Organic Matter Decomposition Rates Research Articles

Microbial community dynamics alleviate stoichiometric constraints during litter decay.

Under the current paradigm, organic matter decomposition and nutrient cycling rates are a function of the imbalance between substrate and microbial biomass stoichiometry. Challenging this view, we demonstrate that in an individual-based model, microbial community dynamics alter relative C and N limitation during litter decomposition, leading to a system behaviour not predictable from stoichiometric theory alone. Rather, the dynamics of interacting functional groups lead to an adaptation at the community level, which accelerates nitrogen recycling in litter with high initial C : N ratios and thus alleviates microbial N limitation. This mechanism allows microbial decomposers to overcome large imbalances between resource and biomass stoichiometry without the need to decrease carbon use efficiency (CUE), which is in contrast to predictions of traditional stoichiometric mass balance equations. We conclude that identifying and implementing microbial community-driven mechanisms in biogeochemical models are necessary for accurately predicting terrestrial C fluxes in response to changing environmental conditions.

Modelling soil carbon and nitrogen dynamics using measurable and conceptual soil organic matter pools in APSIM

Measurable soil organic carbon (SOC) fractions are recommended to be used in soil organic matter (SOM) models to replace the conceptual pools in order to reduce uncertainty related to model initialization. However, changes in SOM pools require derivation of the decomposition rate for the new pools and also impact on simulation of nutrient cycling in soil. Here, we used the Agricultural Production Systems sIMulator (APSIM) to explore the impact of adopting measurable SOM pools on simulated SOC and nitrogen dynamics under three agro-ecosystems at Brigalow, Tarlee and Wagga Wagga in Australia. The decomposition rates for the measurable pools were derived based on the data in the top 30cm soil at Brigalow. With those decomposition rates, the model could predict the variation in observed total SOC, and also captured the dynamics of the measured SOC fractions at the three sites. However, the re-parameterized model overestimated soil nitrogen. Extending the model simulations to centurial scales led to the distinct difference in simulated soil carbon and nitrogen dynamics, due to the difference in pool sizes, decomposition rates and C:N ratios between the two approaches. Sensitivity analysis based on measurable pool approach indicated that simulated soil carbon dynamics was most sensitive to the partitioning of carbon in the sub-pools of new plant material, decomposition rates of particulate and humic organic matter. The simulated soil nitrogen dynamics was most sensitive to the C:N ratio of humic organic matter. In order to accurately simulate the long-term carbon and nitrogen dynamics, more detailed information on the composition of the measurable SOM pools, particularly their C:N ratios and the underlying mechanisms controlling their decomposition and transformation among different pools across different environments are needed.

Cellulose decomposition rate and features of organic matter in forest soils in the Tatra mountains

The cellulose decomposition rate measurement and soil micromorphology have been used to determine the influence of parent material and tree species on mechanisms responsible for organic matter form differentiation in woodland soils in the Tatra Mountains in Poland. The study area is located in the lower montane belt of the Tatra Mountains. Investigated soils are developed on dolomites and shale. In the past, beech and beech-fir forests had been the dominant form of vegetation in the study area. Since the 16th century, these areas were deforested until the 19th century, when reforestation efforts were undertaken. Reforestation efforts provided mainly spruce; hence, it is the dominant species in the lower montane belt at the moment, although in some areas, natural or semi-natural beech and beech-fir forests have survived. Four plots were compared – two with soils developed on calcareous material (Rendzic Leptosols), one under beech forest and one under spruce forest, and two developed on shale (Haplic Cambisols), one under beech forest and one under spruce forest. Cellulose filters were placed in organic O-horizons and humus A-horizons in every plot to measure the cellulose decomposition rate. Before being placed in the soil, cellulose filters were boiled in KOH, rinsed in distilled water, dried, weighed, and set on glass plates in a nylon bag (1.5 mm mesh). The bags were placed in the soil vertically at approx. 15 cm intervals. After taken up, the filters were boiled in KOH, rinsed, dried, and weighed. The amount of ash was determined via combustion. The research was carried out during a period of 10 weeks between June and August as well as during a period of 1 year. Measurements were repeated ten times. A weighted average and standard deviation were calculated for every plot. The cellulose filter method is useful because of the homogeneity of the substrate, which helps to exclude differences connected with the chemical composition of the plant material, a factor that affects the decomposition rate. Undisturbed soil samples were taken from humus A-horizons in every soil profile. The thin sections were prepared and features of organic matter were described. It was concluded that the presence of calcarous material negatively affects organic matter decomposition rates which is pronounced in both: higher amount of organic matter residues in humus-A horizons and slower cellulose decomposition rates in Rendzic Leptosols than in Haplic Cabisols. The influence of tree species on organic matter features is observed only in Haplic Cambisols, where the cellulose decomposition rate under spruce is lower than under beech. This suggests that tree species indirectly affect the cellulitic microflora only in acidic soils.

