Responses of maize grain yield to changes in acid soil characteristics after soil amendments

An experiment was conducted from 1997 to 2000 on an acid soil in Cameroon to assess the effectiveness of cultivating acid tolerant maize (Zea mays L.) cultivar and the use of organic and inorganic fertilizers as options for the management of soil acidity. The factors investigated were: phosphorus (0 and 60 kg ha^?1), dolomitic lime (0 and 2 t ha^?1), organic manure (no manure, 4 t ha^?1 poultry manure, and 4 t ha^?1 of leaves of Senna spectabilis), and maize cultivars (ATP-SR-Y – an acid soil-tolerant, and Tuxpeño sequia – an acid susceptible). On acid soil, maize grain yield of ATP-SR-Y was 61% higher than the grain yield of Tuxpeño sequia. Continuous maize cultivation on acid soil further increased soil acidity, which was manifested by a decrease in pH (0.23 unit), exchangeable Ca (31%) and Mg (36%) and by an increase in exchangeable Al (20%). Yearly application of 60 kg ha^?1 of P for 3 years increased soil acidity through increases in exchangeable Al (8%) and H (16%) and a decrease in exchangeable Ca (30%), Mg (11%) and pH (0.07 unit). Lime application increased grain yield of the tolerant (82%) and susceptible (208%) cultivars. The grain yield increases were associated with a mean decrease of 43% in exchangeable Al, and 51% in H, a mean increase of 0.27 unit in pH, 5% in CEC, 154% in exchangeable Ca, and 481% in Mg contents of the soil. Poultry manure was more efficient than leaves of Senna producing 38% higher grain yield. This yield was associated with increases in pH, Ca, Mg and P, and a decrease in Al. The highest mean grain yields were obtained with lime added to poultry manure (4.70 t ha^?1) or leaves of Senna (4.72 t ha^?1). Grain yield increase was more related to the decrease in exchangeable Al (r = ?0.86 to ?0.95, P<0.01) and increase in Ca (r = 0.78–0.94, P<0.01), than to pH (r = ?0.57 (non-significant) to ?0.58 (P<0.05)). Exchangeable Al was the main factor determining pH (r = ?0.88 to ?0.92, P<0.01). The yield advantage of the acid tolerant cultivar was evident even after correcting for soil acidity. Acid soil-tolerant cultivars are capable of bringing unproductive acid soils into cultivation on the short run. The integration of soil amendments together with acid soil-tolerant cultivar offers a sustainable and comprehensive strategy for the management of acid soils in the tropics.     

Response of soil chemistry to forest dieback after bark beetle infestation

We evaluated changes in the chemistry of the uppermost soil horizons in an unmanaged spruce forest (National Park Bohemian Forest, Czech Republic) for 3 years after dieback caused by a bark beetle infestation, and compared these changes with a similar undisturbed forest area. The soils below the disturbed forest received 2–6 times more elements via litter fall compared to the unaffected plot. The subsequent decomposition of litter and reduced nutrient uptake by trees resulted in a steep increase in soil concentrations of soluble N (NH₄-N, organic-bound N) and P forms in the disturbed plot. The average concentrations of NH₄-N and soluble reactive P increased from 0.8 to 4.4 mmol kg^?1 and from 0.04 to 0.9 mmol kg^?1, respectively, in the uppermost soil horizon. Decomposition of litter at the disturbed plot elevated soil concentrations of Ca²⁺, Mg²⁺ and K⁺, which replaced Al³⁺ and H⁺ ions from the soil sorption complex. Consequently, soil concentrations of exchangeable base cations increased from 120 to 200 meq kg^?1, while exchangeable Al³⁺ and H⁺ decreased 66 and 50 %, respectively, and soil base saturation increased from 40 to 70 %. The Al³⁺ liberation did not elevate concentrations of ionic Al in the soil solution, because most of the liberated Al³⁺ was rapidly complexed by dissolved organic carbon (DOC) and transformed to DOC–Al complexes. The chemical parameters investigated at the unaffected plot remained stable during the study.     

