Soil Total N Research Articles

Methane and nitrous oxide production and their driving factors in Phragmites riparian wetlands of Dianchi Lake, China

The eutrophic lake Dianchi, china, is a hotspot for methane (CH4) and nitrous oxide (N2O) emissions. However, the potential factors driving CH4 and N2O production in the riparian wetlands of Dianchi Lake remain unclear. In the current study, the potential CH4 and N2O production was evaluated using incubation experiments. The abundance and community structure of the methanogenic communities and denitrifying bacteria were measured using quantitative polymerase chain reaction and Illumina MiSeq sequencing. The results indicated that the potential CH4 and N2O production differed significantly among the riparian wetlands of Dianchi Lake, with rates of 0.26–17.65 μg/g.d and 0.09–1.30 ng/g.h, respectively. The soil mcrA, nirS and nosZ gene copies differed significantly among the riparian wetlands, whereas the soil narG and nirk genes did not. Soil methanogenic archaea in the riparian wetlands were dominated by the order Bathyarchaeia (2.36–45.97 %). Forty-one potential denitrifying bacterial genera were detected in soils from the riparian wetlands, among which the majority belonged to the Proteobacteria (31 genera; 1.54–37.78 %). The variation in CH4 production was mediated through soil AP, water NO3−-N and soil mcrA abundance, while water NH4+-N, soil TN and soil NH4+-N were the main factors regulating N2O production in the riparian wetlands of Dianchi Lake. Our study highlighted the important implication of pollution abatement to greenhouse gas emission reduction in the riparian wetland.

Comparison of Root Ecological Stoichiometry between Non-Growing Season and Growing Season of Grassland on the Chang Tang Plateau.

Root C: N: P stoichiometry affect the geochemical cycles of ecosystems, while a few studies were conducted on it and its relationship with soil nutrients, especially in the non-growing season. In this study, we investigated the root C:N:P stoichiometry of alpine steppe(AS), alpine meadow steppe(AMS), and alpine meadow(AM) in April (non-growing season) and August(growing season) in 2013. The results showed that: (1) There were no differences in root C, N, P, C: N, C:P, and N:P with a depth of AS in April. However, root C and C: N increased with depth, while N and N:P decreased with a depth of AS in August. In both months, the variation of root C, N, P, C: N with depth in AM was consistent with that of AS in August, and root C at deep layer decreased in August, which indicated roots of AM began to grow in April No significant difference of root C, N, C: N and N:P with depth was found, while P and C:P varied between the two months of AMS. Root P content at 20-30 cm was higher than that of other soil layers in April, which was significantly higher than that of AS, while no significant difference was found in August. (2) Grassland types had significant effects on soil nutrients (except TP) at 0-10 cm and 20-30 cm soil layers. (3) No significant correlation between soil nutrients and root C, N, P, C: N, C: P, and N: P was found in April. Soil TN and AN content had a significant positive correlation with root N: P, indicating that soil nitrogen was the primary N source of the root. Soil TP and AP were significantly negatively correlated with root C and C: N in August. This study can provide basic data and provide theoretical support for further understanding the role of grassland roots in nutrient cycling.

Long-Term Corn–Soybean Rotation and Soil Fertilization: Impacts on Yield and Agronomic Traits

Although crop rotations have been widely shown as an effective approach for improving yield or soil quality in the long term, the relationship between crop rotations and quality traits of crop or biochar-based fertilization is still unclear. To address this, we conducted a long-term field experiment in the Heilongjiang province of China to investigate the effects of crop rotation and biochar-based fertilizer application on the crop yield, soil parameters, crop quality, and agronomic traits in 2014–2020. The effects of rotations on crop production and soil properties were evaluated with the average yield variability during the 7 years of this study. Our results showed that the diversified corn and soybean rotations had a significant positive effect on average crop yield compared with their monocultures. The corn yield was enhanced by 0.6 Mg ha−1 (5.4%) in the corn–soybean–corn (CSC) crop sequence compared with monoculture corn. Similarly, soybean yield was enhanced by 0.21 Mg ha−1 (9.7%) in the soybean–corn–corn (SCC) crop sequence compared with monoculture soybean. However, a negative effect of crop rotations was detected on the protein content of soybean compared with the monoculture soybean, while a positive effect was detected on oil content. Additionally, no differences were detected in crop yield between biochar-based fertilization and mineral fertilization treatments, but a significant positive effect of biochar-based fertilization was observed for any crop on both protein and oil content. A significant effect of crop rotation was found on the percentage of total soil N (TN), available soil N (AN), and available soil K (AK) content. The SSS crop sequence treatment illustrated the highest TN values at 0.18%. The CCC crop sequence treatment increased AN and AK content by 9.1% and 7.8%, respectively, compared with SSS (p < 0.05). We conclude that crop rotations increase crop yield and biochar-based fertilizer application, improving crop quality traits in the long term. Thus, the addition of biochar-based fertilizer could efficiently enhance the yield and quality of crop in the rotation cropping system. The findings of this study may provide useful information for designing sustainable cropping systems based on rotations.