Diminished soil functions occur under simulated climate change in a sup-alpine pasture, but heterotrophic temperature sensitivity indicates microbial resilience

The pressure of climate change is disproportionately high in mountainous regions, and small changes may push ecosystem processes beyond sensitivity thresholds, creating new dynamics of carbon and nutrient cycling. Given that the rate of organic matter decomposition is strongly dependent upon temperature and soil moisture, the sensitivity of soil respiration to both metrics is highly relevant when considering soil–atmosphere feedbacks under a changing climate. To assess the effects of changing climate in a mountain pasture system, we transplanted turfs along an elevation gradient, monitored in situ soil respiration, incubated collected top-soils to determine legacy effects on temperature sensitivity, and analysed soil organic matter (SOM) to detect changes in quality and quantity of SOM fractions. In situ transplantation down-slope reduced soil moisture and increased soil temperature, with concurrent reductions in soil respiration. Soil moisture acted as an overriding constraint to soil respiration, and significantly reduced the sensitivity to temperature. Under controlled laboratory conditions, removal of the moisture constraint to heterotrophic respiration led to a significant respiration-temperature response. However, despite lower respiration rates down-slope, the response function was comparable among sites, and therefore unaffected by antecedent conditions. We found shifts in the SOM quality, especially of the light fraction, indicating changes to the dynamics of decomposition of recently deposited material. Our findings highlighted the resilience of the microbial community to severe climatic perturbations, but also that soil moisture stress during the growing season can significantly reduce soil function in addition to direct effects on plant productivity. This demonstrated the sensitivity of subalpine pastures under climate change, and possible implications for sustainable use given reductions in organic matter turnover and consequent feedbacks to nutrient cycling.

Relationships between lake transparency, thermocline depth, and sediment oxygen demand in Arctic lakes

The burial of organic matter within lake sediments can be a significant component of landscape carbon cycling. Whether organic matter deposited in lake sediments is sequestered or mineralized depends on factors limiting the decomposition rate of organic matter, such as temperature and the availability of oxygen. In stratified lakes, the distribution of temperature and oxygen is determined by the depth of the thermocline, and therefore sediment organic matter burial should be sensitive to changes in thermocline depth. Using a survey of more than 30 lakes over 3 years in the Alaskan Arctic, we found that thermocline depth during the summer was positively correlated with water transparency. Furthermore, using sediment incubations from 3 lakes, we found that variation in sediment oxygen demand is primarily affected by variation in temperature and the availability of oxygen with limited effect of the source of the sediments. Because variation in temperature and oxygen concentration in stratified lakes is mainly determined by the depth of thermocline, these results indicate that changes in transparency can have indirect effects on the rate of organic matter mineralization in lakes. A reduction in thermocline depth that results from decreased lake transparency may decrease the breakdown of sediment organic matter and increase the storage of organic carbon in lake sediments.

