381. 题目: Effect of biochar incorporation on phosphorus supplementation and availability in soil: a review
Phosphorus (P) retrieval from crop residues has attracted significant attention in sustainable management of P resources. Biochar has the potential to enhance soil P availability and enlarge P pools. However, only few reviews have been reported on the factors and mechanisms of the effect of biochar on replenishing soil P and improving P availability.
Materials and methods
The current studies on biochar effects on improving soil P level, as well as the underlying factors and mechanisms were reviewed.
Results and discussion
Biomass (especially livestock manure and municipal sewage) derived biochar contains abundant nutrients and, hence, can directly increase soil available P levels. Most of the amended biochar could change soil physical and chemical properties, such as soil porous structure, pH, cation exchange capacity, and adsorption potential toward P. These variations are associated with P forms and availability in soil matrix. Moreover, soil biota and phosphatase, which increased in the presence of biochar, could solubilize insoluble inorganic P and mineralize organic P, thus enhancing P availability. However, the efficiency of biochar is governed by the properties of biochar and amended soil, and cultivation strategies.
Studies illustrating the available P sources in biochar-amended soil, quantifying the contribution of biochar-amended soil microorganisms in improving P level, enhancing the slow-release potential of biochar formulations, and inspecting the effects against comprehensive long-term field analyses are considered to expand our knowledge on the effect of biochar amendment on P supplementation and availability in soil.
382. 题目: High rates of organic carbon burial in submarine deltas maintained on geological timescales
Burial of terrestrial organic carbon in marine sediments can draw down atmospheric CO2 levels on Earth over geologic timescales (≥105 yr). The largest sinks of organic carbon burial in present-day oceans lie in deltas, which are composed of three-dimensional sigmoidal sedimentary packages called clinothems, dipping from land to sea. Analysis of modern delta clinothems, however, provides only a snapshot of the temporal and spatial characteristics of these complex systems, making long-term organic carbon burial efficiency difficult to constrain. Here we determine the stratigraphy of an exhumed delta clinothem preserved in Upper Cretaceous (~75 million years ago) deposits in the Magallanes Basin, Chile, using field measurements and aerial photos, which was then combined with measurement of total organic carbon to create a comprehensive organic carbon budget. We show that the clinothem buried 93 ± 19 Mt terrestrial-rich organic carbon over a duration of 0.1–0.9 Myr. When normalized to the clinothem surface area, this represents an annual burial of 2.3–15.7 t km−2 yr−1 organic carbon, which is on the same order of magnitude as modern-day burial rates in clinothems such as the Amazon delta. This study demonstrates that deltas have been and will probably be substantial terrestrial organic carbon sinks over geologic timescales, a long-standing idea that had yet to be quantified.
383. 题目: Application of organic and chemical fertilizers promoted the accumulation of soil organic carbon in farmland on the Loess Plateau
Understanding the accumulation and mineralization of soil organic carbon (SOC) in aggregates under long-term fertilization conditions is of great significance in comprehending the dynamic changes in farmland C pools on the Loess Plateau.
The long-term field experiment has been established for 26 years and includes six fertilization treatments: no fertilization (CK), organic fertilizer (M), organic and nitrogen fertilizers (MN), organic and phosphorus fertilizers (MP), NP and MNP. We determined nutrient content, mineralization characteristics, temperature sensitivity (Q10), and extracellular enzyme activities of soil aggregates (< 0.25 mm, 0.25–1 mm, 1–2 mm, > 2 mm).
(1) M, MN, MP, and MNP significantly increased the SOC content of aggregates by 92.58%, 82.84%, 73.55% and 83.23% compared to NP. The SOC in < 0.25 mm aggregates was significantly highest than other particles. (2) Organic fertilizer treatments (M, MN, MP, and MNP) significantly increased the cumulative mineralization of different-sized aggregates by 97.10–178.75% compared to NP. The average mineralization rate and the cumulative mineralization of < 0.25 mm aggregates was the lowest. (3) The mineralization of aggregates is directly and significantly affected by the available soil nutrients and enzyme activities. (4) Fertilization and aggregate size had significant effects on Q10 and the Q10 of MNP was lower than that of M, MP, and MN.
< 0.25 mm aggregates had the strongest C sequestration effect. MNP reduced the amount of mineralization by regulating enzyme activities and promoted the accumulation of SOC in farmland on the Loess Plateau by increasing the percentage of < 0.25 mm aggregates.
