In order to explore the influences of rice straw mulching on soil fertility in agroforestry systems, the soil C and N contents and enzyme activities were investigated in a C. oleifera–cassia intercropping ecosystem in Central Southern China. Three straw mulching application treatments were set up in this study, in 2021, namely, straw powder mulching (SPM), straw segment mulching (SSM), and non-straw mulching as the control (CK). Soil samples were collected from three soil depths (0–10 cm,10–20 cm, and 20–40 cm) in each treatment on the 90th-day after the treatments. The soil organic carbon (SOC), total nitrogen (TN), microbial carbon (MBC), soil enzyme activities (including acid phosphatase (ACP), urease (UE), cellulase (CL), and peroxidase (POD)), and soil water content (SWC) were determined. The results showed that the SOC significantly increased due to the mulching application in SPM and SSM, in the topsoil of 0–10 cm when compared to the CK. The SWC, SOC, TN, and MBC increased by 0.8 and 56.5, 3.5 and 37.5, 21.3 and 61.6, and 5.8% and 76.8% in the SPM and SSM treatments compared to the CK, respectively. The soil enzyme activities of ACP, UE, CE, and POD increased significantly due to straw mulching compared with CK throughout all soil layers. The soil enzyme activities of CL and POD were significantly higher in SSM than in SPM across the soil depth except for ACP. The enzyme activities of ACP were 14,190, 12,732, and 6490 U/g in SSM, SPM, and control, respectively. This indicated that mulching application enhanced the enzyme activity of ACP. Mulching had no significant effects on UE and CL, while the POD decreased significantly in the order of SPM > SSM > CK across all soil layers, being, on average, 6.64% and 3.14% higher in SSM and SPM, respectively, compared to the CK plots. The SOC and MBC were the key nutrient factors affecting the soil enzyme activities at the study site. The results from this study provided Important scientific insights for improving soil physicochemical properties during the management of the C. oleifera intercropping system and for the development of the C. oleifera industry.

Forests undergo a long-term development process from young to mature stages, yet the variations in soil nutrients, enzyme activities, microbial diversity, and community composition related to forest ages are still unclear. In this study, the characteristics of soil bacterial and fungal communities with their corresponding soil environmental factors in the young, middle, and mature stages (7, 15, and 25-year-old) of Chinese fir plantations (CFP) in the subtropical region of China were investigated in 2021. Results showed that the alpha diversity indices (Chao1 and Shannon) of soil bacteria and fungi were higher in 15 and 25-year-old stands than in 7-year-old stand of CFP, while the soil pH, soil water content, soil organic carbon, total nitrogen, total phosphorus, sucrase, urease, acid phosphatase, catalase, and microbial biomass carbon, nitrogen, and phosphorus showed higher in 7-year-old stand than other two stands of CFP. The nonmetric multidimensional scaling analysis revealed that the soil microbial species composition was significantly different in three stand ages of CFP. The redundancy and canonical correspondence analysis indicated that the soil urease and microbial biomass nitrogen were the main factors affecting soil bacterial and fungal species composition. Our findings suggested that soil microbial diversity and community structure were inconsistent with changes in soil nutrients and enzyme activities during CFP development, and enhancing stand nurturing and soil nutrient accumulation in the mid-development stage were beneficial to the sustainable management of CFP.

Soil and water loss represent a significant environmental challenge in purple soil cropland in China. However, the quantity and mechanism of nutrient loss from purple soil remain unclear. To understand water and soil conservation and address nitrogen (N) and phosphorus (P) mitigation in Camellia oleifera forest stands on purple soil slope farmland, this study aimed to explore the resistance control effect of forest stands on N and P loss in such agricultural landscapes. In the study, a runoff plot experiment was conducted in purple soil slope farmland. The experiment included three distinct treatments: intercropping of oil tea (Camellia oleifera) and ryegrass (Lolium perenne L.), Camellia oleifera monoculture, and barren land served as the control treatment (CK). Water samples were collected and analyzed from the soil surface runoff and the middle soil layer at a depth of 20 cm (interflow) in three treatment plots under natural rainfall conditions in 2023. Various nutrient components, including total nitrogen (TN), dissolved nitrogen (DN), nitrate nitrogen (NO₃⁻-N), ammonium nitrogen (NH₄⁺-N), particulate nitrogen (PN), total phosphorus (TP), dissolved phosphorus (DP), phosphate (PO₄⁺-P), and particulate phosphorus (PP), were measured in the water samples. The results indicated that intercropping effectively mitigated the loss of various forms of N and P in both surface runoff and interflow within purple soil slope farmland. Compared to the CK, the ryegrass intercropping reduced TN and TP loss by 29.3%–37.3% and 25.7%–38.9%, respectively. The ryegrass intercropping led to a decrease in the average total loss of TN, DN, NO₃^—N, and NH₄⁺-N by 63.0, 24.3, 4.5, and 6.8 g/ha, corresponding to reductions of 33.3%, 47.6%, 58.3%, and 49.1%, respectively, compared to the CK. The average total loss of TP, DP, and PP decreased by 4.4, 1.8, and 1.4 g/hm² in the intercropping, reflecting reductions of 32.3%, 31.3%, and 31.1%, respectively. The most significant proportion was observed in PN and PP within the runoff water solution, accounting for 53.3%–74.8% and 56.9%–61.0% of the TN and TP, respectively. These findings establish a foundation for purple soil and water conservation. The research provides valuable insights for land management and policymakers in developing erosion prevention and control programs for sloping cultivated land with Camellia oleifera forests in purple soils. Additionally, it offers guidance for soil and water conservation and prevention of surface source pollution in purple soil regions.