The search for a filter-feeding alternative for integrated shrimp aquacultures– a preliminary study with the polychaete Sabella spallanzanii for water quality improvement

The search for a filter-feeding alternative for integrated shrimp aquacultures– a preliminary study with the polychaete Sabella spallanzanii for water quality improvement

土壤碳库构成研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 土壤碳库构成研究进展 DOI: 10.5846/stxb201301050036 作者: 作者单位: 中国矿业大学环境与测绘学院,安徽师范大学国土资源与旅游学院,中国矿业大学环境与测绘学院,安徽师范大学国土资源与旅游学院,南京林业大学森林资源与环境学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41101529，41101502，31270664）；自然地理学省级重点学科和安徽师范大学国土资源与旅游学院科研团队资助项目（Asdgl102）；安徽师范大学科研培育基金项目（2010xmpy015） A review of the composition of soil carbon pool Author: Affiliation: College of Environment and Spatial Informatics,China University of Ming and Technology,Xuzhou Jiangsu,College of Territorial Resources and Tourism,Anhui Normal University,Wuhu,College of Environment and Spatial Informatics,China University of Ming and Technology,Xuzhou Jiangsu,College of Territorial Resources and Tourism,Anhui Normal University,Wuhu, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤碳库是陆地生态系统中最大的碳库。土壤碳库的构成影响其累积和分解，并直接影响全球陆地生态系统碳平衡，同时也影响土壤质量变化。弄清土壤碳库的组分及构成，是进一步研究土壤碳库变化机制的关键。综述了土壤碳库的组分和构成，对有机碳库进行不稳定性有机碳库和稳定有机碳库归类，描述各类碳库的性质，并对各类碳库的分析测定方法进行了评述。提出在土壤碳构成中增加黑碳和煤炭（碳）以完善土壤有机碳构成框架。在未来研究中，应加强土壤无机碳及湿地土壤和新开发新复垦的重构土壤碳库构成及变化，各类碳库化学构成，交叉重叠的定量关系，碳库之间的转化及在土壤中的迁移，黑碳对土壤碳库稳定性及土壤质量的影响，煤开采扰动区煤炭（碳）对土壤质量的影响及环境效应等科学问题的研究。 Abstract:The soil carbon pool is the biggest one in the terrestrial ecosystem. The composition of soil carbon pool influences carbon accumulation and decomposition, and directly controls global terrestrial carbon balance, and influences soil quality. Making clear the constitutes of soil carbon pool is the key process in revealing the mechanism of soil carbon pools change. This paper overviewed the structure and composition of the soil carbon pools. Soil carbon pools include soil inorganic carbon pool and soil organic carbon pool. Soil inorganic carbon pool includes HCO3- in soil solution,CO2 in soil air, and CaCO3 in soil. And CaCO3 is the main component in soil inorganic carbon pool. Soil inorganic carbon pool can influence soil organic carbon pool by affecting composition of soil aggregates, microbial activity, soil pH, and soil organic matter decomposition rate. Soil organic carbon is a very complex continuous mixture, which includes a variety of organic carbon fractions and forms with different nature. And the content of all kind of soil organic carbon affects the transformation of soil carbon pool and thereby influences soil quality and carbon cycle in terrestrial ecosystem. Soil organic carbon pools are categorized into soil labile organic carbon pool and soil stable organic carbon pool. Among them, soil labile organic carbon can turnover within a certain time, and can be utilized by plant and microorganism, and have a major impact on the carbon balance. Soil labile organic carbon is also named soil activated organic carbon or effective carbon by some authors, and includes terms as available carbon (AC), dissolved organic carbon (DOC), water soil organic carbon (WSOC), readily oxidation carbon (ROC), microbial biomass carbon (MBC), biodegradable carbon, light fraction organic carbon (LFOC), particulate organic carbon (POC) and so on. Black carbon (BC) and coal carbon are suggested to be categorized into soil organic carbon pool to perfect the frame of soil organic carbon pool composition. Black carbon is a C-rich organic material derived from incomplete combustion of fossil fuels and vegetation and from weathering of graphitic C in rocks, and very stabile. Black carbon captures and sequesters carbon from the bio-atmospheric cycle, which, in the long term, reduces greenhouse gas emissions and thus mitigates the greenhouse effect. Meanwhile, resistant black carbon amendation increase soil organic matter, thus regulating soil structure and enhancing soil fertility. Because of its high adsorption capacity, black carbon adsorbs organic pollutants, heavy metals, nutrients to decrease ecosystem risk. The coal (carbon) in the surface layer soil mainly come from outside source; include garbage, filling, atmospheric sedimentation and so on. The coal mine area is usually the district absorbing the most coal (carbon). In future studies, we should strengthen the researches on the scientific issues including the chemical composition, overlapping quantitative relationship of the soil organic carbon pools, transformation and migration of soil organic carbon in the soil, the impact of black carbon on the stability of the soil carbon pool and soil quality, the impact of coal (carbon) on soil quality and environmental effects in the coal mining disturbed zone, and organic carbon change and mechanism in newly developed soil, reclamation soil and reconstruction soil. 参考文献 相似文献 引证文献

