Residual effects of four-year amendments of organic material on N2O production driven by ammonia-oxidizing archaea and bacteria in a tropical vegetable soil

Environmental Adaptability and Roles in Ammonia Oxidation of Aerobic Ammonia-Oxidizing Microorganisms in the Surface Sediments of East China Sea

This study investigated the community characteristics and environmental influencing factors of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in the surface sediments of the East China Sea. The research found no consistent pattern in the richness and diversity of AOA and AOB with respect to the distance from the shore, indicating a complex interplay of factors. The expression levels of AOA amoA gene and AOB amoA gene in the surface sediments of the East China Sea ranged from 4.49 × 102 to 2.17 × 106 copies per gram of sediment and from 6.6 × 101 to 7.65 × 104 copies per gram of sediment, respectively. Salinity (31.77 to 34.53 PSU) and nitrate concentration (1.51 to 10.12 μmol/L) were identified as key environmental factors significantly affecting the AOA community, while salinity and temperature (13.71 to 19.50 °C) were crucial for the AOB community. The study also found that AOA, dominated by the Nitrosopumilaceae family, exhibited higher gene expression levels than AOB, suggesting a more significant role in ammonia oxidation. The expression of AOB was sensitive to multiple environmental factors, indicating a responsive role in nitrogen cycles and ecosystem health. The findings contribute to a better understanding of the biogeochemical processes and ecological roles of ammonia-oxidizing microorganisms in marine sediments.

Co-application of biochar and organic amendments on soil greenhouse gas emissions: A meta-analysis

Biochar has been shown to reduce soil greenhouse gas (GHG) and increase nutrient retention in soil; however, the interaction between biochar and organic amendments on GHG emissions remain largely unclear. In this study, we collected 162 two-factor observations to explore how biochar and organic amendments jointly affect soil GHG emissions. Our results showed that biochar addition significantly increased soil CO2 emission by 8.62 %, but reduced CH4 and N2O emissions by 27.0 % and 23.9 %, respectively. Meanwhile, organic amendments and the co-application with biochar resulted in an increase of global warming potential based on the 100-year time horizon (GWP100) by an average of 18.3 % and 26.1 %. More importantly, the interactive effect of biochar and organic amendments on CO2 emission was antagonistic (the combined effect was weaker than the sum of their individual effects), while additive on CH4 and N2O emissions. Additionally, our results suggested that when biochar is co-applied with organic amendments, soil GHG emissions were largely influenced by soil initial total carbon, soil texture, and biochar feedstocks. Our work highlights the important interactive effects of biochar and organic amendments on soil GHG emissions, and provides new insights for promoting ecosystem sustainability as well as mitigating future climate change.

Organic substitution stimulates ammonia oxidation-driven N2O emissions by distinctively enriching keystone species of ammonia-oxidizing archaea and bacteria in tropical arable soils

Partial organic substitution (POS) is pivotal in enhancing soil productivity and changing nitrous oxide (N₂O) emissions by profoundly altering soil nitrogen (N) cycling, where ammonia oxidation is a fundamental core process. However, the regulatory mechanisms of N₂O production by ammonia oxidizers at the microbial community level under POS regimes remain unclear. This study explored soil ammonia oxidation and related N₂O production, further building an understanding of the correlations between ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) activity and community structure in tropical arable soils under four-year field management regimes (CK, without fertilizer N; N, with only inorganic N; M1N1, with 1/2 organic N + 1/2 inorganic N; M1N2, with 1/3 organic N + 2/3 inorganic N). AOA contributed more to potential ammonia oxidation (PAO) than AOB across all treatments. In comparison with CK, N treatment had no obvious effects on PAO and lowered related N₂O emissions by decreasing soil pH and downregulating the abundance of AOA- and AOB-amoA. POS regimes significantly enhanced PAO and N₂O emissions relative to N treatment by promoting the abundances and contributions of AOA and AOB. The stimulated AOA-dominated N₂O production under M1N1 was correlated with promoted development of Nitrososphaera. By contrast, the increased AOB-dominated N₂O production under M1N2 was linked to the enhanced development of Nitrosospira multiformis. Our study suggests organic substitutions with different proportions of inorganic and organic N distinctively regulate the development of specific species of ammonia oxidizers to increase associated N₂O emissions. Accordingly, appropriate options should be adopted to reduce environmental risks under POS regimes in tropical croplands.

