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The author presents an ecological-necrological perspective on the ontology of the human dead body and remains in the context of Holocaust studies. The article examines the environmental history of mass graves and reflects on the ontological status and condition of human remains. The author proposes an approach that combines humanities and soil sciences while thinking about post-genocidal spaces and sites of mass killings in order to discuss the issue of protecting human remains from politicization and commercialization and to prefigure appropriate long-term approaches to the preservation of sites containing human remains. The article suggests focusing on humus while examining the process of dehumanization through decomposition (organic decay) and unbecoming human by "becoming-soil." To enrich and problematize the humanities' conception of humus, the article draws on conceptions of humus proposed by soil scientists. What is argued here is that the ecological perspective becomes a necessary and essential element in managing post-genocidal (and post-Holocaust) sites, particularly when it comes to planning their conservation and preservation. [ABSTRACT FROM AUTHOR]

Soil humus degradation strengthens nutrient mining, especially phosphorus. This study was carried out on the Ukrainian Forest-Steppe Zone (UFSZ). A total of 21 soil profiles have been investigated: 11 Phaeozems, 6 Luvisols, and 4 Chernozems. Soils were tested for particle size distribution, calcium carbonate (CC), pH, and organic carbon (Corg). The evaluation of humus degradation as a reason of P depletion was performed based on indicators such as Humus Stock Gap (HSG), Humus Stability Index (S), and Yield Gap/Gain (YG/G). In order to evaluate the degree of P depletion, total phosphorus (Ptot) and its five fractions: water soluble - PH2O, exchangeable - PEX, bound to Fe and Al - PFe/Al, bound to Ca - PCa, and residual P - Pres, have been determined. Data revealed that in 14 of 21 investigated soils, S indices were below the threshold its value of nine, considered as the balanced content of humus with respect to soil texture. Next, in 11 of 21 cases, the negative humus balance indicates the yield gap in Phaeozems and Chernozems. The first three P pools (PH2O, P-EX and PAl/Fe) in Phaeozems were exhausted, constituting less than 10% of the Ptot. In Phaeozems, PAl/Fe, in Luvisols, PEX, and in Chernozems, PH2O fractions were basic indicators of available P status. Their pools were directly or indirectly controlled by PCa. Humus content in Phaeozems and Chernozems revealed as the key factor impacting both total P and/or its available resources. Amelioration of P depletion requires efforts oriented on restoration of soil humus stock, concomitant with P fertilization. [ABSTRACT FROM AUTHOR]

Abstract: Extracellular enzymes catalyze rate‐limiting steps in soil organic matter decomposition, and their activities (EEAs) play a key role in determining soil respiration (SR). Both EEAs and SR are highly sensitive to temperature, but their responses to climate warming remain poorly understood. Here, we present a meta‐analysis on the response of soil cellulase and ligninase activities and SR to warming, synthesizing data from 56 studies. We found that warming significantly enhanced ligninase activity by 21.4% but had no effect on cellulase activity. Increases in ligninase activity were positively correlated with changes in SR, while no such relationship was found for cellulase. The warming response of ligninase activity was more closely related to the responses of SR than a wide range of environmental and experimental methodological factors. Furthermore, warming effects on ligninase activity increased with experiment duration. These results suggest that soil microorganisms sustain long‐term increases in SR with warming by gradually increasing the degradation of the recalcitrant carbon pool. [ABSTRACT FROM AUTHOR]

The concepts and classifications of humus forms developed since the time of scientific pedology formation are critically discussed. The concept of humus forms (types) relates to the classification of a set of topsoil organic and organomineral horizons, which reflects morphologically distinct phases of plant litter and soil organic matter decomposition, but not to the fractions of soil organic matter. Humus forms reflect various types of transformation and accumulation of organic matter in the soil. The stages of development and modern classifications of humus forms abroad are described. The taxonomy of humus forms in Russian literature and its application for the mapping and evaluation of forest soils are considered, as well as its use for the mathematical simulation of soil organic matter mineralization and humification. Prospects for the development of the classification of humus forms in combination with the basic soil classification of European Russia are discussed. A call for an understanding and a common language in soil science at the international level is underlined. [ABSTRACT FROM AUTHOR]

Peatlands contain a large portion of Earth's terrestrial soil organic matter in part due to a reduction in decomposition rates. Organic matter decomposition is initially mediated by extracellular enzyme activity, which is in turn controlled by temperature, moisture, and substrate availability; and all are subject to seasonal variation. As depth increases in peatlands, temperature variability and labile carbon inputs decrease. We hypothesized that the more stable recalcitrant subsurface would contain a smaller less diverse enzyme pool, that is better adapted to a narrow temperature range. Thus temperature dependence would be diminished at depth compared to superficial peat. Potential enzyme activity rates were determined across seasons and with depth in peat samples collected from the Marcell Experimental Forest in northern Minnesota, USA. The temperature dependence, assessed by activation energy, was quantified for three hydrolytic enzymes involved in nutrient cycling at up to 15 temperature points ranging from 2 °C to 65 °C. Potential enzyme activity decreased with peat depth as expected and corresponded with changes in peat composition and microbial biomass from the acrotelm to the catotelm. In an environmentally relevant temperature range (2–23 °C), activation energy decreased with depth for β-glucosidase as predicted and leucine amino peptidase activation energy was the lowest of all enzymes. Stable temperatures at depth appear to result in a microbial community containing enzymes that have lower sensitivity to temperature increases. Surprisingly, there was no significant seasonal effect on enzyme temperature dependence observed in our study. Based on these results, and without shifts in microbial community composition, warming of peat could result in increased carbon and phosphorus cycling at the surface but little change at depth. Additionally differences in enzyme temperature sensitivity suggest nitrogen cycling could remain constant with warming, potentially resulting in proteolytic nitrogen cycling being decoupled from carbon and phosphorus cycling. [ABSTRACT FROM AUTHOR]

Current understanding of the effects of long-term application of various organic amendments on soil particulate organic matter (POM) storage and chemical stabilisation remains limited. Therefore, we collected soil samples from the soil profile (0-100 cm) under six treatments in a 31-year long-term fertilisation experiment: no fertiliser (CK), mineral fertilisers (NPK), mineral fertilisers plus 3.8 or 7.5 t ha−1 year−1 (fresh base) the amount of wheat straw (1/2SNPK and SNPK) and mineral fertilisers plus swine or cattle manure (PMNPK and CMNPK). Long-term incorporation of wheat straw and livestock manure amendments significantly (p < 0.05) increased crop yield and sustainable yield index, and POM storage compared with CK and NPK treatments. The mole ratios of H/C in the POM under organic amendment treatments significantly (p < 0.05) decreased by 13.8% and 37.1%, respectively, compared with the NPK treatment. Similarly, solid state NMR spectroscopy showed that the O-alkyl carbon content of POM was greatly decreased, whereas aromatic carbon contents and alkyl to O-alkyl carbon ratios were substantially increased under PMNPK and CMNPK treatments. In conclusion, we recommend long-term livestock manure application as a preferred strategy for enhancing POM quantity and quality (chemical stability), and crop yield of vertisol soil in northern China. [ABSTRACT FROM AUTHOR]

Quantitative constraints on soil organic matter (SOM) dynamics are essential for comprehensive understanding of the terrestrial carbon cycle. Deep soil carbon is of particular interest, as it represents large stocks and its turnover rates remain highly uncertain. In this study, SOM dynamics in both the top and deep soil across a climatic (average temperature ~1-9 °C) gradient are determined using time-series (~20 years) 14C data from bulk soil and water-extractable organic carbon (WEOC). Analytical measurements reveal enrichment of bomb-derived radiocarbon in the deep soil layers on the bulk level during the last two decades. The WEOC pool is strongly enriched in bomb-derived carbon, indicating that it is a dynamic pool. We used a numerical model to determine turnover time of the bulk, slow and dynamic pool as well as the size of the dynamic pool. The presence of bomb-derived carbon in the deep soil, as well as the rapidly turning over WEOC pool and sizeable dynamic fraction at depth across the climatic gradient implies that there likely is a dynamic component of carbon in the deep soil. Precipitation appears to exert a stronger influence on soil C dynamics than temperature. Overall, geology seems to impact the carbon cycling in three key ways: (1) bedrock-derived (petrogenic) carbon can comprise an important component of the soil carbon pool even at relatively shallow depths (< 1 m). (2) Bedrock type influences water logging either by its porosity or by determining texture, and (3) rock and soil mineralogy controls C stabilization. [ABSTRACT FROM AUTHOR]