Distribution of nitrogen storage in density and size fractions varied with tillage practices and cropping systems with residue return in black soil of Northeast China

AbstractCrop residue return can prevent the degradation of cropland caused by conventional tillage practice in Northeast China. Meanwhile, additional nitrogen (N) input from crop residue inevitably changes soil N pools. Our objectives were to evaluate soil N storage changes in soil physical fractions. The residue return treatments consisted of no‐tillage (NT) and moldboard plow (MP), combined with continuous maize (Zea mays L.) (MM) and maize–soybean [Glycine max (L.) Merr.] rotation (MS) cropping systems, that is, NTMM, NTMS, MPMM, MPMS; conventional tillage (removal of crop residue and deep plow) with continuous maize (CTMM) was included as a control. The concentration of total N (TN) in bulk soil and physical fractions (light fraction [LF], sand, silt, and clay) was measured. In 0‐to‐5‐cm layer, TN content was higher in NT than MP, whereas the result was opposite in 10‐to‐20‐cm layer. Thus, the stratification ratio (SR) of soil TN was greater under NT. The TN content in MM was greater than MS under both tillage practices with residue return. Residue return treatments increased soil N storage by 6.44–24.85% in 0–20 cm compared with CTMM. Continuous maize increased the N storage in all physical fractions, whereas the decrease of silt‐N storage was observed in MS. Overall, it was concluded that residue return could enhance soil N storage, whereas the distribution of N storage changes in LF and sand size fractions was influenced by tillage practice, and the distribution of N storage changes in silt size and clay size fractions was influenced by cropping system.

Soil Quality Assessment in Farmland of a Rapidly Industrializing Area in the Yangtze Delta, China.

The comprehensive quality assessment of farmland soil is critical for agricultural production and soil ecological protection. Currently, there is no systematic method for conducting a comprehensive quality assessment of farmland soil; subsequently, as the most developed economic area in China, the comprehensive quality assessment of farmland soil in the Yangtze River Delta is lacking. We chose the farmland soil of Suzhou city as the research object. The soil fertility index (SFI) and soil environment index (SEI) were calculated with the membership function and Nemerow index. Finally, the comprehensive assessment of soil quality was achieved with the TOPSIS model. The results showed that the average values of soil pH, SOM, TN, AHN, AP, and AK were 6.44 (slightly acidic), 28.17 g/kg (medium), 1.63 g/kg (rich), 118.16 mg/kg (medium), 38.31 mg/kg (rich), and 160.63 mg/kg (rich), respectively. For the concentrations of heavy metals, including Cr, Ni, Cu, Zn, Cd, and Pb, in 122 soil samples, the percentages exceeding the background values of Jiangsu province were 5.74%, 8.20%, 8.20%, 10.66%, 86.07%, and 84.43%, respectively. Cd and Pb were the main heavy metal pollutants on farmlands. The soil samples with SFI values below the medium level (SFI < 0.6) accounted for 44.26%, and samples with SEI values below the medium level (SEI < 0.6) accounted for 13.12%. The values of the soil quality index (SQI) ranged from 0.171 to 0.996, with an average SQI value of 0.586 (very poor—V), and approximately half of the farmland soil quality in Suzhou city needed to be further improved. In a word, this study provides a theoretical basis and scientific support for the quality assessment and rational utilization of farmland soil.