384. 题目: Wheat straw biochar and its performance in treatment of phenanthrene containing water and microbial remediation of phenanthrene contaminated soil
In recent years, biochar has been considered as an effective adsorbent and soil conditioner due to its abundant carbon and high porosity. This study applied a kind of biochar from wheat straw pyrolysis to remediate phenanthrene-contaminated water and soil. The performance of the biochar in the removal of phenanthrene was discussed by liquid phase adsorption and soil incubation experiments. Furthermore, this work explored the enhancement effect of wheat straw biochar on soil microbial numbers and soil properties. The result of liquid phase adsorption indicated, 92.2% of phenanthrene was removed after incubating 0.6 g/L of wheat straw biochar for 4 h. Pseudo-second-order kinetic model (
385. 题目: Rice-fish-duck system regulation of soil phosphorus fraction conversion and availability through organic carbon and phosphatase activity
Integrated ecological farming combines rice growing with aquaculture, and is an effective way to improve soil productivity by increasing soil nutrient supply. However, the long-term effects of such integrated farming on phosphorus fractions and phosphorus availability of paddy soils in the Pearl River Delta (PRD) remain unknown. A four-year field experiment compared the phosphorus fractions with paddy field in rice-fish-duck system (RFD), rice-vegetable cropping system (RVS) and conventional rice system (CRS) in the PRD. SOC and phosphorus fractions were significantly influenced by cropping systems. RFD significantly increased SOC and phosphorus in the soil. Soil phosphorus was dominated by moderately labile P (40.67–49.41%). RFD also significantly increased soil microbial biomass carbon, microbial biomass phosphorus, and acid phosphatase activity (ACP) by 67.68, 46.68, and 15.87% compared to RVS, and by 134.14, 65.99, and 30.20% compared to CRS, respectively. SOC and ACP were the primary factors influencing the conversion and effectiveness of soil phosphorus. The RFD can alleviate low phosphorus activity in PRD paddy soils through the combined effect of chemical and biological process, while promoting a sustainable soil nutrient cycle within the ecosystem and guiding the sustainable development of rational soil fertilization in the PRD.
386. 题目: Influencing factors and environmental effects of interactions between goethite and organic matter: A critical review
This paper reviews progresses in the interactions between goethite and organic matter (OM) and their environmental effects in recent decades. The interactions mainly include the effect of organic matter on the surface properties and the crystallization of goethite, molecular changes of OM caused by goethite, and their interaction mechanisms, which can be depicted by the commonly used Langmuir model, the charge distribution multi-site complexation model (CD-MUSIC model), ligand charge distribution model (LCD model), and natural organic matter charge distribution model (NOM-CD model). The influencing factors of the interactions are summarized with emphasis on the external, including pH, ionic strength, carbon dioxide (CO2), and the internal, including the structure of OM and iron species. The goethite—OM complexes caused by the interactions will affect migration and transformation of conventional heavy metals and emerging antibiotics. The complexes, as the carrier of carbon and iron, are also the critical parts of the carbon and iron cycles, which are associated with climate change. This review provides a basis for future mechanism studies of formation, transformation, and effects of goethite—OM complexes (particulate OM or carbon-contained minerals) in different environmental systems at a molecular level.
387. 题目: Dynamics and internal links of dissolved carbon in a karst river system: Implications for composition, origin and fate
Dissolved carbon (DC) deciphers biotic and abiotic processes in aquatic ecosystems, representing a critical component of global carbon cycling. However, underlying drivers of riverine DC dynamics and internal links have yet to be studied. Here, we investigated fluvial physicochemical characteristics, dissolved inorganic carbon (DIC) species, carbon dioxide (CO2) exchange, dissolved organic carbon (DOC) compositions and properties in a karst river system Qijiang, Southwest China. Carbonate dissolution combined with photosynthetic uptake could explain dynamics of DIC species. Carbon sequestration caused low-magnitude of partial pressure of aqueous CO2 (pCO2, 620.3 ± 1028.7 μatm) and water-air CO2 flux (F, 154.3 ± 772.6 mmol/m2/d), yielding an annual CO2 emission of 0.079 Tg CO2/y. Relatively high biological index (BIX, 0.77-0.96 on average) but low humification index (HIX, 0.67-0.78 on average) indicated notable autochthonous processes. Humic-like component was the predominant DOC, accounting for 39.0%-75.2% with a mean of 57.2% ± 6.17%. Meanwhile, tryptophan-like component (5.84% ± 2.31%) was also identified as collective DOC by parallel factor analysis (PARAFAC) across samples. Biological metabolism established internal linkages between DIC and DOC in the karst river system. Our findings highlighted biological process as a determinant for DC cycling in karst aquatic ecosystems.
