241. 题目: The bacterial influencing mechanisms of salinity fluctuations in a brackish-water lake on the dissolved organic matter characteristics of pore water
The dissolved organic matter (DOM) components in lake water have been widely studied; however, few previous studies have considered the growth of Phragmites australis in brackish lakes. It has not been well understood how salinity variations influence the DOM compositions in pore water and its bacterial mechanisms in lakes with Phragmites australis. This experiment included three salinity groups (1,200 mg/L, 3,600 mg/L, and 6,000 mg/L) to study the interactions between bacteria and DOM in pore water under a salinity gradient. The results showed that the maximum fluorescence intensity (Fmax) of DOM measured by excitation-emission fluorescence spectroscopy decreased with increasing salinity. Higher salinity reduced the Fmax of protein-like substances and resulted in DOM becoming more aromatic. Salinity affected DOM composition due to the responses of functional bacterial communities. Thiobacillus was salt-tolerant and dominated in the sediments, and its relative abundance was negatively correlated with the Fmax of protein-like components. The relative abundance of Flavobacterium showed a positive correlation with salinity and a negative correlation with the Fmax of the fulvic acid-like component. Pseudomonas, Brevundimonas, and Polaromonas were negatively correlated with salinity and the Fmax of the fulvic acid-like component, while being positively correlated with the Fmax of tyrosine-like and aromatic protein substances. Higher salinity inhibited the metabolism gene modules of tryptophan and tyrosine. The results of this study may offer a novel perspective on comprehending the biochemical cycling of fluorescent DOM, encompassing tryptophan-like, tyrosine-like, and fulvic acid-like components in brackish lakes with fluctuating salinity.
242. 题目: Significant contribution of different sources of particulate organic matter to the photoaging of microplastics
Particulate organic matter (POM), as an important component of organic matter, can act as a redox mediator and thus intervene in the environmental behavior of microplastics (MPs). However, quantitative information on the role of POM in the photoaging of MPs under ultraviolet (UV) light is still lacking. To raise the knowledge gap, through environmental simulation experiments and qualitative/quantitative experiments of active substances, we found that POM from peat soil has stronger oxidation capacity than POM from sediment, and the involvement of POM at high water content makes the aging of MPs more obvious. This is because the persistent radicals and electron-absorbing groups on the surface of POM indirectly generate reactive oxygen species (ROS) by promoting electron transfer, and the dissolved organic matter (DOM) released from POM under UV light (POM-DOM) is further excited to generate triplet-state photochemistry of DOM (3DOM*) to promote the aging of MPs. Theoretical calculations revealed that the benzene ring, mainly C=C, and C=O in the main chain in the plastic macromolecule structure are more susceptible to ROS attack, and the differences in the vulnerable sites contained in different plastic structures as well as the differences in the energy band gaps lead to differences in their aging processes. This study firstly elucidates the key role and intrinsic mechanism of POM in the photoaging of MPs, providing a theoretical basis for a comprehensive assessment of the effect of POM on MPs in the environment.
243. 题目: Machine learning prediction of higher heating value of biochar based on biomass characteristics and pyrolysis conditions
The higher heating value of biochar is an important parameter for the utilization of biomass energy. In this work, extreme gradient boosting regression and artificial neural network were used to predict it based on the characteristics of biomass and pyrolysis conditions. Besides, empirical correlations were developed for comparison. Results showed that the extreme gradient boosting regression models showed better performance (R2 = 0.83–0.94). The shapley additive explanations and partial dependence plot indicated that lignin content and higher heating value of raw material were highly positively correlated with higher heating value of biochar, and found the better conditions such as pyrolysis temperature (>550 °C), lignin content (>40 wt%) for high-higher heating value biochar preparation. What’s more, a program that predicted higher heating value of biochar was developed through PySimpleGUI library. It offered a new optimization idea for the directional preparation process of biochar.
