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AbstractNitrogen (N) and harvest time are important factors in determining rice production potential. Elucidating reasonable N application rates and the relationship between N rate and harvesting time is necessary to maximize rice yield and efficiency. Two field trials were conducted with four N levels (0, 82.5, 165, and 247.5 kg N ha−1) and five N levels (0, 90, 180, 270, and 360 kg N ha−1) in Shayang (SY) and Wuxue (WX) counties, Hubei Province, respectively. Each was harvested at two time points (T1 and T2), at and after maturation, to investigate grain yield and N use efficiencies of rice. The results showed that the applied N and appropriately adjusted harvesting time significantly increased the grain yield, and compared with zero-N, the N additions increased rice yield by 3.7–26.9% and 8.4–22.5% for the SY and WX sites, respectively. However, with the increase of N application rate, the N use efficiency first increased and then decreased. Effects of harvest time on grain yield and N use efficiency vary with N application rates. At higher N levels, the appropriate delay in harvest time (T2) resulted in an increase in the 1000-grains weight and the rate at which grains were filled. Consequently, this led to an overall increase in grain yield. However, with zero or low N application rates, delayed harvest (T2) resulted in grain abscission, which decreased grain yield. In summary, applying N appropriately significantly increased the rice yield, and adjusting the harvesting time according to the N application rate further increased grain yield and N use efficiency. [ABSTRACT FROM AUTHOR]

• Yield improvement with N was limited under low K levels. • Synergy of N and K increased yield by improving filled spikelet per unit area. • There were significant interactions of N and K on N metabolism activities of root and leaf. • Combined application of N and K significantly improved N uptakes and N use efficiency. Elucidating the mechanism underlying the interactive effects between nitrogen (N) and potassium (K) on rice yield is requisite to further study soil K deficiency in paddy ecosystems in Southeast Asia. Field studies with combined application of four N rates (0, 90, 180, and 270 kg N ha−1) and four K rates (0, 60, 120, and 180 kg K 2 O ha−1) in 2013, 2014 and 2016 and a hydroponic experiment in 2017 were conducted to investigate their effects on rice yield as well as N use efficiencies (NRE). Co-application of N and K significantly promoted the growth and development of root and leaf, grain yield and NRE of rice. The application of N combined with zero-K increased the grain yield by 10.6–22.0%, 24.0–37.4% and 12.7–21.9% in 2013, 2014 and 2016 respectively. Similarly, leaf area index (LAI) increased by 5.9–17.9%, 8.1–19.7% and 27.9–62.7% across the three years. An increase of grain yield by 15.5–32.5%, 26.6–46.1% and 11.5–23.0% and LAI by 22.6–31.5%, 34.2–42.8% and 26.7–79.1% across the three years was recorded due to combined application of N and K. Application of higher doses of K resulted in relatively higher N uptake and N NRE. Application of K improved the N uptake and NRE by 5.6–10.0%, 7.4–16.2%, 10.9–26.4% and 12.0–22.3%, 16.9–36.4%, 20.6–43.3 % respectively across the three years. To deduct the effect of soil N and K background value, we also did a hydroponic experiment to do some physical test. In the hydroponic experiment, the leaf and root glutamine synthetase (GS), glutamate synthetase (GOGAT) and glutamate dehydrogenase (GDH) activities were significantly improved with the improvement of N and K. The leaf and root GS, GOGAT and GDH activity of the treatment with sufficient N and K (+N + K) was significantly increased by 402.3%, 332.5%, 265.2% and 200.0%, 410.4%, 239.0% respectively compared with that of the treatment with deficient N and K (-N-K). These results indicated that the combined use of N and K could further improve the grain yield as well as NRE in rice production. [ABSTRACT FROM AUTHOR]

Highlights • Significant interaction effects existed between nitrogen rate and plant density. • Individual plants and population can be coordinated through N rate and plant density. • A plant density of 24–27 × 104 hills ha−1 with application of 165 kg N ha−1 significantly increased the grain yield. • Increased density could offset adverse effect of reducing nitrogen rate on yield. Abstract With the development of hybrid rice cultivars and mechanized planting technologies, it is hypothesized that the grain yield and nitrogen (N) use efficiency of mechanically transplanted rice could be further improved by harnessing the compensatory effects from the N rate and plant density on individual plants and populations. We evaluated the interactive effects of the N rate and plant density on the grain yield and N use efficiency of rice in two field experiments during 2014 and 2015. The results indicated the significant interaction between the N rate and the plant density on the grain yield. The application of 165 kg N ha−1 along with a plant density of 24–27 × 104 hills ha−1 significantly increased the grain yield. A correlation analysis showed that the spikelet per hectare had a strong correlation with the grain yield. With an increase in the plant density, the N recover efficiency (NRE) was increased by 12.7–40.0% in 2014. However, the higher plant density, as in 33 × 104 hills ha−1 (D33), decreased the NRE by 5.8% in 2015. The N rate and plant density also significantly influenced the leaf area index (LAI) and the interception of photosynthetically active radiation (IPAR), the two important factors for grain yield formation. The LAI values of the 82.5 kg N ha−1 (N82.5), 165 kg N ha−1 (N165) and 82.5 kg N ha−1 (N247.5) treatments was increased by 26.3%, 101.4% and 116.0%, respectively, compared with that of the 0 kg N ha−1 (N0) treatment. Similarly, the LAI of the 21 × 104 hills ha−1 (D21), 27 × 104 hills ha−1 (D27) and D33 was increased by 17.8%, 20.5% and decreased by 12.8%, respectively, compared with that of 15 × 104 hills ha−1 (D15). The highest LAI was recorded when N247.5 was combined with D27. The N application increased the photosynthetically active radiation (IPAR) by 4.1%, 12.4% and 14.4%, respectively, compared with that of the N0 treatment. However, the IPAR increased by 0.8%, 2.6% and 3.3%, respectively, in comparison with that of D15. A moderate increase in the IPAR significantly increased the grain yield, while too much IPAR decreased the photosynthetically active radiation use efficiency (PARUE), leading to the lower synthesis of photosynthetic products. Hence, various combinations of the N rate and plant density are practicable for reducing the N inputs in addition to improving the grain yield and NRE. [ABSTRACT FROM AUTHOR]

