K fertilizer alleviates N2O emissions by regulating the abundance of nitrifying and denitrifying microbial communities in the soil-plant system

Nitrite manipulation in water by structure change of plasma electrolysis reactor

In this study, experimental reactors for cathodic nitrogen plasma electrolysis were designed by the composition of galvanic (voltaic) and electrolytic cells with wide and narrow connectors filled with tap water and agar solutions. The designed reactor can be used to simultaneously perform and manage nitrification in acidic and alkaline environments. According to the reactor's performance, it can be installed on the irrigation system and used depending on the soil pH of the fields for delivering water and nitrogen species that are effective in growth. The nitrification process was investigated by choosing the optimal reactor with a wide connector based on different changes in oxidation-reduction potential and pH on the anode and cathode sides. The nitrite concentration changed directly with ammonium and nitrate concentrations on the cathode side. It changed inversely and directly with ammonium and nitrate concentrations on the anode side respectively. Nitrite concentration decreased from 5.387 ppm with water connector, to 0.326 ppm with 20% agar solution, and 0.314 ppm with 30% agar solution connectors on the anode side. It increased from 0 ppm to 0.191 ppm with a water connector, 0.405 ppm with 20% agar solution, and 7.454 ppm with 30% agar solution connectors on the cathode side.

Optimizing potassium and nitrogen fertilizer strategies to mitigate greenhouse gas emissions in global agroecosystems

The efficient management of fertilizer application in agriculture is vital for both food security and mitigating greenhouse gas (GHG) emissions. However, as potassium fertilizer (KF) is an essential soil nutrient, its impact on soil GHG emissions has received little attention. To address this knowledge gap and identify key determinants of GHG emissions, we conducted a comprehensive meta-analysis of 205 independent experiments conducted worldwide. Our results revealed that, in comparison to sole nitrogen fertilizer (NF) application, the concurrent use of KF elevated nitrous oxide (N2O) and methane (CH4) emissions by 39.5 % and 21.1 %, respectively, while concurrently reducing carbon dioxide (CO2) emissions by 8.1 %. The ratio of nitrogen and potassium fertilizer input (NF/KF) is identified as the primary factor explaining the variation in N2O emissions, whereas the type of KF plays a crucial role in determining CH4 and CO2 emissions. We observed a significant negative correlation between the NF/KF ratio and response ratios of N2O and CH4 emissions and a positive correlation with CO2 emissions response ratios. Furthermore, our findings indicate that when the NF/KF ratio surpasses 1.97, 4.61, and 3.78, respectively, the impact of KF on reducing N2O, CH4, and CO2 emissions stabilizes. Overall, our results underscore that the global integration of KF into agricultural practices significantly influences N2O and CH4 emissions, while simultaneously reducing CO2 emissions at a large scale. These findings provide a foundational framework and practical guidance for optimizing fertilizer application in the development of GHG emission reduction models.

nirS and nosZII bacterial denitrifiers as well as fungal denitrifiers are coupled with N2O emissions in long-term fertilized soils

Fertilizer application plays a critical role in soil fertility and crop yield and has been reported to significantly affect soil denitrification. However, the mechanisms by which denitrifying bacteria (nirK, nirS, nosZI, and nosZII) and fungi (nirK and p450nor) affect soil denitrification are poorly understood. Therefore, in this study, we investigated the effect of different fertilization treatments on the abundance, community structure, and function of soil denitrifying microorganisms in an agricultural ecosystem with long-term fertilization using mineral fertilizer or manure and their combination. The results showed that the application of organic fertilizer significantly increased the abundance of nirK-, nirS-, nosZI-, and nosZII-type denitrifying bacteria as the soil pH and phosphorus content increased. However, only the community structure of nirS- and nosZII-type denitrifying bacteria was influenced by the application of organic fertilizer, which led to a higher contribution of bacteria to nitrous oxide (N2O) emissions than that observed after inorganic fertilizer application. The increase in soil pH reduced the abundance of nirK-type denitrifying fungi, which may have presented a competitive disadvantage relative to bacteria, resulting in a lower contribution of fungi to N2O emissions than that observed after inorganic fertilizer application. The results demonstrated that organic fertilization had a significant impact on the community structure and activity of soil denitrifying bacteria and fungi. Our results also highlighted that after organic fertilizer application, nirS- and nosZII-denitrifying bacteria communities represent likely hot spots of bacterial soil N2O emissions while nirK-type denitrifying fungi represent hot spots for fungal soil N2O emissions.

