Search

It is a concern whether the effect of soil type on N 2 O emissions has to be considered for regional mitigation strategies and emission estimates in mountainous areas with inherent spatial heterogeneities of soil type. To date, there were few field experiments which investigated soil type effects on N 2 O emissions. Thus a 2-year field study was conducted to measure N 2 O emissions and soil environmental variables from three different soils that were formed from similar parental rock under the same climate. Seasonal N 2 O fluxes ranged from 0.18 to 0.40 kg N ha -1 for wheat seasons and 0.40 to 1.50 kg N ha -1 for maize seasons across different experimental soils. The intra- and inter-annual variations in N 2 O emissions were mainly triggered by temporal dynamics of soil temperature and moisture conditions. On average, seasonal N 2 O fluxes for acidic soils were significantly lower than for neutral and alkaline soils in cold-dry wheat seasons while significantly greater than for neutral and alkaline soils in warm-wet maize seasons. These determined differences of N 2 O emissions were mainly caused by differences of initial soil properties across different soils. Moreover, seasonal N 2 O fluxes were positively correlated with soil pH in wheat seasons, but negatively correlated in maize seasons. The temperature sensitivity coefficient (Q 10 ) of soil N 2 O emissions for acidic soil (4.06) were significantly greater than those for neutral (1.82) and alkaline (1.15) soils. Overall, N 2 O emissions for acidic soils were not only higher than those for neutral and alkaline soils but also more sensitive to changing temperature. The present study highlights that soil type is needed to be carefully considered for regional estimate and proposing mitigation strategy of N 2 O emissions especially in subtropical mountain regions with inherent great heterogeneity of soil type., Competing Interests: Declaration of competing interest Herewith we confirm that there are no any interest conflicts in the submitted manuscript., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Wuhan was the first city to adopt the lockdown measures to prevent COVID-19 spreading, which improved the air quality accordingly. This study investigated the variations in chemical compositions, source contributions, and regional transport of fine particles (PM 2.5 ) during January 23-February 22 of 2020, compared with the same period in 2019. The average mass concentration of PM 2.5 decreased from 72.9 μg m -3 (2019) to 45.9 μg m -3 (2020), by 27.0 μg m -3 . It was predominantly contributed by the emission reduction (92.0%), retrieved from a random forest tree approach. The main chemical species of PM 2.5 all decreased with the reductions ranging from 0.85 μg m -3 (chloride) to 9.86 μg m -3 (nitrate) (p < 0.01). Positive matrix factorization model indicated that the mass contributions of seven PM 2.5 sources all decreased. However, their contribution percentages varied from -11.0% (industrial processes) to 8.70% (secondary inorganic aerosol). Source contributions of PM 2.5 transported from potential geographical regions showed reductions with mean values ranging from 0.22 to 4.36 μg m -3 . However, increased contributions of firework burning, secondary inorganic aerosol, road dust, and vehicle emissions from transboundary transport were observed. This study highlighted the complex and nonlinear response of chemical compositions and sources of PM 2.5 to air pollution control measures, suggesting the importance of regional-joint control., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Afforestation is of importance for terrestrial carbon sequestration as well as soil and water conservation in karst landscapes. However, few studies have evaluated the effects of afforestation on soil CH 4 and N 2 O emissions in subtropical karst areas. Thus, a year-round field experiment was conducted to quantify the effects of afforestation on soil CH 4 and N 2 O fluxes from a subtropical karst landscape in South China. In this study, soil CH 4 and N 2 O fluxes were simultaneously monitored using static chamber-gas chromatography from three paired sites, including a cropland site (SC) and adjacent sites at two stages of afforestation, a shrubland (SD) and a woodland (AF). The results showed that annual soil CH 4 uptake for SC, SD, and AF sites were 1.53 ± 0.20 kg C ha -1  yr -1 , 2.90 ± 0.20 kg C ha -1  yr -1 , and 5.68 ± 0.18 kg C ha -1  yr -1 , respectively. Afforestation (i.e., SD and AF sites) significantly increased soil CH 4 uptake compared with the adjacent cropland. Annual soil N 2 O fluxes for SC, SD, and AF sites were 2.38 ± 0.17 kg N ha -1  yr -1 , 0.94 ± 0.14 kg N ha -1  yr -1 , and 0.47 ± 0.01 kg N ha -1  yr -1 , respectively. Afforestation significantly decreased soil N 2 O fluxes compared with the adjacent cropland. The effects of afforestation on soil CH 4 and N 2 O fluxes in the present study were mainly attributed to changes in soil characteristics, such as temperature and moisture, as these were significantly correlated with soil CH 4 and N 2 O fluxes across different experimental sites. The present study highlights that afforestation is an effective land use management practice to mitigate non-CO 2 greenhouse gas emissions from subtropical karst landscapes in South China., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The impact of afforestation and deforestation on the carbon cycle and carbon sequestration in