Background and aims: The rhizosphere priming effect (RPE) plays an important role in the decomposition of soil organic matter (SOM) and the global carbon cycle. Although plant, soil, and environmental factors affecting the RPE have been examined, it is still unclear how soil water and nitrogen (N) status together alter the RPE.Methods: In order to examine plant, water, and N interacting effects on the RPE, we conducted a semi-natural experiment with two plant species (Leymus chinnensis and Medicago sativa) grown at two soil moisture levels (45 and 85% of water holding capacity) with or without N fertilization (0 and 10 g N m−2 y−1). We used a natural 13C abundance tracer method for measuring the RPE, and an N budgeting method for measuring net N mineralization or immobilization.Results: Both positive (up to 253%) and negative (down to −21%) RPEs were observed in different treatment combinations. L. chinensis exhibited greater RPE than M. sativa under low soil moisture, possibly due to specific root architecture and root activity of L. chinensis. High soil moisture significantly reduced the RPE, while N fertilization significantly increased the RPE. To reconcile our current results and previous observations with existing individual hypotheses related to the RPE, we put forward a new hypothesis: when N mineralization dominates, the rhizosphere input enhances the RPE; when N immobilization dominates, the rhizosphere input reduces the RPE.Conclusion: Overall, this study demonstrates that the RPE on soil organic carbon decomposition is intimately linked with N processes and soil water status. [ABSTRACT FROM AUTHOR]

Although the maritime Antarctic has undergone rapid warming, the effects on indigenous soil‐inhabiting microorganisms are not well known. Passive warming experiments using open‐top chamber (OTC) have been performed on the Fildes Peninsula in the maritime Antarctic since 2008. When the soil temperature was measured at a depth of 2–5 cm during the 2013–2015 summer seasons, the mean temperature inside OTC (OTC‐In) increased by approximately 0.8 °C compared with outside OTC (OTC‐Out), while soil chemical and physical characteristics did not change. Soils (2015 summer) from OTC‐In and OTC‐Out were subjected to analysis for change in microbial community and degradation rate of humic substances (HS, the largest pool of recalcitrant organic carbon in soil). Archaeal and bacterial communities in OTC‐In were minimally affected by warming compared with those in OTC‐Out, with archaeal methanogenic Thermoplasmata slightly increased in abundance. The abundance of heterotrophic fungi Ascomycota was significantly altered in OTC‐In. Total bacterial and fungal biomass in OTC‐In increased by 20% compared to OTC‐Out, indicating that this may be due to increased microbial degradation activity for soil organic matter (SOM) including HS, which would result in the release of more low‐molecular‐weight growth substrates from SOM. Despite the effects of warming on the microbial community over the 8‐years‐experiments warming did not induce any detectable change in content or structure of polymeric HS. These results suggest that increased temperature may have significant and direct effects on soil microbial communities inhabiting maritime Antarctic and that soil microbes would subsequently provide more available carbon sources for other indigenous microbes. [ABSTRACT FROM AUTHOR]

Soil water status is one of the most important environmental factors that control microbial activity and rate of soil organic matter decomposition (SOM). Its effect can be partitioned into effect of water energy status (water potential) on cellular activity, effect of water volume on cellular motility and aqueous diffusion of substrate and nutrients, as well as effect of air content and gas-diffusion pathways on concentration of dissolved oxygen. However, moisture functions widely used in SOM decomposition models are often based on empirical functions rather than robust physical foundations that account for these disparate impacts of soil water. The contributions of soil water content and water potential vary from soil to soil according to the soil water characteristic (SWC), which in turn is strongly dependent on soil texture and structure. The overall goal of this study is to introduce a physically based modelling framework of aerobic microbial respiration that incorporates the role of SWC under arbitrary soil moisture status. The model was tested by compariing it with published datasets of SOM decomposition under laboratory conditions. [ABSTRACT FROM AUTHOR]

The article presents analysis of the soil organic matter accumulation in the millennium chronosequence by using a spectral parameter over a 1000-year period. Topics discussed include importance of accumulation of soil organic matter (SOM) as an pedogenic process and utility of deviation of arch (DOA) and analysis of the results.

Hydrological changes during wetland drying alter soil oxidation-reduction (redox) conditions such that soil organic carbon (SOC) decomposition is affected, which may influence global climate-carbon feedbacks. This study aimed to explore whether the temperature sensitivity of soil respiration is affected by changes in soil redox status. We created a gradient of redox potential in wetland soils by adjusting soil moisture content and O 2 concentration in microcosms, and incubated these soils under changing temperature to estimate the temperature sensitivity (indicated by Q 10 ) of soil respiration. Our results showed that Q 10 values under aerobic conditions were 1.5–2.5 times higher than those under anaerobic incubations, with a significant positive correlation between Q 10 and soil redox potential. This study suggested that SOC decomposition through soil respiration during progressive wetland drying may be increasingly sensitive to global warming, which may accelerate SOC loss from wetlands in the future. [ABSTRACT FROM AUTHOR]

The role of soil microorganisms in regulating soil organic matter (SOM) decomposition is of primary importance in the carbon cycle, and in particular in the context of global change. Modelling soil microbial community dynamics to simulate its impact on soil gaseous carbon (C) emissions and nitrogen (N) mineralization at large spatial scales is a recent research field with the potential to improve predictions of SOM responses to global climate change. We here present a SOM model called ORCHIMIC whose input data that are consistent with those of global vegetation models. The model simulates decomposition of SOM by explicitly accounting for enzyme production and distinguishing three different microbial functional groups: fresh organic matter (FOM) specialists, SOM specialists, and generalists, while implicitly also accounting for microbes that do not produce extracellular enzymes, i.e. cheaters. This ORCHIMIC model and two other organic matter decomposition models, CENTURY (based on first order kinetics and representative for the structure of most current global soil carbon models) and PRIM (with FOM accelerating the decomposition rate of SOM) were calibrated to reproduce the observed respiration fluxes from FOM and SOM and their possible interactions from incubation experiments of Blagodatskaya et al. (2014). Among the three models, ORCHIMIC was the only one that captured well both the temporal dynamics of the respiratory fluxes and the magnitude of the priming effect observed during the incubation experiment. ORCHIMIC also reproduced well the temporal dynamics of microbial biomass. We then applied different idealized changes to the model input data, i.e. a 5 K stepwise increase of temperature and/or a doubling of plant litter inputs. Under 5 K warming, ORCHIMIC predicted a 0.002 K-1 decrease in the C use efficiency (defined as the ratio of C allocated to microbial growth to the sum of C allocated to growth and respiration) and a 3% loss of SOC. Under the double litter input scenario, ORCHIMIC predicted a doubling of microbial biomass, while SOC stock increased by less than 1% due to the priming effect. This limited increase in SOC stock contrasted with the proportional increase in SOC stock as modelled by the conventional SOC decomposition model (CENTURY), which cannot reproduce the priming effect. If temperature increased by 5 K and litter input is doubled, the model predicted almost the same loss of SOC as when only temperature was increased. These tests suggest that the responses of SOC stock to warming and increasing input may differ a lot from those simulated by conventional SOC decomposition models, when microbial dynamics is included. The next step is to incorporate the ORCHIMIC model into a global vegetation model to perform simulations for representative sites and future scenarios. [ABSTRACT FROM AUTHOR]

Evaluating how decomposition responds to temperature is important for understanding the soil's response under a changing climate. Our objective in this study was to evaluate the effect of temperature and addition of residue at different soil depths on decomposition of the residue and native soil organic matter (SOM) (i.e. priming). Soil samples from depths of 5–10, 20–25 and 40–45 cm were incubated at 5, 15 and 25 °C with and without 13C‐labelled barley (Hordeum vulgare L.) residue. Respiration, microbial biomass, phospholipid fatty acids (PLFAs) and mineral N were measured during the incubation. Respiration from residue and SOM increased with temperature in all treatments. The activation energy (Ea) was smaller in the control subsurface soil, indicating a more labile substrate, which resulted in greater respiration than surface soil when respiration was standardized to the amount of C. With the addition of residue, the subsurface soil respired less than the surface soil because of preferential use of residue‐C over soil organic carbon (SOC) and mineral N limitation. This resulted in negative priming of native SOC in the subsurface soil when residue was added. All PLFA biomarkers increased in the subsurface soil when incubated, even without the addition of residue, indicating a positive response of microbial activity to the optimized incubation conditions. Subsurface soil with small OC content and with small Ea had an active and efficient microbial community and relatively large rates of respiration. Highlights: The response of residue and SOM decomposition to temperature in soil with a C gradient was evaluated. We assessed residue turnover with 13C in surface and subsurface soils under varying temperatures. Activation energy was smaller in subsurface than surface soil. Temperature response of subsoil with small SOC content was similar to that of topsoil. [ABSTRACT FROM AUTHOR]