Controls on fluxes and export of dissolved organic carbon in grasslands with contrasting soil types

Export of dissolved organic carbon (DOC) from grassland ecosystems can be an important C flux which directly affects ecosystem C balance since DOC is leached from the soil to the groundwater. DOC fluxes and their controlling factors were investigated on two grassland sites with similar climatic conditions but different soil types (Vertisol vs. Arenosol) for a 2.5-year period. Parts of both grasslands were disturbed by deep ploughing during afforestation. Contrary to what was expected, ploughing did not increase DOC export but surface soil DOC concentrations decreased by 28% (Vertisol) and 14% (Arenosol). DOC flux from the soil profile was negatively influences by the clay content of the soil with seven times larger DOC export in the clay-poor Arenosol (55 kg C ha^?1 a^?1) than in the clay-rich Vertisol (8 kg C ha^?1 a^?1). At the Arenosol site, highest DOC concentrations were measured in late summer, whereas in the Vertisol there was a time lag of several months between surface and subsoil DOC with highest subsoil DOC concentrations during winter season. DOC export was not correlated with soil organic carbon stocks. Large differences in ¹⁴C concentrations of 22–40 pMC between soil organic carbon and DOC in the subsoil indicated that both C pools are largely decoupled. We conclude that DOC export at both sites is not controlled by the vegetation but by physicochemical parameters such as the adsorption capacity of soil minerals and the water balance of the ecosystem. Only in the acidic sandy Arenosol DOC export was a significant C flux of about 8% of net ecosystem production.     

A comparative study of dissolved organic carbon transport and stabilization in California forest and grassland soils

For soil carbon to be effectively sequestered beyond a timescale of a few decades, this carbon must become incorporated into passive reservoirs or greater depths, yet the actual mechanisms by which this occurs is at best poorly known. In this study, we quantified the magnitude of dissolved organic carbon (DOC) leaching and subsequent retention in soils of a coniferous forest and a coastal prairie ecosystem. Despite small annual losses of DOC relative to respiratory losses, DOC leaching plays a significant role in transporting C from surface horizons and stabilizing it within the mineral soil. We found that DOC movement into the mineral soil constitutes 22% of the annual C inputs below 40 cm in a coniferous forest, whereas only 2% of the C inputs below 20 cm in a prairie soil could be accounted for by this process. In line with these C input estimates, we calculated advective transport velocities of 1.05 and 0.45 mm year^?1 for the forested and prairie sites, respectively. Radiocarbon measurements of field-collected DOC interpreted with a basic transport-turnover model indicated that DOC which was transported and subsequently absorbed had a mean residence time of 90–150 years. Given these residence times, the process of DOC movement and retention is responsible for 20% of the total mineral soil C stock to 1 m in the forest soil and 9% in the prairie soil. These results provide quantitative data confirming differences in C cycles in forests and grasslands, and suggest the need for incorporating a better mechanistic understanding of soil C transport, storage and turnover processes into both local and regional C cycle models.     

Effect of Vegetation Rehabilitation on Soil Carbon and Its Fractions in Mu Us Desert,Northwest China

Although vegetation rehabilitation on semi-arid and arid regions may enhance soil carbon sequestration, its effects on soil carbon fractions remain uncertain. We carried out a study after planting Artemisia ordosica (AO, 17 years), Astragalus mongolicum (AM, 5 years), and Salix psammophila (SP, 16 years) on shifting sand land (SL) in the Mu Us Desert, northwest China. We measured total soil carbon (TSC) and its components, soil inorganic carbon (SIC) and soil organic carbon (SOC), as well as the light and heavy fractions within soil organic carbon (LF-SOC and HF-SOC), under the SL and shrublands at depths of 100 cm. TSC stock under SL was 27.6 Mg ha^?1, and vegetation rehabilitation remarkably elevated it by 40.6 Mgha^?1, 4.5 Mgha^?1, and 14.1 Mgha^?1 under AO, AM and SP land, respectively. Among the newly formed TSC under the three shrublands, SIC, LF-SOC and HF-SOC accounted for 75.0%, 10.7% and 13.1% for AO, respectively; they made up 37.0%, 50.7% and 10.6% for AM, respectively; they occupied 68.6%, 18.8% and 10.0% for SP, respectively. The accumulation rates of TSC within 0–100 cm reached 238.6 g m^?2y^?1, 89.9 g m^?2y^?1 and 87.9 g m^?2y^?1 under AO, AM and SP land, respectively. The present study proved that the accumulation of SIC considerably contributed to soil carbon sequestration, and vegetation rehabilitation on shifting sand land has a great potential for soil carbon sequestration.     

