Search

Highlights • The effects of N deposition on global WUE were evaluated with IBIS model. • WUE changed in several N deposition hotspots owing to larger change in GPP than in ET. • N deposition has significantly increased the response ratio of WUE to elevated CO 2 in some regions. Abstract Nitrogen (N) deposition changes the availability of N in ecosystems and regulates carbon and water cycles, including ecosystem water use efficiency (WUE). In recent decades, N deposition has been increasing rapidly, especially at several hotspots in China, Europe and the U.S. In this study, a process-based terrestrial ecosystem model, IBIS (Integrated BIosphere Simulator), was used to simulate the effects of N deposition on WUE globally. The results indicated that increasing N deposition led to a global increase in WUE of 0.005 g C kg−1 H 2 O on average over the first 10 years of the 21st century. The effects of N deposition on WUE were more evident in certain hotspots than in other parts of the world. The effect of N deposition on gross primary productivity (GPP) determined the change in WUE. In particular, high N deposition led to decreased ET and consequently increased the WUE in southeastern China. Moreover, increased N deposition has significantly enhanced the WUE in response to elevated CO 2 in southeastern China, indicating the importance of N deposition in regulating the terrestrial carbon cycle. [ABSTRACT FROM AUTHOR]

[Display omitted] • V cmax25 , N a and Chl a of winter wheat and paddy rice exhibited distinguishable seasonality. • The seasonality of leaf N a and Chl a were inconsistent with that of V cmax25. • Differentiating pre- and post-flowering stages significantly improved the estimation of V cmax25 from Chl a. Accurate representation of photosynthetic capacity and its seasonal variations is critical for modeling carbon sequestration of cropland ecosystems through photosynthesis. Previous studies indicated that the maximum carboxylation rate at 25 °C (V cmax25) is the key determinant of photosynthetic capacity and can be mapped according to leaf nitrogen (N) and chlorophyll (Chl) contents. However, whether relationships of V cmax25 with leaf nitrogen and chlorophyll contents in cropland ecosystems change over the whole growing season remain unclear. To address this question, we conducted intensive field campaigns in winter wheat and paddy rice farmlands of Eastern China, with leaf V cmax25 , the maximum electron transport rate at 25 °C (J max25), N, and Chl measured every 7 to 10 days from the tillering stage to maturity. Results showed that V cmax25 and J max25 varied significantly during the growing seasons and maximized at flowering stages. For both winter wheat and paddy rice, Chl a (Chl content at the area unit) showed significantly different relationships with V cmax25 pre- and post- flowering while N a (N content at the area unit) did not. When different empirical models were used for pre- flowering and post- flowering stages, V cmax25 estimated from Chl a was closer to observations (R2 = 0.875, RMSE = 9.479 µmol m−2 s−1) than that estimated from N a (R2 = 0.565, RMSE = 17.718 µmol m−2 s−1). The findings in this study imply that the combination of remotely sensed leaf Chl a content and phenology would improve the mapping of V cmax25 for crops at regional and even global scales. [ABSTRACT FROM AUTHOR]

This study detected the long-term trends in NO 2 concentrations in China from 1997 to 2016 based on the NO 2 columns from GOME, SCIAMACHY, and GOME-2A. Both differences in the time-overlapped NO 2 columns from GOME vs. SCIAMACHAY and SCIAMACHAY vs. GOME-2A showed seasonal variations, and the annual NO 2 columns from GOME were 0.9% higher than those from SCIAMACHY, which exceeded that from GOME-2A by 14%. The long-term trends of the NO 2 columns on a provincial scale could be simulated by cubic models (0.60 < R 2  < 0.96, p < 0.05) and presented three shapes: first decreasing then increasing and decreasing again; first decreasing then increasing; and continuously decreasing. The peak years of NO 2 columns in 17 provinces occurred in 2011 and 2012. These trends in NO 2 columns were determined by the economic developments and enacted air quality policies in nearly all the provinces except for Xizang and Qinghai Provinces, where the trends were determined by natural NO x emission sources. In detail, the panel data analysis showed that the simulated model had fixed effects, and the thermal power generation, consumption of diesel oil in agriculture, passenger traffic by highways, and freight traffic by highways significantly increased NO 2 , while the air quality policies in the 12th five-year plan decreased NO 2 columns from 1997 to 2016. The benefits to decreasing NO 2 columns from the air quality policies issued in the 10th and 11th five-year plans were offset by the quickly increasing economies. [ABSTRACT FROM AUTHOR]