Solar radiation plays an important role in carbon cycling by increasing the decomposition rates of plant litter and soil organic matter (i.e. photodegradation). Previous work suggests that exposure to radiation can facilitate microbial decomposition of litter by altering litter chemistry and consequently litter degradability (i.e. photopriming). However, it remains unclear to what extent photopriming contributes to litter decomposition processes and on what timescale photopriming operates. We conducted laboratory experiments to compare the effects of UV photopriming at two temporal scales (months versus days). In one experiment, we found that four months of UV exposure induced a significant but small (3–4%) mass loss in two of three litter species commonly found in California oak savanna; however, UV exposure did not alter litter degradability as measured by microbial respiration in an incubation experiment. We also found that UV exposure had limited effects on lignin and other cell wall structures, but one month of microbial decomposition (in absence of UV exposure) significantly reduced lignin β-aryl ether inter-unit linkages and acetylated xylans. These results indicate that abiotic photodegradation alone was ineffective at breaking down lignin. In another experiment, litter of a common grass was exposed to either alternating UV radiation and dark conditions or constant darkness for 128 days. We found that the alternating UV exposure increased litter CO 2 production in both dark and UV phases over that observed in constant darkness. This led to a 35% greater release of CO 2 from the alternating UV exposure treatment between days 65 and 128 of the experiment. These results demonstrate that alternating UV exposure with dark conditions is key to enabling photopriming on a timescale of days. Overall, we identify short-term photopriming as a novel mechanism behind photodegradation. Our results also challenge the conventional hypothesis that abiotic processes are primarily responsible for degrading lignin during photodegradation. [ABSTRACT FROM AUTHOR]

Process-based ecosystem models are used increasingly to evaluate the impacts of agricultural practices on soil organic carbon (SOC) stocks at various scales. One of the major sources of error and projection uncertainty in these models is the specification of the initial SOC pools sizes. However, few studies have examined errors and uncertainty over time and for various agricultural practices. The main purposes of our study were 1) to examine the impacts of initialization scenarios on CENTURY model V4.5 performance and 2) to quantify the initialization contribution to the total variance of error of the CENTURY model. We simulated the SOC dynamics of six well-characterized long-term experiments (LTEs) with 25 treatments across France, testing various agricultural practices ( i.e. , inorganic and organic fertilization, various crop rotations and straw and residues removed) using the CENTURY model while keeping the standard parameters unchanged. We applied nine initialization scenarios, each characterized by a unique combination of crop management and relaxation procedures. These relaxation procedures consisted of shifting simulated SOC and nitrogen levels at the end of the initialization period until they matched the stocks at the beginning of the experiment. At the end of the initialization period, the distribution pattern of SOC pools was similar in all scenarios for all LTEs. The slow pool represented the largest proportion of total SOC stocks (average value of 61.5%), whereas the active and passive pools averaged 5.3% and 27.9%, respectively. The overall analysis of CENTURY performance indicated fair results for SOC stocks prediction (R 2 values of the nine initialization scenarios ranged between 0.50 and 0.75) but weak results for SOC change prediction (R 2 values of the nine initialization scenarios, ranged between 0.1 and 0.36). The root mean square error (RMSE) values were moderate compared to the total measured SOC stocks and their confidence intervals. The RMSE values ranged between 6.22 Mg ha − 1 and 15.24 Mg ha − 1 , which corresponded to 13.1% and 32.1% of the initial average total SOC stock for all LTEs, respectively. The highest values were recorded for the no relaxation procedures. CENTURY model errors ( i.e. , simulated - observed SOC stocks) analysis showed a slight sensitivity to the initialization scenarios (approximately 6% of the total variance of the CENTURY error). However, the second-order interaction of scenarios and LTE contributed by 33.6%. Meanwhile, agricultural practices had the greatest impact on the variance of the CENTURY error (44.7%) compared to other factors. Our findings suggest that the contribution of the initialization to the uncertainty in projected SOC changes is negligible compared to the uncertainty related to the model itself and simulated systems characteristics. [ABSTRACT FROM AUTHOR]

Soils on riverine floodplains in Central Europe are commonly enriched in soil organic matter (SOM). We analyzed the quantity and qualitative aspects of SOM in three soil profiles with mollic horizons along the Elbe River (Germany) after physical fractionation by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy to gain deeper insights into the composition of SOM and the formation of these soils. In all horizons, the majority of SOM was recovered in the fraction of particulate OM and in that of sand and aggregates, while SOM in the silt and clay fraction always made up < 20% of soil organic carbon. The C:N ratios of most fractions did not decrease with depth, indicating less decomposed or pyrogenic OM or both. The presence of pyrogenic OM, as a characteristic feature of floodplain soils, was indicated in almost all physical fractions. As derived from DRIFT spectroscopy, SOM was less qualitatively differentiated among the fractions in the soil with the longest duration of flooding, while qualitative differences of SOM were more pronounced in the more aerated ones. The soils have developed from stratified fluviatile sediments and fulfil the criteria of a mollic horizon, irrespective of differences in the composition of SOM. From a soil-genetic point of view, we strongly suggest to classify these soils as Mollic Fluvisols instead of Fluvic Phaeozems, which would accord to the latest WRB classification. [ABSTRACT FROM AUTHOR]

Pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) of humic acids (HAs) from 30 agricultural soils from a volcanic island (Tenerife, Spain) was used to discern the molecular characteristics of soil organic matter (SOM) associated to resilience. For faster perceptual identification of the results, the yields of the pyrolysis products in the form of surface density plots were compared in an update of the Van Krevelen graphical statistical method. This approach, with respect to data reduction and visualization, was also used to collectively represent statistical indices that were obtained after simple and partial least squares (PLS) regression. The resulting plots illustrate different SOM structural domains (for example, carbohydrate- and lignin-derived and condensed lipid). The content of SOM and total mineralization coefficient (TMC) values can be well estimated from the relative abundance of 57 major pyrolysis compounds: SOM content and composition parallels the accumulation of lignin- and carbohydrate-derived structures (lignocellulosic material) and the depletion of condensed polyalkyl structures. In other words, in the volcanic ash soils that were studied, we found that the higher the amount of SOM, the lower its quality in terms of resilience. Although no cause-and-effect is inferred from this fact, it is evident that the resistance to biodegradation of the SOM is related to its molecular composition. [ABSTRACT FROM AUTHOR]

Soil particulate organic matter (POM) has rapid turnover and metal enrichment, but the interactions between organic matter (OM) and metals have not been well studied. The present study aimed to investigate changes in the OM concentration and composition of the POM fraction and their corresponding effects on metal distribution and extractability in long-term polluted paddy soils. Soil 2000–53 μm POM size fractions had higher contents of C–H and C=O bonds, C–H/C=O ratios and concentrations of fulvic acid (FA), humic acid (HA), cadmium (Cd) and zinc (Zn) than the bulk soils. Cadmium and Zn stocks in soil POM fractions were 24.5–27.9% and 7.12–16.7%, respectively, and were more readily EDTA-extractable. Compared with the control soil, the 2000–250 μm POM size fractions had higher organic carbon concentrations and C/N ratios in the polluted soils. However, there were no significant differences in the contents in C–H and C=O bonds or C–H/C=O ratios of POM fractions among the control, slightly and highly polluted soils. In accordance with the lower contents of C=O bonds and FA and HA concentrations, the Cd and Zn concentrations in 250–53 μm POM size fractions were lower than those in 2000–250 μm POM size fractions. Enrichment of Cd in POM fractions increased with increasing soil pollution level. These results support the view that changes in the OM concentration and the size and composition of POM fractions play a key role in determining the distribution of Cd and Zn in paddy soils. [ABSTRACT FROM AUTHOR]

The effects of leaf Cannabis on soil organic matter biodegradation and on soil chemical properties in an incubation experiment 15 weeks were studied. The air dried cannabis plant tissues incorporated at five different rates (0, 0.2, 0.4, 0.6 and 0.8 g per 50 g of soil mixture with 9.74g of manure) resulted increase in organic carbon mineralization, nitrogen nitrate and exchangeable potassium. The levels of the available forms of P and Mn was increased at the two higher rates of the added cannabis. The level of the available forms of Cu and Zn did not show statistically significant differences in comparison with the control at the end of the incubation period. Also, the addition of leaf Cannabis resulted in a increase in total forms of Na, K, P and Mn. The results of this study indicated that the leafs of Cannabis could be applied to the soil without negative effects on the soil chemical and biological properties. [ABSTRACT FROM AUTHOR]