Co-Compost Application of Magnesium Salts and Orthophosphate Adjusted Biochar and Cyanobacteria for Fixing Nitrogen, Improving Maize Quality, and Reducing Field Nutrient Loss

To solve the problem of nitrogen loss and harmful gas emissions in the co-composting of cyanobacteria with other wastes and agricultural non-point source pollution in the Chaohu Lake Basin (CHLB), this study selected cyanobacteria as the main material, spent mushroom and rice hulls as excipients, and biochar (B) and Mg2+/PO43− salt as an additive. The nitrogen fixation rate, maturity, toxicity, and fertilizer efficiency indexes were analyzed to explore the best rate of biochar application. Additionally, three different fertilization treatments (C0: No fertilization, CF: Chemical fertilizer, OF: Organic fertilizer) were applied to agricultural field experiments in the CHLB. The results showed that the cyanobacteria composting experiment with 10% B as additives had the lowest cumulative NH3 emission (603.00 g) and the highest nitrogen fixation rate (61.54%). We used this compost product for maize cultivation in field experiments. The results show that OF treatment can reduce field nutrient loss, and the increase in the rate of soil TN fixation was as follows: OF (18.62%) &gt; CF (10.34%) &gt; C0 (−9.66%). Moreover, the TN and TK losses in runoff were 33.33% and 22.74% lower than CF in farmland runoff. The OF treatment increased the content of crude fat, crude protein, and crude starch by 4.40%, 8.34%, and 2.66% compared with the CF treatment, respectively. Overall, the N, P, and K source agronomic coefficients of cyanobacteria organic fertilizer were 1.424, 1.001, and 1.16, respectively. These results indicated that cyanobacterial organic fertilizer could replace chemical fertilizer to reduce agricultural non-point source pollution and improve maize quality. Meanwhile, the amendment of B and Mg/P salt additives could reduce air pollution and improve the quality of compost products. This study provides a theoretical basis and reference for nitrogen fixation and extension of multiple wastes co-composting field experiments.

KARAKTERISTIK VEGETASI, HARA NITROGEN DAN KARBON ORGANIK TANAH PADA TEGAKAN HUTAN TAMAN NASIONAL GUNUNG-MERBABU DAN TEGALAN (The Characteristics of Vegetation, Soil Nutrients of Nitrogen and Soil Organik Carbon at Forest Stands of Mount-Merbabu National Park and Dry Field)

Java island, which has a wet tropical climate, has a variety of vegetation stands. This study examines the characteristics of vegetation, nutrient levels of N, and soil organic carbon (SOC) under forest stands of Mount-Merbabu National Park (Pine/ Pinus merkusii, Puspa/ Schima noronhae theaceae, Acacia/ Acacia decurren fabaceae, Bintamin/Cupressus sp, and Mixed) and dry field at a soil depth of 0-30 cm (0-10, 10-20, 20-30cm). Observations the characteristics of vegetation were made by Observing Plot Units measuring 50 m x 50 m with 3 replications, while the observations of N nutrients and SOC included: total-N, Organic-C, and bulk density soil with 3 replications as well. The research data were analyzed descriptively, followed by the F-Test and DMRT Test at 5% level. The results showed that the forest stands of Mount-Merbabu National Park has the highest species density value in Puspa forest stand, followed by Mixed, Pine, Acacia, and Bintamin. Soil tota-N and Organic-C content decreased with the increasing soil depth. The highest soil total-N content in the depth of 0-10 cm was in the Puspa forest stand (1.34%), while Acacia is 0.74%, and dry field is 0.34%. The highest of soil organic-C content was in the Puspa forest stand (9.53%), the lowest was Pine (2.85%) and dry field (2.12%). Puspa (Schima noronhae theaceae) can be recommended as a good type of reforestation plant.

Long-term cultivation alter soil bacterial community in a forest-grassland transition zone.