A highly efficient cascade sequence for syntheses of 2,3-disubstituted imidazo[1,2- a ]pyridines with exclusive regioselectivity in moderate to excellent yields has been developed. This cascade was initiated through propargylation of 2-aminopyridines at pyridine-nitrogen with propargyl alcohol derivatives using Cu(II)-Pybox as catalyst and followed by an intramolecular cyclization and isomerization. Besides 2-aminopyridine, less reactive 2-aminopyrimidine, 2-aminopyrazine and 3-aminopyridazine were also suitable in this cascade. [ABSTRACT FROM AUTHOR]

Abstract The Qinling Mountain Range (QMR) in central China encompasses innumerable Paleolithic sites. The hominin settlement in the QMR is comparable with that in the Nihewan Basin in northern China. The recorded information on the loess deposition in the QMR include both hominin remains and environmental changes. Since 2004, geological, geomorphological, archaeological, and chronological investigations were conducted by our team. By systematically using luminescence, paleomagnetic, and 26Al/10Be burial dating methods to obtain age controls, and by correlating the pedostratigraphy and magnetic susceptibility of the Luochuan loess section, we established the loess–paleosol sequence and chronology of the lithic artifact levels for 35 Paleolithic sites and spots in the QMR. This work remarkable found shifts from glacial-to interglacial-driving hominin settlement patterns. During the stage between 1.2 and 0.7 Ma, large drying events, such as L15 (MIS 38) and L9 (MIS 22, 23 and 24), may have driven hominin migrations when the Loess Plateau was depopulated; moreover, the southern QMR was a glacial refugium. During the stage after ∼0.60 Ma, the contrasts between glacial and interglacial scales are the greatest; furthermore, longer and warmer humid interglacial environments were dominant. S5 (MIS 13, 14, 15) and S1 (MIS 5) interglacial periods provided the optimal environments for hominin settlement and dispersal. On the basis of investigations, we also found that the hominin settlement is relatively continuous from ∼1.20 Ma to ∼0.05 Ma in the QMR. The human occupation of the QMR decreased considerably after ∼0.05 Ma, probably because of changes in climate and human adaptations. Highlights • We had dated 35 Paleolithic sites and the spot in the Qinling Mountain Range in central China. • We investigated how hominin groups responded to glacial–interglacial shifts from ∼1.20 Ma to ∼0.05 Ma. • The drastic decline of human occupation after ∼0.05 Ma can be linked to the decline in Gross primary productivity. [ABSTRACT FROM AUTHOR]

Remote sensing technology has great potential to expand the observation of ground-level nitrogen deposition from local monitoring sites to a regional scale, with high spatial and temporal resolutions. A new methodology is developed to estimate the spatial distribution of monthly bulk nitrogen deposition on a regional scale, based on precipitation amounts and HNO 3 and aerosol nitrate (NO 3 − ) columns, derived from OMI NO 2 columns and the relationship of NO 2 , HNO 3 and NO 3 − from MOZART. The accuracy assessment shows that the proposed model has achieved a reasonably high predictive power for monthly NO 3 − -N deposition (slope = 0.96, intercept = 0.35, R = 0.83, RMSE = 0.72) across China. The spatial NO 3 − -N deposition shows a significant gradient from industrial areas to undeveloped regions, ranging from 0.01 to 26.76 kg N ha − 1 y − 1 with an average of 5.77 kg N ha − 1 y − 1 over China during 2010–2012. The bulk NO 3 − -N deposition shows a clear seasonal variation, with high depositions occurring in the warm season (March–November) and peaking in July and August, and low bulk NO 3 − -N deposition appearing in winter (December–February). This study proves for the first time that the atmospheric boundary layer (ABL) HNO 3 and NO 3 − columns and precipitation are powerful to predict the bulk nitrate deposition. [ABSTRACT FROM AUTHOR]

Climate change has significantly influenced the productivity of terrestrial ecosystems through water cycles. Water use efficiency (WUE) is an important indicator for understanding how water couples with the carbon cycle. Abiotic factors such as climatic factors and CO 2 concentration have been investigated to understand the mechanisms involved in the coupled carbon-water cycle of terrestrial ecosystems in response to climate change. However, the effects of biotic factors on WUE are less clear. By analyzing 66 site-years of flux and meteorological data obtained from 8 temperate deciduous broadleaf forest sites across North America and Europe, we found that ecosystem-scale WUE (defined here as the ratio of gross primary production (GPP) to evapotranspiration (ET)) in the spring significantly increased with the advance of the flux-based photosynthetic onset (FPO), mainly because an earlier FPO could lead to a steeper increase in GPP than in ET. However, the advance of FPO probably reduced summer WUE as a result of the enhancement of water stress by ET in the spring in temperate deciduous broadleaf forest. Our results also implied that spring warming had an indirectly positive effect on WUE through advancing spring phenology, but such a positive effect will likely weaken once the sensitivity of spring phenology to warming decreases as reported. Here, we argue that phenology, which exerts critical biotic control over most ecological processes, plays a larger role than expected in the regulation of the seasonal WUE and cannot be ignored in earth system models. [ABSTRACT FROM AUTHOR]

