Satellite observations show that leaf area index (LAI) has increased globally since 1981, but the impact of this vegetation structural change on the global terrestrial carbon cycle has not been ...systematically evaluated. Through process-based diagnostic ecosystem modeling, we find that the increase in LAI alone was responsible for 12.4% of the accumulated terrestrial carbon sink (95 ± 5 Pg C) from 1981 to 2016, whereas other drivers of CO
fertilization, nitrogen deposition, and climate change (temperature, radiation, and precipitation) contributed to 47.0%, 1.1%, and -28.6% of the sink, respectively. The legacy effects of past changes in these drivers prior to 1981 are responsible for the remaining 65.5% of the accumulated sink from 1981 to 2016. These results refine the attribution of the land sink to the various drivers and would help constrain prognostic models that often have large uncertainties in simulating changes in vegetation and their impacts on the global carbon cycle.
Urban air quality in China has been declining substantially in recent years due to severe haze episodes. The reduction of sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions since 2013 does not ...yet appear to yield substantial benefits for haze mitigation. As the reductions of those key precursors to secondary aerosol formation appears not to sufficient, other crucial factors need to be considered for the design of effective air pollution control strategies. Here we argue that ammonia (NH3) plays a - so far - underestimated role in the formation of secondary inorganic aerosols, a main component of urban fine particulate matter (PM2.5) concentrations in China. By analyzing in situ concentration data observed in major cities alongside gridded emission data obtained from remote sensing and inventories, we find that emissions of NH3 have a more robust association with the spatiotemporal variation of PM2.5 levels than emissions of SO2 and NOx. As a consequence, we argue that urban PM2.5 pollution in China in many locations is substantially affected by NH3 emissions. We highlight that more efforts should be directed to the reduction of NH3 emissions that help mitigate PM2.5 pollution more efficiently than other PM2.5 precursors. Such efforts will yield substantial co-benefits by improving nitrogen use efficiency in farming systems. As a consequence, such integrated strategies would not only improve urban air quality, but also contribute to China's food-security goals, prevent further biodiversity loss, reduce greenhouse gas emissions and lead to economic savings.
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•NH3 plays an underestimated role in the formation of PM2.5 in China.•More efforts should be directed to reducing NH3 emissions to mitigate PM2.5 pollution.•Reducing NH3 emissions also contributes to China's food-security goals.•Results of panel model analysis on in situ PM2.5 data agree well with global observation.
PM2.5 pollution in China is substantially affected by NH3 emissions and more efforts should be directed to reducing NH3 emissions to mitigate PM2.5 pollution more efficiently.
Drought has been one of the most important limiting factors for crop production, which deleteriously affects food security worldwide. The main objective of the present study was to quantitatively ...assess the effect of drought on the agronomic traits (e.g., plant height, biomass, yield, and yield components) of rice and wheat in combination with several moderators (e.g., drought stress intensity, rooting environment, and growth stage) using a meta-analysis study. The database was created from 55 published studies on rice and 60 published studies on wheat. The results demonstrated that drought decreased the agronomic traits differently between rice and wheat among varying growth stages. Wheat and rice yields decreased by 27.5% and 25.4%, respectively. Wheat grown in pots showed greater decreases in agronomic traits than those grown in the field. Rice showed opposite growing patterns when compared to wheat in rooting environments. The effect of drought on rice increased with plant growth and drought had larger detrimental influences during the reproductive phase (e.g., blooming stage, filling stage, and maturity). However, an exception was found in wheat, which had similar decreased performance during the complete growth cycle. Based on these results, future droughts could produce lower yields of rice and wheat when compared to the current drought.