388. 题目: Variations in microbial carbon metabolic activities in sedge peatlands along an altitudinal gradient in the Changbai Mountain, China
Microbial metabolic activity plays a critical role in the peatland carbon cycle; nevertheless, the mechanisms behind the change in the microbial metabolic activities in peatlands along an altitudinal gradient have not been well elucidated. We measured the stable carbon isotopic composition (δ13C) of soil microbial phospholipid fatty acids (PLFAs) as well as climate factors and soil properties in several sedge peatlands along an altitudinal gradient from 400 m to 1500 m in the Changbai Mountain, northeast China. The δ13C composition of microbial PLFAs was more depleted (−35.1‰ ∼ −29.8‰) than that of bulk peat (−25.8‰ ∼ −27.5‰), and the δ13C fractionation of microbial PLFAs was larger at lower altitudes (400–1000 m) than at higher altitudes (1000–1500 m). The carbon isotope fractionation in microbial PLFAs was significantly correlated with mean annual precipitation, mean annual temperature, total phosphorus, dissolved organic carbon concentration and pH. The climate factors had greater influences on δ13C fractionation than soil environmental factors in sedge peatlands along an altitudinal gradient. The variations in the δ13C composition of microbial PLFAs in our study indicated that the microbial carbon metabolic activity decreased with altitude, and microorganisms decomposed more soil organic matter and released more CO2 into the atmosphere at lower altitudes. In a future warming climate, peatland microbial activity in mid- to high-altitude regions could change significantly and affect greenhouse gas emissions.
389. 题目: Biosolids and microorganisms synergistically enhance aggregate stability and organic carbon sequestration of bauxite residue
390. 题目: Optimizing duration of incubation experiments for understanding soil carbon decomposition
Laboratory incubation is a commonly used method to measure the decomposition of soil organic carbon (SOC). While incubation experiments are conducted across a wide range of durations that may vary from hours to years, no method is available to determine an optimal duration of the incubation experiment so that SOC decomposition can be best understood. Here we presented a novel approach to determine the optimal duration called OPtimal Incubation Duration (OPID). The OPID approach quantifies information gained from an ongoing incubation experiment and determines the time point when SOC decomposition rates can be well quantified. Statistically, the OPID approach is based on a progressive data assimilation algorithm that iteratively assimilates data from an ongoing incubation experiment into a three-pool first-order SOC decomposition model. Using a published incubation data set under different temperatures as a case study, we first generated synthetic daily data, and then fed the data into the three-pool model iteratively to observe the changes of model performance. We found that the accuracy of model projections increased with incubation period and exhibited a trade-off between initial model performance and the time towards accurate projection among different temperatures of incubation. The optimal incubation duration was 347, 212, and 126 days under incubation temperatures of 15 °C, 25 °C and 35 °C, respectively. Comparing the parameters with which from the synthetic daily data, if the incubation period was shorter than the optimal durations, then the decomposition rate of the fast-turnover pool was underestimated and those of the slow pools were overestimated. Sensitivity analysis indicated that optimal incubation duration was negatively correlated with proportion of slow-turnover carbon pools, turnover rates, and initial carbon content, respectively. Our study suggested that long-term incubation experiments are necessary for capturing the dynamics of slow-turnover carbon pools. However, the additional data may not be helpful for model performance if the incubation duration is longer than the optimum. Our study provides a tool for soil scientists to design more effective incubation experiments.
