Organic Carbon Linkage with Soil Colloidal Phosphorus at Regional and Field Scales: Insights from Size Fractionation of Fine Particles.

Nano and colloidal particles (1-1000 nm) play important roles in phosphorus (P) migration and loss from agricultural soils; however, little is known about their relative distribution in arable crop soils under varying agricultural geolandscapes at the regional scale. Surface soils (0-20 cm depth) were collected from 15 agricultural fields, including two sites with different carbon input strategies, in Zhejiang Province, China, and water-dispersible nanocolloids (0.6-25 nm), fine colloids (25-160 nm), and medium colloids (160-500 nm) were separated and analyzed using the asymmetrical flow field flow fractionation technique. Three levels of fine-colloidal P content (3583-6142, 859-2612, and 514-653 µg kg-1) were identified at the regional scale. The nanocolloidal fraction correlated with organic carbon (Corg) and calcium (Ca), and the fine colloidal fraction with Corg, silicon (Si), aluminum (Al), and iron (Fe). Significant linear relationships existed between colloidal P and Corg, Si, Al, Fe, and Ca and for nanocolloidal P with Ca. The organic carbon controlled colloidal P saturation, which in turn affected the P carrier ability of colloids. Field-scale organic carbon inputs did not change the overall morphological trends in size fractions of water-dispersible colloids. However, they significantly affected the peak concentration in each of the nano-, fine-, and medium-colloidal P fractions. Application of chemical fertilizer with carbon-based solid manure and/or modified biochar reduced the soil nano-, fine-, and medium-colloidal P content by 30-40%; however,the application of chemical fertilizer with biogas slurry boosted colloidal P formation. This study provides a deep and novel understanding of the forms and composition of colloidal P in agricultural soils and highlights their spatial regulation by soil characteristics and carbon inputs.

Helicobacter pylori infection increases the risk of thyroid nodules in adults of Northwest China.

Background: Thyroid nodules (TNs) are very common in the adults of Northwest China. The role of Helicobacter pylori (H. pylori) infection in TNs is poorly investigated and even with controversial conclusions. Our study aimed at highlighting the relationship between H. pylori infection and the risk of TNs. Methods: 9,042 individuals were enrolled with thyroid ultrasonography and 14C-urea breath test (14C-UBT). Baseline characteristics and relevant covariates were obtained, including basic and laboratory indicators. After applying the exclusion criteria, 8,839 patients were included and divided into 2 groups: a cross-sectional study of single follow-up (n=8,711) and a retrospective cohort study of multiple follow-ups for 5 years (n=139). Results: The prevalence of H. pylori infection and TNs was 39.58% and 47.94% in the adults of Northwest China, respectively. The prevalence of TNs was significantly higher among H. pylori-positive individuals than those without infection (52.55% vs. 44.92%, p<0.01). The result of binary logistic regression revealed that the crude odds ratio (OR) was 1.624 (95% CI 1.242~2.123) in Model 1 without adjustment compared to H. pylori-negative group, and was also positive in Model 2, 3, and 4 (Model 2: OR=1.731, 95% CI 1.294~2.316; Model 3: OR=2.287, 95% CI 1.633~3.205; Model 4: OR=2.016, 95% CI 1.390~2.922) after the adjustment. The data of 5-year follow-up showed that the annual incidence of TNs was significantly higher in individuals with persistent H. pylori infection than non-infected counterparts (all p<0.05). Conclusions: H. pylori is an independent risk factor for TNs in the adults of Northwest China.

Influence of environmental factors on soil organic carbon in different soil layers for Chinese Mollisols under intensive maize cropping.