Changes in land use types can significantly affect soil porperties and microbial community composition in many areas. However, the underlying mechanism of shift in bacterial communities link to soil properties is still unclear. In this study, Illumina high-throughput sequencing was used to analyze the changes of soil bacterial communities in different land use types in a forest-grassland transition zone, North China. There are two different land use types: grassland (G) and cultivated land (CL). Meanwhile, cultivated land includes cultivated of 10 years (CL10) or 20 years (CL20). Compared with G, CL decreased soil pH, SOC and TN, and significantly increased soil EC, P and K, and soil properties varied significantly with different cultivation years. Grassland reclamation increases the diversity of bacterial communities, the relative abundance of Proteobacteria, Gemmatimonadetes and Bacteroidetes increased, while that of Actinobacteria, Acidobacteria, Rokubacteria and Verrucomicrobia decreased. However, the relative abundance of Proteobacteria decreased and the relative abundance of Chloroflexi and Nitrospirae increased with the increase of cultivated land years. Mantel test and RDA analysis showed that TP, AP, SOC and EC were the main factors affecting the diversity of composition of bacterial communities. In conclusion, soil properties and bacterial communities were significantly altered after long-term cultivation. This study provides data support for land use and grassland ecological protection in this region.

Comprehensive effects of integrated management on reducing nitrogen and phosphorus loss under legume-rice rotations

Paddy fields-based cropping systems are usually located in areas with dense water networks, so nitrogen (N) and phosphorus (P) losses from rice paddy fields caused by runoff might pose a serious pollution risk to their surrounding water bodies. However, current research over establishing a low fertilizer input paddy-based cropping system with comprehensive management for reducing runoff losses of N and P is insufficient. A five-year field trial was carried out with a rice-fava planting system in the Erhai Lake watershed from 2015 to 2019. Three treatments were designed namely chemical fertilizer plus manure (CMF), reduced chemical fertilizer combined with manure at the same application rate under CMF treatment (RF), and returning straw plus chemical and organic fertilizers at the same rate with RF treatment (RFS). The mean annual runoff losses of total N (TN) and total P (TP) range from 0.99 to 1.39 kg ha −1 yr −1 and 0.09–0.12 kg ha −1 yr −1 . Compared with CMF treatment, RF had lower runoff losses of TN and TP by 20.86% and 23.05%, respectively, but the yields and soil fertility were also reduced. After returning straw, soil organic carbon (SOC), TN, and crop yields were maintained or even increased, and runoff losses of TN and TP were further reduced by 9.48% and 7.41%, respectively, compared with RF. Therefore, the runoff losses of N and P decreased by selecting the rice-fava rotation system and reducing chemical fertilizer input through manure application and straw returning, which greatly reduced the surplus N and P in this system. Moreover, the temporal variation in the concentration of TN and TP, along with the N:P ratio approved the existence of potential risk caused by TN and TP losses to the watershed in the early stage of rice growth. Overall, in addition to taking field measures to reduce the N and P runoff losses from paddy fields, the runoff water with high N and P concentrations in early rice growth stage cannot be ignored. • Rice-fava system with low fertilizer maintained yield and had low environment risk. • Straw returning ensured crop yields under substituting chemical fertilizer by manure. • Combined of straw returning and manure substitution reduced nutrient runoff loss. • Runoff N/P concentration and N:P ratio in early stage of rice may need interception.

Environmental factors affect the arbuscular mycorrhizal fungal community through the status of host plants in three patterns of Chinese fir in southern China

Arbuscular mycorrhizal (AM) fungi play a critical role in promoting plant growth and sustainability of a healthy ecosystem. Chinese fir (Cunninghamia lanceolata), most extensively grown in southern China, form a symbiotic association with AM fungi. However, most studies have exclusively focused on AM fungi associated with different aged Chinese fir plantations. It remains poorly understood how different forest patterns of Chinese fir regulate the AM fungal community. Therefore, Chinese fir with three different patterns (i.e., monoculture plantation, mixed plantation, and natural forest) were studied to evaluate the AM fungal communities under different planting patterns through Illumina Miseq high-throughput sequencing. Overall, 96 AM fungal operational taxonomic units (OTUs) were identified, belonging to genus Glomus, Archaeospora, Acaulospora, Diversispora, Gigaspora, and Scutellospora. However, monoculture showed the maximum number of AM fungal species (82) compared to mixed (55) and natural forests (73). Non-metric multi-dimensional scaling (NMDS) analysis revealed significant AM fungal community differences among different forest patterns. Canonical correlation analysis and mantel test revealed that edaphic factors, including soil pH, TN, TP, TK, AN, AK, SOM, Mg and Mn had a significant effect in shaping the AM fungal communities. These findings could provide a microbial basis for local forest management and diversity protection.