agricultural landscape has been well studied, while the direction and magnitude of the effects on soil CH 4 fluxes remain uncertain in particular in the subtropical region. Thus, multi-site and multi-year field experiments were conducted to measure soil CH 4 fluxes from an afforestation chronosequence (cropland [wheat-maize rotation], 15-year old forest, 20-year old forest and 30-year forest) and a deforestation chronosequence (secondary forest, grassland, cropland without fertilization and cropland with fertilization [wheat-maize rotation]) in a subtropical agricultural landscape from 2012 to 2017. The soil at all land uses functioned exclusively as a sink for atmospheric CH 4 through the whole experimental years. Soil CH 4 uptakes showed great seasonal and inter-annual variations along with those of temporal patterns of soil environmental variables. At the afforestation chronosequence, annual CH 4 uptake rates averaged 1.37, 1.68, 1.80 and 2.97 kg C ha -1  yr -1 for cropland, 15-year old forest, 20-year old forest and 30-year old forest. Compared to cropland, afforestation increased annual CH 4 uptake by 23 to 117%. Soil CH 4 uptake decreased with increasing soil content, soil NH 4 + content and soil NO 3 - content but increased with increasing soil DOC content at the afforestation chronosequence (P < 0.05). At the deforestation chronosequence, annual CH 4 uptake rates were 1.37, 1.70, 1.77 and 2.01 kg C ha -1  yr -1 for secondary forest, grassland, cropland without fertilization and cropland with fertilization. Compared to secondary forest, deforestation increased annual CH 4 uptake by 24 to 47%. Soil CH 4 uptakes were negatively correlated with soil water content and positively correlated with soil NO 3 - content. We conclude that both afforestation and deforestation have the potential to increase the sink capacities of atmospheric CH 4 in the subtropical agricultural landscape and consequently provide the negative feedbacks to climate system., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Particulates smaller than 1.0 μm (PM 1.0 ) have strong associations with public health and environment, and considerable exposure data should be obtained to understand the actual environmental burden. This study presented a PM 1.0 estimation strategy based on the generalised regression neural network model. The proposed strategy combined ground-based observations of PM 2.5 and satellite-derived aerosol optical depth (AOD) to estimate PM 1.0 concentrations in China from July 2015 to June 2017. Results indicated that the PM 1.0 estimates agreed well with the ground-based measurements with an R 2 of 0.74, root mean square error of 19.0 μg/m 3 and mean absolute error of 11.4 μg/m 3 as calculated with the tenfold cross-validation method. The diurnal estimation performance displayed remarkable single-peak variation with the highest R 2 of 0.80 at noon, and the seasonal estimation performance showed that the proposed method could effectively capture high-pollution events of PM 1.0 in winter. Spatially, the most polluted areas were clustered in the North China Plain, where the average estimates presented a bimodal distribution during daytime. In addition, the quality of satellite-derived AOD, the robustness of the interpolation algorithm and the proportion of PM 1.0 in PM 2.5 were confirmed to affect the estimation accuracy of the proposed model., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Annual nitrous oxide (N 2 O) emissions from high-altitude alpine meadow grasslands have not been effectively characterized because of the scarcity of whole-year measurements. The authors performed a year-round measurement of N 2 O fluxes from three conventionally grazed alpine meadows that represent the typical meadow landscape in the eastern Qinghai-Tibetan Plateau (QTP). The results showed that annual N 2 O emissions averaged 0.123±0.053 (2SD, i.e., the double standard deviation indicating the 95% confidence interval) kgNha -1 yr -1 across the three meadow sites. N 2 O flux pulses during the spring freezing-thawing period (FTP) were observed at only one site, indicating a large spatial variability in association with soil moisture differences. Approximately 34-57% (mean: 46%) of the annual N 2 O emissions occurred in the non-growing season, highlighting the substantial importance of accurate flux observations during this period. The simultaneous observations showed conservative, marginal nitric oxide (NO) fluxes of 0.058±0.032 (2SD) kgNha -1 yr -1 . The N 2 O fluxes across the three field sites correlated negatively with the soil nitrate concentrations during the entire year-round period (P<0.05). Furthermore, a significant joint regulatory effect of topsoil temperature and moisture on the N 2 O and NO fluxes was observed during the relatively warm periods. Based on the results of the present and previous studies, a simple extrapolation roughly estimated the annual total N 2 O emission from Chinese grasslands to be 73±15 (2SD) GgNyr -1 (1Gg=10 9 g). A linear dependence of the annual N 2 O fluxes on the aboveground net primary productivity (ANPP) was also found. This result may provide a simple approach for estimating the N 2 O emission inventories of frigid alpine or temperate grasslands that are ungrazed either in the summer or year round. However, further confirmation of this relationship with a wider ANPP range is still needed in the future studies., (Copyright © 2017 Elsevier B.V. All rights reserved.)