Effects of climatic and soil properties on cellulose decomposition rates in temperate and tropical forests

Cellulose decomposition experiments were conducted under field conditions to analyze the effects of climatic and soil properties on rates of organic matter decomposition in temperate and tropical forests. The mass loss rates of cellulose filter papers buried in the soil surface were measured to estimate the respiratory C fluxes caused by cellulose decomposition and mean residence time (MRT) of cellulose. The rates of cellulose decomposition increased with soil temperature, except for during the dry season, while rate constants of decomposition (normalized for temperature) decreased with decreasing pH because of lower cellulase activity. The estimated MRTs of soil cellulosic carbohydrates varied from 81 to 495 days for the temperate forests and from 31 to 61 days for the tropical forests. As a major organic substrate, the C fluxes from cellulose decomposition can account for a substantial fraction of heterotrophic (basal) soil respiration. However, the respiratory C fluxes can be limited by the low substrate availability and low pH in tropical soils, despite high microbial activity. The rate-regulating factors of cellulose decomposition, i.e., temperature, soil pH, and substrate availability, can accordingly influence the rates of heterotrophic soil respiration.

Rice Rotation and Tillage Effects on Water-Stable Soil Macroaggregates and Their Associated Carbon and Nitrogen Contents in a Silt-Loam Soil

Rice (Oryza sativa L.)-based cropping systems are different from other crop rotations because of the flood-irrigation scheme, which can influence the rate of soil organic matter decomposition, water-stable soil aggregation, and carbon (C) and nitrogen (N) sequestration over time. A study was conducted on a silt-loam soil (fine, smectitic, thermic, Typic Albaqualf) in eastern Arkansas to evaluate the effects of rice-based crop rotations (with maize (Zea mays L.), soybean (Glycine max L.), and winter wheat (Triticum aestivum L.)), tillage (conventional tillage and no-tillage (NT)), and soil depth (0–5 cm and 5–10 cm) after 10 years of management on water-stable macroaggregates (WSA) and their C and N concentrations (g kg−1), C:N ratios, and contents (g m−2). The total amount of WSA (WSATotal >0.25 mm in diameter) and the distribution of WSA among five different size classes (0.25–0.5, 0.5–1, 1–2, 2–4, and >4 mm in diameter) within each treatment combination were evaluated. The concentration of WSATotal was 1.2 to four times greater under NT/0- to 5-cm soil depth (9.2–16.0 g kg−1) than under other tillage-depth combinations. Macroaggregate concentration in the 0.25- to 0.5-mm size class was greater under continuous rice (9.3 g kg−1) and rice rotations with maize (7.6–8.0 g kg−1) than in rotations with wheat (4.9–6.5 g kg−1). The NT/0- to 5-cm combination had three to six times greater WSATotal C (235 g m−2) and N (20.6 g m−2) contents than all other tillage-depth combinations (C, 38.3–80.5 g m−2; N, 3.5–5.7 g m−2), which did not differ. Despite field management differences from using seasonal flood-irrigation in rice, this study demonstrates that the extent of tillage and crop rotation effects on soil macroaggregation and the associated macroaggregate-associated C and N contents were proportionate to trends commonly reported in dryland crop rotations.