244. 题目: Differential photodegradation processes of adsorbed polychlorinated biphenyls on biochar colloids with various pyrolysis temperatures
Despite the crucial role of photodegradation in the environmental transformation of organic pollutants, the photodegradation process of organic pollutants irreversibly absorbed on biochar colloids (BCCs) remains poorly understood. This study investigated the photodegradation processes and mechanisms of 2,4,4’-trichlorobiphenyl (PCB28) adsorbed on BCCs released from bulk biochars derived from bamboo chips at pyrolysis temperatures of 300, 500, and 700°C. Results show that BCCs-adsorbed PCB28 could be degraded under simulated solar illumination (95-105 mW·cm−2) but at decreased photodegradation rates compared to the dissolved PCB28. The inhibition effect of BCCs on the PCB28 photodegradation increased with increasing pyrolysis temperature. After adsorptive binding to BCCs, the half-life of PCB28 (0.1 mg/L) was prolonged from 2.65 h for the dissolved PCB28 alone in deionized water to 7.48, 40.67, and 81.82 h in the presence of BCC300, BCC500, and BCC700 (5.0 mg/L), respectively. Mechanistically, the photodegradation of adsorbed pollutants was regulated by the photogenerated free radicals and surface functional groups of the low-temperature BCCs, as well as the defects and direct electron transfer capabilities of the high-temperature BCCs; PCB28 adsorbed on the low-temperature BCCs accepted electrons from persistent free radicals under light illumination, which led to PCB28 dechlorination, followed by ring-opening oxidation through hydroxyl radical attack, ultimately resulting in progressive mineralization; singlet oxygen caused preferential ring opening of adsorbed PCB28 on the high-temperature BCCs, preceding dechlorination. The photodegradation of BCCs-adsorbed PCB28 remained significant though more or less being inhibited under the effects of water pH, ionic strength, dissolved organic matters (humic acid and fulvic acid), and in natural water samples. These findings contribute to a better understanding of the structural properties of BCCs that impact phototransformation processes of adsorbed pollutants and facilitate an accurate assessment of the environmental risk associated with biochar application.
245. 题目: Molecular-level insights into the temperature-dependent formation dynamics and mechanism of water-soluble dissolved organic carbon derived from biomass pyrolysis smoke
Water soluble organic carbon (WSOC) derived from biomass pyrolytic smoke is deposited through atmospheric aerosols, negatively affecting aquatic ecological quality and safety. However, the temperature-dependent molecular diversity and dynamic formation of smoke-derived WSOC remain poorly understood in water. Herein, we explored the molecular-level formation mechanism of pyrolytic smoke-derived WSOC in water to explain the evolution, heterogeneous correlations, and sequential responses of molecules and functional groups to increasing pyrolysis temperature. Two-dimensional correlation spectroscopy was used to innovatively establish the characteristic correlations between spectroscopy and Fourier transform-ion cyclotron resonance mass spectrometry. Temperature-dependent formation of WSOC exhibited diversity in absorbance/fluorescent components, unique/common molecules, and their chemical parameters, showing the simultaneous formation and degradation reactions. The common WSOC molecules with lower and higher degrees of oxidation showed significant positive and negative correlations with the fluorescent components, respectively. The primary sequential response of WSOC molecules to increasing pyrolysis temperature (lignin-like molecules → unsaturated hydrocarbons, condensed aromatic molecules → lipid-like/aliphatic-/peptide-like molecules) corresponded to the temperature response of functional groups (carboxylic/alcoholic → polysaccharides → aromatics/amides/phenolic/aliphatic groups), demonstrating well synergistic relationships between them. These novel findings will contribute to the comprehensive understanding and assessments of potential environmental behavior or risks of WSOC in aquatic ecosystems.
