[Effects of Biochar Application on Soil Organic Carbon Component in Eucalyptus Plantations After Five Years in Northern Guangxi].

To investigate the effects of biochar(BC) addition on soil organic carbon(SOC) contents and its fractions under different biochar applications, Eucalyptus waste twigs in Northern Guangxi were used to produce BC at 500℃. Additionally, we sought to clarify and define the carbon sequestration potential of soil and provide a basis for the preparation of biochar from Eucalyptus forest wastes and soil improvement. In a long-term positioning test of biochar application from 1997, six different treatments were selected:0(CK), 0.5%(T1), 1%(T2), 2%(T3), 4%(T4), and 6%(T5). The contents of SOC, light fraction organic carbon(LFOC), heavy fraction organic carbon(HFOC), easily oxidized organic carbon(EOC), dissolved organic carbon(DOC), particulate organic carbon(POC), microbial biomass carbon(MBC), and carbon stock(CS) following the different treatments were measured. The results showed that:① compared to that in the control, biochar application induced an increase in each soil organic carbon fraction with increasing application rate and reached a maximum under the T4 or T5 treatments; with the increase in biochar application, the contents of SOC, DOC, EOC, POC, MBC, and CS increased significantly by 101.62%, 67.46%, 143.03%, 164.78%, 110.88%, and 41.73%, respectively. ② The contents of LFOC and HFOC in the 0-10, 10-20, and 20-30 cm soil layers increased significantly by 41.41%-140.63%, 9.26%-87.04%, and -19.54%-106.90% and 15.32%-78.99%, 15.72%-75.25%, and 89.49%-148.64%, respectively, with the increase in biochar application. The average contents of LFOC and HFOC in the 0-30 cm soil layer also increased gradually. The soil carbon pool of the Eucalyptus forest was dominated by a relatively stable heavy fraction organic carbon. ③ The contents of carbon stock, soil organic carbon, and its fractions decreased with the increase in soil depth. In conclusion, the application of forestry waste biochar for five years could significantly increase the content of SOC and its components, thereby increasing soil organic carbon activity. Therefore, increasing the amount of biochar was an effective measure to enhance the carbon storage, soil stable carbon pool, and soil quality of the Eucalyptus plantation field. This study provides a reference for the resource utilization of forestry waste and improvements in soil fertility of Eucalyptus plantations.

[Effects of Biochar Application on Soil Organic Nitrogen Component and Active Nitrogen in Eucalyptus Plantations After Five Years in Northern Guangxi].

The objective of this study was to research the characteristics of fractions of organic nitrogen and active nitrogen and their relationship under different biochar applications and to provide a basis for the preparation and practical application of biochar from Eucalyptus forest wastes. In a long-term positioning test of biochar application from 2017, six different treatments were selected:0(CK), 0.5%(T1), 1%(T2), 2%(T3), 4%(T4), and 6%(T5). The contents of soil organic nitrogen components, total nitrogen(TN), dissolved organic nitrogen(DON), and microbial biomass nitrogen(MBN) following the different treatments were measured. The results showed that:① compared with that of the control, with the increase in biochar application, the contents of soil TN, acidolysis of total organic nitrogen(AHON), ammonia nitrogen(AN), amino acid nitrogen(AAN), MBN, DON, and nitrogen storage(NS) increased significantly by 45.48%-156.32%, 44.31%-171.31%, 38.06%-223.37%, 39.42%-163.32%, 36.72%-109%, 23.27%-113.51%, and 29.45%-62.37%, respectively. The contents of soil hydrolyzable unknown nitrogen(HUN) and non-hydrolyzable nitrogen(NHN) also increased significantly by 88.41%-158.71% and 50.24%-139.01%, respectively. The contents of soil amino sugar nitrogen(ASN) decreased by 7.72%-32.73%. The contents of different forms of organic nitrogen fractions in all treatments displayed an order of AN > AAN > NHN > HUN > ASN. Compared with the no biochar treatment, each biochar treatment increased the contents and proportion of AHON in the TN. ② With the exception of HUN, the contents of other soil organic nitrogen components and active nitrogen content decreased with the increase in soil depth. ③ There were significantly positive correlations between TN, MBN, and DON and AHON, NHN, and NS contents. The principal component analysis showed that bulk density and ASN and TN and HUN, AAN, DON, and AHON were closely related, respectively. In conclusion, the application of forestry waste biochar for five years could significantly increase the content of soil organic nitrogen component and active nitrogen, thereby improving the capacity of the soil to supply nitrogen. AHON, AN, and AAN were the main factors contributing to soil active nitrogen content.

Enhanced electrosorption selectivity of phosphate using an anion-exchange resin-coated activated carbon electrode.