Crop residue return sustains global soil ecological stoichiometry balance

Although soil ecological stoichiometry is constrained in natural ecosystems, its responses to anthropogenic perturbations are largely unknown. Inputs of inorganic fertilizer and crop residue are key cropland anthropogenic managements, with potential to alter their soil ecological stoichiometry. We conducted a global synthesis of 682 data pairs to quantify the responses of soil carbon (C), nitrogen (N), and phosphorus (P) and grain yields to combined inputs of crop residue plus inorganic fertilizer compared with only inorganic fertilizer application. Crop residue inputs enhance soil C (10.5%-12%), N (7.63%-9.2%), and P (2.62%-5.13%) contents, with an increase in C:N (2.51%-3.42%) and C:P (7.27%-8.00%) ratios, and grain yields (6.12%-8.64%), indicating that crop residue alleviated soil C limitation caused by inorganic fertilizer inputs alone and was able to sustain balanced stoichiometry. Moreover, the increase in soil C and C:N(P) ratio reached saturation in ~13-16 years after crop residue return, while grain yield increase trend discontinued. Furthermore, we identified that the increased C, N, and P contents and C:N(P) ratios were regulated by the initial pH and C content, and the increase in grain yield was not only related to soil properties, but also negatively related to the amount of inorganic N fertilizer input to a greater extent. Given that crop residual improvement varies with soil properties and N input levels, we propose a predictive model to preliminary evaluate the potential for crop residual improvement. Particularly, we suggest that part of the global budget should be used to subsidize crop residue input management strategies, achieving to a win-win situation for agricultural production, ecological protection, and climate change mitigation.

Proper organic substitution attenuated both N2O and NO emissions derived from AOB in vegetable soils by enhancing the proportion of Nitrosomonas

The ammonia oxidation process driven by microorganisms is an essential source of nitrous oxide (N₂O) and nitric oxide (NO) emissions. However, few evaluations have been performed on the changes in the community structure and abundance of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) under substituting portion of chemical fertilizers with organic manure (organic substitution) and their relative contribution to the ammonia oxidation process. Here, five long-term fertilization strategies were applied in field (SN: synthetic fertilizer application; OM: organic manure; M1N1: substituting 50 % of chemical N fertilizer with organic manure; M1N4: substituting 20 % of chemical N fertilizer with organic manure; and CK: no fertilizer). We investigated the response characteristics of AOB and AOA community structures by selective inhibitor shaking assays and high-throughput sequencing and further explained their relative contribution to the ammonia oxidation process during three consecutive years of vegetable production. Compared to SN and M1N4, the potential of ammonia oxidation (PAO) was significantly reduced by 26.4 % and 22.3 % in OM and 9.5 % and 4.4 % in M1N1, resulting in N₂O reductions of 38.9 % and 30.8 % (OM) and 31.2 % and 21.1 % (M1N1), respectively, and NO reductions of 45.0 % and 34.1 % (OM) and 40.1 % and 28.3 % (M1N1). RDA and correlation analyses showed that the soil organic carbon and ammonium nitrogen content increased while AOB gene abundance and diversity significantly decreased with increasing organic replacement ratio; however, the relative abundance of Nitrosomonas in AOB increased in OM and M1N1, which further demonstrates that AOB are the main driver in vegetable soils. Therefore, the appropriate proportion of organic substitution (OM and M1N1) could decrease the N₂O and NO emissions contributed by AOB by affecting the soil physicochemical properties and AOB community structure.