Biochar and Microbial Signaling: Production Conditions Determine Effects on Microbial Communication

Charcoal has a long soil residence time, which has resulted in its production and use as a carbon sequestration technique (biochar). A range of biological effects can be triggered by soil biochar that can positively and negatively influence carbon storage, such as changing the decomposition rate of organic matter and altering plant biomass production. Sorption of cellular signals has been hypothesized to underlie some of these effects, but it remains unknown whether the binding of biochemical signals occurs, and if so, on time scales relevant to microbial growth and communication. We examined biochar sorption of N-3-oxo-dodecanoyl-L-homoserine lactone, an acyl-homoserine lactone (AHL) intercellular signaling molecule used by many gram-negative soil microbes to regulate gene expression. We show that wood biochars disrupt communication within a growing multicellular system that is made up of sender cells that synthesize AHL and receiver cells that express green fluorescent protein in response to an AHL signal. However, biochar inhibition of AHL-mediated cell-cell communication varied, with the biochar prepared at 700 °C (surface area of 301 m(2)/g) inhibiting cellular communication 10-fold more than an equivalent mass of biochar prepared at 300 °C (surface area of 3 m(2)/g). These findings provide the first direct evidence that biochars elicit a range of effects on gene expression dependent on intercellular signaling, implicating the method of biochar preparation as a parameter that could be tuned to regulate microbial-dependent soil processes, like nitrogen fixation and pest attack of root crops.

Litter quality versus soil microbial community controls over decomposition: a quantitative analysis

The possible effects of soil microbial community structure on organic matter decomposition rates have been widely acknowledged, but are poorly understood. Understanding these relationships is complicated by the fact that microbial community structure and function are likely to both affect and be affected by organic matter quality and chemistry, thus it is difficult to draw mechanistic conclusions from field studies. We conducted a reciprocal soil inoculum × litter transplant laboratory incubation experiment using samples collected from a set of sites that have similar climate and plant species composition but vary significantly in bacterial community structure and litter quality. The results showed that litter quality explained the majority of variation in decomposition rates under controlled laboratory conditions: over the course of the 162-day incubation, litter quality explained nearly two-thirds (64%) of variation in decomposition rates, and a smaller proportion (25%) was explained by variation in the inoculum type. In addition, the relative importance of inoculum type on soil respiration increased over the course of the experiment, and was significantly higher in microcosms with lower litter quality relative to those with higher quality litter. We also used molecular phylogenetics to examine the relationships between bacterial community composition and soil respiration in samples through time. Pyrosequencing revealed that bacterial community composition explained 32 % of the variation in respiration rates. However, equal portions (i.e., 16%) of the variation in bacterial community composition were explained by inoculum type and litter quality, reflecting the importance of both the meta-community and the environment in bacterial assembly. Taken together, these results indicate that the effects of changing microbial community composition on decomposition are likely to be smaller than the potential effects of climate change and/or litter quality changes in response to increasing atmospheric CO2 concentrations or atmospheric nutrient deposition.

Nutrient Availability and Soil Organic Matter Decomposition Response to Prescribed Burns in Mid-Atlantic Brackish Tidal Marshes

Prescribed fire in tidal marshes has been shown to generate short-term increases in plant-available nutrients, but the long-term implications of fire on nutrient availability and organic matter decomposition have not been well established. Two manipulative experiments were conducted over 1 yr within long-term annual burn and no-burn blocks at the Blackwater National Wildlife Refuge in Cambridge, MD to study the effects of canopy removal and ash deposition on nutrient availability and organic matter decomposition rates following burning. Ash deposition had no significant effects on study variables. At no-burn sites, porewater NH4+ and PO43+ were significantly lower in July in sites with canopy removal (0.15 mg NH4+ L−1 and 0.04 mg PO43+ L−1) compared to sites with a canopy (0.73 mg NH4+ L−1 and 0.08 mg PO43+ L−1). Similar results were found through a canopy replacement treatment at annual burn sites. Decreased porewater NH4+ and PO43+ corresponded to increased total biomass nutrient content. No-burn sites with canopy removal treatments showed significantly lower organic matter decomposition rates than did treatments with a canopy in July (66.5 vs. 74.1% cotton tensile strength loss), corresponding to decreases in porewater NH4+ and PO43+. Plant ash provided a fertilizer pulse of 0.22 g N m−2 and 0.16 g P m−2, which were amounts of N and P likely too small to increase plant productivity when deposited during late winter/early spring. Prescribed fire appears to affect nutrient availability and organic matter decomposition in these marsh soils primarily through the mechanism of increased biomass production due to canopy removal.

