Soil chemical quality assessment and spatial distribution of pomelo orchards in acidic red soil hilly regions of China

Fruit quality assessment based on mineral elements and juice properties in nine citrus cultivars

Introduction

Citrus fruit is considered a superfood due to its multiple nutritional functions and health benefits. Quantitative analysis of the numerous quality characteristics of citrus fruit is required to promote its sustainable production and industrial utilization. However, little information is available on the comprehensive quality assessment of various fruit quality indicators in different citrus cultivars.

Methods

A total of nine different fresh citrus fruits containing seeds were collected as the experimental materials. The objectives of this study were: (i) to determine the morphological and juice properties of citrus fruits, (ii) to measure the mineral elements in the peel, pulp, and seeds, and (iii) to evaluate the fruit quality index (FQI) using the integrated quality index (IQI) and the Nemoro quality index (NQI) methods.

Results

There were significant differences in fruit quality characteristics, including morphological, mineral, and juice quality, among the investigated citrus cultivars. The proportion of pulp biomass was the highest, followed by that of peel and seeds. N and Cu had the highest and lowest concentrations, respectively, among the measured elements across all citrus fruits, and the amounts of N, P, Mg, Cu, and Zn in seeds, K and Al in pulp, and Ca, Fe, and Mn in peel were the highest, dramatically affecting the accumulation of minerals in the whole fruit and their distribution in various fruit parts. Additionally, Ningmeng fruits had the highest vitamin C and titratable acidity (TA) but the lowest total soluble solids (TSS) and total phenolic (TP) contents, resulting in the lowest TSS/TA and pH values. In contrast, Jinju fruits had the highest TSS and TP contents. Based on the mineral element and juice quality parameters, principal component analysis showed that the citrus fruits were well separated into four groups, and the dendrogram also showed four clusters with different distances. The FQI range based on the IQI method (FQIIQI) and NQI method (FQINQI) was 0.382-0.590 and 0.106-0.245, respectively, and a positive relationship between FQIIQI and FQINQI was observed.

Conclusion

Our results highlight the great differences in mineral and juice characteristics among fruit parts, which mediated fruit quality. The strategy of fruit quality assessment using the FQI can be expanded for targeted utilization in the citrus industry.

Regulation of magnesium and calcium homeostasis in citrus seedlings under varying magnesium supply

Magnesium (Mg) and calcium (Ca) are two essential macronutrients in plants; however, the characteristics of Mg and Ca concentrations in organ, subcellular and chemical forms and their relationships in citrus plants, especially under varying Mg supply, are not well understood. In this study, Citrus sinensis seedlings (cv. Xuegan) were cultivated in conditions of Mg deficiency (0 mmol Mg2+ L-1) and Mg sufficiency (2 mmol Mg2+ L-1) to investigate the responses of Mg and Ca homeostasis in different organs and fractions. Compared with Mg sufficiency, Mg deficiency significantly decreased root and shoot growth, with the shoot biomass reduction of branch organs was greater than that of parent organs. In addition to increasing the Ca concentration in the parent stem and lateral root organs, Mg deficiency significantly decreased the concentrations and accumulations of Mg and Ca in citrus seedlings, further altering their distribution in different organs. More than 50% of Ca and Mg were sequestrated in the cell wall and soluble fractions, respectively, with Mg concentration decreasing by 15.4% in roots and 46.9% in leaves under Mg deficiency, while Ca concentration decreased by 27.6% in roots and increased by 23.6% in parent leaves. Approximately 90% of Mg exists in inorganic, water-soluble, and pectate and protein-bound forms, and nearly 90% of Ca exists in water-soluble, pectate and protein-bound, phosphate and oxalate acid forms. Except for the decreased inorganic Mg in roots and water-soluble Mg and Ca in leaves, Mg deficiency increased the proportions of Mg and Ca in all chemical forms. However, Mg deficiency generally increased the Ca/Mg ratio in various organs, subcellular and chemical forms, with negative relationships between Mg concentration and Ca/Mg ratio, and the variations of Mg and Ca were highly separated between Mg supply and organs. In conclusion, our results provide insights into the effects of Mg supply on Mg and Ca homeostasis in citrus plants.

Ecological insight into antibiotic resistome of ion-adsorption rare earth mining soils from south China by metagenomic analysis

Antibiotic resistome has led to growing global threat to public health. Rare earth elements play important roles in modern society and mining activity for them has caused serious impact on soil ecosystems. However, antibiotic resistome in, especially, ion-adsorption rare earth-related soils is still poorly understood. In this work, soils were collected from ion-adsorption rare earth mining areas and adjacent regions of south China and metagenomic analysis was employed for profile, driving factors and ecological assembly of antibiotic resistome in the soils. Results show prevalence of antibiotic resistance genes conferring resistance to tetracycline/fluoroquinolone (adeF), peptide (bcrA), aminoglycoside (rpsL), tetracycline (tet(A)) and mupirocin (mupB) in ion-adsorption rare earth mining soils. Profile of antibiotic resistome is accompanied by its driving factors, i.e., physicochemical properties (La, Ce, Pr, Nd and Y of rare earth elements in 12.50-487.90 mg kg^-1), taxonomy (Proteobacteria, Actinobacteria) and mobile genetic elements (MGEs, plasmid pYP1, Transposase_20). Variation partitioning analysis and partial least-squares-path modeling demonstrate that taxonomy is the most important individual contributor and pose most direct/indirect effect to antibiotic resistome. Further, null model analysis reveals stochastic processes as dominant ecological assembly of antibiotic resistome. This work advances our knowledge on antibiotic resistome with emphasis on ecological assembly in ion-adsorption rare earth-related soils for ARGs mitigation, mining management and mine restoration.