DA: data assimilation; PDA: progressive data assimilation; Cum CO2: cumulative CO2 emission from soil; opt: optimal duration;
391. 题目: Bacterial biofilm and extracellular polymeric substances in the treatment of environmental pollutants: Beyond the protective role in survivability
Increased tolerance to toxic pollutants and enhanced degradation capabilities of the bacterial biofilm is often attributed to the matrix of extracellular polymeric substances (EPS). This biopolymeric matrix provides structure, stability, and shelter to the cells within a biofilm and the major constituent of this matrix is exopolysaccharides. However, the role of EPS extends beyond offering protection to the bacterial cells under stress. Bacterial EPS exhibits a double-layered structure consisting of the loosely bound EPS (LB-EPS) and the tightly bound EPS (TB-EPS). Both these EPS layers interact with noxious environmental pollutants through emulsification, solubilization, binding, precipitation, complexation, and ion exchange. Different functional groups of EPS, such as carboxyl, amide, phosphoryl, and hydroxyl, are involved in the removal of toxic pollutants from contaminated environments. Biofilm-EPS participate in several remedial functions such as sequestration of heavy metals, emulsification of petroleum hydrocarbons, binding and solubilization of polycyclic aromatic hydrocarbons (PAHs), and sorption and degradation of dyes and pesticides. Thus, bacterial biofilm and EPS present an attractive solution for decontaminating heavily polluted environments. This review discusses a comprehensive account of biofilm physiology, EPS components, and synthesis mechanisms of exopolysaccharides. The interaction mechanisms of bacterial biofilm and EPS with pollutants have been discussed in detail, and the application of biofilm-forming bacteria and associated EPS in the bioremediation of the environment has been summarized. A deeper understanding of the bacterial biofilm and EPS-mediated pollutant removal will help develop technologies for field-scale applications.
392. 题目: Transport, retention and release of phytate in soil with addition of Mg–Al layered double hydroxides
Organic fertilizers have been excessively used for agricultural production, raising P loss risk to river systems. Phytate is the most abundant organic phosphorus (OP) in organic fertilizers. In this study, Mg–Al layered double hydroxides (LDHs) as environmentally friendly materials were applied to soils to control phytate loss from soil and improve the sustainable utilization of phytate. Adsorption kinetic experiments, XRD, and zeta potential measurements were conducted to investigate adsorption mechanisms of phytate on LDHs. Saturated soil column experiments and numerical modeling were conducted to investigate the transport, retention, and release behaviors of phytate in natural soil with and without LDHs. The KCl and CaCl2 solutions were chosen as leachate to simulate different types of soil solutions. Adsorption modes of phytate on LDHs contained electrostatic attraction and surface complexation but not interlayer anion exchange. Retention of phytate in the soil increased with the addition of LDHs or the presence of Ca2+ due to irreversible retention. The retention of phytate in soil-LDHs column reduced with increasing ionic strength (IS) of KCl due to the competition of Cl− with anionic groups of phytate on the LDHs (Meff: 1 mM, 12.1% of total phytate; 20 mM, 16.6% of total phytate; 100 mM, 20.7% of total phytate). On the other side, the release of phytate from soil-LDHs occurred by the competition of phosphate but was not obvious by IS reduction. The injection of phytate brought release of organic substances from soil and the dissolution of LDHs with increasing IS of KCl.
393. 题目: Long-term continuous farmyard manure application increases soil carbon when combined with mineral fertilizers due to lower priming effects
Organic and synthetic fertilizers not only increase soil fertility and crop productivity but also enhance soil organic carbon (SOC). However, the priming effect (PE) leads to increased soil carbon (C) loss through native SOC mineralization. To date, the mechanisms by which long-term (>66 years) synthetic and/or organic fertilization alters net SOC sequestration remain a matter of debate. This study aimed to assess the effects of different fertilization practices on SOC decomposition and PE in agricultural systems subjected to long-term annual synthetic and/or organic fertilizer application. This aim was achieved by collecting topsoil samples (0–20 cm) from four long-term fertilization practices, i.e., unfertilized, synthetic supplemental (+s), cattle farmyard manure (+m, similar nutrient amount to +s), and synthetic fertilizer with farmyard manure (+s +m, the highest nutrient amount). The soil samples were incubated for 33 days with and without 13C-glucose addition, and a CO2 isotope analyzer combined with a modeling approach was used to establish a real-time method to monitor CO2 and 13CO2 production rates during the incubation period. Overall, +m increased the cumulative SOC-derived CO2 (SOC-CO2) by 107, 74, and 24 % compared to the unfertilized, +s and +s +m, respectively. The higher SOC-CO2 in +m treatment was associated with the greatest priming effect (PE, 390 ± 21 mg C kg soil−1), which corresponded to a 30 % increase compared to the average of the treatments that involved synthetic fertilizer (+s and +s +m) and a 137 % increase compared to the unfertilized control. The results were explained by the lower dissolved nitrogen (N), a proxy of available mineral N, in +m compared to +s +m, thus enhancing microbial mining for additional N via increasing SOC mineralization. However, the combined application of synthetic fertilizer and manure in the +s +m treatment provided enough easily accessible nutrients for microbial growth and activities from the applied synthetic fertilizer, leading to lower SOC mineralization than manure (+m) alone. Nevertheless, the treatments with manure application (i.e., +m and +s +m) significantly increased net SOC compared to the synthetically fertilized treatment and unfertilized control, suggesting greater C inputs than outputs and leading to high SOC accumulation over time. These results indicated that organic manure has a great potential to mitigate climate change by increasing SOC over time, which can be fostered by the addition of synthetic fertilizer; however, caution still needs to be taken regarding the quality and quantity of the added fertilizer.