Logging residue piles have been suggested to markedly increase the decomposition of the underlying peat soil leading to large carbon dioxide emissions. We aimed at scrutinizing this postulate with straightforward decomposition (mass loss) measurements. For the purpose, authentic soil organic matter (humus and peat) was incubated in mesh bags under piles and at control plots. The effect of piles was assumed to result from physical (shading and insulation on soil surface) and chemical-biological (leaching of nutrients and fresh organic matter) sources. To distinguish between the two, artificial piles of inorganic matter were established to mimic the bare physical effects. Enhancement of decomposition in the soil under the real and artificial piles was assessed by measuring the mass loss of cellulose strips. Logging residue piles had clear physical effects on soil: temperatures were lowered and their diurnal variation subdued, and relative humidity at the soil surface was higher. The effect on soil moisture was also evident, but more variable, including both decreases and increases. These effects, mimicked by the artificial piles, decreased rather than increased cellulose mass loss. As the real piles, on the other hand, increased mass loss, we conclude that logging residue piles may enhance decomposition in soil due to chemical-biological mechanisms. Also the results on humus and peat mass loss indicate that piles can both increase and decrease decomposition. Consistent, remarkable increase in mass loss was not observed. Thus, our results do not support the postulate of logging residue piles dramatically increasing decomposition of soil organic matter. Rather, they hint that the effect of logging residue piles on soil is an interplay of physical and chemical-biological effects and carbon transport via roots and fungi. To fully understand and quantify these effects, vertical C fluxes between piles and soil and horizontal C fluxes within soil need to be assessed in addition to decomposition in soil and piles. [ABSTRACT FROM AUTHOR]

Background and aims: Evidence from growth chamber and greenhouse experiments indicates that the rhizosphere priming effect (RPE, stimulation or suppression of soil organic matter (SOM) decomposition by live roots and their rhizospheric biota) may be sensitive to environmental factors such as temperature and level of sunlight. However, little is known about potential variations of the RPE under different latitudinal regions that vary in temperature and sunlight levels. Methods: We explored the RPE of soybean ( Glycine max) and cottonwood ( Populus × euramericana cv. '74/76') at two different latitudinal locations under variable conditions of light and temperature for two growing seasons using a natural C tracer method. Results: Different plant species at different time of season produced significantly different RPEs. The RPE of both soybean and cottonwood was small at the initial stage when the plants were small. The RPE of soybean ranged from 0.4% to135%, reached the highest level at the flowering stage and declined afterward. The RPE of cottonwood ranged from −17% to 121% and tended to increase in both growing seasons. The cumulative RPE of soybean was significantly higher than that of cottonwood at both locations and during the two growing seasons. Overall the cumulative RPE values were larger at low latitude than at high latitude. The cumulative RPE of soybean at the low latitudinal location was 1.7 times higher than at the high latitudinal location. The RPE of both plant species was significantly related to specific rhizosphere respiration, but negatively related to soil dissolved total nitrogen content. Conclusions: The RPE of both plant species varied at both locations during the two growing seasons. Particularly for soybean, the cumulative RPE was higher at the low latitudinal location than at the high latitudinal location, possibly because of higher light levels. Our results further indicate that plant species, time of season, specific rhizosphere respiration, and soil dissolved total nitrogen are important variables in controlling the RPE. Overall, these results provide the needed support for using RPE data in a broader context. [ABSTRACT FROM AUTHOR]

Landuse can alter soil organic carbon (SOC) fractions by affecting carbon inflows and outflows. This study evaluated changes in SOC fractions in response to different landuses under variable rainfalls. We compared cropland, grassland and forest soils in high rainfall (Islamabad ~1142 mm) and low rainfall (Chakwal ~667 mm) areas of Pothwar dryland, Pakistan. Forest soils in both rainfall areas had highest SOC (11.32 g kg−1), particulate organic carbon (POC, 1.70 g kg−1), mineral-associated organic carbon (MOC, 7.17 g kg−1) and aggregate-associated organic carbon (AOC, 7.86 g kg−1). However, in rangeland and cropland soils, these varied with rainfall. Under high rainfall, SOC and MOC were 12% and 17% higher in rangeland than in cropland while POC and AOC were equal. Under low rainfall, SOC and MOC were higher in rangeland than in cropland by 7.21 and 1.79 g kg−1at 0–15 cm and equal at 15–30 cm depth. POC and AOC were higher in rangeland than in cropland, in both depths. Averagely, SOC, POC, MOC and AOC were 26%, 68%, 76% and 30% higher in high rainfall than in low rainfall soils. Sensitivity of SOC fractions to landuses observed under different rainfalls could provide useful information for soil management in subtropical drylands. [ABSTRACT FROM AUTHOR]

The decomposition of soil organic matter, as an essential part of nutrient cycling, has a crucial role in maintaining soil fertility and the regulation of climate. This function of the soil is likely to be affected by extreme weather events that are expected to be more frequent and severe in the future. We conducted an experiment from March 2014 to March 2015 to test the effects of extreme drought on composition of the bacterial community and decomposition of plant tissue with soil microclimate variables such as soil temperature and moisture. Precipitation was excluded for a 5-month period by transparent roofs. To follow organic matter decomposition, we used the tea bag method. Soil samples were taken to determine the effects of extreme drought on the bacterial community 6 months after the dry period (mid-term). Drought plots were drier ( P < 0.001) and warmer ( P < 0.001) than control plots as a consequence of the extreme drought treatment. The permanova test showed that the dry period altered soil bacterial communities accordingly ( F permanova = 10.36, P = 0.002). However, there was no significant difference between the control and drought-treated plots 6 months after the dry period in terms of bacterial alpha diversity. Furthermore, rates of organic matter decomposition in the control plots were significantly larger by an average of 93.7% than in the drought plots. The results also indicated that soil temperature and moisture had significant effects on decomposition. Overall, the findings demonstrate clearly the response of soil bacteria and soil function to experimental drought. The strong effect of changes in precipitation and increasing temperature on mass loss suggests that extreme weather events, such as extreme droughts, can markedly change the composition of soil bacterial communities and processes of decomposition. This effect is expected to be more pronounced during dry periods of increasing severity and frequency. Highlights We studied the effects of extreme drought on plant tissue decay and soil bacterial diversity., Microbial degradation of organic matter was followed by the novel tea bag method., Changes in soil microclimate altered bacterial community structure and decomposition., Microbiota and soil function were markedly affected by extreme weather events like droughts. [ABSTRACT FROM AUTHOR]

The priming effect induced by carbon ( C) that is easily available to microbes has been shown to increase the mineralization of soil organic matter ( SOM) that is resistant to decomposition, but the combined effects of easily available carbon and the living root system have rarely been studied. The aim of this research was to study the decomposition of SOM fractions of different solubility in water and their 13C, 14C and 15N abundance with and without the presence of a living root system and easily available carbohydrate in the form of glucose. The SOM collected from the organic horizon of a boreal forest soil in Hyytiälä, southern Finland (61°51′N, 24°17′E), and exposed to laboratory incubations with and without the presence of Pinus sylvestris L. seedlings and glucose, was separated into three chemical fractions with accelerated solvent ( ASE) and pressurized hot water extractions ( PHWE). Changes in the natural abundance of 13C, 14C and 15N, spectral properties assessed by Fourier transform infrared spectroscopy ( FTIR) and the C and N pools of SOM fractions were studied after incubation for 6 months. The extractions separated SOM into fractions with distinctive isotopic composition. The most easily soluble SOM fraction showed the largest abundance of 15N and 14C, and the living root system induced changes in the abundance of 15N and FTIR spectra. Our research suggests that plant roots may induce SOM degradation and N uptake from soluble SOM fractions, but 13C, 14C, 15N or FTIR alone cannot be used to describe the recalcitrance of SOM and its accessibility to microorganisms. It is better to use several methods in parallel to study the decomposability of SOM. Highlights We studied the effects of tree roots and addition of glucose on the solubility of soil organic matter ( SOM)., SOM can be separated into pools with distinctive isotopic concentrations with pressurized hot water., Roots may induce organic matter degradation and N uptake from soluble SOM fractions., Larger 14C abundance in soluble SOM indicated it contained older C than the recently assimilated C. [ABSTRACT FROM AUTHOR]

Inputs of labile carbon (C) and nitrogen (N) affect the intensity and direction of priming effects (i.e., increase or decrease of soil organic matter (SOM) decomposition caused by labile inputs). Increased temperature is also an important factor affecting SOM decomposition. However, the effects of temperature on priming of SOM decomposition remain unclear. To investigate how temperature affects priming of SOM decomposition through changing microbial composition, we added 13 C-labeled glucose with or without NO 3 − or NH 4 + to a subtropical plantation soil in southern China and incubated the soil at 15 °C and 25 °C for 10 days. Soil microbial composition was assessed by analysis of phospholipid fatty acids (PLFAs). Glucose led to positive priming (release of additional CO 2 ) at both temperatures. In contrast, glucose addition with NO 3 − or NH 4 + resulted in negative priming. Temperature did not show a significant effect on SOM decomposition, while the effects of temperature on priming of SOM decomposition were dependent on labile C and N. Labile C addition induced stronger priming at 25 °C than at 15 °C, while combined C and N addition more strongly reduced priming at the high than the low temperature. Although PLFA composition was affected by temperature and labile C and N inputs, changes in PLFA composition were not correlated with priming. We conclude that temperature changes may have limited effects on SOM decomposition in this subtropical soil, while the availability of labile organics has a much stronger effect on priming under warming. [ABSTRACT FROM AUTHOR]