Soil organic matter dynamics after C3–C4 vegetation change of red soil in Southern, China: Evidence from natural 13C abundance

Soil samples from natural forests and adjacent farmland were analyzed to investigate the dynamics of soil organic matter of red soil in Southern, China. Based on the δ13C values and the content of soil organic matter, the data indicated that the turnover of soil organic matter under the virgin forest was slower than that under cultivation. Soil organic matter is fresh in coarse sand and oldest in fine silt and clay. Also, the soil light fraction contained the younger organic matter than soil heavy fraction and bulk soil. Deforestation has accelerated the decomposition rate of soil organic matter and reduced the proportion of active components in SOM and thus soil fertility.

시화호 인공습지에서 수생식물의 유기물 생산과 낙엽 분해

To provide the information for the wetland management considering the water treatment ability of macrophytes, the growth characteristics and primary production by reed (Phragmites australis) and cattail (Typha angustifolia), and the decomposition rate of organic matter produced were investigated in two sub-wetlands (Banweol and Donhwa wetlands) of the Sihwa Constructed Wetland (CW) with different chemistry of inflows. The shoot height of P. australis and Typha angustifolia began to increase in March, and reached its peaks in July and August (340cm and 320cm, respectively). The shoot density of P. australis ranging was higher than that of T. angustifolia (max. ). Standing biomass of P. australis ranged from , with maximal biomass in Banwol Upper Wetland. And it was larger in upper wetlands than lower wetlands. On the other hand standing biomass of T. angustifolia () was similar to that of P. australis in Banwol Upper Wetland. Primary productivity of P. australis was in the order of Banwol Upper Wetland () > Donghwa Lower Wetland () > Banwol Lowerr Wetland () Donghwa Lower Wetland (), and that of T. angustifolia () was higher than P. australis. Annual production of organic matter produced by P. australis and T. angustifolia was 845 ton DM/yr (423 ton C/yr), and about 90% was comprised of that by P. australis. From the litter decomposition rate (k) (P. australis: leaf 0.0062/day, stem 0.0018/day; T. angustifolia: leaf 0.0031/day, stem 0.0018/day), leaf was rapid degraded compare to stem in both P. australis and T. angustifolia. The litter decomposition rate of leaf was two times rapid P. australis than T. angustifolia, whereas that of stem was same in both. Annual litter decomposition amount of P. australis than T. angustifolia was 285 ton C/yr(67.3% of organic matter produced by macrophytes), indicating that 32.7% of organic matter produced by macrophytes is accumulated in the Sihwa CW.

Synthesis and modeling perspectives of rhizosphere priming

The rhizosphere priming effect (RPE) is a mechanism by which plants interact with soil functions. The large impact of the RPE on soil organic matter decomposition rates (from 50% reduction to 380% increase) warrants similar attention to that being paid to climatic controls on ecosystem functions. Furthermore, global increases in atmospheric CO2 concentration and surface temperature can significantly alter the RPE. Our analysis using a game theoretic model suggests that the RPE may have resulted from an evolutionarily stable mutualistic association between plants and rhizosphere microbes. Through model simulations based on microbial physiology, we demonstrate that a shift in microbial metabolic response to different substrate inputs from plants is a plausible mechanism leading to positive or negative RPEs. In a case study of the Duke Free-Air CO2 Enrichment experiment, performance of the PhotoCent model was significantly improved by including an RPE-induced 40% increase in soil organic matter decomposition rate for the elevated CO2 treatment--demonstrating the value of incorporating the RPE into future ecosystem models. Overall, the RPE is emerging as a crucial mechanism in terrestrial ecosystems, which awaits substantial research and model development.

