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Purpose: This study explores the accumulation of phenolic acids in soil within monoculture plantations of Eucalyptus, Acacia mangium, contrasting with mixed species plantations containing both species, across various seasons. The research aims to provide insights into how different plantation types and species compositions influence the presence and levels of phenolic acids in soil. Methods: Soil phenolic acid concentrations were determined using HPLC, analyzing seven phenolic acids, including p-hydroxybenzoic, ferulic, coumaric, and benzoic acids. The kinetic adsorption experiments evaluated phenolic acid adsorption rates and quantities across various soil types. An adsorption kinetic model compared these concentrations between monoculture and mixed forest soils. Results: Our findings showed that plantation types, soil positions and seasons significantly impact phenolic acid accumulation. Non-rhizosphere soil in monoculture Eucalyptusplantations exhibited the highest phenolic acid concentration an average (32 µg g-1) across all seasons compared to mixed species plantations. Conversely, the rhizosphere soil of monoculture Acacia mangiumdisplayed the highest content, reaching 71 µg g-1in March. Notably, four phenolic acids (p-hydroxybenzoic, ferulic, coumaric, and benzoic acids) varied significantly between monoculture and mixed forests. Additionally, adsorption kinetic studies revealed that monoculture Eucalyptusand Acacia mangiumsoils had higher adsorption capacity compared to mixed species soils. The application of Elovich model yielded the best fit for ferulic and coumaric acids (R2> 0.45). Conclusion: Mixed species plantations of Eucalyptusand Acacia mangiumsignificantly influence soil phenolic acid levels compared to monoculture forests and induce alterations in soil adsorption characteristics for phenolic acids, potentially impacting soil fertility and productivity.

Revealing the metabolic activity and diversity of soil bacteria is an effective way for evaluating soil fertility and health status. Despite this, it is still unclear how soil bacterial metabolism vary in a chronosequence of Chinese fir (Cunninghamia lanceolata) plantations. Based on the Biolog Eco micro-plate technology, this study focused on assessing the metabolic activity and diversity of soil bacteria in Chinese fir plantations with various stand ages (3, 9, 17, and 26 years) at the aggregate scales (>2, 2-1, 1-0.25, and <0.25 mm) in Guangxi, China. Regardless of stand age, large macro-aggregates (>2 mm) had the highest soil bacterial metabolic activity (based on the total average well color development) and diversity (based on the Shannon and McIntosh indices) in Chinese fir plantations. During late stage (from 17 to 26 years) of Chinese fir planting, large macro-aggregates being disintegrated into micro-aggregates (<0.25 mm) resulted in the decreases of soil bacterial metabolic activity and diversity. Besides, redundancy analysis and Pearson's correlation analysis indicated that the decreases of soil organic matter contents (based on the organic C and total N contents) and soil acidification (based on the pH) were also the main factors that inhibited the bacterial metabolism in soil during late stage. Therefore, during Chinese fir planting, increases in large macro-aggregates are conducive to the bacterial metabolism in soil, thus improving soil fertility and health status, especially during late stage, in Guangxi, China.

Afforestation is often considered to be an effective solution to alleviate soil degradation; however, unreasonable successive monoculture of Chinese fir results in further soil nutrient losses in impoverished soil systems. To determine the nutritional deficiency type of soil, it is critical to clarify the interactions between soil microbial and soil nutrients since the nutritional need of the microbial biomass is restricted by specific nutrients. Thus, the evaluation of such interactions can further reflect the situation of nutrient levels in soil. Nutrient stoichiometry and microbial communities within soil aggregates (> 2 mm, 2–1 mm, 1–0.25 mm, and < 0.25 mm) were determined in soils collected from Chinese fir plantations along the chronosequence (control, 9-, 17-, and 26-yr) in 2019, Guangxi, China. All soil microbial taxonomic groups (total microbial biomass, general bacteria, fungi, Gram-positive bacteria, Gram-negative bacteria, and actinomycete) showed the highest concentrations in micro-aggregates (< 0.25 mm), in line with the trends of soil carbon to nitrogen (C:N) ratios, carbon to phosphorus (C:P) ratios, and nitrogen to phosphorus (N:P) ratios. Compared with control (CK), soil C:N, C:P ratios, and all microbial taxonomic groups were significantly higher in the 17-yr of plantations, which elevated by 91–108%, 23–53%, and 31–204%, respectively. In contrast, N:P ratios significantly decreased by 30–65% in 9–26 yr plantations compared with CK. These results indicate that afforestation with Chinese fir contributed to the accumulation of soil nutrients and microbial biomass. In this area, soil phosphorus (P) was the main nutrient limiting soil quality in Chinese fir plantation. To prevent significant soil nutrient losses and the decline of soil microbial biomass, it is crucial to monitor the dynamic changes in microbial activities and P losses within aggregates, especially in micro-aggregates.