Soil nutrient contents and stoichiometry within aggregate size classes varied with tea plantation age and soil depth in southern Guangxi in China

Abstract. Soil ecological stoichiometry offers a tool to explore the distribution, cycling, limitation, and balance of chemical elements in tea plantation ecosystems. This study aimed to explore how soil organic C (OC) and nutrient contents (total N (TN), total P (TP), Ca2+, Mg2+, Fe2+, and Mn2+) as well as their stoichiometric ratios (C/N, C/P, N/P, Ca/Mg, and Fe/Mn) varied with tea plantation age (8, 17, 25, and 43 years) and soil depth (0–10, 10–20, 20–40, and 40–60 cm) within aggregates in southern Guangxi in China. Our results showed that tea plantation age and soil depth significantly affected soil nutrient stoichiometry in different sizes of aggregates. Among different ages of tea plantations, soil OC, TN, and TP contents as well as C/N, C/P, and N/P ratios significantly decreased as the soil depth increased. In addition, soil Ca2+ and Mg2+ contents were significantly lower in the surface soil layer than the deeper soil layer, whereas soil Fe2+ and Mn2+ contents showed opposite trends, and no significant differences were detected in Ca/Mg and Fe/Mn ratios among different soil depths. At the 0–40 cm soil depth, continuous planting of tea corresponded to increases in soil OC, TN, Fe2+, and Mn2+ contents, whereas soil Ca2+ and Mg2+ contents significantly decreased over time. During the process of tea growth, the losses of soil Ca2+ and Mg2+, especially Ca2+ (as indicated by the decrease in the soil Ca/Mg ratio), led to soil acidification, which reduced Fe2+ absorption and enhanced Mn2+ uptake by tea plants (as indicated by the increase in the soil Fe/Mn ratio). In general, tea plantation age affected the variations of soil nutrient contents and stoichiometry, and such effects were more obvious at the 0–40 cm soil depth, in contrast to the 40–60 cm soil depth.

Effects of Organic Fertilizer Combined with Chemical Fertilizer on Nutrients, Enzyme Activities, and Rice Yield in Reclaimed Soil

ABSTRACT A field experiment was conducted to explore the effects of combined application of organic and chemical fertilizers (organic-chemical fertilizers) on reclaimed soil fertility and rice yield. The experiment involved five treatments: no nitrogen (N) fertilizer (CK1), 100% chemical fertilizer N (CK2), 40% chicken manure N + 60% chemical fertilizer N (T1), 40% vermicompost N + 60% chemical fertilizer N (T2), 40% rapeseed meal fertilizer N + 60% chemical fertilizer N (T3). Organic-chemical fertilizers maintained or increased rice yield. Rice yields of T2 and T3 increased by 6.7% and 8.9%, respectively, as compared with CK2. T1 showed similar value of rice yield with CK2. Organic-chemical fertilizers application increased contents of soil organic C (SOC), total N (TN), alkali-hydrolyzable N (AN), NH4 +-N, NO3 –N, available phosphorus (AP), available potassium (AK) as well as CEC by 10.5%~15.9%, 8.9%~39.3%, 16.9%~74.5%, 38.1%~77.2%, 18.3%~136.5%, 27.7%~75.0%, 16.1%~24.7% and 7.2 ~ 26.0%. T3 had highest soil TN, AN, NH4 +-N, NO3 –N, CEC as well as T2 showed the highest contents of soil AP and AK. Organic-chemical fertilizers application increased soil sucrase (S-SC), urease (S-UE) and catalase (S-CAT) activities. The highest soil S-SC activity was detected in T3, and the highest soil S-UE and soil alkaline phosphatase (S-AKP) activities were observed in T2. Rice yield was positively related to SOC, TN, AN, NH4 +-N, NO3 –N, AP and AK as well as S-SC, S-UE and S-AKP activities. In conclusion, 40% organic N + 60% chemical N application could improve soil fertility and rice yield in reclaimed soils, with rapeseed meal fertilizer the most effective organic N source, followed by vermicompost and chicken manure.

