Pedosphere最新文献

The application of butachlor as an herbicide in paddy fields is widely practiced, aiming to increase rice yield by directly or indirectly influencing the paddy environment. Periphytic biofilms, which form at the soil-water interface in paddy fields, are complex bioaggregates that play an important role in nitrogen (N) cycling. The objective of this study was to investigate the effect of butachlor on periphytic biofilm growth and N cycling under both light and dark conditions in the laboratory. The results revealed that butachlor application hindered the growth of periphytic biofilms and led to the dominance of Cyanobacteria as the primary prokaryotes, while inhibiting the development of eukaryotic Trebouxiophyceae. Furthermore, the application of butachlor reduced the richness and diversity of prokaryotes, but increased those of eukaryotes in periphytic biofilms. The light treatments exhibited higher total N loss because light favored periphytic biofilm growth and enhanced ammonium (NH₄⁺) assimilation and nitrification. Additionally, butachlor application resulted in the increased retention of NH₄⁺-N and nitrate (NO₃^-)-N and an increase in N loss via denitrification. The abundances of functional genes encoding enzymes such as ammonia monooxygenase, nitrite reductase, and nitrous oxide reductase were increased by butachlor application, favoring nitrification and denitrification processes. Overall, the results suggest that butachlor application leads to an increase in total N loss mainly through denitrification in paddy systems, particularly in the presence of periphytic biofilms. Thus, the results may provide valuable insights into the changes in periphytic biofilm growth and N cycling induced by butachlor, and future studies can further explore the potential implications of these changes in paddy soils.

Coastal ecosystems are highly susceptible to salt-related problems due to their formation process and geographical location. As such ecosystems are the most accessible land resources on Earth, clarifying and quantifying the effects of salt-alkali conditions on N concentration and ammonia (NH₃) volatilization are pivotal for promoting coastal agricultural productivity. The challenge in establishing this effect is to determine how salt-alkali conditions impact NH₃ volatilization through direct or indirect interactions. An incubation experiment using a coastal soil from a paddy farmland, combined with the structural equation modeling (SEM) method, was conducted to reveal the net effects of salt-alkali on NH₃ volatilization and the role of environmental and microbial factors in mutual interaction networks. The specific experimental design consisted of four salt treatments (S1, S2, S3, and S4: 1‰, 3‰, 8‰, and 15‰ NaCl by mass of soil, respectively), four alkaline treatments (A1, A2, A3, and A4: 0.5‰, 1‰, 3‰, and 8‰ NaHCO₃ by mass of soil, respectively) and a control without NaCl or NaHCO₃ addition (CK), and each treatment had three urea concentrations (N1, N2, and N3: 0.05, 0.10, and 0.15 g N kg^-1 soil, respectively) and three replicates. At the N1, N2, and N3 levels, NH₃ volatilization increased by 9.31%–34.98%, 3.07%–26.92%, and 2.99%–43.61% as the NaCl concentration increased from 1‰ to 15‰, respectively, compared with CK. With an increase in the NaHCO₃ concentration from 0.5‰ to 8‰, NH₃ volatilization increased by 8.36%–56.46%, 5.49%–30.10%, and 30.72%–73.18% at the N1, N2, and N3 levels, respectively, compared with CK. According to the SEM method, salinity and alkalinity had positive direct effects on NH₃ volatilization, with standardized path coefficients of 0.40 and 0.19, respectively. Considering the total effects (net positive and negative effects) in the SEM results, alkalinity had a greater influence than salinity (total standardized coefficient 0.104 > 0.086). Nitrogen concentrations in the incubation system showed a direct positive effect on NH₃ volatilization (standardized path coefficient = 0.78), with an obvious decrease under elevated salinity and alkalinity levels. Additionally, gene abundances of nitrogen-transforming microbes indirectly increased NH₃ volatilization (total indirect standardized coefficient = 0.31). Our results indicated that potential NH₃ emissions from coastal saline areas could be enhanced more by soil alkalization than by salinization.

The use of trichlorphon in large quantities causes a large number of organic pollutants to enter water, sediments, and soils. Phyllosilicate minerals are considered effective adsorbents for organic pollutants. However, the adsorption behavior of organic pollutants on soil minerals affected by low-molecular-weight organic acids (LMWOAs) is not fully understood. In this study, the effect of LMWOAs on the adsorption behavior of trichlorphon on phyllosilicate minerals was investigated using a combination of adsorption measurements and molecular spectroscopic techniques (attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)). The adsorption of trichlorphon onto kaolinite (KAO) and montmorillonite (MON) was suppressed by increasing pH, indicating that electrostatic interaction played a key role in adsorption, especially at low pH. In the presence of citric acid (CA), there was an obvious promotion of trichlorphon adsorption on KAO and MON. In the presence of oxalic acid (OA), the adsorption of trichlorphon on KAO was promoted, whereas the adsorption on MON was inhibited, especially at pH 4.0. The presence of CA and OA increased the adsorption by increasing the exposure of hydrophobic sites of KAO and MON. The results from ATR-FTIR and XPS also indicated that the hydrophobic Si–O sites of phyllosilicate minerals were the preferred adsorption sites for trichlorphon in the presence of CA and OA, probably driven by the hydrophobic effect. However, the weak effect of OA on MON caused an increase in the electrostatic repulsion between MON and trichlorphon molecules, thus inhibiting adsorption. This study is significant for a deeper understanding of self-purification of soil and sediment systems in the presence of organic pollutants.