Exploring the activities of soil carbon-cycle enzymes (CCE) and nitrogen-cycle enzymes (NCE) at the aggregate scale is essential for improving our understanding of soil resources’ sustainable use in Chinese fir plantations. However, the impact of stand age on these enzyme activities in soil aggregates remains poorly understood. In this study, the activities of soil CCE (including β‑glucosidase and invertase) and NCE (including urease and protease) were examined in different-sized aggregates (> 2, 2–1, 1–0.25, and < 0.25 mm) from the 0–20 cm depth in Chinese fir plantations with different stand ages (3, 9, 17, and 26 years) in Guangxi, China. Regardless of the stand age, the percentage contribution of enzyme activities (including β‑glucosidase, invertase, urease, and protease) in the > 2 and < 0.25 mm fractions to bulk soil was higher compared with that in other fractions, suggesting that the > 2 and < 0.25 mm fractions were the primary carriers of soil enzymes in Chinese fir plantations. During Chinese fir planting, soil enzyme activities were first increased and then decreased, and their peaks were observed in the 17-year Chinese fir plantations. According to the redundancy analysis and Pearson’s correlation analysis, soil organic carbon (Corg) content is the key factor affecting the changes of soil enzyme activities. Therefore, following 17 years of Chinese fir planting, the accumulation of soil Corgcontent (i.e., appropriate application of organic manure) is important to enhance soil enzyme activities and promote soil nutrient cycle in Guangxi, China.

Soil aggregate stability is an integrated parameter related to soil structure, soil quality, and erodibility. Although mixed stands have been proven to improve soil quality and productivity, there is limited knowledge regarding how mixed with broadleaf tree species affects soil aggregate stability in Chinese fir (Cunninghamia lanceolata) plantations in the subtropical region of China. In this study, soil samples were selected at the 0–20 cm and 20–40 cm depths from the three plantations of Chinese fir, including C. lanceolata× Michelia macclurei(stand type I), C. lanceolata× Mytilaria laosensis(stand type II), and pure stand of C. lanceolata(stand type III). The Le Bissonnais method was chosen to determine the soil aggregate stability, which included fast wetting (FW), slow wetting (SW), and wet stirring (WS) disruptive treatments. Our findings showed that compared to pure stand, mixed stands had higher levels of soil chemical properties (including organic carbon (OC), total nitrogen (TN), and free aluminum oxides (Ald)) and more stable soil structure, especially stand type I. Soil OC and TN contents were significantly positively correlated with soil mean weight diameter (MWD) and geometric mean diameter (GMD) and were significantly negatively correlated with the soil erodibility Kvalues, which are the key indicators reflecting the stability of soil aggregates. The FW treatment simulates the slaking of soil under heavy rains, which caused the greatest damage to the soil aggregate structure, regardless of the stand type. Appropriate development of mixed forests can play a vital role in stabilizing soil structure in Chinese fir plantations, thereby promoting soil resources to be sustainably utilized in the subtropical red soil area in China.