Erosion intensity and check dam size affect the horizontal and vertical distribution of soil particles, carbon and nitrogen: Evidence from China’s Loess Plateau

Check dams are effective soil and water conservation structures worldwide that play an important role in preserving sediments containing carbon (C) and nitrogen (N). However, in terms of the depositional characteristics of C and N in check dams, research on the relative effects of erosion intensity and depositional area is limited, hindering our understanding of the fates of eroded C and N. This study compared the horizontal and vertical distributions of soil particles, organic C (OC), and total N (TN) in check dams of various sizes and erosion intensities in the Loess Plateau. The results showed greater variations in the horizontal and vertical patterns of soil particles of smaller check dams and highly serious erosion (erosion modulus = 15040 t km-2 a-1) than those that of larger check dams and strong erosion regions (erosion modulus = 5151 t km-2 a-1). Soil OC and TN contents decreased from the dam body to the gully head, especially in the highly serious erosion region. Notably, the effect of smaller check dam on the vertical distributions of soil OC and TN was more intense than that of the larger check dam in the strong erosion region. In contrast, a minor effect of check dam size was observed in the highly serious erosion region. Moreover, a closer relationship between the distribution of OC and TN with silt content rather than with clay content in check dams was observed, and this relationship was enhanced by an increase in erosion intensity. Overall, the synergistic effects of erosion intensity and check dam size affected the spatial patterns of OC and TN in sediments on the Loess Plateau. Careful consideration of these two factors is beneficial for accurately assessing the C and N fates in depositional areas.

Effects of habitat gradient and agro-climatic variation on selected soil physical and chemical properties in the Bale Mountains national park, south-eastern Ethiopia

BackgroundIncreasing evidence suggests that anthropogenic effects are responsible for drastic changes in landscape patterns and ecosystem services. This study aims to assess the effects of landscape change and agro-climatic variation on selected soil physical and chemical properties in the Bale Mountains national park. A combination of stratified and systematic sampling techniques was employed to draw representative soil samples. A total of 72 soil samples (3 agro-climatic zones × 3 land cover types × 2 habitat gradients × 4 replications = 72) at a depth of 0–20 cm were collected for the soil physical and chemical property analysis. A two-way analysis of variance was conducted to determine the level of variation in soil parameters. Tukey’s honest significance difference (HSD) test was used to compare treatment means at a 0.05 level of significance.ResultsThe results suggest that soil parameters differed significantly (p < 0.05) among agro-climatic zones, land cover, and habitat gradients. The soil pH, SOC, TN, AP, CEC and clay content were significantly higher in the lower altitude, natural vegetation and interior habitat, whereas the soil sand and silt content as well as the soil bulk density were significantly higher in the farmland and edge habitat.ConclusionsConservation and restoration priority should be given to those vegetation types and ecosystems that are highly affected by human interferences such as the grassland in the middle altitude, ericaceous land in the higher altitude, and moist forest in the lower altitudes.

Partial Substation of Organic Fertilizer With Chemical Fertilizer Improves Soil Biochemical Attributes, Rice Yields, and Restores Bacterial Community Diversity in a Paddy Field.

Conventional farming systems are highly reliant on chemical fertilizers (CFs), which adversely affect soil quality, crop production and the environment. One of the major current challenges of current agriculture is finding ways to increase soil health and crop yield sustainably. Manure application as a substitute for CF is an alternative fertilization strategy for maintaining soil health and biodiversity. However, little is known about the complex response of soil bacterial communities and soil nutrients to manure and CFs application. This study reports the response of soil nutrients, rice yield, and soil microbial community structure to 2 years of continuous manure and CFs application. The study consisted of six treatments: no N fertilizer control (Neg-Con); 100% CF (Pos-Con); 60% cattle manure (CM) + 40% CF (High-CM); 30% CM + 70% CF (Low-CM); 60% poultry manure (PM) + 40% CF (High-PM), and 30% PM + 70% CF (Low-PM). We used high-throughput sequencing of 16S ribosomal RNA gene amplicons to characterize the soil bacterial communities. Results revealed that the addition of manure significantly altered the soil bacterial community composition and structure; and enhanced the relative abundance of phyla Proteobacteria, Chloroflexi, Firmicutes, Acidobacteria, and Planctomycetes. Organic fertilizer treatments, particularly high CM and PM had the highest measured soil bacterial diversity of all treatments. Similarly, integrated application of manure and CFs increased the soil biochemical traits [i.e., pH, total N (TN), soil organic C (SOC), microbial biomass N (MBN), and microbial biomass C (MBC)] and rice grain yield. Average increases in SOC, TN, MBN, and MBC were 43.66, 31.57, 24.34, and 49.45%, respectively, over the years in the High-PM compared with Pos-Con. Redundancy analysis showed that the dominant bacteria phyla were correlated with soil pH, SOC, TN, and microbial biomass, but the relative abundance of Proteobacteria was strongly correlated with environmental factors such as soil pH, SOC, TN, and MBC. We employed a structural equation model to examine the relationship between microbial biomass, soil nutrients and grain yield among treatments. This analysis supported the hypothesis that soil nutrient content and availability directly affect rice grain yield while soil bacteria indirectly affect grain yield through microbial biomass production and nutrient levels. Overall, the findings of this research suggest that the integrated application of CF and manure is a better approach for improving soil health and rice yield.