Evolution of carbon fluxes during initial soil formation along the forefield of Damma glacier, Switzerland

Soil carbon (C) fluxes, soil respiration and dissolved organic carbon (DOC) leaching were explored along the young Damma glacier forefield chronosequence (7–128 years) over a three-year period. To gain insight into the sources of soil CO₂ effluxes, radiocarbon signatures of respired CO₂ were measured and a vegetation-clipping experiment was performed. Our results showed a clear increase in soil CO₂ effluxes with increasing site age from 9 ± 1 to 160 ± 67 g CO₂–C m^?2 year^?1, which was linked to soil C accumulation and development of vegetation cover. Seasonal variations of soil respiration were mainly driven by temperature; between 62 and 70 % of annual CO₂ effluxes were respired during the 4-month long summer season. Sources of soil CO₂ effluxes changed along the glacier forefield. For most recently deglaciated sites, radiocarbon-based age estimates indicated ancient C to be the dominant source of soil-respired CO₂. At intermediate site age (58–78 years), the contribution of new plant-fixed C via rhizosphere respiration amounted up to 90 %, while with further soil formation, heterotrophically respired C probably from accumulated ‘older’ soil organic carbon (SOC) became increasingly important. In comparison with soil respiration, DOC leaching at 10 cm depth was small, but increased similarly from 0.4 ± 0.02 to 7.4 ± 1.6 g DOC m^?2 year^?1 over the chronosequence. A strong rise of the ratio of SOC to secondary iron and aluminium oxides strongly suggests that increasing DOC leaching with site age results from a faster increase of the DOC source, SOC, than of the DOC sink, reactive mineral surfaces. Overall, C losses from soil by soil respiration and DOC leaching increased from 9 ± 1 to 70 ± 17 and further to 168 ± 68 g C m^?2 year^?1 at the <10, 58–78, and 110–128 year old sites. By comparison, total ecosystem C stocks increased from 0.2 to 1.1 and to 3.1 kg C m^?2 from the young to intermediate and old sites. Therefore, the ecosystem evolved from a dominance of C accumulation in the initial phase to a high throughput system. We suggest that the relatively strong increase in soil C stocks compared to C fluxes is a characteristic feature of initial soil formation on freshly exposed rocks.     

Three-Year Soil Carbon and Nitrogen Responses to Sugarcane Straw Management

Green harvest sugarcane management has increased soil organic C and N stocks over time. However, emerging sugarcane straw removal to meet increasing bioenergy demands has raised concerns about soil C and N depletions. Thus, we conducted a field study in southeast Brazil over nearly three years (1100 days) for assessing soil C and N responses to increasing sugarcane straw removal rates. In order to detect the C input as a function of the different amounts of straw over three years, a field simulation was performed, where the original soil layer (0–0.30 m) was replaced by another from an adjacent area with low total C and δ¹³C. The treatments tested were as follows: (i) 0 Mg ha^?1 year^?1 (i.e., 100% removal), (ii) 3.5 Mg ha^?1 year^?1 (i.e., 75% removal), (iii) 7.0 Mg ha^?1 year^?1 (i.e., 50% removal), (iv) 14.0 Mg ha^?1 year^?1 (i.e., no removal), and (v) 21.0 Mg ha^?1 year^?1 (i.e., no removal + extra 50% of the straw left on the field). The results showed that sugarcane straw removal affected the soil C and total N pools. In the first 45 days of straw decomposition, a small but important straw-derived C portion enters into the soil as dissolved organic carbon (DOC). The lower the straw removal rate, the higher was straw-derived DOC content found into the soil, down to 0.50 m depth. After 3 years of management, keeping sugarcane straw on soil surface significantly increased C and N stocks within surface soil layer (0–0.025 m). Our findings suggest that under no straw removal management (i.e., 14 Mg ha^?1), approximately 364 kg ha^?1 of C and 23 kg ha^?1 of N are annually stored into this low-C soil. The contribution of the straw-derived C (C-C4) to the total soil C increases over time, which accounted for about 60% under no straw removal rate. The greatest contribution of the C storage preferentially occurs into the fraction of organic matter (<?0.53 μm) associated with soil clay minerals. We concluded that indiscriminate sugarcane straw removal to produce cellulosic ethanol or bioelectricity depletes soil C stocks and reduces N cycling in sugarcane fields, impairing environmental gains associated with bioenergy production. Therefore, this information, linked with other agronomic and environmental issues, should be taken into account towards a more sustainable straw removal management for bioenergy production in Brazil.     