246. 题目: Transport of per-/polyfluoroalkyl substances from leachate to groundwater as affected by dissolved organic matter in landfills
The transport of per- and polyfluoroalkyl substances (PFAS) from landfill leachate to surrounding soil and groundwater poses a threat to human health via the food chain or drinking water. Studies have shown that the transport process of PFAS from the solid to liquid phase in the environment is significantly affected by dissolved organic matter (DOM) adsorption. However, the mechanism of PFAS release from landfill solids into leachate and its transport to the surrounding groundwater remains unclear. In this study, we identified the composition of PFAS and DOM components and analyzed the association between DOM components, physicochemical factors, and PFAS concentrations in landfill leachate and groundwater. This study demonstrated that the frequency of PFAS detection in the samples was 100%, and the PFAS concentrations in leachate were greater than in the groundwater samples. Physicochemical factors, such as ammonium-nitrogen (NH4+-N), sodium (Na), calcium (Ca), DOM components C4 (macromolecular humic acid), SUVA254 (aromatic component content), and A240−400 (humification degree and molecular weight), were strongly correlated with PFAS concentrations. In conclusion, PFAS environmental risk management should be enhanced in landfills, especially in closed landfills, or landfills that are scheduled to close in the near future.
247. 题目: Relation between hydrophilic/hydrophobic characteristics of sludge extracellular polymeric substances and sludge moisture-holding capacity in hot-pressing drying
Sludge poses a serious threat to the environmental health. Hot-pressing drying has been proven efficient in sludge treatment because of the reduced thermal contact resistance, rapid increase in sludge temperature, and high drying rate. Sludge extracellular polymeric substances (EPS) significantly influence moisture transfer. However, whether in hot-pressing or traditional thermal drying, the effect of EPS on sludge moisture-holding capacity is rarely reported. Thereby, this study investigated the relationship between hydrophilic/hydrophobic characteristics of EPS and sludge moisture-holding capacity at various drying time and mechanical compression using XAD resin fractionation. Thermodynamic analysis indicated that sludge moisture desorption isotherms, net isosteric heat of desorption, and differential entropy presented a downward trend with the increase in drying time and mechanical compression, suggesting reduced sludge moisture-holding capacity. EPS analysis showed that at the same drying time, applying 25 kPa mechanical compression increased sludge temperature by 16 % and protein content by 13.8 %. At the same sludge temperature, protein content rose by 7.3 % compared to the drying without mechanical compression. It was concluded that the fast rise in sludge temperature and the mechanical extrusion facilitated the destruction of sludge microbial flocs, accelerating the release of intracellular and EPS-bound moisture and contributing to the decrease in moisture-holding capacity. Besides, tryptophan protein-like substances were the major source of hydrophilic/hydrophobic organic matter, compared to polysaccharide and humic acid-like substances. The gradually reduced sludge moisture-holding capacity was divided into three stages. Below 67 °C, the moisture desorption was dominated by the release of intracellular moisture. Below 85 °C, the increase in protein and the enhanced exposure of hydrophobic functional groups in protein improved the hydrophobicity of EPS. Above 85 °C, protein consumption due to thermal decomposition and browning reaction facilitated the desorption of EPS-bound moisture. Hence, this study provided novel insights into the mechanism of sludge drying.
248. 题目: Remote sensing-based prediction of organic carbon in agricultural and natural soils influenced by salt and sand mining using machine learning
It is important to keep soil organic carbon (SOC) in balance to ensure soil health and quality. In this manner, mining activities have crucial impacts on SOC stocks, especially in semi-arid and arid regions such as Iran. For this purpose, SOC was measured at 180 randomly selected points in both natural and agricultural soils in the central part of Iran. Machine learning methods, such as GEP (Genetic Expression Programming), SVR (Support Vector Regression), and ANNs (Artificial Neural Networks), were developed and employed to estimate SOC for all sampled points, including both natural and agricultural soils. Following that, topography and remotely sensed data were employed as input variables to improve SOC prediction influenced by mining. The remotely sensed data and topography factors were extracted from Landsat 9 images and Digital Elevation Models (DEMs), respectively. Input variables were considered in three scenarios, including the use of topography factors (scenario I), the use of remote sensing data (scenario II), and the use of both topography factors and remote sensing data (scenario III). The results of this study showed that the most effective model for predicting SOC across all sampled data was SVR (ME = −0.1539%, R2 = 0.642 and RMSE = 0.620%) when employing scenario III. Furthermore, the results indicated that the optimal method for both natural and agricultural soils was the SVR method when employing scenario III. Further analysis through mapping SOC contents showed that mining activities influenced the distribution of SOC in the studied region. Overall, the predicted maps of SOC contents indicated that lower SOC contents were predominantly distributed in the vicinity of salt and sand mines, particularly in salt-rich areas, for both natural and agricultural soils.