Nitrogen Addition Effects on Wetland Soils Depend on Environmental Factors and Nitrogen Addition Methods: A Meta-Analysis

Identifying the effects of nitrogen (N) addition under key environmental factors and N addition methods can aid in understanding the paradigm of N addition in wetland ecosystems. In this study, we conducted a meta-analysis of 30 field studies of wetland ecosystems and selected 14 indicators. We found that the changes in soil TN and SOC contributed significantly to the changes in microbial community structure under N additions. The environmental factors and N addition methods altered the direction or size of N addition effects on wetland soil properties, microbial diversity and key C and N cycling genes. N-limited conditions and climate conditions determined the N addition effect direction on SOC, and saline-alkali conditions determined the N addition effect direction on microbial diversity and AOB abundance. Environmental heterogeneity and N addition methods determine the response of wetland soil to nitrogen application. Therefore, it is crucial to study the effects of environmental factors and N addition methods on the N deposition of wetland soils.

Vegetation and Topographic Factors Affecting SOM, SOC, and N Contents in a Mountainous Watershed in North China

This study aimed to reveal the main environmental factors affecting PH, SOM, SOC, TN, and AHN in mountainous areas of Beijing, using the Chaoguan Xigou watershed as the research object. The relationship among pH, SOM, SOC, TN, AHN, topographic factors, and vegetation factors was analyzed by correlation and redundancy analysis (RDA). The results showed that altitude was significantly positively correlated with vegetation types in the study area (p &lt; 0.01). Menhinnick richness index (D), Shannon–Wiener diversity index (H), and Alatalo evenness index (E) ranged from 0.35–0.79, 0.86–1.73, and 0.39–0.7, respectively, indicating moderate variations. E was significantly positively correlated with stand type (p &lt; 0.05), altitude (p &lt; 0.05), and H (p &lt; 0.01). The variation ranges of PH, SOM, SOC, TN, and AHN in soil were 5.78–7.13, 54.73–90.38 g/kg, 23.77–60.25 g/kg, 1.71–4.22 g/kg, and 95.64–223.26 mg/kg, respectively. All soil nutrient indexes had medium variation except for pH (weak variation). In this study, RDA results showed that altitude is the main environmental factor affecting the soil pH, SOM, SOC, TN, and AHN in this area and could explain 25.9% of the total variance. However, the effects of factors associated with altitude on pH, SOM, SOC, TN, and AHN need to be further studied.

Atmospheric CCl4 degradation in Antarctic tundra soils and the evaluation on its partial atmospheric lifetime with respect to soil

Carbon tetrachloride (CCl4) is an anthropogenic gas with a long atmospheric lifetime and can catalyze the destruction of stratospheric ozone. Natural soils are believed to be important and widespread sinks of atmospheric CCl4, although poorly characterized due to a limited number of measurements. In this study, for the first time in situ static-chamber measurements and laboratory-based incubations for CCl4 fluxes were conducted at coastal Antarctic tundra. Results showed that soil in remote Antarctica is also acting as a CCl4 sink, with an average uptake rate of −2.2 ± 0.6 nmol m−2 d−1, which is comparable to the reported soil sinks in other regions of the world. No significant difference (p > 0.05) was found across different types of tundra, such normal upland tundra, coastal marsh tundra, and tundra in the sea animal colonies. Soil CCl4 fluxes did not show significant correlations (p > 0.05) with soil moisture, pH, TOC, TN, TP and Cl contents. Laboratory-based anoxic incubations showed that the uptake rates of CCl4 in tundra soil were suppressed; post-thermal sterilization incubations showed that soil CCl4 sink was enhanced; these results suggested that CCl4 degradation in tundra soil was likely an abiotic process preferring oxic environments. A rough extrapolation suggested that Antarctic tundra may degrade about 2.4 metric tons of atmospheric CCl4 each year. Combining soil CCl4 fluxes from this study and other literature reports, CCl4 partial lifetime with respect to the soil sink was evaluated to be 354 (235–474) years, which supported the recent viewpoint that the soil sink of CCl4 is smaller than previously thought.