Regenerable methods for phosphate (P) recycling have received intense attention due to their potential environmental and economic benefits. In this study, to improve the electrosorptive removal of P in membrane capacitive deionization, an activated carbon (AC) electrode was coated with a heterogeneous anion-exchange resin layer, and named the AE-AC composite electrode. It was shown that the AE-AC electrode exhibited a good capacitive behavior for electrical double-layer charging. The batch-mode experiments indicted that when the solution pH changed from 5 to 8, the predominant P species shifted from monovalent H2PO4- to divalent HPO42- that was preferentially electroadsorbed for competitive electrosorption with Cl-. Importantly, the AE-AC composite electrode significantly increased the selectivity coefficient of P over Cl- to 0.56 that was 2.24-fold greater than that of the uncoated AC electrode, at 1.2 V in single-pass mode operation. This improvement can be ascribed to the preferential transport of P through the thin coating layer containing quaternary amine functional groups. The permselectivity of the coating also significantly increased the electrosorption capacity of P from 0.031 to 0.101 mmol/g with a high charge efficiency (97%) by the reduction in the co-ion repulsion effect. When the reverse voltage (-1.2 V) was applied, electroadsorbed P was reversibly desorbed from the AE-AC electrode in repeated operation. This work suggests that coating an anion-exchange resin layer on the surface of a carbon electrode shows great potential to improve the selective removal of P through electrosorption.

Exploring the electrosorption selectivity and recovery of indium ions with capacitive deionization in acidic solution.

High-efficiency recycling technology for endangered elements effectively mitigates the risk of resource shortages and promises the sustainability of supply chains, which is significant to the industry. In this study, an activated carbon (AC)-based capacitive deionization (CDI) for the selective electrosorption and recovery of indium ions (In3+) from acidic aqueous solution is proposed. The effects of applied voltage, pH, and initial concentration of indium were investigated to optimize the operation parameters for In3+ electrosorption. The results of cyclic voltammetry and the galvanostatic charge/discharge measurements indicate that the AC electrode shows good capability for the electrosorption of In3+ based on electrical double-layer capacitance. As demonstrated, In3+ can be successfully removed by CDI without deposition when the pH < 4, as confirmed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The deionization capacity of In3+ is 7.95 mg/g with an energy consumption of 0.84 kWh/mol in single-pass mode CDI with an initial concentration of 50 mg/L (pH = 3) at 1.2 V. However, the removal of In3+ is affected by the solution pH since hydrogen ions (H+) compete for electrosorption. Note that In3+ ions with high valence are preferentially electrosorbed on the electrode surface over H+ ions, exhibiting a selectivity coefficient of 2.12. Herein, in the charging step, a large number of H+ ions in solution are rapidly electrosorbed onto the electrode, while these H+ ions are gradually replaced by a small number of In3+ ions in solution. Therefore, this electrosorption process shows great potential for effectively recovering indium ions from acidic aqueous solutions.

[Effects of Eucalyptus Branches Biochar Application on Soil Physicochemical Properties of Acidified Soil in a Eucalyptus plantation in Northern Guangxi].

This study aims to explore the effects of different biochar applications on soil physical and chemical properties in a Eucalyptus plantation in Northern Guangxi, find the best biochar application amount, and provide scientific guidance for the efficient utilization of forest residue and soil improvement. The soil of a four-year Eucalyptus plantation at the Huangmian forest farm in Northern Guangxi was selected as the study area, and six treatments including 0 (CK), 0.5% (T1), 1.0% (T2), 2% (T3), 4% (T4), and 6% (T5) were set through a field-positioning experiment to analyze the changes in soil physical and chemical properties under different application rates. Compared with the 0-30 cm soil layer of the control treatment, biochar application decreased the mean soil bulk by 3.82%-33.55%, while it increased the soil natural water content, capillary porosity, and total capillary porosity by 7.67%-31.75%, 8.95%-33.19%, and 9.28%-35.86%, respectively. The contents of exchangeable acid, exchangeable aluminum, exchangeable hydrogen, and exchangeable sodium in the soil decreased by 8.28%-70.03%, 5.55%-70.34%, 5.10%-21.78%, and 12.81%-49.27%. Biochar application increased the cation exchange capacity, electrical conductivity, exchangeable magnesium, and exchangeable calcium by 27.08%-160.39%, 117.00%-546.64%, 17.10%-66.14%, and 17.38%-71.38%, respectively. Soil pH increased by 0.17-1.29 after biochar addition. Similarly, the contents of soil organic carbon, total phosphorus, total potassium, available nitrogen, available phosphorus, and available potassium increased by 10.94%-51.37%, 14.29%-59.45%, 6.48%-59.57%, 6.28%-29.41%, 4.79%-19.81%, and 7.72%-75.87%. There was a positive correlation among the main physical and chemical factors. The physical and chemical properties reached their maximum values in the T4 or T5 treatment (4% or 6%). Biochar application provided considerable relief from soil acidification in the Eucalyptus plantation and had a positive effect on soil physicochemical properties. The addition 4%-6% of ripe Eucalyptus biochar produced the optimum results. The results show that biochar can improve the physical and chemical properties of soil, increase soil fertility, and enhance the soil's ability to retain water and fertilizer after twelve months. The findings of this study can be used as a reference in practical applications for soil improvement and sustainable management of Eucalyptus plantations.

