Chengfu Zhang

The additions of microbial organic fertilizer (MOF), a microbial inoculant (MI), and quicklime (Q) are considered to be sustainable practices to restore land that has been damaged by continuous cropping of pepper (Capsicum annuum L.). However, the combined effects of these three additives on pepper yield, soil chemical properties, and soil microbial communities were unclear. The experimental design consists of 13 treatment groups: the untreated soil (control); soil amended solely with three treatments for each of MOF (1875–5625 kg ha⁻¹), MI (150–450 mL plant⁻¹), and Q (1500–4500 kg ha⁻¹); and soil amended with combinations of MOF, MI, and Q at three comparable concentrations. A significant increase in pepper fruit diameter, length, yield, and soil available nitrogen, phosphorus, and potassium contents occurs upon exclusive and combined applications of MOF, MI, and Q. Pepper yield was greatest (29.89% more than control values) in the combined treatment with concentrations of 1875 kg ha⁻¹ MOF, 150 mL plant⁻¹ MI, and 1500 kg ha⁻¹ Q. The application of Q increased soil pH and reduced soil–fungal richness. The application of MOF, MI, and Q increased the relative abundance of bacterial genera and the complexity of bacterial and fungal co-occurrence networks compared with control levels. The combined application of MOF, MI, and Q resulted in the greatest microbial network complexity. A Mantel test revealed the key role of soil available nitrogen content and bacterial diversity in the regulation of pepper growth and yield. We conclude that the combined application of MOF, MI, and Q improves soil nutrient availability and modifies soil microbial community composition, significantly promoting plant growth and pepper yield during continuous cultivation.

The formation of mineral-protected organic carbon (MPOC) is a vital process for soil organic carbon (SOC) accumulation and stabilization, influenced by factors such as exogenous carbon (C) input and soil microorganisms. However, the dynamics of MPOC and soil microorganisms following exogenous C input, and the key microorganisms driving MPOC formation, remain poorly understood. To address this, we conducted exogenous C addition culture experiments to investigate changes in MPOC and soil microorganisms and identify the primary microorganisms influencing MPOC formation. We observed that the MPOC content in treated soils increased over time, ranging from 0.43 to 2.06 g kg⁻¹. MPOC showed a significant positive correlation with soil bacterial diversity and a significant negative correlation with fungal diversity. Soil samples contained 248 bacterial families and 189 fungal genera, with Oxalobacteraceae (7.42%) and unclassified_k__Fungi (24.82%) being the most abundant, respectively. Using FAPROTAX and FunGuild ecological function prediction methods, we analyzed soil bacteria and fungi functional profiles and abundances. We identified the main bacterial families influencing MPOC formation as Microbacteriaceae, Mycobacteriaceae, Pseudomonadaceae, Streptomycetaceae, and Xanthomonadaceae. The primary fungal genera were Cylindrocarpon, Leohumicola, Metarhizium, Neobulgaria, Neopestalotiopsis, Olpidium, and Tetracladium. These findings provide theoretical support for understanding microbial regulation mechanisms in soil C sequestration and emission reduction.

In forest ecosystems, variations in aboveground litter input caused by global changes, substantially alter soil N cycling. In field-grown plants, few studies have directly measured root exudation rates and quantified their effects on N transformations under litter manipulation. We quantified soil N transformation rate responses to litter manipulation in a Pinus massoniana plantation, and unravelled the effect of root exudation on soil N transformations. We measured in situ P. massoniana root exudation rates as well as soil microbial biomass, soil C and N concentrations, the activities of four soil enzymes involved in soil N transformations, and net N mineralization and net nitrification rates after experimental litter removal and litter addition treatments. Litter removal and litter addition treatments had little impact on soil C and N concentrations, microbial biomass, soil enzyme (urease, hydroxylamine reductase, nitrate reductase, and nitrite reductase) activity, and net N mineralization rates. However, both litter removal and addition increased net N nitrification rates. Additionally, litter removal significantly decreased root C exudation rates (in April 2021 and annually), whereas litter addition had no significant effects on root C exudation rates across all seasons. Furthermore, root C exudation rates were positively associated with urease and nitrate reductase activities, but negatively associated with hydroxylamine reductase and nitrite reductase activities, as well as net N nitrification rate. Overall, we demonstrated that root exudates may be an important physiological adjustment by which trees respond to changes in litter input caused by global environmental changes, regulating underground N biochemical processes. Furthermore, we provide new evidence from root exudates for understanding the potential influence of litter inputs on soil N cycling. A strong correlation exists between root exudates and N transformation, shedding new light on the dynamics of rhizosphere nutrient cycling crucial for maintaining forest ecosystem stability and productivity under changing environmental conditions.

Soil organic carbon (SOC) forms the largest terrestrial organic carbon (C) pool, which is regulated by complex connections between exogenous C input, microbial activity, and SOC conversion. Few studies have examined the changes in natural abundance C due to microbial activity after exogenous C inputs in karst lime soils in China. In this research, the ¹³C isotope tracer technique was employed to investigate the priming effect of SOC on typical lime soil (0~20 cm) of ¹³C_litter and ¹³C_calcium carbonate (CaCO₃) through a mineralization incubation experiment. Samples were collected at 5, 10, 20, 40, 60, and 80 days of incubation and analyzed for SOC mineralization, SOC distribution across fractions (>250 μm, 53~250 μm, and 250 μm) and microaggregate (53~250 μm) C fractions by 2150.13, 2229.06, and 1575.06 mg C kg⁻¹ C_bulk on average and increased the mineral particulate C fraction (−1 C_bulk. As the incubation time extended, a significantly positive correlation was apparent between SOC priming and soil fungal diversity, as well as between the mineral particulate C fraction and soil bacterial diversity. The effect of soil fungal diversity on SOC priming (R = 0.40, p = 0.003) significantly exceeded that of bacterial diversity on SOC sequestration (R = 0.27, p = 0.02). Our results reveal that after adding litter or CaCO₃, soil fungi stimulate SOC mineralization and decomposition and soil bacteria enhance SOC sequestration, with the effects of fungi being more pronounced. These findings can provide a theoretical basis for understanding C sequestration and emission reduction in karst lime soils.