Zokors are common subterranean rodents that inhabit agricultural fields, shrublands, and grasslands in the arid and semi-arid regions of China. Zokor burrowing activities can alter soil structure and affect soil hydrological processes; however, there are few studies regarding their effects on soil preferential flow in the Mu Us sandy land. An evaluation of the effects of zokor disturbance on their habitat and soil water is important for understanding the ecological role of zokors in the soil ecosystem of the Mu Us sandy land. A field dye-tracing experiment was conducted in the Gechougou watershed on the southeastern edge of the Mu Us sandy land to investigate the effect of zokor burrowing activity on soil preferential flow characteristics. Our results showed that the density of zokor tunnels was the highest (0.40–0.46 m m^-2) under 30%–50% vegetation coverage and that the tunnels were approximately 3 cm from the surface. Both stained area ratio and stained path number were higher at sites with zokors than without zokors. Stained path widths were 10–80 and > 80 mm at zokor-harboring sites exhibiting homogeneous flow and heterogeneous finger flow, respectively. In the absence of zokors, homogeneous flow and highly interacted macropore flow were predominant. Soil water content below the zokor tunnels was higher than that above the tunnels. Moderate disturbance of soil structure by zokor activity facilitated soil water infiltration. These results enabled a better understanding of the effect of soil fauna on soil structure and hydrological processes and provided recommendations for ecological construction and renovation in arid and semi-arid regions.

Investigating the impacts of soil conversion on soil organic carbon (OC) content and its fractions within soil aggregates is essential for defining better strategies to improve soil structure and OC sequestration in terrestrial ecosystems. However, the consequences of soil conversion from paddy soil to upland soil for soil aggregates and intra-aggregate OC pools are poorly understood. Therefore, the objective of this study was to quantify the effects of soil conversion on soil aggregate and intra-aggregate OC pool distributions. Four typical rice-producing areas were chosen in North and South China, paired soil samples (upland soil converted from paddy soil more than ten years ago vs. adjacent paddy soil) were collected (0–20 cm) with three replicates in each area. A set of core parameters (OC preservation capacity, aggregate carbon (C) turnover, and biological activity index) were evaluated to assess the responses of intra-aggregate OC turnover to soil conversion. Results showed that soil conversion from paddy soil to upland soil significantly improved the formation of macro-aggregates and increased aggregate stability. It also notably decreased soil intra-aggregate OC pools, including easily oxidized OCa (EOCa), particulate OCa (POCa), and mineral-bound (MOCa) OC, and the sensitivity of aggregate-associated OC pools to soil conversion followed the order: EOCa (average reduction of 21.1%) > MOCa (average reduction of 15.4%) > POCa (average reduction of 14.8%). The potentially mineralizable C (C₀) was significantly higher in upland soil than in paddy soil, but the corresponding decay constant (k) was lower in upland soil than in paddy soil. Random forest model and partial correlation analysis showed that EOCa and pH were the important nutrient and physicochemical factors impacting k of C mineralization in paddy soil, while MOCa and C-related enzyme (β-D-cellobiohydrolase) were identified as the key factors in upland soil. In conclusion, this study evidenced that soil conversion from paddy soil to upland soil increased the percentage of macro-aggregates and aggregate stability, while decreased soil aggregate-associated C stock and k of soil C mineralization on a scale of ten years. Our findings provided some new insights into the alterations of soil aggregates and potential C sequestration under soil conversion system in rice-producing areas.

Paddy fields play an important role in global carbon (C) cycling and are an important source of methane (CH₄) emissions. Insights into the processes influencing the dynamics of soil organic C (SOC) in paddy fields are essential for maintaining global soil C stocks and mitigating climate change. Periphytic biofilms composed of microalgae, bacteria, and other microorganisms are ubiquitous in paddy fields, where they directly mediate the transfer of elements at the soil-water interface. However, their contributions to C turnover and exchange have been largely neglected. Periphytic biofilms affect and participate in soil C dynamics by altering both abiotic (e.g., pH and redox potential) and biotic conditions (e.g., microbial community composition and metabolism). This review summarizes the contributions of periphytic biofilms to soil C cycling processes, including carbon dioxide fixation, SOC mineralization, and CH₄ emissions. Future research should be focused on: i) the mechanisms underlying periphytic biofilm-induced C fixation and turnover and ii) quantifying the contributions of periphytic biofilms to soil C uptake, stabilization, and sequestration in paddy fields.