Soil multifunctionality is essential for the enhancement of soil carbon sequestration, but disturbances such as thinning practices can influence soil microbial activity and carbon cycling. Microbial residues, particularly microbial residue carbon (MRC), are important contributors to soil organic carbon (SOC), but the effects of thinning intensity on MRC accumulation remain poorly understood. This study evaluated the impact of four thinning treatments—control (CK, 0%), light-intensity thinning (LIT, 20%), medium-intensity thinning (MIT, 30%), and high-intensity thinning (HIT, 45%)—on soil multifunctionality in Chinese fir plantations five years after thinning. Soil nutrient provision, microbial biomass, enzyme activity, and microbial residue carbon were assessed. The results showed that thinning intensity significantly affected soil nutrient provision and microbial biomass, with MIT and HIT showing higher nutrient levels than CK and LIT. Specifically, MIT’s and HIT’s total nutrient provision increased by 0.04 and 0.15 compared to that of CK. Enzyme activity was highest in LIT (+0.89), followed by MIT (+0.07), with HIT showing a decline (−0.84). Microbial biomass, including bacterial PLFAs (B-PLFAs), fungal PLFAs (F-PLFAs), microbial biomass carbon (MBC), and nitrogen (MBN), was highest in CK and MIT, and lowest in HIT, with MIT showing a 0.13 increase compared to CK. Microbial residue carbon (MRC) accumulation was positively correlated with soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), and easily oxidized organic carbon (EOC). The highest MRC content in the 0–20 cm soil layer was observed in MIT and CK (10.46 and 11.66 g/kg, respectively), while the MRC in LIT and HIT was significantly lower, reduced by 24% and 12%, respectively. These findings highlight the significant role of thinning intensity in microbial activity and carbon cycling. Medium-intensity thinning (MIT, 30%) was identified as the most effective approach for promoting microbial biomass and enhancing carbon cycling in Chinese fir forest soils, making it an optimal approach for forest management aimed at increasing soil carbon sequestration.

On a global scale, soil respiration (R_s), representing the CO₂ flux between the soil surface and the atmosphere, ranks as the second-largest terrestrial carbon (C) flux. Understanding the dynamics between R_s and its autotrophic (R_a) and heterotrophic (R_h) components is necessary for accurately evaluating and predicting global C balance and net ecosystem production under environmental change. In this study, we conducted a two-year root exclusion experiment in subtropical China’s Camphor (Cinnamomum camphora (L.) Presl.) forests to assess seasonal changes in R_a and R_h and their relative contributions to R_s. Additionally, we examined the influence of environmental factors on the dynamics of R_a, R_h, and R_s. Our results showed that seasonal mean R_s values were 2.88 µmol m⁻² s⁻¹, with mean R_a and R_h of 1.21 and 1.67 µmol m⁻² s⁻¹, respectively, in the studied forests. On an annual basis, the annual values of mean R_s in the studied forests were 405 ± 219 g C m⁻² year⁻¹, with R_h and R_a accounting for 240 ± 120 and 164 ± 102 g C m⁻² year⁻¹, respectively. The seasonal mean ratio of R_h to R_s (R_h/R_s) was 58%, varying from 45 to 81%. Seasonal changes in R_s and R_h were strongly correlated with soil temperature but not soil water content. Both R_h and R_s increased exponentially with the average soil temperature measured in the topsoil layer (about 5 cm), with Q₁₀ values of 2.02 and 1.73 for R_h and R_s, respectively. Our results suggest that the composition and activity of soil microbes and fauna play a primary role in releasing carbon flux from soil to the atmosphere in the studied forest ecosystems.

Urban forests are crucial components of cities, serving as vital ‘green lungs’ that embody urban civilization and sustainability. Despite their significance in maintaining the urban environment and ecological functions, management practices for urban forests can be unreasonable at times. This study investigated the impact of two common practices, litter removal and biochar application, on soil properties in an urban forest in Changsha city, China. The aim was to understand how these practices affect soil carbon, nutrients, and microbial activity in urban settings. The results showed that soil water content (SWC), pH, available phosphorus (AP), and soil microbial biomass carbon (SMBC) were significantly reduced in areas where litter was removed compared to areas where litter was retained. Conversely, biochar application led to a significant increase in SWC, pH, AP, and SMBC. The treatment alone had no significant effects on total nitrogen (TN), soil organic carbon (SOC), and soluble soil organic carbon (SSOC) in the examined urban forests. However, the SOC and SSOC contents significantly increased over time with biochar application. Our results demonstrated that the influences of litter removal and biochar application on soil property were attributed to the regulation of AP and SMBC in the studied urban forests. This study provides a scientific basis and reference for understanding the sustainable management of urban environments and guiding future conservation efforts in urban greening spaces.