High-latitude ecosystems have the capacity to release large amounts of carbon dioxide (CO2) to the atmosphere in response to increasing temperatures, representing a potentially significant positive feedback within the climate system. Here, we combine aircraft and tower observations of atmospheric CO2 with remote sensing data and meteorological products to derive temporally and spatially resolved year-round CO2 fluxes across Alaska during 2012-2014. We find that tundra ecosystems were a net source of CO2 to the atmosphere annually, with especially high rates of respiration during early winter (October through December). Long-term records at Barrow, AK, suggest that CO2 emission rates from North Slope tundra have increased during the October through December period by 73% ± 11% since 1975, and are correlated with rising summer temperatures. Together, these results imply increasing early winter respiration and net annual emission of CO2 in Alaska, in response to climate warming. Our results provide evidence that the decadalscale increase in the amplitude of the CO2 seasonal cycle may be linked with increasing biogenic emissions in the Arctic, following the growing season. Early winter respirationwas not well simulated by the Earth System Models used to forecast future carbon fluxes in recent climate assessments. Therefore, these assessments may underestimate the carbon release from Arctic soils in response to a warming climate. [ABSTRACT FROM AUTHOR]

The degradation of soil organic matter (SOM) is determined by its compositional and structural properties, but the properties of the remaining SOM can be modified during the mineralization process. In this study, 12 soils (Ultisols, Alfisols and Inceptisols) from subtropical forests were incubated under laboratory conditions (25 °C, aeration) for 90 days. The mechanisms underlying the changes of these properties were investigated by analyzing pre- and post-incubation soils using UV absorption, fluorescence spectroscopy and acid hydrolysis methods. The turnover rate of SOM decreased with increasing soil depth. The amount of CO 2 released ranged from 90 to 620 mg CO 2 -C kg −1 , representing c. 0.9–3.1% of soil organic C (SOC). The proportion of nonhydrolyzable (recalcitrant) N in total N ( R N ) increased with soil depth, whereas it was not apparent in relation to the proportion of nonhydrolyzable (recalcitrant) C in total C ( R C ). Furthermore, a negative correlation was observed between SOM mineralization and R N ( P < 0.05) rather than R C , implying that the availability of N was a limiting factor in SOM decomposition when compared with C. The decrease in E 2 -to-E 4 ratio and fluorescence intensity (FI) of water-extractable organic C (WEOC) with increasing soil depth suggested that WEOC in the deeper horizons was probably rich in electron-withdrawing groups (COOH) but poor in electron-donating groups (OH, NH 2 ), and it was composed of components with larger molecular size, higher humification degree and structural complexity. These could be responsible for the lower SOM mineralization rates in deeper horizons. After 90 days of incubation, a blue shift of wavelengths in the synchrotron-scan spectra, and an obvious increase of FI values, together with the increase in E 2 -to-E 4 ratio of WEOC implied a reduction in molecular size and the degree of aromatic condensation and humification, resulting in a shift to less complicated structures of WEOC. [ABSTRACT FROM AUTHOR]

Laboratory soil incubations provide controlled conditions to investigate carbon and nutrient dynamics; however, they are not free of artefacts. As carbon and nitrogen cycles are tightly linked, we aimed at investigating whether the incubation-induced accumulation of mineral nitrogen (Nmin) biases soil organic carbon (SOC) mineralisation. For this, we selected two soils representative of the C:N ratio values found in European temperate forests, and applied two incubation systems: ‘closed’ beakers and ‘open’ microlysimeters. The latter allowed leaching the soil samples during the incubation. By the end of the 121-day experiment, the low C:N soil significantly accumulated more Nmin in beakers (5.12 g kg-1 OC) than in microlysimeters (3.00 g kg-1 OC) but there was not a significant difference in SOC mineralisation at any point of the experiment. On the other hand, Nmin did not accumulate in the high C:N soil but, by the end of the experiment, leaching had promoted 33.9% more SOC solubilisation than beakers. Therefore, we did not find evidence that incubation experiments introduce a bias on SOC mineralisation. This outcome strengthens results from soil incubation studies. [ABSTRACT FROM AUTHOR]

Priming of soil organic matter decomposition has attracted much research interest, yet a conclusive mechanistic explanation of the phenomenon remains elusive. One proposal is that low molecular weight organic substances might “trigger” an acceleration of microbial metabolism. For the first time, we applied a glucose analogue to soil to demonstrate triggering of microbial metabolism, and to estimate its relative contribution to priming. “Non-metabolizable” glucose analogues have been widely used in pure culture studies to mimic glucose, but never in soil biochemistry. We hypothesized that analogue molecules will elicit a metabolic response in microorganisms despite limited catabolism, and thereby confirm the proposed triggering. The effect of 14 C-labeled 3- O -methyl- d -glucose (OMG) – a common “non-metabolizable” glucose analogue – on soil organic matter mineralization was compared to that of 14 C-labeled d -glucose. OMG was mineralized, but its mineralization was initially impeded and substantially delayed, relative to glucose. OMG caused brief but strong priming in the first 24 h, increasing unlabeled CO 2 efflux by 173%, 89% and 36% above control for additions of 0.49, 2.4 and 4.9 μmol OMG g −1 soil, respectively. In contrast, glucose caused low or negative priming on the first day. On the first day after OMG addition, a negative correlation between priming and OMG mineralization indicated that triggering is a valid mechanism of microbial activation during a famine-feast transition, but is short-lived. Glucose mineralization peaked on the second day for medium and high additions, coinciding with peaks in positive priming. Maximum substrate mineralization also coincided with peaks in priming for medium and high OMG levels, but these occurred 9 and 11 days after addition, respectively. This revealed non-triggering priming mechanisms, which contributed most to priming and were closely coupled to substrate mineralization. By separating energy- and substrate-dependent metabolic processes from triggering processes, the glucose analogue 3- O -methyl- d -glucose enabled triggering to be demonstrated, but triggering by glucose occurs without contributing greatly to priming. [ABSTRACT FROM AUTHOR]

The boreal forest ecosystem stores substantial amounts of soil organic matter (SOM), which may act either as a source or as a sink for atmospheric CO 2 under climate change and that is why enzymatic SOM degradation is gaining increasing attention. The boreal forest ecosystem is rich in plant secondary compounds and in particular tannins which are seen as enzyme inhibitors. We studied changes in enzymatic activity after the addition of tannins. Our experimental design combined direct studies of the tannin effects on enzymes with laboratory soil mesocosm experiments. Our results showed that the addition of tannins directly led to both decreases and increases in the catalytic activity of enzymes, however, some differences between enzymes were observed. Overall, low concentrations of tannins increased the coiled structures of the enzymes boosting their catalytic activity. High concentrations of tannins acted in the opposite way, thereby diminishing the catalytic activity. We observed that tannins caused a similar change in enzymatic activity in soil mesocosm experiments. Tannin-enzyme synergy needs more study as these interactions can potentially play an important role in SOM decomposition of future climate, especially in the tannin-rich ecosystems. [ABSTRACT FROM AUTHOR]

Temperature effects on enzyme kinetics and on the spatial distribution of microbial hotspots are important because they are crucial to soil organic matter decomposition. We used soil zymography ( in situ method for the two dimensional quantification of enzyme activities) to study the spatial distributions of enzymes responsible for P (phosphatase), C (cellobiohydrolase) and N (leucine-aminopeptidase) cycles in the rhizosphere (living roots of maize) and root-detritusphere (7 and 14 days after cutting shoots). Soil zymography was coupled with enzyme kinetics to test temperature effects (10, 20, 30 and 40 °C) on the dynamics and localization of these three enzymes in the root-detritusphere. The percentage area of enzyme activity hotspots was 1.9–7.9 times larger and their extension was broader in the root-detritusphere compared to rhizosphere. From 10 to 30 °C, the hotspot areas enlarged by a factor of 2–24 and V max increased by 1.5–6.6 times; both, however, decreased at 40 °C. For the first time, we found a close positive correlation between V max and the areas of enzyme activity hotspots, indicating that maximum reaction rate is coupled with hotspot formation. The substrate turnover time at 30 °C were 1.7–6.7-fold faster than at 10 °C. The K m of cellobiohydrolase and phosphatase significantly increased at 30 and 40 °C, indicating low affinity between enzyme and substrate at warm temperatures. We conclude that soil warming (at least up to 30 °C) increases hotspot areas of enzyme activity and the maximum reaction rate (V max ) in the root-detritusphere. This, in turn, leads to faster substrate exhaustion and shortens the duration of hot moments. [ABSTRACT FROM AUTHOR]