A systematic dataset of an observation network on a national scale has been organized to investigate the spatial distribution of bulk sulfur (S) deposition (S dep ) throughout China during 2000–2013, representing by far the most detailed data set to track the bulk sulfur deposition throughout China since 2000. Such a dataset is needed for ecosystem studies and for developing emission control policies. Bulk S dep values showed great variations, ranging from 2.17 to 70.55 kg ha −1 y −1 , with an average of 22.99 kg ha −1 y −1 . The average rate of bulk S dep located in East Coastal region (35.97 kg ha −1 y −1 ), Middle Yangtze region (57.90 kg ha −1 y −1 ), Middle Yellow River region (23.42 kg ha −1 y −1 ), North Coastal region (42.19 kg ha −1 y −1 ), Northeast region (34.28 kg ha −1 y −1 ), South Coastal region (36.97 kg S ha −1 y −1 ), Southwest region (33.85 kg ha −1 y −1 ) was 4.50, 7.24, 2.93, 5.28, 4.29, 4.63 and 4.24 times than that in Northwest region (7.99 kg ha −1 y −1 ). Bulk S dep over China was mainly from fossil fuel combustion (76.96%), biomass burning (7.64%), crust (6.22%), aged sea salt (5.48%) and agriculture (3.68%). A systematic observation network on a national scale should be established to conduct a long-term monitoring atmospheric S dep (including wet and dry deposition), based on exiting ecological stations administrated by different departments in China. [ABSTRACT FROM AUTHOR]

China has the largest reactive nitrogen deposition worldwide. Understanding the change of nitrogen deposition and its socioeconomic drivers in China is crucial for the function and sustainability of regional and global ecosystems. Here we presented satellite-derived nitrogen deposition constrained with the national ground-based measurements over China. We found that oxidized nitrogen deposition peaked at 7.0 kg N ha−1 in 2012, then decreased to 6.2 kg N ha−1 in 2017. In contrast, reduced nitrogen deposition increased continuously, and reached 12.6 kg N ha−1 in 2017. The Chinese Clean Air Act is responsible for the reduction of oxidized nitrogen emissions, while there is no current effective control policy for ammonia emissions in place resulting in reduced nitrogen deposition reaching levels of approximately twice that of oxidized nitrogen in 2017. The ratio of reduced to oxidized nitrogen deposition decreased from 1.30 in 2008 to 1.08 in 2011, while this ratio began to increase from 1.08 in 2011 to 1.56 in 2017. This suggests reduced nitrogen deposition would become more important in the air quality and their ecological consequences in the future. The total nitrogen deposition in China was about 3–4 times that in the US and Europe. The policy of controlling nitrogen pollution is urgent, especially for reducing ammonia emissions, while ensuring the sustainable production of agriculture and maintaining food security. Image 1 • Methods were developed to obtain N deposition using satellite observations. • The ratio of reduced to oxidized N deposition in China increased since 2011. • N deposition in China was about 3–4 times that in the US and Europe. [ABSTRACT FROM AUTHOR]

• DNDC has the potential to assess the effect of N deposition on rice ecosystems. • The N deposition increased 0.6% national rice production. • 1.8% N deposition is used for rice growth; the remaining is in the surroundings. • The recommended fertilizer application can be basically for rice growth. The influence of enhanced nitrogen (N) deposition on rice ecosystems was evaluated across China using the DNDC (DeNitrification-DeComposition) model. The simulated grain, leaf, stem, root and total biomass had good consistency with the ground measurements in controlled experiments, with absolute relative errors of 4.5, 7.3, 7.7, 7.3 and 4.7%, respectively. On a national scale, the absolute relative errors of the measured and simulated early, late and single cropping rice was 2.2, 6.6 and 5.9%, respectively. The N deposition increased rice yield accounted for 0.6% of the national rice production. Under the current fertilization conditions, The N deposition was barely absorbed and utilized for rice growth (only accounted for 1.8% of the N deposition). About 57.7% of the N deposition remained in the soil as inorganic and organic forms, and the other 40.5% of the N deposition was emitted to the environment, as nitrogen oxide emissions (24.8%), ammonia volatilization (5.6%), leaching and runoff (10.1%). These results will provide scientific bases for recommending fertilizer rates and enacting policies to protect the eco-environment. [ABSTRACT FROM AUTHOR]