394. 题目: Sulphur-doped zero-valent iron supported on biochar for tetracycline adsorption and removal
BM-S/ZVI@BC was further synthesized from common agricultural waste maize straw and applied to the adsorption of aqueous tetracycline using a simple ball milling method. SEM, XRD, FTIR, and XPS were used to characterize the structural features and surface properties of BM-S/ZVI@BC. The effects of time, temperature, pH, and interfering ions on the adsorption were investigated, and the adsorption performance and possible mechanisms of BM-S/ZVI@BC on tetracycline were explored. The results showed that the adsorption of tetracycline by BM-S/ZVI@BC was more inclined to acidic conditions, The higher the temperature, the better the adsorption of tetracycline, and the maximum saturation adsorption capacity of BC/S/Fe0 in the optimum ratio of 2:1:1 was up to 505.68 mg·g−1 at a temperature of 313 K, and the adsorption process was both physical and chemical. The electrostatic interaction, hydrogen bonding, π-π stacking, and complexation are the main mechanisms of tetracycline adsorption by BM-S/ZVI@BC. BM-S/ZVI@BC had excellent oxidation resistance and good adsorption performance for tetracycline after aging in the air (60 d) and water (120 h). BM-S/ZVI@BC maintained a high adsorption capacity after five times of reuse and had a good removal capacity for tetracycline in different water bodies. In conclusion, BM-S/ZVI@BC had a good application prospect for tetracycline removal in water.
395. 题目: Evaluating wetland soil carbon stability related to iron transformation during redox oscillations
Redox shifts threaten to reduce the massive soil organic carbon (SOC) stocks in wetlands. However, ferrous iron [Fe(II)] oxidation may stabilize wetland SOC by reducing phenol oxidative activity, inhibiting CO2 emissions, and promoting SOC association with ferric Fe [Fe(III)] (oxyhydr)oxides. Yet the prevalence and efficacy of this mechanism are not clear. Here we select six contrasting soils from fens and bogs with different pH for microcosm incubation under cyclic redox conditions, with or without Fe(II) addition, and compared to static oxic incubation. CO2 emissions, microbial composition, enzyme activities, Fe species, and organic matter properties were measured to test the related mechanism. We found that compared to static oxic conditions, the response of Fe(II) to cyclic redox conditions (indicated by the response ratio of −0.48 to 0.53) was positively correlated with that of phenol oxidative activity and cumulative CO2 at the end of the incubation. Redox cycling had little effect on Fe-bound SOC (assessed by the modified citrate-bicarbonate-dithionite extraction), although Fe(II) addition increased Fe-bound SOC in all soils under cyclic redox owing to the production of short-range-ordered Fe(III) (oxyhydr)oxides (quantified by oxalate extraction). Furthermore, Fe(II) addition decreased CO2 emissions from three soils with pH > 6 but increased CO2 emissions from the Sphagnum-dominated soil, which had elevated Fe(II) levels after the incubation. These findings highlight the SOC stabilization potential of Fe(II) addition to wetland soils experiencing redox oscillations by promoting the accumulation of Fe-bound SOC as well as decreasing CO2 emissions (in response to phenol oxidative activity), especially in non-Sphagnum-dominated freshwater wetlands with relatively high pH.