Vulnerability of wetland soil carbon stocks to climate warming in the perhumid coastal temperate rainforest

The perhumid coastal temperate rainforest (PCTR) of southeast Alaska has some of the densest soil organic carbon (SOC) stocks in the world (>300 Mg C ha^?1) but the fate of this SOC with continued warming remains largely unknown. We quantified dissolved organic carbon (DOC) and carbon dioxide (CO₂) yields from four different wetland types (rich fen, poor fen, forested wetland and cedar wetland) using controlled laboratory incubations of surface (10 cm) and subsurface (25 cm) soils incubated at 8 and 15 °C for 37 weeks. Furthermore, we used fluorescence characterization of DOC and laboratory bioassays to assess how climate-induced soil warming may impact the quality and bioavailability of DOC delivered to fluvial systems. Soil temperature was the strongest control on SOC turnover, with wetland type and soil depth less important in controlling CO₂ flux and extractable DOC. The high temperature incubation increased average CO₂ yield by ~40 and ~25% for DOC suggesting PCTR soils contain a sizeable pool of readily biodegradable SOC that can be mineralized to DOC and CO₂ with future climate warming. Fluxes of CO₂ were positively correlated to both extractable DOC and percent bioavailable DOC during the last few months of the incubation suggesting mineralization of SOC to DOC is a strong control of soil respiration rates. Whether the net result is increased export of either carbon form will depend on the balance between the land to water transport of DOC and the ability of soil microbial communities to mineralize DOC to CO₂.     

Soil Washing Enhanced by Humic Substances and Biodegradable Chelating Agents

Industrial timber treatment sites have resulted in widespread soil contamination by Cu, Cr, and As, presenting potential long-term liability and associated risks to human health and the environment. This study evaluated the roles of natural humic substances (lignite-derived humic substances, standard and commercially available humic acids) and biodegradable chelating agents (ethylenediamine-N,N-disuccinic acid (EDDS) and glutamic-N,N-diacetic acid (GLDA)) for soil washing. Batch kinetic experiments revealed that humic substances promoted Cu extraction at pH 8, but they were significantly adsorbed on the soil at pH 4, possibly posing impediment to soil remediation. The metal extraction by EDDS and GLDA was comparable to that of EDTA (ethylenediamine-tetraacetic acid), and it was more effective at pH 4 than pH 8, probably due to acidic dissolution of metal precipitates and oxides. Metal distribution analysis indicated that the carbonate fraction of Cu and the oxide fraction of As and Cr were mainly extracted, while the exchangeable fraction of Cu increased. The residual leachability tests showed that humic substances reduced the Cu and As leachability but the reduction was insufficient. In contrast, EDDS was able to reduce the leachate concentrations of Cu and As to below 5 mg L^?1, meeting the waste acceptance criteria for landfill disposal. Nevertheless, soil washing methods and remediation strategy may need further modifications to facilitate site restoration and promote soil recycling.     

