Herein, greenhouse experiments were designed to reveal
the role
of nitrogen-doped carbon dots (N-CDs) in enhancing maize drought tolerance.
Two humidity conditions were created: adequate watering (soil moisture,
75%) and drought stress (soil moisture, 35%). Corn seedlings were
harvested after spraying the N-CD solution (5 mg·L–1) on maize leaves for 5 days. The results indicated that foliar application
of N-CDs increased the net photosynthesis rate (28.6%) of maize, and
the fresh and dry weights of roots and shoots increased by 224.5,
360.0, 230.8, and 63.3% under drought stress, respectively. N-CDs
showed high reactive oxygen species (ROS)-scavenging activity, resulting
in enhanced superoxide dismutase activity (26.7%) and reduced malondialdehyde
enzyme activity (18.9%). Besides, N-CDs could be used as light-harvesting
materials to improve the light utilization efficiency, upregulate psbA gene expression (81.7-fold), and promote fast synthesis
of the D1 protein, which could repair photosystem II under drought
stress. Therefore, foliar-sprayed N-CDs could improve photosynthesis
through multiple pathways under drought stress: light harvesting,
photoprotection, and light repairing. Then, N-CD exposure reduced
the corn yield loss under drought by nearly 30% compared with those
of the control groups in a full life cycle study. Therefore, this
study found for the first time that N-CD-enabled nanoagriculture could
ensure crop growth and yield under drought stress, which would be
important for global crop cultivation and a promising alternative
to deal with the global climate change.
SUMMARY
Ten years (2008–2017) of continuous measurements from 40 electric and 36 magnetic sites collected in China for earthquake prediction research represent a unique EM array data set, which can be used to explore the challenging problem of very long-period MT data acquisition, to study source characteristics, and ultimately to learn about electric conductivity of Earth's mantle beneath East Asia. In this study, we focus on basic noise and signal characteristics in this data set, and on estimation of the MT impedances. We report a novel method to fix the numerous timing errors in the electric data caused by limitations in instrumentation and data acquisition. Then, we use multivariate array analysis to study signal and noise characteristics for periods from 250 s to 3.5 × 105 s (4 d). Signal-to-noise ratios (SNR) are above 30 dB in magnetic fields for the first two dominant modes, which correspond roughly to N–S and E–W quasi-uniform sources. SNRs for electric fields are lower, especially at very long periods, and especially for N–S electric components. There are clear peaks in signal strength at the daily variation (DV) periods, but source structure becomes more complex, and significant biases in MT impedance tensors are more often seen at these periods. The MT quasi-impedance, computed using the closest magnetic site for each electric site, is estimated by robust remote reference techniques (RR) and by using linear combinations of PCA (principal component analysis) modes that best approximate a uniform or plane-wave source (PW). For almost all sites, smooth impedances are obtained for periods up to 104 s using either approach. This result, and a more detailed analysis of impedances estimates obtained with shorter-wavelength (gradient) sources extracted from the array, suggests that source effects in MT impedances are minimal for periods below 104 s, at least at the latitude of China. At many sites curves can be extended a decade further, to 105 s, but here results are improved by carefully omitting DV bands and (at a few sites) with the PW approach. For longer periods (>105 s) SNR is very low in electric field channels at most sites, making estimation challenging. However, at a few sites, even some near big cities (e.g. including a site within 40 km of Beijing) smooth impedance components related to N–S magnetic sources (Zxx and Zyx) are obtained to periods to 3.5 × 105 s (4 d). This result suggests that cultural noise may not be the main impediment to collecting very long-period MT data.
Nanoenable agriculture has been rapidly developed. However, foliar application of nanofertilizers results in them dripping off the leaves, which would effectively limit their bioavailability. Herein, a nanocarrier method of using nanoporous SiO 2 (NanoSi) was found to enhance the adhesion of carbon dots (CDs) on crop leaf surfaces. Foliar application of NanoSi-CDs (10 mg•L −1 ) could significantly increase the net photosynthetic rate (Pn; 110.0−140.0%), fresh weight (327.1% in roots and 247.2% in shoots), and dry weight (212.0% in roots and 118.5% in shoots) of maize. Moreover, NanoSi-CDs showed a long-term promotion effect. Specifically, the Pn remained significantly increased on day 20 after spraying with NanoSi-CDs, whereas the CDs had no such effect at the same time. Furthermore, the rainfall simulation experiments demonstrated that the water resistances of NanoSi-CDs and CDs were 2.5 and 1.5 cm, respectively. Compared with the control, NanoSi-CDs could increase the Pn by 22.3% on the 20th day after rainfall. Collectively, NanoSi nanocarriers can be a promising method to improve the bioavailability of engineering nanomaterials in sustainable agriculture.
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