396. 题目: Iron speciation changes and mobilization of colloids during redox cycling in Fe-rich, Icelandic peat soils
Soils of Iceland are characterized by an abundance of short-range order (SRO) iron (Fe) minerals and aluminosilicates. Interactions between these SRO mineral phases and soil organic carbon (OC) promote long-term stabilization of the latter through the formation of mineral-organic complexes and aggregates. However, Icelandic soils are also exposed to high rainfall events, which induce anoxic conditions, facilitate microbial reduction of ferric Fe, and may lead to the mobilization of mineral-associated OC. Here, we explored the fate of OC during Fe redox cycling by incubating six organic-rich soil horizons from three typical soil types across Iceland (Histosols, Histic and Gleyic Andosols) as soil slurries under anoxic conditions for up to 5 weeks and followed the effects of re-oxidation after 1, 2, and 5 weeks. Changes in solid-phase Fe speciation were assessed by combining Fe K-edge X-ray absorption spectroscopy with time-resolved parallel selective chemical extractions, and trends in aqueous element contents were measured in both the dissolved (<3 kDa) and fine colloidal fractions (3 kDa to 0.45 µm). In all soils, anoxic incubation resulted in microbial reduction of Fe(III) and concomitant increases in soil solution pH. However, soils containing SRO Fe minerals underwent more extensive Fe reduction. Rapid (<1 wk) increases in aqueous element contents (including Fe, Al, and OC) were recorded in all soil slurries, and mobilization of colloids occurred in soil horizons which reached the highest pH values (>4.6). Mobilized colloids persisted during re-oxidation of the soil slurries, which also resulted in the formation of new Fe mineral phases, the composition of which was influenced by initial soil Fe mineralogy. Collectively, our results suggest that increases in the frequency of redox cycles in Icelandic soils are likely to result in shifts in Fe mineralogy and may contribute to the increased mobilization of soil OC as organic-Fe-/Al-colloids.
397. 题目: Responses of soil carbon and nitrogen mineralization to nitrogen addition in a semiarid grassland: The role of season
Elevated atmospheric N deposition can profoundly alter soil carbon (C) mineralization (Cmin) and nitrogen (N) mineralization (Nmin), which could severely impact long-term productivity of grassland ecosystem. However, little is known about how N addition, season, and their interaction affect soil Cmin and Nmin rates and their relationships by regulating soil abiotic and biotic factors. Here we investigated the seasonal variations in soil Cmin and Nmin rates and their relationship in response to multi-level N additions in a semiarid grassland in 2014–2015, and further identified direct and indirect pathways by which soil abiotic and biotic factors regulated these variations using structural equation modeling. We documented the statistically significant impacts of N addition and its interaction with season on soil Cmin rates. In contrast, only a significant seasonal effect on the soil Nmin rate was observed. Random forest analysis revealed that across all seasons, dissolved organic carbon (DOC), soil water content (SWC), catalase, urease, sucrase, microbial biomass carbon (MBC), soil organic carbon (SOC) to total nitrogen (TN) ratio, and TN were the most pivotal predictors of the soil Cmin rate. Comparatively, catalase, MBC, DOC, NO3–-N, urease, TN, NH4+-N, SWC, and the MBC to microbial biomass nitrogen (MBN) ratio were the most dominant drivers of the soil Nmin rate. SEM results indicated that the identified potential drivers that regulated the soil Cmin and Nmin rates in response to N addition varied seasonally. Additionally, N addition decoupled the soil Cmin and Nmin rates, which was a consistent relationship among most seasons. In summary, our results show that, in this semiarid grassland, current N additions can enhance soil N immobilization across all seasons; however, its impacts on soil C sequestration were seasonally variable. These findings provide evidence that season and its interactions with elevated atmospheric N deposition have important implications for the grassland biogeochemical cycling.