Increasing inputs of colored dissolved organic matter (cDOM), which is mainly composed of humic substances (HS), are a widespread phenomenon of environmental change in aquatic ecosystems. This process of brownification alters the chemical conditions of the environment, but knowledge is lacking of whether elevated cDOM and HS levels interfere with the ability of prey species to evade chemical predator cues and thus affect predator-prey interactions. We assessed the effects of acute and prolonged exposure to HS at increasing concentrations on the ability of freshwater zooplankton to avoid predator threat (imposed by fish kairomones) in laboratory trials with two calanoid copepods ( Eudiaptomus gracilis and Heterocope appendiculata). Populations of both species clearly avoided water containing fish kairomones. However, the avoidance behavior weakened with increasing HS concentration, suggesting that HS affected the ability of copepods to perceive or respond to the predator cue. The behavioral responses of the two copepod populations to increasing HS concentrations differed, with H. appendiculata being more sensitive than E. gracilis in an acute exposure scenario, whereas E. gracilis responded more strongly after prolonged exposure. Both showed similar physiological impairment after prolonged exposure, as revealed by their oxidative balance as a stress indicator, but mortality increased more strongly for H. appendiculata when the HS concentration increased. These results indicate that reduced predator threat evasion in the presence of cDOM could make copepods more susceptible to predation in future, with variation in the strength of responses among populations leading to changes in zooplankton communities and lake food-web structure. [ABSTRACT FROM AUTHOR]

Periodic changes in temperature commonly occur diurnally and seasonally. However, the response of soil heterotrophic respiration to rising and decreasing temperatures during these periods remains poorly understood; thus the feedback between climate change and carbon (C) cycling requires further investigation. In this study, soils from three grasslands in the Qinghai-Tibet Plateau were incubated separately at rising (from 5 °C to 31 °C) and decreasing (from 31 °C to 5 °C) temperatures modes over 161 days, to explore how soil heterotrophic respiration rates ( R S ) respond to different temperature changes. The parameters of R S and temperature sensitivity ( Q 10 ) were used for the analyses. In addition, microbial biomass C (MBC), microbial biomass nitrogen (N) (MBN), dissolved organic C (DOC), and other soil properties were measured. The results indicated a pronounced hysteresis of R S for both rising and decreasing temperatures. Furthermore, the hysteresis loops differed in the different sites. R S values were significantly higher for rising temperature (2.71 μg C g −1 d −1 ) versus decreasing temperature (1.75 μg C g −1 d −1 ) in all three alpine grasslands. The Q 10 values were significantly higher for decreasing temperature (2.42) versus increasing temperature (1.55), with these differences being observed over the 161-d incubation period. Furthermore, soil microbes (specifically, MBC and MBC/MBN) explained 46–77% of the total variation in Q 10 , followed by substrate and other properties. Our results provide experimental evidence for the asymmetric responses of soil heterotrophic respiration to rising and decreasing temperatures. In addition, the microbial effect was primarily associated with soil heterotrophic respiration, suggesting strong asymmetric responses to rising and decreasing temperatures that require investigation in future studies. [ABSTRACT FROM AUTHOR]

Soil erosion and subsequent land degradation contributed to societal collapse in the past and are a leading cause of desertification in arid and semi-arid regions. Biological soil crusts (biocrusts) are ubiquitous living covers in many arid and semiarid ecosystems that have an important role in soil stabilization and erosion prevention. The “Grain for Green” ecological project improved vegetation recovery, and led to an extensive development of biocrusts across the Loess Plateau region in China, one of the most eroded regions in the world. The expansion of biocrusts was instrumental in reducing soil loss in a very large, severely eroded region of the Loess Plateau. We hypothesized that development of biocrusts would change soil organic matter (SOM) and soil particle size distribution (PSD), thereby reducing soil erodibility and soil loss. We sampled 56 sites that were passively revegetated grasslands on former croplands and 3 bare soil sites in the Loess Plateau region, and used the erosion productivity impact calculator (EPIC) model combined with simulated rainfall to test our assumption. The PSD and SOM content varied significantly among biocrust types and successional stages. The SOM content was 4 times higher in moss dominated biocrust and 1.5 times greater in cyanobacterially dominated biocrust than bare soil. More fine-particles (< 0.01 mm) and fewer coarse-particles (0.05–0.25 mm) were present in biocrusts than in bare soil. Modeled soil erodibility decreased significantly as biocrust biomass increased, mainly due to increase in SOM content, reducing the predicted soil loss by up to 90%. Finally, the prevalence of moss biocrust was a better predictor of soil erodibility than cyanobacteria in the Loess Plateau region. We conclude that biocrusts were a decisive factor for the initial reduction of soil erosion, which must be considered explicitly in models that aim to predict and manage soil loss on the Loess Plateau. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) dynamics plays a crucial role in soil ecosystem functioning and global warming. SOM is normally degraded slowly, but its decomposition rate can change substantially after addition of easily decomposable C sources. This process, known as “the priming effect”, has already been described in 1926 but is still poorly understood. Priming can be positive (extra decomposition of SOM) or negative (reduction of SOM decomposition), depending on the amount and physicochemical characteristics of added compounds, the composition of SOM and the metabolic abilities of responding microorganisms. We propose that the understanding of priming effects can be greatly advanced by investigating the level of convergence between the chemical characteristics of the added compound and SOM fractions, and the functional potential of microbial communities. This can be achieved by combining two different disciplines-microbial ecology and biogeochemistry. Such knowledge will deliver information under which conditions sequestration of soil carbon can be expected and provide possibilities to steer soil carbon dynamics in sustainable agricultural systems. [ABSTRACT FROM AUTHOR]

Labile carbon (C) input to soil can accelerate or slow the decomposition of soil organic matter, a phenomenon called priming. However, priming is difficult to predict, making its relationship with C input elusive. To assess this relationship, we added 13 C-glucose at five levels (8 to 1606 μg C g −1 week −1 ) to the soil from four different ecosystems for seven weeks. We observed a positive linear relationship between C input and priming in all soils: priming increased from negative or no priming at low C input to strong positive priming at high C input. However, the sensitivity of priming to C input varied among soils and between ways of expressing C input, and decreased with elevation. Positive substrate thresholds were detected in three soils (56 to 242 μg C g −1 week −1 ), suggesting the minimum C input required to trigger positive priming. Carbon input expressed as a fraction of microbial biomass explained 16.5% less variation in priming than did C input expressed as a fraction of dry soil mass, indicating that priming is not strongly related to the size of the soil microbial biomass. We conclude that priming increases with the rate of labile C input, once that rate exceeds a threshold, but the magnitude of increase varies among soils. Further research on mechanisms causing the variation of priming sensitivity to increasing labile C input might help promote a quantitative understanding of how such phenomenon impacts soil C cycling, offering the potential to improve earth system models. [ABSTRACT FROM AUTHOR]

The recycling of exogenous organic matter (EOM) through agriculture is an efficient way to enhance soil organic matter (SOM) and to supply crops with readily available nutrients. It can also cause environmental damage, such as nitrate leaching. Characterisation of EOM to predict the C and N dynamics of mineralisation when applied to cropped soils is essential to improve its use in agriculture. The measurement of C and N mineralisation through soil laboratory incubation of 18 types of EOM and EOM biochemical fractionation were used to parameterise the NCSOIL model to simulate the mineralisation kinetics of C and N. The soil type did not significantly interfere with EOM mineralisation and parameterisation, enabling extrapolation of the parameters for one soil to other soil types. Four groups of EOM were distinguished based on their C and N dynamics: (1) stable compost, (2) more reactive compost and stable manure, (3) manure and (4) very reactive EOM as sludge and litter that should be used as fertiliser. The use of easily accessible indicators, such as I ROC (Lashermes et al., 2009) and the measured organic C:N ratio (CN EOM ), was appropriate for parameterising groups 1 and 4. Regression relating the optimised resistant pool size and Van Soest fractions and CN EOM was found (R 2 of 0.967) to improve the pool sizes for the remaining EOM. Further research is required to improve the parameterisation. [ABSTRACT FROM AUTHOR]

In this paper, a family of first-order hyperbolic integro-differential equations introduced to model the decomposition of organic matter (OM) are studied. These original equations depend on an extra variable named "quality". We prove that these equations admit solutions in particular Banach spaces ensuring the continuity and the N-order closure of equations (N ∈ N*) according to "quality". We first give a result of existence, uniqueness and smoothness in a general framework. Then, this result is applied to specific transport equations. Finally, a numerical illustration of solutions properties is given by using an implicit-explicit finite difference scheme. [ABSTRACT FROM AUTHOR]