Chemically modified DNA has been widely developed to fabricate various nucleic acid nanostructures for biomedical applications. Herein, we report a facile strategy for construction of branched ...antisense DNA and small interfering RNA (siRNA) co‐assembled nanoplatform for combined gene silencing in vitro and in vivo. In our design, the branched antisense can efficiently capture siRNA with 3′ overhangs through DNA–RNA hybridization. After being equipped with an active targeting group and an endosomal escape peptide by host–guest interaction, the tailored nucleic acid nanostructure functions efficiently as both delivery carrier and therapeutic cargo, which is released by endogenous RNase H digestion. The multifunctional nucleic acid nanosystem elicits an efficient inhibition of tumor growth based on the combined gene silencing of the tumor‐associated gene polo‐like kinase 1 (PLK1). This biocompatible nucleic acid nanoplatform presents a new strategy for the development of gene therapy.
A nucleic acid nanoplatform‐based co‐delivery system containing a pair of functionalized branched antisenses and siRNA with 3′ overhangs was constructed through controlled co‐assembly for combined gene silencing and tumor therapy in vivo.
In contrast to the well‐studied asymmetric catalyzed synthesis of tetrahydroquinolines, the asymmetric methodologies toward 3,4‐dihydroquinolin‐2‐ones are quite rare. Herein, the first asymmetric ...cascade reaction is reported between ethynyl benzoxazinanones and mixed‐anhydrides generated from aryl acetic acids and pivaloyl chloride, based on synergistic catalysis. This allowed the formation of attractive 3,4‐dihydroquinolin‐2‐ones bearing two vicinal chiral centers at C3 and C4 in high yields with excellent diastereo‐ and enantioselectivities. A plausible chiral induction model for this reaction was proposed. The utility of this methodology was exemplified by further elaboration of the cyclization products by removal of the N‐protecting groups.
Synergistic catalysis: An asymmetric cascade reaction synergistically catalyzed by a Cu–Pybox complex and a benzotetramisole‐type Lewis‐base catalyst is developed, affording 3,4‐dihydroquinolin‐2‐ones bearing two vicinal chiral centers in high yields with excellent stereoselectivities.
DNA nanotechnology has been employed in the construction of self-assembled nano-biomaterials with uniform size and shape for various biological applications, such as bioimaging, diagnosis, or ...therapeutics. Herein, recent successful efforts to utilize multifunctional DNA origami nanoplatforms as drug-delivery vehicles are reviewed. Diagnostic and therapeutic strategies based on gold nanorods, chemotherapeutic drugs, cytosine-phosphate-guanine, functional proteins, gene drugs, and their combinations for optoacoustic imaging, photothermal therapy, chemotherapy, immunological therapy, gene therapy, and coagulation-based therapy are summarized. The challenges and opportunities for DNA-based nanocarriers for biological applications are also discussed.
Atmospheric nitrogen (N) deposition (Ndep), an important component of the global N cycle, has increased sharply in recent decades in China. Although there were already some studies on Ndep on a ...national scale, there were some gaps on the magnitude and the spatial patterns of Ndep. In this study, a national-scale Ndep pattern was constructed based on 139 published papers from 2003 to 2014 and the effects of precipitation (P), energy consumption (E) and N fertilizer use (FN) on spatial patterns of Ndep were analyzed. The wet deposition flux of NH4(+)-N, NO3(-)-N and total Ndep was 6.83, 5.35 and 12.18 kg ha(-1) a(-1), respectively. Ndep exhibited a decreasing gradient from southeast to northwest of China. Through accuracy assessment of the spatial Ndep distribution and comparisons with other studies, the spatial Ndep distribution by Lu and Tian and this study both gained high accuracy. A strong exponential function was found between P and Ndep, FN and Ndep and E and Ndep, and P and FN had higher contribution than E on the spatial variation of Ndep. Fossil fuel combustion was the main contributor for NO3(-)-N (86.0%) and biomass burning contributed 5.4% on the deposition of NO3(-)-N. The ion of NH4(+) was mainly from agricultural activities (85.9%) and fossil fuel combustion (6.0%). Overall, Ndep in China might be considerably affected by the high emissions of NOx and NH3 from fossil fuel combustion and agricultural activities.
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•Vcmax25, Na and Chla of winter wheat and paddy rice exhibited distinguishable seasonality.•The seasonality of leaf Na and Chla were inconsistent with that of Vcmax25.•Differentiating ...pre- and post-flowering stages significantly improved the estimation of Vcmax25 from Chla.