Ecological function of constructed perennial stream channels on reclaimed surface coal mines

Mountaintop removal–valley fill mining results in the conversion of steep, forested headwater catchments to low gradient and open canopy channels. We compared the ecological functions of five reference stream channels to five constructed channels (age ranging from 3 to 20 years) on reclaimed mines in southern West Virginia. Variables included stream flow, habitat, water chemistry, riparian vegetation, organic matter (OM) processing, and invertebrate and amphibian communities. Although dissolved metal concentrations remained low, constructed channels produced significantly higher levels of conductivity and total dissolved solids as compared to reference streams. Macroinvertebrate and amphibian richness were comparable between constructed and reference channels; however, there was a distinct shift from sensitive lotic taxa in reference channels to tolerant lentic taxa in constructed channels. Constructed channels also had reduced OM decomposition rates. Nevertheless, constructed channels had significantly higher OM retention than reference channels, and consequently exhibited significantly higher overall OM processing and higher dissolved carbon concentrations. As the time since reclamation increased, we observed slight declines in conductivity and significant increases in total invertebrate richness. Our results provide measures of functional equivalencies between reference and constructed streams, which can serve as a basis for informed permitting and mitigation decisions in mined watersheds.

Iron oxidation stimulates organic matter decomposition in humid tropical forest soils

Humid tropical forests have the fastest rates of organic matter decomposition globally, which often coincide with fluctuating oxygen (O2 ) availability in surface soils. Microbial iron (Fe) reduction generates reduced iron [Fe(II)] under anaerobic conditions, which oxidizes to Fe(III) under subsequent aerobic conditions. We demonstrate that Fe (II) oxidation stimulates organic matter decomposition via two mechanisms: (i) organic matter oxidation, likely driven by reactive oxygen species; and (ii) increased dissolved organic carbon (DOC) availability, likely driven by acidification. Phenol oxidative activity increased linearly with Fe(II) concentrations (P<0.0001, pseudo R(2) =0.79) in soils sampled within and among five tropical forest sites. A similar pattern occurred in the absence of soil, suggesting an abiotic driver of this reaction. No phenol oxidative activity occurred in soils under anaerobic conditions, implying the importance of oxidants such as O2 or hydrogen peroxide (H2 O2 ) in addition to Fe(II). Reactions between Fe(II) and H2 O2 generate hydroxyl radical, a strong nonselective oxidant of organic compounds. We found increasing consumption of H2 O2 as soil Fe(II) concentrations increased, suggesting that reactive oxygen species produced by Fe(II) oxidation explained variation in phenol oxidative activity among samples. Amending soils with Fe(II) at field concentrations stimulated short-term C mineralization by up to 270%, likely via a second mechanism. Oxidation of Fe(II) drove a decrease in pH and a monotonic increase in DOC; a decline of two pH units doubled DOC, likely stimulating microbial respiration. We obtained similar results by manipulating soil acidity independently of Fe(II), implying that Fe(II) oxidation affected C substrate availability via pH fluctuations, in addition to producing reactive oxygen species. Iron oxidation coupled to organic matter decomposition contributes to rapid rates of C cycling across humid tropical forests in spite of periodic O2 limitation, and may help explain the rapid turnover of complex C molecules in these soils.

Carbon cycling and sequestration in a Japanese red pine (Pinus densiflora) forest on lava flow of Mt. Fuji

AbstractBiometric‐based carbon flux measurements were conducted in a pine forest on lava flow of Mt. Fuji, Japan, in order to estimate carbon cycling and sequestration. The forest consists mainly of Japanese red pine (Pinus densiflora) in a canopy layer and Japanese holly (Ilex pedunculosa) in a subtree layer. The lava remains exposed on the ground surface, and the soil on the lava flow is still immature with no mineral soil layer. The results showed that the net primary production (NPP) of the forest was 7.3 ± 0.7 t C ha−1 year−1, of which 1.4 ± 0.4 t C ha−1 year−1 was partitioned to biomass increment, 3.2 ± 0.5 t C ha−1 year−1 to above‐ground fine litter production, 1.9 t C ha−1 year−1 to fine root production, and 0.8 ± 0.2 t C ha−1 year−1 to coarse woody debris. The total amount of annual soil surface CO2 efflux was estimated as 6.1 ± 2.9 t C ha−1 year−1, using a closed chamber method. The estimated decomposition rate of soil organic matter, which subtracted annual root respiration from soil respiration, was 4.2 ± 3.1 t C ha−1 year−1. Biometric‐based net ecosystem production (NEP) in the pine forest was estimated at 2.9 ± 3.2 t C ha−1 year−1, with high uncertainty due mainly to the model estimation error of annual soil respiration and root respiration. The sequestered carbon being allocated in roughly equal amounts to living biomass (1.4 t C ha−1 year−1) and the non‐living C pool (1.5 t C ha−1 year−1). Our estimate of biometric‐based NEP was 25 % lower than the eddy covariance‐based NEP in this pine forest, due partly to the underestimation of NPP and difficulty of estimation of soil and root respiration in the pine forest on lava flows that have large heterogeneity of soil depth. However, our results indicate that the mature pine forest acted as a significant carbon sink even when established on lava flow with low nutrient content in immature soils, and that sequestration strength, both in biomass and in soil organic matter, is large.