Spatial distribution and risk assessment of fluorine and cadmium in rice, corn, and wheat grains in most karst regions of Guizhou province, China

The pollution status of crops planted in Guizhou province of Southwestern China with high background values of Fluorine (F) and Cadmium (Cd) has attracted people’s concern. The present study aimed to investigate the spatial distributions of F and Cd in rice, corn and wheat grains, and further evaluate their health risks to residents in Guizhou province. The contents of F and Cd were measured by fluoride ion-selective electrode and inductively coupled plasma mass spectrometry (ICP-MS) methods, respectively. Additionally, the inverse distance weighted (IDW) technique was conducted to analyze spatial distribution, and the health risk was estimated by target hazard quotient (THQ) and hazardous index (HI). The results indicate that Cd contents in samples varied from 0.000 to 0.463 for rice, 0.000 to 0.307 for corn, and 0.012 to 0.537 (mg/kg) for wheat, while F contents ranged from 0.825 to 5.193 (rice), 0.946 to 8.485 (corn), and 0.271 to 9.143 (wheat) mg/kg. The Cd exceeding ratios were 11.600% for rice, 13.500% for corn, and 45.100% for wheat grains, respectively. In terms of spatial distribution, high levels of F and Cd in rice were found in the northern and central in Guizhou, while Cd in corn was distributed in the eastern and F in corn were distributed in the west area of Guizhou. Moreover, the high levels of F and Cd in wheat were distributed in the western and eastern areas. The mean carcinogenic risks (R) of Cd in rice, corn, and wheat in children were 4.150 × 10^–4, 1.670 × 10^–4 and 3.470 × 10^–4, respectively, and that in adults were 3.430 × 10^–4, 0.471 × 10^–4, and 2.190 × 10^–4, respectively. The HI for adults in rice, corn and wheat grains were 0.756, 0.154, and 0.514, respectively, and that for children were 0.913, 0.549, and 0.814, respectively. Collectively, the potential risks produced by F and Cd to the local residents should not be ignored.

Spatial distribution of soil quality under different vegetation types in the Yellow River Delta wetland

The soils from four typical natural wetlands, namely, Phragmites australis, Tamarix chinensis, Suaeda salsa, and tidal flat, as well as reclaimed wetland, were selected to evaluate the soil quality in the Yellow River Delta. Fourteen soil physicochemical property indexes were employed to build a minimum data set (MDS). Combined with vegetation type and soil depth, the soil quality index (SQI) was conducted. A fuzzy logic model was applied for data normalization. The contrast test was conducted to verify the accuracy of the MDS. The results showed that the MDS consists of TOC, NO3--N, soil salinity, TS, TP, Mg, C/N and pH. The soil quality decreased from the inland to the coastline and from reclaimed wetland to tidal flat with the change of vegetation type. The soil quality of 0–10 cm soil depth was better than that of 20–30 cm soil depth. The soil qualities of reclaimed land were significantly better than those of natural wetlands at the same soil depth. Correlation analysis results showed that agricultural reclamation has become an important factor of soil quality change in the study area. Comparative results of two methods of MDS and the total data set (TDS) testified that the method of MDS was credible and accurate for soil quality assessment of the study area. Our results indicated that wetland protection and agricultural reclamation in coastal areas should keep a rational balance.

Differential response of bacterial diversity and community composition to different tree ages of pomelo under red and paddy soils

Rhizosphere soil microbial communities substantially impact plant growth by regulating the nutrient cycle. However, dynamic changes in soil microbiota under different tree ages have received little attention. In this study, changes in soil physicochemical properties, as well as bacterial diversity and community structures (by high-throughput Illumina MiSeq sequencing), were explored in pomelo trees of different ages (i.e., 10, 20, and 30 years) under red and paddy soils cultivated by farmers with high fertilizer input. Moreover, soil factors that shape the bacterial community, such as soil pH, AP (available phosphorous), AK (available potassium), and AN (available nitrogen), were also investigated. Results showed that pH significantly decreased, while AP, AK, and AN increased with increasing tree age under red soil. For paddy soil, pH was not changed, while AP was significantly lower under 10-year-old pomelo trees, and AK and AN contents were minimum under 30-year-old pomelo trees. Both soil types were dominated by Proteobacteria, Acidobacteria, and Actinobacteria and showed contrasting patterns of relative abundance under different tree age groups. Bacterial richness and diversity decreased with increasing tree age in both soil types. Overall, bacterial community composition was different under different tree ages. RDA analysis showed that soil pH, AP, and AN in red soil, and pH and AP in paddy soil showed the most significant effects in changing the bacterial community structure. A random forest model showed Sinomonas and Streptacidiphilus in red soil, while Actinoallomurus and Microbacterium in paddy soil were the most important genera explaining the differences among different age groups. The ternary plot further revealed that genera enrichment for Age_30 was higher than that for Age_10 and Age_20 in red soil, whereas specific genera enrichment decreased with increasing tree age under paddy soil. Co-occurrence network revealed that bacterial species formed a complex network structure with increasing tree age, indicating a more stable microbial association under 20 and 30 years than 10-year-old pomelo trees. Hence, contrasting patterns of changes in soil physicochemical properties and soil microbial communities were recorded under different tree ages, and tree ages significantly affected the bacterial community structure and richness. These findings provide valuable information regarding the importance of microbes for the sustainable management of pomelo orchards by optimizing fertilizer input for different ages of trees.