Soil texture is an easily overlooked factor affecting the temperature sensitivity of N2O emissions

A meta-analysis of afforestation impacts on soil greenhouse gas emissions

Afforestation is a natural climate solution and a key strategy to mitigate climate change. While tree planting primarily achieves this mitigation via above-ground carbon sequestration, soils also play a dual role as sources and sinks of greenhouse gases (GHG). Understanding afforestation impacts on soil GHG flux is essential for leveraging afforestation to combat global warming. In this research, we conducted a global meta-analysis of 157 studies to assess the effects of afforestation on soil GHG emissions across different prior land uses and to identify key emission drivers. Our results indicated that afforestation significantly reduced CO2 emissions in former grasslands and deforested land and decreased CH4 emissions across most prior land uses. However, soil N2O flux was mostly unaffected by afforestation. The type of forest planted also influenced soil GHG emissions. Hardwood planting reduced CH4 emissions, but no clear trends emerged for N2O emissions from either softwood or hardwood forests. Tree planting density had no significant effect on GHG fluxes. GHG responses to afforestation also changed over time and were influenced by environmental factors. CO2 emissions correlated positively with soil organic carbon, mean annual precipitation, C:N ratio, and soil temperature. N2O flux increased with soil NO3- and microbial nitrogen and decreased with soil organic carbon and moisture. Additionally, soil microbial biomass carbon and soil organic carbon were positively correlated with CH4 emissions. These findings highlight the importance of selecting tree species, site conditions, and environmental factors to optimize afforestation's GHG mitigation potential.

Determinants of environmental changes in human-modified ecosystems: Effects of plastics on moisture gradients, nutrients, and clay properties

Plastic pollution poses a significant threat to ecosystem health worldwide. This study examines the determinants of environmental changes in human-modified ecosystems through a quantitative-qualitative system dynamics modeling approach: field experiments conducted on a 310 m2 unsaturated clay-rich bed and a 2.5 m2 clay-rich shore of a plastic-impacted pond in Shenzhen, China, and a 1.17 ha plastic-impacted clay pit in Musanze, Rwanda; laboratory experiments involving Modified Proctor (MP) and California Bearing Ratio (CBR) tests on natural clay reinforced with polyethylene terephthalate (PET) microplastics, with diameters ranging from 0.25 to 5 mm and at concentrations of 1.25 %, 2.5 %, 3.75 %, 5 %, and 10 % by weight of clay; and plastic dynamic flows analyzed by modeling the life cycle of PET. Field experiments showed that mulch type and thickness were critical factors influencing crack distribution in a plastic-impacted pond bed. Specifically, cracks were dominant in areas with pronounced desiccation and lacking filamentous green algae and PET-dominated plastic waste. Along the 2.5 m moisture gradient in a plastic-impacted pond bed, temperature and moisture significantly influenced nutrients, particularly in pronounced desiccation zones. Laboratory experiments showed that microplastics altered the structural properties of natural clay, decreasing moisture content while increasing dry density and load-bearing capacity. The plastic life cycle underscored the roles of industrial and consumer practices, environmental conditions, and waste management and recycling inefficiencies in driving environmental changes in human-modified ecosystems. The findings underscore the need for effective plastic waste management and recycling to mitigate the ecological impacts of plastic pollution in ecosystems.

Differential responses of temperature sensitivity of greenhouse gases emission to seasonal variations in plateau riparian zones

Riparian zones, regarded as hotspots for greenhouse gas (GHG) emissions, where the variation in temperature sensitivity (Q10) of GHG emissions is crucial for assessing GHG budgets under global warming. However, the seasonal Q10 of GHG emissions from high-elevation riparian zones and underlying microbial mechanisms are poorly documented. This study focuses on seasonal Q10 patterns of GHG emissions from riparian zones along the Lhasa River on the Tibetan Plateau. CO2 and CH4 emissions from riparian soils were more sensitive to temperature in spring than in summer. The opposite trend was observed for Q10 of N2O emissions. Soil organic carbon (SOC) had relatively large direct effects on the Q10-CO2 value in summer, whereas soil nitrate nitrogen (SNO3--N) was the determinant of Q10-CO2 value in spring. mcrA:pmoA and soil microbial biomass C (SMBC) had strong direct effects on the Q10 of CH4 emissions in summer; the Q10-CH4 value in spring was significantly affected by the mcrA abundance. SMBC and the nirK + nirS abundance were key factors affecting the Q10-N2O value. Q10-CO2 and Q10-CH4 values exhibited strong seasonalities in the lower reaches of riparian soils, mainly due to the seasonalities of SNO3--N and mcrA:pmoA, respectively. The Q10-N2O value in the middle and upper reaches of riparian soils presented seasonality, which was largely due to the seasonalities of soil ammonia nitrogen and microbial biomass carbon. During thawing, plant productivity increased, substrate carbon was sufficient, microbial biomass increased, and inorganic nitorgen and denitrifier abundance decreased, causing 29.67% and 37.47% decreases in the Q10-CO2 and Q10-CH4 values, respectively, and a 70.85% increase in the Q10-N2O value, indicating that the potential release of N2O from riparian zones along the plateau river was more susceptible to seasonal variations. Our findings are conducive to accurately evaluating the potential contribution of GHG emissions from high-elevation riparian zones to global warming.