Estimates of gaseous carbon (C) fluxes in wetlands are heavily based on temperature. However, isolating specific effects of temperature on anaerobic C processing from other controls (C quality and nutrients) has proven difficult. Here, we test the hypothesis that temperature sensitivity of soil organic matter (SOM) decomposition is more influenced by C quality than nutrient availability in subtropical freshwater, sawgrass ( Cladium jamaicense)-based peats. Carbon age (characterized by depth: 0-10 and 10-20 cm) was used as a surrogate of C quality while two sites were selected with contrasting levels of nutrient (P) availability. In anaerobic laboratory incubations temperature was increased in 5 °C steps to assess the proportion of C available at a given temperature (i.e. thermo-labile C) as productions of gaseous (CO and CH) and dissolved organic C (DOC) fractions. Thermo-labile C increased 3.1-3.6 times from 15 °C to 30 °C in all soils. Disproportionate increase in the production of gaseous forms versus DOC as well as CH:CO was observed with warming. Observed Q values followed the trend of CH (~14) ≫ CO (~2.5) > DOC (~1.7) and temperature sensitivity was more dependent on C quality than nutrient availability over the entire temperature range. Spectral analysis indicated more bio-available DOC production at higher temperature. Regression analysis also indicated that C quality primarily influenced SOM decomposition at lower temperature, while at higher temperature nutrient limitation dominantly controlled SOM decomposition. These findings confirm the role of C quality in temperature sensitivity of warm peat soils, but also indicate an increased importance of nutrient limitation at higher temperature. [ABSTRACT FROM AUTHOR]

Determining environmental controls on soil organic matter decomposition is of importance for developing models that predict the effects of environmental change on global soil carbon stocks. There is uncertainty about the environmental controls on decomposition rates at temperature and moisture extremes, particularly at high water content levels and high temperatures. It is uncertain whether observed declines of decomposition rates at high temperatures are due to declines in the heat capacity of extracellular enzymes as predicted by thermodynamic theory, or due to simultaneous declines in soil moisture. It is also uncertain whether oxygen limits decomposition rates at high water contents. Here we present results from a full factorial experiment using organic arctic soils incubated at high temperatures (25 and 35 degrees C), a wide range of water-filled pore space WFPS (15, 30, 60, 90 %), and contrasting oxygen concentrations (1 and 20 %). We found support for the hypothesis that decomposition rates increase at high temperatures provided enough moisture and oxygen is available for decomposition. Furthermore, we found that decomposition rate is mostly limited by oxygen concentrations at high moisture levels; even at 90 % WFPS, decomposition proceeded at high rates in the presence of oxygen. Our results suggest an important degree of interactions among temperature, moisture, and oxygen in determining decomposition rates at the soil-core scale. [ABSTRACT FROM AUTHOR]

Rising global temperatures may increase the rates of soil organic matter decomposition by heterotrophic microorganisms, potentially accelerating climate change further by releasing additional carbon dioxide (CO2) to the atmosphere. However, the possibility that microbial community responses to prolonged warming may modify the temperature sensitivity of soil respiration creates large uncertainty in the strength of this positive feedback. Both compensatory responses (decreasing temperature sensitivity of soil respiration in the long-term) and enhancing responses (increasing temperature sensitivity) have been reported, but the mechanisms underlying these responses are poorly understood. In this study, microbial biomass, community structure and the activities of dehydrogenase and ß-glucosidase enzymes were determined for 18 soils that had previously demonstrated either no response or varying magnitude of enhancing or compensatory responses of temperature sensitivity of heterotrophic microbial respiration to prolonged cooling. The soil cooling approach, in contrast to warming experiments, discriminates between microbial community responses and the consequences of substrate depletion, by minimising changes in substrate availability. The initial microbial community composition, determined by molecular analysis of soils showing contrasting respiration responses to cooling, provided evidence that the magnitude of enhancing responses was partly related to microbial community composition. There was also evidence that higher relative abundance of saprophytic Basidiomycota may explain the compensatory response observed in one soil, but neither microbial biomass nor enzymatic capacity were significantly affected by cooling. Our findings emphasise the key importance of soil microbial community responses for feedbacks to global change, but also highlight important areas where our understanding remains limited. [ABSTRACT FROM AUTHOR]

Priming of soil organic matter decomposition by fresh carbon inputs is a key ecological process determining soil carbon (C) and nutrient cycling in terrestrial ecosystems. Although this priming effect (PE) has been studied under various environmental conditions, the conclusions are inconsistent across space and time and the underlying mechanisms unclear. We used a meta-analysis with extensive datasets of CO 2 effluxes from soils with 13 C or 14 C labelled fresh C inputs and without fresh C inputs under various soil conditions to synthesize and assess the temporal dynamics of the PE. The results indicated that the PE declined in 20 days on average from 67 − 21 + 26 % (95% confidence interval) immediately following the fresh C inputs to less than 7.6 − 1.8 + 2.0 % and remained relatively stable thereafter. We also assessed the variability of the temporal dynamics of the PE in the collected datasets and the underlying drivers. The results showed that the magnitude of PE at a specific time (i.e., the instantaneous PE after the fresh C inputs) was significantly and positively correlated with the instantaneous quantity of remaining fresh C. Under the same quantity of remaining fresh C, the PE varied significantly across ecosystems (in the order of grasslands < farmlands < forests < other ecosystems such as lake beds and volcanic soils), but, contrary to our expectation, the PE was independent of the quality of the added fresh C. We found that the PE experienced a faster decrease in soils with higher clay and moisture contents. These results describe the temporal dynamics of PE and the underlying drivers, underpinning the robust predictions of PE dynamics and their impact on soil C and nutrient balances. [ABSTRACT FROM AUTHOR]

Two features distinguishing soil organic matter simulation models are the type of kinetics used to calculate pool decomposition rates, and the algorithm used to handle the effects of nitrogen (N) shortage on carbon (C) decomposition. Compared to widely used first-order kinetics, Monod kinetics more realistically represent organic matter decomposition, because they relate decomposition to both substrate and decomposer size. Most models impose a fixed C to N ratio for microbial biomass. When N required by microbial biomass to decompose a given amount of substrate-C is larger than soil available N, carbon decomposition rates are limited proportionally to N deficit (N inhibition hypothesis). Alternatively, C-overflow was proposed as a way of getting rid of excess C, by allocating it to a storage pool of polysaccharides. We built six models to compare the combinations of three decomposition kinetics (first-order, Monod, and reverse Monod), and two ways to simulate the effect of N shortage on C decomposition (N inhibition and C-overflow). We conducted sensitivity analysis to identify model parameters that mostly affected CO2 emissions and soil mineral N during a simulated 189-day laboratory incubation assuming constant water content and temperature. We evaluated model outputs sensitivity at different stages of organic matter decomposition in a soil amended with three inputs of increasing C to N ratio: liquid manure, solid manure, and low-N crop residue. Only few model parameters and their interactions were responsible for consistent variations of CO2 and soil mineral N. These parameters were mostly related to microbial biomass and to the partitioning of applied C among input pools, as well as their decomposition constants. In addition, in models with Monod kinetics, CO2 was also sensitive to a variation of the half-saturation constants. C-overflow enhanced pool decomposition compared to N inhibition hypothesis when N shortage occurred. Accumulated C in the polysaccharides pool decomposed slowly; therefore model outputs were not sensitive to a variation of its decay constant. Six-month organic matter decomposition was generally higher for models implementing classical Monod kinetics, followed by models with first-order and reverse Monod kinetics, due to the effect of soil microbial biomass growth on decomposition rates. Moreover, models implementing Monod kinetics predicted positive priming effects of native organic matter after soil amendment, according to co-metabolism theory. Thus, priming was proportional to the increase of the microbial biomass and in turn to the decomposability of applied organic matter. We conclude that model calibration should focus only on the few important parameters. [ABSTRACT FROM AUTHOR]

The root-derived carbon (C) input to the soil, whose quantification is often neglected because of methodological difficulties, is considered a crucial C flux for soil C dynamics and net ecosystem productivity (NEP) studies. In the present study two independent methods to quantify this C input to the soil were compared in a young forest plantation in Italy. Specifically, a mass balance approach to the soil C balance and a new dual in-growth core (IGC) isotopic technique that accounts for both root- and non-root-derived C inputs were compared. No statistically significant difference between the results obtained by the two methods was found (3.09 ± 0.50 vs 5.30 ± 2.92 Mg C ha − 1 ). Both estimates matched with the results obtained by other authors for similar ecosystems. The application of this new dual IGC isotopic technique has shown that the traditional IGC isotopic technique can lead to a significant overestimation (60% in the present study) of root C input to the soil as it doesn't take into account changes in the soil C isotopic signature due to factors other than root derived inputs. These include isotopic discrimination that could take place during the decomposition of original soil organic matter (SOM), the contamination due to dissolved organic C (DOC) leaching, or the C input via leaf litter. The proposed dual IGC isotope technique, taking into account the abovementioned non-root derived inputs seems to be a promising and reliable method to estimate root-derived C input to the soil in terrestrial ecosystems [ABSTRACT FROM AUTHOR]