Recovery of soil carbon and nitrogen stocks following afforestation with xerophytic shrubs in the Tengger Desert, North China

Afforestation, as a key measure to curb land degradation and to drive the changes in soil C and N stocks and cycles, has been increasingly implemented in drylands worldwide. However, the long-term effects of this restoration practice on C accumulation in soil are still uncertain, especially because C-N interactions are poorly understood, which constrains the accurate assessment of potential soil C sequestration. In this study, we investigated the soil organic C (SOC) and soil total N (STN) storage in artificial shrublands in chronosequences in the Tengger Desert to address the hypothesis that afforestation with xerophytic shrubs significantly enhanced SOC and STN stocks in desert regions and that SOC and STN stocks would be positively correlated during the restoration processes. Our results showed that afforestation significantly enhanced SOC and STN accumulation. The SOC and STN stocks in 17-, 52- and 60-year-old artificial shrublands were 1.22, 2.67, 2.80 and 1.21, 2.33, 2.47 times greater than those in mobile sand dunes, respectively, with increased rates of 5.61 g C m−2 yr−1, 14.25 g C m−2 yr−1 and 13.30 g C m−2 yr−1 and 1.27 g N m−2 yr−1, 2.61 g N m−2 yr−1 and 2.50 g N m−2 yr−1, respectively. The significant enhancement of SOC and STN stocks primarily occurred in the upper 0–20 cm soil layer. SOC stocks were positively correlated with STN stocks and the C:N ratio, and the regression slopes increased with vegetation age, indicating a coupling relationship between SOC and STN stocks. Additionally, this finding suggests that the increase in STN stocks was slower than that of SOC during restoration, leading to an asynchrony in N supply and the demand and subsequent N limitations on SOC accumulation. It would take approximately 139 and 177 years to fully recover SOC and STN stocks in the 100 cm soil profile, respectively, in mobile sand dunes through afforestation with xerophytic shrubs in the Tengger Desert, which implied that afforestation-induced soil quality improvements were a long-term process and that soil conservation was a key issue in water-limited ecosystems; therefore, optimized management strategies are urgently needed.

Response of soil microbial community structure and function to different altitudes in arid valley in Panzhihua, China

BackgroundAltitude affects biodiversity and physic-chemical properties of soil, providing natural sites for studying species distribution and the response of biota to environmental changes. We sampled soil at three altitudes in an arid valley, determined the physic-chemical characteristics and microbial community composition in the soils, identified differentially abundant taxa and the relationships between community composition and environmental factors.ResultsThe low, medium and high altitudes were roughly separated based on the physic-chemical characteristics and clearly separated based on the microbial community composition. The differences in community composition were associated with differences in soil pH, temperature, and SOC, moisture, TN, TP, AN, AP and SMBC contents. The contents of organic and microbial biomass C, total and available N and available P, and the richness and diversity of the microbial communities were lowest in the medium altitude. The relative abundances of phyla Proteobacteria, Gemmatimonadetes, Actinobacteria and Acidobacteria were high at all altitudes. The differentially abundant amplified sequence variants (ASVs) were mostly assigned to Proteobacteria and Acidobacteria. The highest number of ASVs characterizing altitude were detected in the high altitude. However, the predicted functions of the communities were overlapping, suggesting that the contribution of the communities to soil processes changed relatively little along the altitude gradient.ConclusionsThe low, medium and high altitudes were roughly separated based on the physicochemical characteristics and clearly separated based on the microbial community composition. The differences in community composition were associated with differences in soil pH, temperature, and SOC, moisture, TN, TP, AN, AP and SMBC contents.