Seasonal isotopic and isotopomeric signatures of nitrous oxide produced microbially in a eutrophic estuary

Anthropogenic input of excess nutrients stimulates massive nitrous oxide (N2O) production in estuaries with distinct seasonal variations. Here, nitrogen isotopic and isotopomeric signatures were utilized to investigate the seasonal dynamics of N2O production and nitrification at the middle reach of the eutrophic Pearl River Estuary in the south of China. Elevated N2O production primarily via ammonia oxidation (> 1 nM-N d-1) occurred from April to November, along with increased temperature and decreased dissolved oxygen concentration. This consistently oxygenated water column showed active denitrification, contributing 20-40 % to N2O production. The water column microbial N2O production generally constituted a minor fraction (10-15 %) of the estuarine water-air interface efflux, suggesting that upstream transport and tidal dilution regulated the dissolved N2O inventory in the middle reach of the estuary. Nitrification (up to 3000 nM-N d-1) played a critical role in bioavailable nitrogen conversion and N2O production, albeit with N2O yields below 0.05 %.

Inoculation with Stutzerimonas stutzeri strains decreases N₂O emissions from vegetable soil by altering microbial community composition and diversity

Inoculation with plant growth-promoting rhizobacteria (PGPR) strains has promoted plant growth and decreased nitrous oxide (N₂O) emissions from agricultural soils simultaneously. However, limited PGPR strains can mitigate N₂O emissions from agricultural soils, and the microbial ecological mechanisms underlying N₂O mitigation after inoculation are poorly understood. In greenhouse pot experiments, the effects of inoculation with Stutzerimonas stutzeri NRCB010 and NRCB025 on tomato growth and N₂O emissions were investigated in two vegetable agricultural soils with contrasting textures. Inoculation with NRCB010 and NRCB025 significantly promoted tomato growth in both soils. Moreover, inoculation with NRCB010 decreased the N₂O emissions from the fine- and coarse-textured soils by 38.7% and 52.2%, respectively, and inoculation with NRCB025 decreased the N₂O emissions from the coarse-textured soil by 76.6%. Inoculation with NRCB010 and NRCB025 decreased N₂O emissions mainly by altering soil microbial community composition and the abundance of nitrogen-cycle functional genes. The N₂O-mitigating effect might be partially explained by a decrease in the (amoA + amoB)/(nosZI + nosZII) and (nirS + nirK)/(nosZI + nosZII) ratios, respectively. Soil pH and organic matter were key variables that explain the variation in abundance of N-cycle functional genes and subsequent N₂O emission. Moreover, the N₂O-mitigating effect varied depending on soil textures and individual strain after inoculation. This study provides insights into developing biofertilizers with plant growth-promoting and N₂O-mitigating effects.

IMPORTANCE

Plant growth-promoting rhizobacteria (PGPR) have been applied to mitigate nitrous oxide (N₂O) emissions from agricultural soils, but the microbial ecological mechanisms underlying N₂O mitigation are poorly understood. That is why only limited PGPR strains can mitigate N₂O emissions from agricultural soils. Therefore, it is of substantial significance to reveal soil ecological mechanisms of PGPR strains to achieve efficient and reliable N₂O-mitigating effect after inoculation. Inoculation with Stutzerimonas stutzeri strains decreased N₂O emissions from two soils with contrasting textures probably by altering soil microbial community composition and gene abundance involved in nitrification and denitrification. Our findings provide detailed insight into soil ecological mechanisms of PGPR strains to mitigate N₂O emissions from vegetable agricultural soils.

Novel annual nitrogen management strategy improves crop yield and reduces greenhouse gas emissions in wheat-maize rotation systems under limited irrigation

Excessive irrigation and nitrogen application have long seriously undermined agricultural sustainability in the North China Plain (NCP), leading to declining groundwater tables and intensified greenhouse gas (GHG) emissions. Developing low-input management practices that meet the growing food demand while reducing environmental costs is urgently needed. Here, we developed a novel nitrogen management strategy for a typical winter wheat-summer maize rotation system in the NCP under limited irrigation (wheat sowing irrigation only (W0) or sowing and jointing irrigation (W1)) and low nitrogen input (360 kg N ha-1, about 70 % of traditional annual nitrogen input). Novel nitrogen management strategy promoted efficient nitrogen fertilizer uptake and utilization by both crops via optimization of nitrogen fertilizer allocation between the two crops, i.e., increasing nitrogen inputs to wheat (from 180 to 240 kg N ha-1) while reducing nitrogen inputs to maize (from 180 to 120 kg N ha-1). Three-year field study demonstrated that integrated management practices combining novel nitrogen management strategy with limited irrigation increased annual yields and PFPN by 1.9-5.7 %, and reduced TGE by 55-68 kg CO2-eq ha-1 and GHGI by 2.2-10.3 %, without any additional cost. Our results provide agricultural operators and policymakers with practical and easy-to-scalable integrated management strategy, and offer key initiative to promote grain production in the NCP towards agriculture sustainable intensification with high productivity and efficiency, water conservation and emission reduction.