Long-term excessive application of K2SO4 fertilizer alters bacterial community and functional pathway of tobacco-planting soil

To improve tobacco leaf quality, excessive K2SO4 fertilizers were applied to soils in major tobacco-planting areas in China. However, the effects of K2SO4 application on soil microbial community and functions are still unclear. An eight-year field experiment with three kinds of K2SO4 amounts (low amount, K2O 82.57 kg hm-2, LK; moderate amount, K2O 165.07 kg hm-2, MK; high amount, K2O 247.58 kg hm-2, HK) was established to assess the effects of K2SO4 application on the chemical and bacterial characteristics of tobacco-planting soil using 16S rRNA gene and metagenomic sequencing approaches. Results showed that HK led to lower pH and higher nitrogen (N), potassium (K), sulfur(S) and organic matter contents of the soil than LK. The bacterial community composition of HK was significantly different from those of MK and LK, while these of MK and LK were similar. Compared to LK, HK increased the relative abundance of predicted copiotrophic groups (e.g. Burkholderiaceae, Rhodospirillaceae families and Ellin6067 genus) and potentially beneficial bacteria (e.g. Gemmatimonadetes phylum and Bacillus genus) associated with pathogens and heavy metal resistance, N fixation, dissolution of phosphorus and K. While some oligotrophic taxa (e.g. Acidobacteria phylum) related to carbon, N metabolism exhibited adverse responses to HK. Metagenomic analysis suggested that the improvement of pathways related to carbohydrate metabolism and genetic information processing by HK might be the self-protection mechanism of microorganisms against environmental stress. Besides, the redundancy analysis and variation partitioning analysis showed that soil pH, available K and S were the primary soil factors in shifting the bacterial community and KEGG pathways. This study provides a clear understanding of the responses of soil microbial communities and potential functions to excessive application of K2SO4 in tobacco-planting soil.

Fungi and Archaea Control Soil N2O Production Potential in Chinese Grasslands Rather Than Bacteria

Nitrous oxide (N₂O) is a powerful greenhouse gas and the predominant stratospheric ozone-depleting substance. Soil is a major source of N₂O but remains largely uncertain due to the complicated processes of nitrification and denitrification performed by various groups of microbes such as bacteria, fungi, and archaea. We used incubation experiments to measure the total fungal, archaeal, and bacterial N₂O production potential and the microbial functional genes in soils along 3,000 km Chinese grassland transect, including meadow steppe, typical steppe, desert steppe, alpine meadow, and alpine steppe. The results indicated that fungi, archaea, and bacteria contributed 25, 34, and 19% to nitrification and 46, 29, and 15% to denitrification, respectively. The AOA and AOB genes were notably correlated with the total nitrification enzyme activity (TNEA), whereas both narG and nirK genes were significantly correlated with total denitrification enzyme activity (TDEA) at p < 0.01. The correlations between AOA and ANEA (archaeal nitrification enzyme activity), AOB and BNEA (bacterial nitrification enzyme activity), and narG, nirK, and BDEA (bacterial denitrification enzyme activity) showed higher coefficients than those between the functional genes and TNEA/TDEA. The structural equation modeling (SEM) results showed that fungi are dominant in N₂O production processes, followed by archaea in the northern Chinese grasslands. Our findings indicate that the microbial functional genes are powerful predictors of the N₂O production potential, after distinguishing bacterial, fungal, and archaeal processes. The key variables of N₂O production and the nitrogen (N) cycle depend on the dominant microbial functional groups in the N-cycle in soils.

Fertilizer Efficiency and Risk Assessment of the Utilization of AOD Slag as a Mineral Fertilizer for Alfalfa (Medicago sativa L.) and Perennial Ryegrass (Lolium perenne L.) Planting

Argon oxygen decarburization (AOD) slag is the by-product of the stainless steel refining process, which has caused considerable environmental stress. In this work, the utilization of AOD slag as mineral fertilizer for alfalfa (Medicago sativa L.) and perennial ryegrass (Lolium perenne L.) planting were investigated by pot experiments. The morpho-physiological parameters of biomass, plant height, root morphology and the biochemical parameters of malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, catalase (CAT) activity, peroxidase (POD) activity, and chlorophyll were measured. The accumulation of chromium in plants was also determined for an environmental safety perspective. It was found that low rates (≤0.5 wt.% for alfalfa and ≤2 wt.% for perennial ryegrass) of AOD slag fertilization are beneficial to the growth of these two plants. However, the soil enrichment with higher AOD slag amounts resulted in the reduction of biomass, plant height, and root growth. Compared with the alfalfa, the perennial ryegrass showed higher tolerance for AOD slag fertilization. The toxicity of the utilization of AOD slag as mineral fertilizer for perennial ryegrass planting is slight. Health risks induced by the consumption of the alfalfa grown on the soil with high AOD slag rates (≥8 wt.%) were detected.