249. 题目: An effective global biochar application strategy for reducing global cropland nitrogen emissions without compromising crop yield: Findings from a global meta-analysis and density functional theory calculation
Biochar is widely used to mitigate nitrogen (N) emissions in global croplands. However, its effectiveness varies due to spatial disparities in external factors such as soil properties and climate conditions, as well as biochar characteristics such as pH and carbon content. In this study, we used a molecular model to assess the distinct impacts of biochar and soil on soil N emissions. We employed a back-propagation neural network optimized using a genetic algorithm (GA-BPNN) to simulate N emissions in global croplands, utilizing data from 351 peer-reviewed papers. Then, a global biochar application strategy aimed at optimizing the reduction of N emissions across global croplands was devised by aligning biochar and soil parameters. Our findings indicate that the high electrophilic and nucleophilic properties of biochar's reactive surface significantly contribute to the reduction of soil N emissions. The GA-BPNN-based machine learning (ML) technology demonstrated superior predictive performance (with R2 ranging from 0.47 to 0.69) in predicting changes in soil N emissions post-biochar application compared to other machine learning algorithms. Our simulations show that optimized global biochar application increases NH3 volatilization but achieves the most significant reduction in global cropland N emissions, amounting to 16.04 Tg N yr-1 and representing approximately 28.45% of the estimated total N emissions from global croplands, all while preserving crop yields. Therefore, aligning biochar properties with specific soil parameters and environmental conditions could be a promising strategy for mitigating N emissions in global croplands and addressing climate degradation.
250. 题目: Removal of dissolved organic matter via a combination of UV/persulfate oxidation and biological activated carbon (BAC) process
The combination process of UV/peroxydisulfate (UV/PDS) oxidation and BAC (UV/PDS-BAC) is examined as an advanced treatment for conventional drinking water treatment through a continuous flow experimental apparatus with actual sand filter effluent as feed water. The effect of three key parameters (UV dosage, PDS dosage, and water temperature) on dissolved organic matter (DOM) is evaluated via long-term monitoring data. The removal behavior of DOM in the UV/PDS-BAC process is also compared with that in the O3-BAC process. Further, this study delves into the mechanisms behind the enhanced DOM removal achieved by UV/PDS-BAC. The achieved results reveal that impressive removal rates of 42.1 % for total organic carbon (TOC) and 62.9 % for UV254 could be achieved in the presence of specific conditions: a UV input of 200 mJ/cm2 and a PDS dosage of 0.5 mM. The efficiency of DOM removal by UV/PDS-BAC exhibits a positive correlation with the UV dosage ranging from 50 to 200 mJ/cm2, and the water temperature in the range of 4–30 ℃. While increasing the PDS dosage from 0.01 to 0.5 mM results in improved DOM removal, any further increase yields reduced removal efficiency. In comparison, subjected to similar operating conditions, UV/PDS-BAC outperforms O3-BAC in removing DOM. The superior DOM removal achieved by the UV/PDS-BAC process can be essentially attributed to several factors: firstly, it exhibits excellent mineralization capacity for low molecular weight organics (<1 kDa) and leads to increased biodegradable fraction of organics by oxidatively degrading DOM with a molecular weight >3 kDa. Secondly, the appropriate exposure of activated carbon pores is chiefly maintained by suitably controlling the biomass. Lastly, the enhanced biodegradability of BAC influent stimulated the growth of bacteria proficient in degrading DOM.