A two-year measurement of methane and nitrous oxide emissions from freshwater aquaculture ponds: Affected by aquaculture species, stocking and water management

Aquaculture ponds are of increasing worldwide concerns as critical sources of atmospheric methane (CH₄) and nitrous oxide (N₂O), but little is known about these gases emissions as affected by aquaculture species, stocking and water management in aquaculture ponds. Here, a two-year study was carried out to quantify CH₄ and N₂O emissions from freshwater crab and fish aquaculture ponds in subtropical China. We further explored how the microbial functional genes [CH₄: mcrA and pmoA; N₂O: archaeal and bacterial amoA (AOA + AOB), nirS, nirK, nosZ] may drive CH₄ and N₂O release in the crab aquaculture pond typically undergoing flooding-to-drainage alteration. Over the two-year period, annual CH₄ and N₂O fluxes averaged 0.95 mg m^-2 h^-1 and 20.94 μg m^-2 h^-1 in the fish aquaculture, and 0.78 mg m^-2 h^-1and 28.48 μg m^-2 h^-1 in the crab aquaculture, respectively. The direct N₂O emission factors were estimated to be 0.77% and 0.36% of the total N input by feed or 1.59 g N₂O-N kg^-1 and 1.06 g N₂O-N kg^-1 aquaculture yield in the crab and fish ponds, respectively. Among three functional stocking areas, CH₄ and N₂O emissions were consistently the highest at the feeding area (FA) in the both aquaculture ponds, followed by at the undisturbed area (UA) and aerated area (AA). The shift in sediment soil moisture from waterlogging to drainage conditions significantly increased the abundance of AOB relative to AOA and pmoA, decreased those of denitrifying functional genes (nirS, nirK, nosZ) and mcrA, while did not alter the functional group ratio of nirS + nirK relative to nosZ. Our results highlight that a better understanding of CH₄ and N₂O emissions from aquaculture ponds requires taking into consideration of data sourced from more diverse aquaculture systems with different management patterns. In addition, a deep analysis of the microbial processes that drive CH₄ and N₂O production and consumption from aquaculture ponds remains to be addressed in future studies.

Combining Organic Fertilizer With Controlled-Release Urea to Reduce Nitrogen Leaching and Promote Wheat Yields

Soil deterioration, low nitrogen use efficiency (NUE), and environmental risks caused by excessive chemical N fertilizer use are key factors restricting sustainable agriculture. It is extremely critical to develop effective N management strategies that consider both environmental and agronomic benefits. From 2017 to 2019, a field experiment was conducted to assess the effects of combinations of organic fertilizers (OF, provided at 30, 50, and 70% of the total applied N) and controlled-release urea (CU) on the NUE, N leaching and wheat yield compared with the effects of urea and CU. The results suggested that OF released N slowly in the early stage and showed a significant residual effect, while CU released N quickly in the first 2 months. The OF substitutes with 30-50% CU increased wheat yield by 4.2-9.2%, while the 70%OF+30%CU treatment showed no significant difference relative to the urea treatment. The average maximum apparent NUE recovery (50.4%) was achieved under the 50%OF+50%CU treatment, but the partial factor productivity was not affected by the N type. As the OF application rate increased, the total carbon content increased, and the total N value decreased. The NO 3 - -N and NH 4 + -N concentrations in the OF+CU treatments were lower before the jointing stage but higher from the grain-filling to mature stages than those in the urea treatment. NO 3 - -N and NH 4 + -N were mainly concentrated in the 0-60-cm layer soil by OF substitution, and N leaching to the 60-100-cm soil layer was significantly reduced. Hence, the results suggest that the combination of 30-50% OF with CU synchronizes absorption with availability due to a period of increased N availability in soils and proved to be the best strategy for simultaneously increasing wheat production and reducing N leaching.