[Soil Organic Carbon Distribution and Components in Different Plant Communities Along a Water Table Gradient in the Huixian Karst Wetland in Guilin].

In order to reveal the effect of vegetation type and soil physicochemical properties on the distribution of soil organic carbon and its components, a field survey was carried out on nine different plant communities along a water table gradient in the Huixian wetland with samples of soil at 0-10 cm, 10-20 cm, and 20-30 cm in depth. The soil organic carbon (SOC), light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), easily oxidized organic carbon (EOC), dissolved organic carbon (DOC), particulate organic carbon (POC), and microbial biomass carbon (MBC) were measured. The correlations among soil organic carbon components and soil physicochemical properties were also examined. The results showed that:① The average proportion of LFOC and HFOC to SOC at 0-30 cm soil depth was 11.10% and 88.90%, respectively. The distribution ratio of the heavy component was much higher than of the light component in soils. ② The content of SOC, DOC, EOC, POC, and MBC (except in the Panicum repens community) and the values of DOC/SOC, EOC/SOC, and POC/SOC all decreased with increase of the soil depth. ③ Among the nine different plant communities, the contents of SOC, LFOC, HFOC, MBC, DOC, EOC, and POC of Cladium chinense were significantly higher than for other communities in same soil layers. ④ There were significantly positive correlations among soil organic carbon components (SOC) and soil total nitrogen (TN). LFOC, HFOC, DOC, and POC were also positively correlated with soil pH. The soil bulk density was significantly negative correlated with LFOC, HFOC, DOC, EOC, and POC, and the content of clay was also negatively correlated with LFOC, HFOC, DOC, POC, and MBC. ⑤ Path analysis showed that TN, soil pH, soil sand content, and soil water content (SWC) has indirect effects on HFOC by influencing other soil factors. Soil TN had strong positive effects on EOC, DOC, and POC, and SWC also has the largest direct negative effect on MBC. This showed that there were close interactions between soil physicochemical properties and soil organic carbon components. This study may provide a reference base for sustainable development and scientific predictions regarding the Huixian Karst wetland.

[Effects of Reclamation on Soil Nutrients and Microbial Activities in the Huixian Karst Wetland in Guilin].

To investigate the effect of reclamation on soil quality in the Huixian Karst Wetland, samples from different soil levels were collected from marsh wetland, reclaimed paddy field, and reclaimed dry farmland, for analyzing soil nutrient (carbon, nitrogen, phosphorous, and potassium) contents, microbial biomass carbon/nitrogen (MBC/MBN), and microbial activity indicators[i.e. basal respiration (BR), potential respiration (PR), microbial quotient (qMB), and metabolic quotient (qCO2)]. The correlations between the soil nutrient contents and soil microbial activity indictors were examined. The results showed that:①Artificial reclamation led to the trend of slight acidity in the soil and a marked loss in soil nutrients, while, the pH value, soil water content (SWC), and the contents of soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP), available phosphorus (AP), total potassium (TK), and available potassium (AK) decreased with reclamation. ②Among all the microbes, bacteria were the most numerous, followed by actinomycetes, and fungi were the least numerous. The microbial quantity decreased with the increase in the soil depth on the whole. The proportion of bacteria and actinomycetes were much higher in the paddy field, and that of fungi was the highest in the dry farmland. ③ In total, protease, sucrase, urease, catalase, and polyphenol oxidase activities decreased with the increasing of soil depths. Soil reclamation reduced the soil enzyme activities. ④qCO2 decreased after an initial increase in the marsh wetland, while it rose gradually in the reclaimed paddy field and reclaimed dry farmland. The contents of MBC, MBN, BR, PR, and qMB were the highest in the marsh wetland, followed by those in the reclaimed paddy field, with the lowest contents occurring in the reclaimed dry farmland. The trend of qCO2 contents in the 0-10 cm and 10-20 cm soil layers followed the order of marsh wetland > paddy field > dry farmland, but in the 20-30 cm and 30-40 cm soil layers, it showed the order dry farmland > paddy field > marsh wetland. The continuation of reclamation resulted in the decrease in soil microbial activity, and soil quality as well, especially in the dry farmland. Meanwhile, we should reduce the areas of paddy fields and dry farmlands under reclamation during the process of wetland ecological restoration in future. Conversion of farmlands to wetlands or lakes, to improve and increase the size of wetland ecosystems of nearby lands, should be done gradually.