251. 题目: Dissolved organic matter promoted hydroxyl radical formation and phenanthrene attenuation during oxygenation of iron-pillared montmorillonites
The oxygenation of Fe(II)-bearing minerals for hydroxyl radicals (HO•) formation and contaminant attenuation receives increasing attentions. However, information on dissolved organic matter (DOM) with different types, concentrations, and molecular weights (MWs) in manipulating HO• formation and contaminant attenuation during mineral oxygenation remain unclear. In this study, four iron-pillared montmorillonites (IPMs) and two DOM samples [e.g., humic acids (HA) and fulvic acids (FA)] were prepared to explore the HO• formation and phenanthrene attenuation during the oxygenation of IPMs in the presence or absence of DOMs. Results showed that iron-pillared and high-temperature calcination procedures extended the interlayer domain of IPMs, which provided favorable conditions for a high HO• production from 1293 to 14537 μmol kg−1. The surface-absorbed/low crystalline Fe(Ⅱ) was the predominant Fe(Ⅱ) fractionations for HO• production, and presence of DOMs significantly enhanced the HO• production and phenanthrene attenuation. Moreover, regardless of the types and concentrations, the low MW (LMW, <1 kDa) fraction within DOM pool contributed highest to HO• production and phenanthrene attenuation, followed by the bulk and high MW (HMW-, 1 kDa∼0.45 μm) fractions, and FA exhibited more efficient effects in promoting HO• production and phenanthrene attenuation than HA. The fluorescent spectral analysis further revealed that phenolic-like fluorophores in LMW-fraction were the main substances responsible for the enhanced HO• production and phenanthrene attenuation. The results deepen our understandings toward the behaviors and fate of aquatic HO• and contaminants, and also provide technical guidance for the remediation of contaminated environments.
252. 题目: The structural transformation reversibility of biogas slurry derived dissolved organic matter and its binding properties with norfloxacin under temperature fluctuation
The widespread use of biogas slurry could potentially raise the environmental risk of antibiotics. Dissolved organic matter (DOM), as the most active part of biogas slurry, was able to interact with antibiotics and play a crucial role in the structure and function of soil and aquatic ecosystems. The recent shifts in global climate patterns have garnered significant attention due to their substantial impact on temperature, thereby exerting a direct influence on the characteristics of DOM and subsequently on the environmental behavior of antibiotics. However, there is limited research concerning the impact of temperature on the binding of DOM and antibiotics. Thus, this study aimed to explore the temperature-dependent structural transformation and driving factors of biogas slurry-derived DOM (BSDOM). Additionally, the binding characteristics between BSDOM and the commonly used antibiotic norfloxacin (NOR) at different temperatures were studied by using multi spectroscopic methods and two-dimensional correlation spectroscopy (2D-COS) analysis. The results suggested that the temperature-dependent structural transformation of BSDOM was reversible, with a slight lag in the transition temperature under cooling (13 °C for heating and 17 °C for cooling). Heating promoted the conversion of protein-like to humic-like substances while cooling favored the decomposition of humic-like substances. BSDOM and NOR were static quenching, with oxygen-containing functional groups such as C-O and -OH playing an important role. Temperature influenced the order of binding, the activity of the protein fraction, and its associated functional groups. At temperatures of 25 °C and 40 °C, the fluorescent components were observed to exhibit consistent binding preferences, whereby the humic-like component demonstrated a greater affinity for NOR compared to the protein-like component. However, the functional group binding order exhibited an opposite trend. At 10 °C, a new protein-like component appeared and bound preferentially to NOR, when no C-O stretch corresponding to the amide was observed. The finding will contribute to a comprehensive understanding of the interaction mechanisms between DOM and antibiotics under climate change, as well as providing a theoretical basis to reduce the environmental risks of biogas slurry and antibiotics.