Studying the patterns of change in soil aggregate stability and ecological stoichiometry in different forest types is of significant importance to the research on the distribution, limitations, balance, and cycling of soil organic carbon, nitrogen, and phosphorus (C–N–P). However, the impacts of pure Eucalyptusforests and mixed artificial forests on the stability of aggregates and the stoichiometric characteristics of organic carbon (OC), total nitrogen (TN), and total phosphorus (TP) remain unclear. Samples were collected from the 0–20 cm and 20–40 cm soil layers of a Eucalyptus–Mytilaria laosensismixed forest, a Eucalyptus–Erythrophleum fordiimixed forest, and a pure Eucalyptusforest. Soil samples were dry sieved into four types of aggregates according to particle size (> 2 mm, 1–2 mm, 0.25–1 mm, and < 0.25 mm). The OC, TN, and TP contents and composition were measured to evaluate the soil structure stability; soil OC, TN, and TP stock potential; and ecological stoichiometric characteristics. Our results showed that the structural stability of the soil and the contents and stocks of OC, TN, and TP were significantly higher in mixed forests than in the pure Eucalyptusforest: the 0.25- to 1-mm-sized aggregates had the highest soil OC, TN, and TP contents, and the aggregates > 2 mm in size had the greatest contribution to the soil OC, TN, and TP stocks in bulk soil. The aggregates > 2 mm in size generally had the lowest C/N, C/P, and N/P ratios (0–20 cm). The mean weight diameter (MWD) was the main factor affecting the stoichiometric characteristics of the 0–20 cm soil layer. The Eucalyptus–M. laosensismixed forest promoted soil-aggregate stability and improved soil fertility. Increasing the proportion of soil aggregates with large sizes (> 2 mm) is key to improving soil ecological environments. Thus, selecting suitable tree species mixed with Eucalyptuscan play a vital role in alleviating the reduction of soil aggregate stability, thereby causing the accumulation of soil C, N, and P contents and protecting soil productivity, quality, and health in subtropical China.

A hybrid storage energy system is proposed to integrate both hydrogen and electric energy storage components to improve the economic and environmental performances of community integrated energy system. The hourly electricity allocation ratio is optimized throughout the year to realize the operation of allocating the proportion of electricity storage and hydrogen storage under the optimal strategy. The design of a new grid-connected integrated energy system for low-carbon communities with a coordinated supply of cold, heat, and electricity is realized. A detailed model of the energy device is established. To select the optimal solution from the Pareto front, a combined evaluation method using the analytic hierarchy process (AHP) and the technique for order preference by similarity to an ideal solution is applied. Compared to systems using only electrical storage, only hydrogen storage, and traditional hydrogen-electric hybrid energy storage, the proposed system, which employs an electricity allocation ratio strategy, achieves reductions in carbon dioxide emissions by 6.14 %, 10.9 %, and 13.9 %, respectively, while also lowering annual costs by 4.62 %, 26.73 %, and 4.7 %. However, the system exhibits certain drawbacks in terms of renewable energy consumption, with reductions of 34.15 % and 12.9 % compared to systems using only electrical and hydrogen storage, respectively, it increases renewable energy consumption rate by 31 % relative to the traditional hydrogen-electric hybrid system. These findings highlight the substantial environmental and economic advantages conferred by the proposed system.

Background: Revealing the variations in soil aggregate-related organic carbon (OC) and labile organic carbon (LOC) fractions in a chronosequence of Chinese fir plantations plays an important role in better understanding the impact of soil carbon sink or source on the Chinese fir plantation ecosystem. In this study, soil samples in a depth of 0–20 cm were collected from Chinese fir plantations at different stand ages (0, 9, 17, and 26 years old) in Guangxi, China. With the optimal moisture sieving method adopted, the soil aggregates of 4 different sizes were obtained, including > 2-mm, 2–1-mm, 1–0.25-mm, and &lt; 0.25-mm aggregates. Soil OC and LOC fractions were measured in the aggregates of different sizes. The LOC fractions included readily oxidizable carbon (ROC), particulate organic carbon (POC), microbial biomass carbon (MBC), water-soluble organic carbon (WOC), and mineralized organic carbon (MOC). Results: Soil aggregate stability, as indicated by the mean weight diameter (MWD), was the highest in the 17-year-old Chinese fir plantations and was significantly positively related (p&lt; 0.05) to the concentrations of OC and LOC fractions (except for the ROC and MOC), with the POC in particular. As for all stand ages of Chinese fir plantations, the concentrations of soil OC and LOC fractions were significantly increased as the aggregate size decreased. Consequently, there were more OC and LOC fractions distributed in the &lt; 0.25-mm aggregates. During the stand development, the concentrations of soil OC and LOC fractions first increased and then decreased, with the highest levels detected in the 17-year-old Chinese fir plantations, indicating that the 17-year-old Chinese fir plantations were conducive to the accumulation of soil OC and LOC fractions. Conclusion: After 17 years of planting, promoted soil carbon (especially for the POC) accumulation contributes significantly to enhancing soil aggregate stability for the Chinese fir plantations in Guangxi, China.