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 (Vcmax25) is the key determinant of photosynthetic capacity and can be mapped according to leaf nitrogen (N) and chlorophyll (Chl) contents. However, whether relationships of Vcmax25 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 Vcmax25, the maximum electron transport rate at 25 °C (Jmax25), N, and Chl measured every 7 to 10 days from the tillering stage to maturity. Results showed that Vcmax25 and Jmax25 varied significantly during the growing seasons and maximized at flowering stages. For both winter wheat and paddy rice, Chla (Chl content at the area unit) showed significantly different relationships with Vcmax25 pre- and post- flowering while Na (N content at the area unit) did not. When different empirical models were used for pre- flowering and post- flowering stages, Vcmax25 estimated from Chla was closer to observations (R2 = 0.875, RMSE = 9.479 µmol m−2 s−1) than that estimated from Na (R2 = 0.565, RMSE = 17.718 µmol m−2 s−1). The findings in this study imply that the combination of remotely sensed leaf Chla content and phenology would improve the mapping of Vcmax25 for crops at regional and even global scales.
Abstract
The maximum rate of carboxylation (Vcmax), a key parameter indicating photosynthetic capacity, is commonly fixed as a constant by vegetation types and/or varies according to empirical ...scaling functions in Earth system models (ESMs). As such, the setting of Vcmax results in uncertainties of estimated carbon assimilation. It is known that the coupling between leaf chlorophyll and Rubisco (ribulose-1,5-biphosphate carboxylase-oxygenase) contents can be applied to estimate Vcmax. However, how this coupling is affected by environmental changes and varies among plant functional types (PFTs) has not been well investigated yet. The effect of varying coupling between chlorophyll and Rubisco contents on the estimation of Vcmax is still not clear. In this study, we compiled data from 76 previous studies to investigate the coupling between Chlorophyll (Chl) and Rubisco (Rub), in different PFTs and under different environmental conditions. We also assessed the ability of a Rub-based semi-mechanistic model to estimate Vcmax normalized to 25 °C (Vcmax
25
) based on the Rub–Chl relationship. Our results revealed strong, linear Rub-Chl relationships for different PFTs (
R
2
= 0.73, 0.67, 0.54 and 0.72 for forest, crop, grass and shrub, and C4 plants, respectively). The Rub–Chl slope of natural C3 PFTs was consistent and significantly different from those of crops and C4 plants. A meta-analysis indicated that reduced light intensity, elevated CO
2
, and nitrogen addition strongly altered Rub/Chl. A semi-mechanistic model based on PFT-specific Rub–Chl relationships was able to estimate Vcmax
25
with high confidence. Our findings have important implications for improving global carbon cycle modeling by ESMs through the improved parameterization of Vcmax
25
using remotely sensed Chl content.
Urban forests have the potential to sink atmospheric CO2. With the improvement of coverage of vegetation in urban environments, more attention has been paid to the carbon sequestration potential of ...the urban forest. However, the high fragmentation of urban forests makes it difficult to evaluate their carbon budget on a regional scale. In this study, the GPP-NIRv relationship model was employed to estimate GPP in Suzhou by MODIS, Landsat-8 and Sentinel-2 remote sensing data, and to further explore what kind of remote images can figure out the spatial-temporal pattern of GPP in urban forests. We found that the total GPP of the terrestrial ecosystem in Suzhou reached 8.43, 8.48, and 9.30 Tg C yr-1 for MODIS, Landsat-8, and Sentinel-2, respectively. Monthly changes of GPP were able to be derived by MODIS and Sentinel-2, with two peaks in April and July. According to Sentinel-2, urban forests accounted for the majority of total GPP, with an average of about 44.63%, which was larger than the results from GPP products with coarser resolutions. Additionally, it is clear from the high-resolution images that the decline of GPP in May was due to human activities such as the rotation of wheat and rice crops and the pruning of urban forests. Our results improve the understanding of the contribution of the urban forest to the carbon budget and highlight the importance of high-resolution remote sensing images for estimating urban carbon assimilation.
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