their integration into the forest floor and long-term preservation remains questionable. In contrast, chemical composition of well-decayed coniferous logs resembles that of lignic forest floor (i.e., forest floor originating from deadwood decomposition), with preserved lignins, carbohydrates, and alkyl carbon compounds. Decomposed coniferous wood thus contributes to chemical heterogeneity of the forest floor, possibly promoting diversity of decomposers as well as carbon retention in soils.

Estimating carbon retention in soils amended with composted beef cattle manure

Composted cattle manure is often used as a soil amendment to replenish nutrient pools and to supply a source of stable C. Compost composition affects the availability of nutrients and the stability of C following the addition of compost to soil. We investigated C mineralization in a loamy sand and a loam soil amended with nine composts, two fresh manures and alfalfa (Medicago sativa L.) hay at a target rate of 10 mg total C g-1 soil. Soils were incubated at 25°C for 168 d. There was a significant interaction between amendment and soil type on C mineralization but generally, the effect of soil texture on amendment decomposition was small. The composts were very dissimilar in composition and resulted in substantial differences in the amount of C retained in the soils (2-39% C added evolved as CO2). Total C evolved during the incubation period could be predicted from the NH4-N content and the NH4-N/NO3-N ratio of the composted manures (R2 = 0.91–0.93). Estimation of the C retained in soils amended with compost as a function of simple chemical properties of the compost provides an important tool for evaluating the effectiveness of compost as a soil amendment, helping to calculate net retention of C. Key words: Compost, mineralization, soil carbon, amendment

Dissolved Organic Carbon Retention in Soils

Interactions between dissolved organic C (DOC) and mineral soils were examined in a laboratory column study. Specific emphasis was given to comparisons of soil and solution measurements of organic C (OC) retention in four soil parent materials. Soil columns were leached with one of three concentrations of forest floor (FF) leachate or distilled water every third day for 1 yr. The concentration of DOC in solution was analyzed before and after percolation through soil columns to assess net release or retention of DOC. Changes in soil chemical properties (pH, loss‐on‐ignition [LOI], extractable Al and Fe) following leaching were consistent with podzolization. Micromorphological investigation of the soil materials following leaching showed increased accumulation of organo‐metallic coatings in materials treated with high concentrations of DOC relative to distilled water or low concentrations of DOC. The most dramatic changes in soil chemical properties were found in soils leached with high concentrations of DOC. Comparison of solution and soil measures of OC retention indicates that only ∼50% of the DOC lost from solution was measured as soil OC at the end of the experiment. This finding suggests that microbial decomposition is a significant factor regulating OC concentrations in soils and that soil solution data alone do not yield a complete picture of soil OC dynamics.

Dissolved Organic Carbon Retention in Soils

Dissolved Organic Carbon Retention in Soils