High precipitation causes large fluxes of dissolved organic carbon and nitrogen in a subtropical montane <Emphasis Type="Italic">Chamaecyparis</Emphasis> forest in Taiwan

Fluxes of dissolved organic carbon (DOC) and nitrogen (DON) may play an important role for losses of C and N from the soils of forest ecosystems, especially under conditions of high precipitation. We studied DOC and DON fluxes and concentrations in relation to precipitation intensity in a subtropical montane Chamaecyparis obtusa var. formosana forest in Taiwan. Our objective was, to quantify DOC and DON fluxes and to understand the role of high precipitation for DOC and DON export in this ecosystem. From 2005 to 2008 we sampled bulk precipitation, throughfall, forest floor percolates and seepage (60 cm) and analyzed DOC, DON and mineral N concentrations. Average DOC fluxes in the soil were extremely high (962 and 478 kg C ha^?1 year^?1 in forest floor percolates and seepage, respectively) while DON fluxes were similar to other (sub)tropical ecosystems (16 and 8 kg N ha^?1 year^?1, respectively). Total N fluxes in the soil were dominated by DON. Dissolved organic C and N concentrations in forest floor percolates were independent of the water flux. No dilution effect was visible. Instead, the pool size of potentially soluble DOC and DON was variable as indicated by different DOC and DON concentrations in forest floor percolates at similar precipitation amounts. Therefore, we hypothesized, that these pools are not likely to be depleted in the long term. The relationship between water fluxes in bulk precipitation and DOC and DON fluxes in forest floor percolates was positive (DOC r = 0.908, DON r = 0.842, respectively, Spearman rank correlation). We concluded, that precipitation is an important driver for DOC and DON losses from this subtropical montane forest and that these DOC losses play an important role in the soil C cycle of this ecosystem. Moreover, we found that the linear relationship between bulk precipitation and DOC and DON fluxes in forest floor percolates of temperate ecosystems does not hold when incorporating additional data on these fluxes from (subtropical) ecosystems.     

Changes in bacterial CO2 fixation with depth in agricultural soils

Soils were incubated continuously in an atmosphere of ¹⁴CO₂ and the distribution of labeled C into soil organic carbon (¹⁴C-SOC) was determined at 0–1, 1–5, and 5–17 cm down the profile. Significant amounts of ¹⁴C-SOC were measured in paddy soils with a mean of 1,180.6?±?105.2 mg kg^–1 at 0–1 cm and 135.3?±?47.1 mg kg^?1 at 1–5 cm. This accounted for 5.9?±?0.7 % and 0.7?±?0.2 %, respectively, of the total soil organic carbon at these depths. In the upland soils, the mean ¹⁴C-SOC concentrations were 43 times (0–1 cm) and 11 times (1–5 cm) lower, respectively, than those in the paddy soils. The amounts of ¹⁴C incorporated into the microbial biomass (MBC) were also much lower in upland soils (5.0?±?3.6 % and 2.9?±?1.9 % at 0–1 and 1–5 cm, respectively) than in paddy soils (34.1?±?12.4 % and 10.2?±?2.1 % at 0–1 and 1–5 cm, respectively). Similarly, the amount of ¹⁴C incorporated into the dissolved organic carbon (DOC) was considerably higher in paddy soils (26.1?±?6.9 % and 6.9?±?1.3 % at 0–1 and 1–5 cm, respectively) than in upland soils (6.0?±?2.7 % and 4.3?±?2.2 %, respectively). The observation that the majority of the fixed ¹⁴C-SOC, RubisCO activity and cbbL gene abundance were concentrated at 0–1 cm depth and the fact that light is restricted to the top few millimeters of the soil profiles highlighted the importance of phototrophs in CO₂ fixation in surface soils. Phylogenetic analysis of the cbbL genes showed that the potential for CO₂ fixation was evident throughout the profile and distributed between both photoautotrophic and chemoautotrophic bacteria such as Rhodopseudomonas palustris, Bradyrhizobium japonicum, Rubrivivax gelatinosus and Ralstonia eutropha.     