253. 题目: Effect of biochar with various pore characteristics on heavy metal passivation and microbiota development during pig manure composting
Understanding the porosity of biochar (BC) that promotes the heavy metal (HM) passivation during composting can contribute to the sustainable management of pig manure (PM). The current work aimed to explore the influence of BC with varying pore sizes on the physicochemical properties and morphological changes of HMs (including Zn, Cu, Cr, As, and Hg), and microbiota development during PM composting. The various pore sizes of BC were generated by pyrolyzing pine wood at 400 (T1), 500 (T2), 600 (T3) and 700 (T4) °C, respectively. The results revealed a positive correlation between specific surface area of BC and pyrolysis temperature. BC addition contributed to a significantly extended compost warming rate and duration of high-temperature period, as well as HM passivation, reflected in the decrease in Exc-Zn (63-34%) and Red-Cu (28-13%) content, and the conversion of Oxi-Cr (29-21%) and Red-Hg (16-5%) to more stable forms. Moreover, BC at T4 exhibited the best effect on Zn and Cu passivation due to the highest specific surface area (380.03 m2/g). In addition to its impact on HM passivation, BC addition improved the microbial environment during PM composting, leading to enhanced microbial diversity and richness. Notably, Chloroflexi and Bacteroidota played key roles in promoting the transformation of Exc-Cu and Red-Hg into stable forms. This phenomenon further stimulated the enhanced decomposition of organic matter (OM) when BC prepared at 600–700 °C was added. Therefore, it can be concluded that the regulation of BC porosity is an effective strategy to improve HM passivation and the overall effectiveness of PM composting.
254. 题目: Thermal responses of dissolved organic matter under global change
The diversity of intrinsic traits of different organic matter molecules makes it challenging to predict how they, and therefore the global carbon cycle, will respond to climate change. Here we develop an indicator of compositional-level environmental response for dissolved organic matter to quantify the aggregated response of individual molecules that positively and negatively associate with warming. We apply the indicator to assess the thermal response of sediment dissolved organic matter in 480 aquatic microcosms along nutrient gradients on three Eurasian mountainsides. Organic molecules consistently respond to temperature change within and across contrasting climate zones. At a compositional level, dissolved organic matter in warmer sites has a stronger thermal response and shows functional reorganization towards molecules with lower thermodynamic favorability for microbial decomposition. The thermal response is more sensitive to warming at higher nutrients, with increased sensitivity of up to 22% for each additional 1 mg L-1 of nitrogen loading. The utility of the thermal response indicator is further confirmed by laboratory experiments and reveals its positive links to greenhouse gas emissions.
255. 题目: Differential Adsorption of Dissolved Organic Matter and Phosphorus on Clay Mineral in Water-Sediment System
256. 题目: Seasonal temperature dependency of aquatic branched glycerol dialkyl glycerol tetraethers: A mesocosm approach
BrGDGTs, membrane-spanning lipids produced by bacteria are at the basis of the MBT’5ME, a biomarker ratio that has been used as paleotemperature proxy. However, the response of the MBT’5ME to temperature changes, particularly in freshwater systems, remains incompletely understood. In this study, oxic mesocosms are used to assess the temperature sensitivity of brGDGTs and their producers, sampled from a lake (Lake Rot) and river (Sihl River) in three different seasons. Three temperature treatments are employed (10-17.5-25℃), representing control (in-situ temperatures), cooling, and/or warming treatments, with GDGTs and the bacterial community measured at several timepoints (24h, 1, 2, 3 and 5 weeks). The control experiments showed that this experimental approach could not replicate natural conditions exactly, with small changes in chemistry (pH, conductivity, alkalinity) and bacterial community composition. Still, our mesocosm setup yielded valuable insights into the temperature-dependent production of lacustrine brGDGTs and MBT’5ME values, especially in warming treatments, while no response was observed in cooling treatments, potentially indicating limited sensitivity to cold temperatures. In the river mesocosms not the MBT’5ME but the IR ratio showed a temperature dependency, potentially driven by small changes in the water pH. Coeval changes in the composition of the bacterial community and the MBT’5ME and IR are determined to constrain potential GDGT producers. Although an increase in MBT’5ME in response to some warming incubations is observed, the temperature-sensitivity of MBT’5ME, as expected from GDGT studies on a global scale, is not supported by this experiment.