The effects of simulated nitrogen deposition on extracellular enzyme activities of litter and soil among different-aged stands of larch

Aims Nitrogen (N) addition could affect the rate of forest litter and soil organic matter decomposition by regulating extracellular enzyme activity (EEA). The impact of N addition on EEA may differ across different age stands with different organic matter quality. We were interested in whether the impact of N addition on EEA in litter and mineral soil during the growing season was dependent on stand age of a larch plantation in North China. Methods We added three levels of N (0, 20 and 50 kg N ha −1 year −1 ) in three age stands (11, 20 and 45 years old) of Larix principis-rupprech- tii plantation in North China. We measured potential activities of β-1,4-glucosidase (BG), cellobiohydrolase (CB), β-1,4-N-acetyl- glucosaminidase (NAG) and phenol oxidase (PO) in litter (organic horizon) and mineral soil (0-10 cm) during the second growing sea- son after N amendment. We also measured C and N concentrations, microbial biomass C and N, and KCl-extractable ammonium and nitrate in both litter and mineral soil. temperature. Stand age had a strong effect on EEA in both litter and mineral soil, and this effect differed between litter and mineral soil as well as between different enzymes. N addition did not signifi- cantly affect the activities of BG or CB but significantly suppressed the activity of NAG in litter. We also found stand age-specific responses of PO activity to N addition in both litter and mineral soil. N addition suppressed PO activity of the high C:N ratio litters in 20- and 45-year-old stands but had no significant effect on PO activity of the low C:N ratio litter in 11-year-old stand. Moreover, N addition inhibited PO activity of the high C:N ratio soil in 20-year- old stand but had no significant impact on PO activity of the low C:N ratio soils in 11- and 45-year-old stands. Overall, stand age had a greater effect on EEA in litter and mineral soil compared to 2 years of N addition. Moreover, the effect of N addition on PO activity is stand age dependent, which may affect the long-term soil carbon storage in this forest.

Influence of mangrove zonation on CO2 fluxes at the sediment–air interface (New Caledonia)

Mangroves are the major ecosystems of tropical and subtropical coastlines. They are considered as a sink for atmospheric CO2 because they are characterized both by high net primary production, and by low rates of organic matter decomposition. However, a recent reassessment of the global mangrove budget suggests that organic carbon sinks have been underestimated, notably CO2 efflux from sediments and creek waters, and tidal export of dissolved inorganic carbon. Our objective was to understand the influence of mangrove zonation on the magnitude of CO2 fluxes at the sediment–air interface. Transparent and opaque dynamic closed chamber systems, coupled with an infra-red gas analyzer were used to measure CO2 fluxes. In addition, the physico-chemical properties (salinity, redox potential) of pore waters were determined, as well as the carbon content and the origin of surface sediments (Chlorophyll-a and δ13C). Depending on the type of measurement (in the dark with or without biofilm, in the light with biofilm) and mangrove stand (saltflat, Avicennia sp., or Rhizophora spp.), mean surface sediment CO2 fluxes ranged between 40±56 and 199±95mmol·m−2·d−1. We suggest that these differences mainly result both from the organic content and the redox conditions of the sediments, which are influenced by the physiological activities of the root system, and by the position and the elevation of the stand in the intertidal zone. In addition, the quality and abundance of biofilm, which also vary with the mangrove stand, also appear to strongly affect sediment CO2 fluxes as a result of chemical (metabolism) and also physical (barrier) processes.