Dissolved organic carbon production and flux under long-term litter manipulations in a Pacific Northwest old-growth forest

Dissolved organic carbon (DOC) flux is an important mechanism to convey soil carbon (C) from aboveground organic debris (litter) to deeper soil horizons and can influence the formation of stable soil organic C compounds. The magnitude of this flux depends on both infiltration and DOC production rates which are functions of the climatic, soil, topographic and ecological characteristics of a region. Aboveground litter quantity and quality was manipulated for 20 years in an old-growth Douglas fir forest under six treatments to study relationships among litter inputs, DOC production and flux, and soil C dynamics. DOC concentrations were measured at two depths using tension lysimeters, and a hydrologic model was created to quantify water and DOC flux through the soil profile. DOC concentrations ranged from 3.0–8.0 and 1.5–2.5 mg C/L among treatments at 30 and 100 cm below the soil surface, respectively. Aboveground detrital inputs did not have a consistent positive effect on soil solution DOC; the addition of coarse woody debris increased soil solution DOC by 58% 30 cm belowground, while doubling the mass of aboveground leaf litter decreased DOC concentrations by 30%. We suggest that high-quality leaf litter accelerated microbial processing, resulting in a “priming” effect that led to the lower concentrations. Annual DOC flux into groundwater was small (2.7–3.7 g C/m²/year) and accounts for < 0.1% of estimated litter C at the site. Therefore, direct DOC loss from surface litter to groundwater is relatively negligible to the soil C budget. However, DOC flux into the soil surface was much greater (73–210 g C/m²/year), equivalent to 1.4–2.4% of aboveground litter C. Therefore, DOC transport is an important source of C to shallow soil horizons.

     

Topographically regulated traps of dissolved organic carbon create hotspots of soil carbon dioxide efflux in forests

Soil carbon pools are an essential but poorly understood factor in heterotrophic soil respiration on forested landscapes. We hypothesized that the topographically regulated distribution of dissolved organic carbon (DOC) is the dominant factor contributing to soil CO₂ efflux. We tested this hypothesis by monitoring soil CO₂ efflux and sampling particulate and dissolved substrates (both mobile DOC in soil solution and DOC potentially sorbed onto Fe and Al oxyhydroxides) in surface (freshly fallen leaves (FFL) and forest floor) and near-surface (A-horizon or top 10 cm of peat) soils along three hillslope transects (15°, 25° and 35° slopes) that included upland (crest, shoulder, backslope, footslope, and toeslope) and wetland (periphery and central) topographic features during the snowfree season within a sugar maple forest. We observed that median snowfree season soil CO₂ efflux ranged from <1 to >5 μmol CO₂ m^?2 s^?1. Substrates in the near-surface mineral soil were most strongly related to median soil CO₂ efflux, and when combined mobile DOC and sorbed DOC together explained 78% of the heterogeneity in median soil CO₂ efflux (p < 0.001). When the carbon pool in FFL (an important source of DOC to the forest soils) was included, the explanation of variance increased to 81% (p < 0.001). Topographically regulated processes created high concentrations of mobile DOC at the footslope, and high concentrations of sorbed DOC further downslope at the toeslope, forming distinct traps of DOC that can become hotspots for soil CO₂ production. A reduction in the uncertainty of forest carbon budgets can be achieved by taking into consideration the topographic regulation of the substrates contributing to soil CO₂ efflux.     

Influence of Rapeseed Cake on Heavy Metal Uptake by a Subsequent Rice Crop After Phytoextraction Using Sedum plumbizincicola

A glasshouse pot experiment was conducted to study the effects of phytoextraction by Sedum plumbizincicola and application of rapeseed cake (RSC) on heavy metal accumulation by a subsequent rice (Oryza sativa L.) crop in a contaminated paddy soil collected from east China. After phytoextraction by S. plumbizincicola the soil and brown rice Cd concentrations effectively declined. After phytoextraction, RSC application reduced brown rice Cd concentrations in the subsequent rice crop to 0.23–0.28 mg kg^?1, almost down to the standard limit (0.2 mg kg^?1). After phytoextraction and then application of RSC, the soil solution pH, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations increased during early stages of rice growth resulting directly and indirectly in lowering the bioavailability of the heavy metals. Thus the grain yield of the subsequent rice crop increased and the heavy metals in the brown rice declined significantly. In this contaminated acid soil, growing the hyperaccumulator S. plumbizincicola and rice in rotation together with RSC application may therefore be regarded as a viable strategy for safe grain production and bioremediation.     