The Mollisol region of Northeast China has a large soil organic carbon (SOC) storage which is important for maintaining soil fertility. SOC is susceptible to various environmental factors; however, the responses of SOC content to environmental factors in different soil layers of cropland remain unclear, particularly in deep soil layers. In this study, we collected 138 soil samples from the surface, subsurface, and subsoil layers among 46 sample sites with monocropping maize and intensive conventional tillage in this region. We assessed the relative importance and effect paths of 12 environmental factors (including geography, climate, and soil properties) on SOC content in different layers using redundancy analysis (RDA), structural equation model (SEM), and variation partitioning analysis (VPA). The VPA results showed that SOC content was mainly affected by climatic factors that explained 68% and 57% for the surface and subsurface layers, respectively. However, SOC content in the subsoil layer was greatly affected by soil properties that explained 27%. Furthermore, the SEMs results suggested that geographical factors indirectly affected SOC content by influencing the climatic factors. Mean annual temperature was the most important factor affecting SOC content directly or indirectly, and its negative effects significantly diminished with soil depth, as it explained 63%, 52%, and 17% of the variation in SOC content for the surface, subsurface and subsoil layers, respectively. In addition, the effects of soil water-holding capacity on SOC content also decreased with soil depth, whereas pH and clay content showed a contrasting pattern. This implies that pH and clay content play important roles in the sequestration of SOC in deep soil layers. Moreover, the organic C content within >53 µm aggregates was more sensitive to environmental factors. This study can be useful for forecasting SOC dynamics and establishing reasonable C management strategies under climate change conditions.

Distributions of straw-derived carbon in Mollisol's aggregates under different fertilization practices.

Straw incorporation is an effective measure for increasing soil organic carbon (SOC) thereby improving soil quality and crop productivity. However, quantitative assessments of the transformation and distribution of exogenous carbon (C) in soil aggregates under various field fertilization practices have been lacking. In this study, we collected topsoil samples (0-20 cm) from three fertilization treatments (no fertilization control, CK; inorganic fertilizer, IF; inorganic fertilizer plus manure, IFM) at a 29-year long-term Mollisol experiment in Northeast China. We then mixed the soil samples with 13C-labeled maize straw (δ13C = 246.9‰), referred as CKS, IFS, and IFMS, and incubated them in-situ for 360 days. Initial and incubated soil samples were separated into four aggregate fractions (> 2, 1-2, 0.25-1, and < 0.25 mm) using the dry-sieving method, which counted 18%, 17%, 45%, and 21% (averages from the three initial soil samples), respectively. Organic C content was highest in 0.25-1 mm aggregate (6.9-9.6 g kg-1) prior to incubation, followed by > 2 mm aggregates (2.2-5.8 g kg-1), 1-2 mm aggregates (2.4-4.6 g kg-1), and < 0.25 mm aggregates (3.3-4.5 g kg-1). After 360-day incubation with straw incorporation, organic C content was 2.3-4.5 g kg-1, 2.9-5.0 g kg-1, 7.2-11 g kg-1 and 1.8-3.0 g kg-1 in > 2, 1-2, 0.25-1, and < 0.25 mm aggregates, respectively, with the highest in the IFMS treatment. Straw-derived C content was 0.02-0.05 g kg-1, 0.03-0.04 g kg-1, 0.11-0.13 g kg-1, and 0.05-0.10 g kg-1 in > 2, 1-2, 0.25-1, and < 0.25 mm aggregates, respectively. The relative distribution of straw-derived C was highest (40-49%) in 0.25-1 mm aggregate, followed by < 0.25 mm aggregates (21-31%), 1-2 mm aggregates (13-15%), and > 2 mm aggregates (9.4-16%). During the incubation, the relative distribution of straw-derived C exhibited a decrease in > 2 mm and 1-2 mm aggregates, but an increase in the < 0.25 mm aggregate. At the end of incubation, the relative distribution of straw-derived C showed a decrease in the 0.25-1 mm aggregate but an increase in the < 0.25 mm aggregate under the IFMS treatment. This study indicates that more straw-derived C would be accumulated in smaller aggregates over longer period in Mollisols, and combined inorganic and organic fertilization is an effective measure for C sequestration in Northeast China.