257. 题目: Microplastic-derived dissolved organic matter and its biogeochemical behaviors in aquatic environments: A review
258. 题目: Interactions of Goethite and Natural Organic Matter: Fractionation and Impact on Contaminant Reduction
259. 题目: Effect of deforestation on soil organic carbon fate and pool, a case study in Mazandaran, Iran
Deforestation and agricultural operations greatly impact soil organic carbon (SOC) and its fractions. In order to decrease carbon dioxide emissions, prevent threats to ecosystem stability, and apply efficient land use planning for sustainable soil management, it is essential to have a deep understanding of variations in soil organic carbon pools and their fractions. Soil samples were collected from six land uses of the undisturbed forest, pasture, orchard, and agricultural lands (cultivated with Oat, Maize, and three-carbon plants including wheat and soybean, which are indicated by the plant names of Oat, Maize + C3, and Maize + C3 (R) (R = rotationally)) with three replications at 0–30, 30–60, and 60–100 cm depths. The objective of this study was to evaluate the effect of land use on SOC, active carbon (AC), passive carbon (PC), dissolved organic carbon (DOC) content and pools, its fractions, carbon management index (CMI), soil respiration (SR), soil microbial biomass carbon (MBC), invertase (INV), and cellulase (CEL) enzymes activities in Dasht-e Naz region of northern Iran. Results illustrated that the different forms of organic carbon and enzyme activities were sensitive to land use change. The highest values of SOC (167.197, 39.179, 33.211 Mg ha−1), AC (24.596, 1.955, 1.637 Mg ha−1), and PC (142.6, 37.224, 31.575 Mg ha−1) pools were observed in the pasture land at all three depths. the highest value of DOC was seen in the pasture land at 0–30 and 60–100 depths and in the orchard at 30–60 cm depth. The values of SR (1.001 mg CO2 g dry soil−1 week−1), MBC (1367.7 µg organic carbon g soil−1), and CEL enzyme activity (648.04 µg glucose g dry soil−1 24 h−1) in the undisturbed forest were significantly greater relative to other land uses in 0–30 cm depth, along with significantly higher INV enzyme activity in the pasture and the orchard lands. The largest amount of SOC in 2–4.75 and 0.053–0.25 mm aggregates in all depths was related to the pasture and Maize + C3 land use, respectively. The concept of physical protection confirms the importance of aggregation in the stabilization processes of soil organic carbon, as a physical shield against microorganism attacks. The results of CMI demonstrated that the carbon storage capacity decreased due to the agricultural and orchard lands establishment in the region. Also, the change of land use towards pasture land increased the amount of organic carbon, preventing soil degradation.
260. 题目: Abiotic and stand age-induced changes in tree diversity and size inequality regulate aboveground biomass and soil organic carbon stock in temperate forests of South Korea
Forest biomass and soil organic carbon are vital for the terrestrial carbon cycle. However, the mechanisms underlying the interaction between trees and site properties (e.g., tree diversity, stand age, climatic and edaphic conditions) that determine the soil organic carbon stock (SOC) remain unclear. Here, we hypothesized that tree diversity, functional identity, and stand structure regulate SOC and aboveground biomass (AGB). To clarify these relationships, we used data from 125 plots dominated by 11 major tree species in South Korea. We analyzed the effects of stand age, tree diversity, functional identity, stand structural attributes, and abiotic drivers (i.e., topographic, climatic, and edaphic variables) on AGB and SOC. We also examined the effect of AGB on the biotic and abiotic drivers of SOC. We performed model averaging and piecewise structural equation modeling to compare and quantify the effects of the drivers on AGB and SOC. Stand age, species richness, and stand structural attributes significantly affected AGB, but their effect on AGB varied depending on the dominant tree species. For SOC, climate, soil pH, and AGB directly regulate SOC. In particular, species richness was the primary biotic driver that directly controlled SOC in termperate forests of South Korea. Dominant tree species also modulated the SOC changes. Our results show that the relationships of biotic and abiotic drivers with dominant tree species are important in both AGB and SOC despite the differences in the direction and magnitude of their effects. Therefore, our study suggests that understanding the relationships of biotic drivers with environmental conditions, which determine the forest ecosystem’s carbon cycle, is vital in predicting the global carbon cycle.