Permafrost and fire as regulators of stream chemistry in basins of the Central Siberian Plateau

Stream chemistry in permafrost regions is regulated by a variety of drivers that affect hydrologic flowpaths and watershed carbon and nutrient dynamics. Here we examine the extent to which seasonal dynamics of soil active layer thickness and wildfires regulate solute concentration in streams of the continuous permafrost region of the Central Siberian Plateau. Samples were collected from 2006 to 2012 during the frost-free season (May–September) from sixteen watersheds with fire histories ranging from 3 to 120 years. The influence of permafrost was evident through significantly higher dissolved organic carbon (DOC) concentrations in the spring, when only the organic soil horizon was accessible to runoff. As the active layer deepened through the growing season, water was routed deeper through the underlying mineral horizon where DOC underwent adsorption and concentrations decreased. In contrast, mean concentrations of major cations (Ca²⁺ > Na⁺ > Mg²⁺ > K⁺) were significantly higher in the summer, when contact with mineral horizons in the active zone provided a source of cations. Wildfire caused significantly lower concentrations of DOC in more recently burned watersheds, due to removal of a source of DOC through combustion of the organic layer. An opposite trend was observed for dissolved inorganic carbon and major cations in more recently burned watersheds. There was also indication of talik presence in three of the larger watersheds evidenced by Cl^? concentrations that were ten times higher than those of other watersheds. Because climate change affects both fire recurrence intervals as well as rates of permafrost degradation, delineating their combined effects on solute concentration allows forecasting of the evolution of biogeochemical cycles in this region in the future.     

Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance

Estimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH₄), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ¹³C signature. Leaching of biogenic DIC was 8.3±4.9 g m^?2 yr^?1 for forests, 24.1±7.2 g m^?2 yr^?1 for grasslands, and 14.6±4.8 g m^?2 yr^?1 for croplands. DOC leaching equalled 3.5±1.3 g m^?2 yr^?1 for forests, 5.3±2.0 g m^?2 yr^?1 for grasslands, and 4.1±1.3 g m^?2 yr^?1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m^?2 yr^?1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO₂ in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO₂. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO₂ in acidic forest soil solutions and large NEE. Leaching of CH₄ proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems.     

Evaluating the Adsorption Potential of Alachlor and Its Subsequent Removal from Soils via Activated Carbon

Alachlor, a globally used aniline herbicide, has great agronomic interest for controlling the development of broadleaved weeds and grasses. This research aspires to evaluate the sorption attributes of Alachlor through batch equilibrium method and its successive removal through biomass based activated carbon prepared from Sawdust (Cedrus deodara). Six soil samples were collected from selected regions of Pakistan to assess the adsorption and removal phenomena. Adsorption capacity for Alachlor varied in soils depending upon their physicochemical properties. Adsorption coefficient (K_d) values ranged from 12 to 31 µg ml^?1 with the highest K_d value observed in soil sample with highest organic content (1.4%) and least pH (5.62). The Gibbs free energy values ranged from ?17 to ?20 kJ mol^?1 proposing physio-sorption and exothermic interaction with soils. Values of R² (0.96–0.99) exhibited the best fit to linear adsorption model. Adsorption coefficient displayed a negative correlation (r = ?0.97) with soil pH and positive correlation with organic matter (r = 0.87). The effect of contact time and pesticide concentration on the removal efficiency by activated carbon was investigated. The highest removal percentages observed through activated carbon were 66% and 64% at concentrations of 5 and 7.5 ppm respectively. Activated carbon from sawdust (Cedrus deodara) was investigated as a suitable adsorbent for the removal of Alachor from selected soils. Biomass based activated carbon can prove to be an effective and a sustainable mean to remove pesticides from soil.     