398. 题目: Soil organic matter accumulation before, during, and after the last glacial maximum in Byers Peninsula, Maritime Antarctica
Organic matter is incorporated into soil by biological activity, and its preservation depends on composition and organic-mineral interactions. Frost activity, dry and cold climate, and glacial retreat-advance dynamics complexify soil organic matter storage in Antarctica. Byers Peninsula is the largest ice-free area in Antarctica and hosts a high diversity of vegetable and animal species. We hypothesize that (i) the SOM in the Byers Peninsula may reveal a distinct composition due to the antiquity of the ice-free areas not entirely obliterated by the advancing glaciers during the LGM; and (ii) the advancing ice caps at Byers allowed the accumulation of organic carbon at sheltered points of the Peninsula. Thus, the objectives of this work were: i) to characterize physically and chemically selected soils at Byers Peninsula, with emphasis on organic C and N stocks in different soil types, and ii) SOM dating of representative soil profiles. Thirteen soil profiles were dug, described, and classified. The plant species present at each site were identified. Chemical and physical attributes were determined. The C and N contents, δ13C and δ15N ratio isotopes were determined in the SOM physical size-fractionated particles. The C and N stocks were calculated for each SOM fraction. The deepest horizon of six soil profiles were dated by the 14C method.. Soils from Byers Peninsula showed a diverse and varied biochemical nature of SOM, resulting in varying content of C and N. The δ13C weighted mean of the SOM reflects the dominant vegetation type present in each sampling location, except for pre-Holocene soils and soils influenced by ornithogenesis. The highest organic C and N pools were recorded at subsurface horizons and attributed to the organo-mineral association fraction in upper platforms. For all soil groups, there was a significant overlap of δ13C and enrichment of δ15N in all fractions of SOM, requiring the combination of these two signatures to identify possible sources of contribution to SOM in this environment. The oldest soils, subjected to early-mid Holocene uplift, revealed an endolithic signature of pre-LGM age, the first recorded in Maritime Antarctica to this day. This first pre-LGM SOC record can indicate the initial modern colonization of Maritime Antarctica and suggests that ice caps advance during LGM was limited. Soils formed during and after the LGM in low platforms have a lacustrine signature indicating an influence of snowmelt, ice thawing, and permafrost degradation in selecting hygrophilous species. Soils formed in raised beaches have the lowest organic C and N stocks, and the isotopic composition of SOM indicates ancient ornithogenic influence.
399. 题目: Rice straw biochar alters inorganic nitrogen availability in paddy soil mainly through abiotic processes
Nitrogen (N) is an important element for crop yield and its availability may be affected by biochar. The mechanisms through which biochar influences N availability and thus crop productivity remain largely unclear, although they seem to be principally mediated by microbial processes. The objective of this study was to assess the effects of rice straw biochar on soil N availability and microbial functional genes (MFG) involved in N transformations under field experiment.
Materials and methods
The field experiment was performed using biochar amendment (0, 20, 40 t ha−1) with or without N fertilizer application in a rice paddy in central China.
The results suggested that the soil NH4+-N content showed a decreasing trend during the early stage of rice growing season while increasing its availability during the later stage in the plots with biochar amendment as compared with control. Nonetheless, soil NO3−-N was not affected by biochar addition, N fertilization, and their interaction at most of the sampling times. With the increase of N fertilizer and biochar application, soil MBC and MBN increased in most of the sampling times during the first and second seasons. The N uptake was significantly positively correlated with soil MBC and MBN in the first and second seasons. Biochar addition also affected some MFG involved in N transformations, causing a general decrease in the abundance of bacterial ammonia oxidizers during mature stage and narG (nitrate reduction) at heading stage during the second season independent of biochar application rates, while increase in nifH (nitrogen fixation) at heading stage during the first season in 40 t ha−1 biochar treatments with N application, as compared with the control. However, there is lack of significant relationships between measured soil inorganic N and genetic data for each season.
As a result, the application of biochar had a slow release effect on soil NH4+-N and regulated the N uptake in rice. However, we believe that the dynamic of soil N availability during rice growing seasons may have been dominantly driven by abiotic factors rather than microbially mediated processes in double rice-cropping system.
400. 题目: Various beneficial microorganisms colonizing on the surface of biochar primarily originated from the storage environment rather than soil environment
Recently, the effects of biochar on soil microbial communities have gained a lot of interest. However, researchers have paid little attention to microbial colonization of biochar surfaces and the effect of soil potassium (K) availability on specific colonization In this study, the microbial colonization on the surface of biochar was systematically investigated using carbon-13 nuclear magnetic resonance (13C NMR), scanning electron microscopy (SEM), and metagenomics based on a four-year pot culture experiment. The results showed that the main microorganisms colonizing the surface of biochar were all potentially beneficial bacteria (g_Streptomyces, g_Pseudonocardia, g_Amycolatopsis). The main carbon source for microbial colonization was the alkoxy carbon component of biochar. Under normal storage conditions, biochar colonized a large number of beneficial microorganisms from the storage environment, but the amount of colonization increased when applied to the soil. Among them, the amount of colonization in the high-K environment was slightly higher than in the low-K environment, but the primary composition and functions of microorganisms were the same (carbon metabolism, biosynthesis of amino acids, ABC transporters). In general, a large number of beneficial microorganisms can colonize the surface of biochar in any environment, which provides more cutting-edge theoretical support for the application of biochar in agriculture.