Rice fields are a major source of greenhouse gases, such as nitrous oxide (N₂O) and methane (CH₄). Organic fertilizers may potentially replace inorganic fertilizers to meet the nitrogen requirement for rice growth; however, the simultaneous effects of organic fertilizers on N₂O and CH₄ emissions and crop yield in paddy fields remain poorly understood and quantified. In this study, experimental plots were established in conventional double-cropping paddy fields in the Pearl River Delta, China, including an unfertilized control and five fertilizer treatments with fresh organic fertilizer (FOF), successively composted organic fertilizer (SOF), chemically composted organic fertilizer (COF), COF supplemented with inorganic fertilizer (COIF), and chemical fertilizers (CFs) (TFOF, TSOF, TCOF, TCOIF, and TCF, respectively). Paddy field soils behaved simultaneously as an N₂O sink (cumulative N₂O emission: −196 to −381 g N ha^-1) and as a CH₄ source (cumulative CH₄ emission: 719 to 2 178 kg ha^-1). Compared to CFs, the effects of organic fertilizers on N₂O emission were not significant. In contrast, total annual CH₄ emission increased by 157%, 132%, 125%, and 37% in TFOF, TCOF, TSOF, and TCOIF, respectively, compared to TCF. In TCOIF, rice yield was maintained, while CH₄ emission was not significantly increased from the paddy fields characterized by a prolonged flood period. An important next step is to extend these field-based measurements to larger rice cultivation areas to quantify the regional and national-scale impacts on greenhouse gas emissions and to help determine the optimum practice for fertilizer use

The combination of organic carbon (OC) and reactive minerals is a crucial mechanism of soil carbon (C) storage, which is regulated by the formation of organo-mineral complexes on the surface of soil colloids. The effect of organic fertilizer on the storage mechanism of OC in soil colloids was studied through an 8-year field experiment, which included four treatments: i) no fertilization (control, CK), ii) only mineral N, P, and K fertilization (NPK), iii) NPK plus a low level (450 kg C ha^-1 year^-1) of organic fertilization (NPKC1), and iv) NPK plus a high level (900 kg C ha^-1 year^-1) of organic fertilization (NPKC2). The main results indicated that organic fertilizer addition significantly increased the content of aromatic-C, which was 158.7% and 140.0% higher in soil colloids than in bulk soil in the NPKC1 and NPKC2 treatments, respectively. X-ray photoelectron spectroscopy further demonstrated that the relative proportion of C=C group on the surface of soil colloids was increased by 20.1% and 19.1% in the NPKC1 and NPKC2 treatments, respectively, compared with the CK. In addition, compared with the NPK treatment, the content of reactive minerals (such as Fe and Al oxides) significantly increased with organic fertilization, which was positively correlated with C=C group in soil colloids. This indicates that aromatic-C may be retained by the formation of aromatic-mineral complexes with reactive minerals in soil colloids. Organic fertilization also significantly increased OC storage efficiency (OCSE), which was significantly higher in the NPKC1 treatment than in the NPKC2 treatment. Therefore, a moderate amount of organic fertilizer application is a better agronomic practice to increase OCSE and OC storage in saline-alkaline paddy soils.

The creation of controlled-release urea (CRU) is a potent substitute for conventional fertilizers in order to preserve the availability of nitrogen (N) in soil, prevent environmental pollution, and move toward green agriculture. The main objectives of this study were to assess the impacts of CRU's full application on maize production and to clarify the connection between the nutrient release pattern of CRU and maize nutrient uptake. In order to learn more about the effects of CRU application on maize yields, N uptake, mineral N (N_min) dynamics, N balance in soil-crop systems, and economic returns, a series of field experiments were carried out in 2018–2020 in Dalian City, Liaoning Province, China. There were 4 different treatments in the experiments: no N fertilizer input (control, CK); application of common urea at 210 kg ha^-1 (U), the ideal fertilization management level for the study site; application of polyurethane-coated urea at the same N input rate as U (PCU); and application of PCU at a 20% reduction in N input rate (0.8PCU). Our findings showed that using CRU (i.e., PCU and 0.8PCU) may considerably increase maize N absorption, maintain maize yields, and increase N use efficiency (NUE) compared to U. The grain yield showed considerable positive correlations with total N uptake in leaf in U and 0.8PCU, but negative correlations with that in PCU, indicating that PCU caused excessive maize absorption while 0.8PCU could achieve a better yield response to N supply. Besides, PCU was able to maintain N fertilizer in the soil profile 0–20 cm away from the fertilization point, and higher N_min content was observed in the 0–20 cm soil layer at various growth stages, particularly at the middle and late growing stages, optimizing the temporal and spatial distributions of N_min. Additionally, compared to that in U, the apparent N loss rate in PCU was reduced by 36.2%, and applying CRU (PCU and 0.8PCU) increased net profit by 8.5% to 15.2% with less labor and fertilization frequency. It was concluded that using CRU could be an effective N fertilizer management strategy to sustain maize production, improve NUE, and increase economic returns while minimizing environmental risks.