The impacts of different long-term fertilization regimes on the bioavailability of arsenic in soil: integrating chemical approach with Escherichia coli arsRp::luc-based biosensor

An Escherichia coli arsRp::luc-based biosensor was constructed to measure the bioavailability of arsenic (As) in soil. In previous induction experiments, it produced a linear response (R ²?=?0.96, P?<?0.01) to As from 0.05 to 5 μmol/L after a 2-h incubation. Then, both chemical sequential extraction, Community Bureau of Reference recommended sequential extraction procedures (BCR-SEPs) and E. coli biosensor, were employed to assess the impact of different long-term fertilization regimes containing N, NP, NPK, M (manure), and NPK?+?M treatments on the bioavailability of arsenic (As) in soil. Per the BCR-SEPs analysis, the application of M and M?+?NPK led to a significant (P?<?0.01) increase of exchangeable As (2–7 times and 2–5 times, respectively) and reducible As (1.5–2.5 times and 1.5–2.3 times, respectively) compared with the no fertilization treated soil (CK). In addition, direct contact assay of E. coli biosensor with soil particles also supported that bioavailable As in manure-fertilized (M and M?+?NPK) soil was significantly higher (P?<?0.01) than that in CK soil (7 and 9 times, respectively). Organic carbon may be the major factor governing the increase of bioavailable As. More significantly, E. coli biosensor-determined As was only 18.46–85.17 % of exchangeable As and 20.68–90.1 % of reducible As based on BCR-SEPs. In conclusion, NKP fertilization was recommended as a more suitable regime in As-polluted soil especially with high As concentration, and this E. coli arsRp::luc-based biosensor was a more realistic approach in assessing the bioavailability of As in soil since it would not overrate the risk of As to the environment.     

Effects of a Combined Amendment on Pb,Cd, and As Availability and Accumulation in Rice Planted in Contaminated Paddy Soil

The objectives of the present study were to investigate the mitigation of lead (Pb), cadmium (Cd), and arsenic (As) in a multi-metal contaminated soil and their accumulation in rice plants (Oryza sativa L., cv II You 93) using a combined amendment (CMF, calcium carbonate + metakaolin + fused calcium–magnesium phosphate fertilizer). The results showed that application of CMF was effective in reducing the acid-extractable concentrations of soil Pb and Cd. The exchangeable concentrations of soil As showed an initial decrease followed by a gradual increase. The application of 0.2% CMF notably reduced the concentrations of Pb, Cd, and As in brown rice by 46.5%, 43.6%, and 32.0%, respectively. The concentration of As in brown rice was 0.179 mg kg^?1 at 0.2% CMF, which met the maximum levels of contaminants in foods of China (MLs) (the ML of Pb, Cd, and As is 0.2 mg kg^?1 according to the China national standard GB 2762-2012). At 1.6% CMF, the concentrations of Pb and Cd in brown rice were 0.002 and 0.185 mg kg^?1, respectively, i.e., reductions of 99.6% and 74.1%, and these values also fell within the MLs.     

Short-term responses of ecosystem carbon fluxes to experimental soil warming at the Swiss alpine treeline

Climatic warming will probably have particularly large impacts on carbon fluxes in high altitude and latitude ecosystems due to their great stocks of labile soil C and high temperature sensitivity. At the alpine treeline, we experimentally warmed undisturbed soils by 4 K for one growing season with heating cables at the soil surface and measured the response of net C uptake by plants, of soil respiration, and of leaching of dissolved organic carbon (DOC). Soil warming increased soil CO₂ effluxes instantaneously and throughout the whole vegetation period (+45%; +120 g C m y^?1). In contrast, DOC leaching showed a negligible response of a 5% increase (NS). Annual C uptake of new shoots was not significantly affected by elevated soil temperatures, with a 17, 12, and 14% increase for larch, pine, and dwarf shrubs, respectively, resulting in an overall increase in net C uptake by plants of 20–40 g C m^?2y^?1. The Q ₁₀ of 3.0 measured for soil respiration did not change compared to a 3-year period before the warming treatment started, suggesting little impact of warming-induced lower soil moisture (?15% relative decrease) or increased soil C losses. The fraction of recent plant-derived C in soil respired CO₂ from warmed soils was smaller than that from control soils (25 vs. 40% of total C respired), which implies that the warming-induced increase in soil CO₂ efflux resulted mainly from mineralization of older SOM rather than from stimulated root respiration. In summary, one season of 4 K soil warming, representative of hot years, led to C losses from the studied alpine treeline ecosystem by increasing SOM decomposition more than C gains through plant growth.