Abstract. Phosphorus (P) enrichment induced by anthropogenic activities results in modified plant nutrient status, which potentially alters the stoichiometry of carbon (C), nitrogen (N), and P in plants. However, how increased P availability changes plant C:N:P stoichiometry at different hierarchical scales is unclear in N-limited ecosystems. In this study, we conducted a four-level P addition experiment (0, 1.2, 4.8, and 9.6 g P m − 2 year − 1 ) to elucidate the effect of P enrichment on plant C:N:P stoichiometric ratios at both the species and community levels in a freshwater wetland in the Sanjiang Plain, Northeast China. We found that species- and community-level plant C:N:P stoichiometry responded consistently to six years of P addition, although there was a shift in species dominance. Phosphorus addition increased plant N and P concentrations and thus decreased C:N, C:P, and N:P ratios irrespective of the P addition levels. These similar change trends at different scales resulted from the identical responses of plant N and P concentrations in different species to P addition. Moreover, plant N concentration exhibited an increasing trend with increasing P addition levels, whereas plant C:N ratio showed a declining trend. At the community level, P addition at the rates of 1.2, 4.8, and 9.6 g P m − 2 year − 1 decreased the C:N ratio by 24%, 27%, and 34%; decreased the C:P ratio by 33%, 35%, and 38%; and decreased the N:P ratio by 12%, 10%, and 6%, respectively. Our results indicate that the stoichiometric responses to P addition are scale-independent, and suggest that altered plant C:N:P stoichiometry induced by P enrichment would stimulate organic matter decomposition and accelerate nutrient cycles in N -limited temperate freshwater wetlands. [ABSTRACT FROM AUTHOR]

While most models describing soil organic matter dynamics relate the turnover of soil organic matter to its chemical structure, there is increasing evidence that microbial accessibility to the organic matter is predominant in controlling its stability and its decay. This finding has major implications for forecasting the impacts of land management and climate change on soil organic carbon cycling and there is a need for further research to understand the role of microbial accessibility. Further progress is problematic because of difficulties in partitioning total soil respiration ( R S ) into its components soil heterotrophic respiration ( R H ) and soil autotrophic respiration ( R A ) in undisturbed ecosystems. To overcome this problem, we used an improved natural abundance of 13 C technique to partition R S into R H and R A at one and six months after irrigation and addition of nitrogen fertiliser treatments was imposed in a grassland ecosystem. Addition of nitrogen had no significant effect on the components of soil respiration compared with the values for the control. Irrigation resulted in differential effects on R H and R A , leading to strong differences in the proportion of R H contributing to R S (f R H ) with (mean ± standard error) 0.65 ± 0.09 and 0.30 ± 0.06 for the non-irrigated and irrigated plots, respectively, six months after the treatments began. R S and R A were strongly correlated and both showed strong linear relationships with gravimetric soil water content ( W S ) resulting in strong differences between irrigation treatments. Soil temperature ( T S ) and the amount of dissolved organic carbon were also correlated with both R S and R A . In contrast, R H was not related to variation in W S and T S but was correlated with the amounts of particulate organic matter carbon, a labile fraction of carbon defined as physically unprotected, and specific surface area, an indicator of soil protection capacity. There were, however, no differences in the labile carbon fraction and specific surface area between the irrigation treatments. We showed that R H was insensitive to irrigation and remained constant throughout the entire experimental period with a mean value of 1.7 ± 0.2 μmol m 2 s − 1 . Our findings support for the growing evidence that microbial accessibility to substrate, rather than its chemical structure, is predominant in regulating soil organic matter decomposition. [ABSTRACT FROM AUTHOR]

We developed a continuous, nonlinear model (FLOG-CN) linking carbon mineralization and nitrogen mineralization–immobilization with respect to time that successfully reproduced the complex CO 2 -C and SMN dynamics for a collection of 70 paired C and N soil datasets. Application of the model to diverse C and N datasets showed that incorporating latency into the model of C mineralization, and using C to drive N dynamics, allows heterogeneous data from many different soil amendments to be described by the same model. We successfully modeled complex CO 2 -C and SMN dynamics of widely different shapes and from a variety of soil amendments containing plant and animal residues. The re-interpretation of these datasets with the FLOG-CN models improved the quantitative analysis of C and N dynamics, yielding new insights into how amendment characteristics and experimental conditions influence the timing and quantity of C and N mineralized. Model parameters were responsive to varying soil characteristics (pH, C, N, C:N), amendment N:C, amendment rate, incubation temperature, and N additions. Stepwise regression was used to predict model parameters using metadata available for 56 of these datasets. Significant relationships were developed to estimate model parameters independently using measured system properties or other model parameters that could be independently estimated. Estimates of C and N dynamics both fell along a 1:1 line indicating that the model parameters could be adequately described by the measured properties, but the available metadata was not able to describe C dynamics with high precision. Nitrogen mineralization–immobilization was strongly related to amendment N:C, and switched between the two processes at an amendment N:C between 0.077 and 0.085 (C:N between 11.7 and 12.9). We believe that the modeling approach described here will allow quantitative and objective comparisons of diverse C and N datasets that have been hindered by subjective descriptions of the past. [ABSTRACT FROM AUTHOR]

Peatlands export significant amounts of dissolved organic carbon (DOC) to freshwaters, but the quantity of DOC reaching marine environments is typically less than the input to the fluvial system due to processing within the water column. Key removal processes include photo-chemical degradation, and heterotrophic bacterial respiration. In this study we examined these processes using C-labelled DOC to quantify the extent of DOC breakdown and to determine its fate following irradiation under controlled laboratory conditions. We examined the influence of microbial processes occurring within the water column, the potential role of stream-bed biofilms, and the possible modifying effects of downstream mixing, as DOC in water from the peatland encounters runoff from upland mineral soils ('Mountain'), nutrient-rich runoff from agricultural soils, and seawater in an estuary. Our results demonstrated conservative mixing of DOC from Peatland and Mountain waters but interactive effects when Peatland water was mixed with Agricultural and Estuary waters and exposed to solar radiation. The mixing of Peatland and Agricultural waters led to net DOC production, suggesting that DOC was only partially degraded by solar radiation and that the products of this might have fuelled autotrophic microbial growth in the samples. The mixing of Peatland water with saline estuary water resulted in net DOC loss following irradiation, suggesting a role for sunlight in enhancing the flocculation of DOC to particulate organic carbon (POC) in saline environments. [ABSTRACT FROM AUTHOR]

Permafrost soils contain more than 1300 Pg of carbon (C), twice the amount of C in the atmosphere. Temperatures in higher latitudes are increasing, inducing permafrost thaw and subsequent microbial decomposition of previously frozen C, which will most likely feed back to climate warming through release of the greenhouse gases CO 2 and CH 4 . Understanding the temperature sensitivity (Q 10 ) and dynamics of soil organic matter (SOM) decomposition under warming is essential to predict the future state of the climate system. Alaskan tundra soils from the discontinuous permafrost zone were exposed to in situ experimental warming for two consecutive winters, increasing soil temperature by 2.3 °C down to 40 cm in the soil profile. Soils obtained at three depths (0–15, 15–25 and 45–55 cm) from the experimental warming site were incubated under aerobic conditions at 15 °C and 25 °C over 365 days in the laboratory. Carbon fluxes were measured periodically and dynamics of SOM decomposition, C pool sizes, and decay rates were estimated. Q 10 was estimated using both a short-term temperature manipulation (Q 10-ST ) performed at 14, 100 and 280 days of incubation and via the equal C method (Q 10-EC , ratio of time taken for a soil to respire a given amount of C), calculated continuously. At the same time points, functional diversities of the soil microbial communities were monitored for all incubation samples using a microbial functional gene array, GeoChip 5.0. Each array contains over 80,000 probes targeting microbial functional genes involved in biogeochemical cycling of major nutrients, remediation strategies, pathogenicity and other important environmental functions. Of these, over 20,000 probes target genes involved in the degradation of varying C substrates and can be used to quantify the relative gene abundances and functional gene diversities related to soil organic matter turnover. The slow decomposing C pool (C S ), which represented close to 95% of total C in the top 25 cm soils, had a higher Q 10 than the fast decomposing C pool (C F ) and also dominated the total amount of C released by the end of the incubation. Overall, C S had temperature sensitivities of Q 10-ST = 2.55 ± 0.03 and Q 10-EC = 2.19 ± 0.13, while the C F had a temperature sensitivity of Q 10-EC = 1.16 ± 0.30. In contrast to the 15 °C incubations, the 25 °C microbial communities showed reduced diversities of C-degradation functional genes in the early stage of the incubations. However, as the incubations continued the 25 °C communities more closely paralleled the 15 °C communities with respect to the detection of microbial genes utilized in the degradation of labile to recalcitrant C substrates. Two winter seasons of experimental warming did not affect the dynamics and temperature sensitivity of SOM decomposition or the microbial C-degradation genes during incubation. However, under the projected sustained warming attributable to climate change, we might expect increased contribution of C S to organic matter decomposition. Because of the higher Q 10 and the large pool size of C S , increased soil organic matter release under warmer temperatures will contribute towards accelerating climate change. [ABSTRACT FROM AUTHOR]