Abstract: Deformations and stresses are produced not by mechanical forces alone, but by temperature variation as well. The thermal stress caused by heat is likely to be the decisive factor. Thus it is necessary to consider the thermal effect at a certain temperature range for analysis and design of a precision compliant mechanism. Firstly, the generalized equations of motion of the compliant mechanism considering the thermal effects are developed based on the finite element method. Secondly, the right-circular flexure hinge is treated as a three nodes element, in which there are three degrees of freedom at each node. The closed-form solutions of the element stiffness and mass matrices for the flexure hinge are obtained. Finally, analytical and experimental studies are carried out to an ultra-precision positioning stage. The analytical results have a good match with that of the experimental results, which indicate that the analytical method developed in this study is valid. The thermal effect has a strong impact on the performances of the precision positioning stage, and it is essential to consider the thermal effect when analysis and design a compliant mechanism system. [Copyright &y& Elsevier]

Abstract: Deformation and stresses are produced not by mechanical forces alone, but by temperature variation as well. The additional stresses of a flexible mechanism caused by the temperature change should not be ignored. The generalized equations of motion for flexible linkage mechanisms, in which the thermal effects are taken into account, are developed by utilizing the virtual work method and the finite element theory in this paper. Since the determination of thermal stresses plays an important role in the design of mechanisms operating at elevated temperatures, the stress–strain relationship should include the effects of temperature. Based on the closed-form numerical algorithm, the equations are solved and the recursive scheme is proved to be efficient and converged in a few iterations for the cases examined. The Runge–Kutta method is also applied to study the transient response of the temperature change. Numerical solution results show that a small change of temperature will cause a significant change of the stresses of a flexible mechanism. The effects of temperature change should not be ignored when analyzing the dynamic performance of flexible mechanisms. [Copyright &y& Elsevier]

Background: Nitrogen (N) and potassium (K) are two important mineral nutrients in regulating leaf photosynthesis. Studying the interactive effects of N and K on regulating N allocation and photosynthesis (Pn) of rice leaves will be of great significance for further increasing leaf Pn, photosynthetic N use efficiency (PNUE) and grain yield. We measured the gas exchange of rice leaves in a field experiment and tested different kinds of leaf N based on N morphology and function, and calculated the interactive effects of N and K on N allocation and the PNUE. Results: Compared with N0 (0 kg N ha− 1) and K0 (0 kg K2O ha− 1) treatments, the Pn was increased by 17.1 and 12.2% with the supply of N and K. Compared with N0K0 (0 kg N and 0 kg K2O ha− 1), N0K120 (0 kg N and 120 kg K2O ha− 1) and N0K180 (0 kg N and 180 kg K2O ha− 1), N supply increased the absolute content of photosynthetic N (Npsn) by 15.1, 15.5 and 10.5% on average, and the storage N (Nstore) was increased by 32.7, 64.9 and 72.7% on average. The relative content of Npsn was decreased by 5.6, 12.1 and 14.5%, while that of Nstore was increased by 8.7, 27.8 and 33.8%. Supply of K promoted the transformation of Nstore to Npsn despite the leaf N content (Na) was indeed decreased. Compared with N0K0, N180K0 (180 kg N and 0 kg K2O ha− 1) and N270K0 (270 kg N and 0 kg K2O ha− 1), K supply increased the relative content of Npsn by 17.7, 8.8 and 7.3%, and decreased the relative content of Nstore by 24.2, 11.4 and 8.7% respectively. Conclusions: This study indicated the mechanism that K supply decreased the Na but increased the Npsn content and then increased leaf Pn and PNUE from a new viewpoint of leaf N allocation. The supply of K promoted the transformation of Nstore to Npsn and increased the PNUE. The decreased Nstore mainly resulted from the decrease of non-protein N. Combined use of N and K could optimize leaf N allocation and maintain a high leaf Npsn content and PNUE. [ABSTRACT FROM AUTHOR]

The mixture of controlled-release urea (CRU) and normal urea (MCU) applied as one-time basal fertilizer is a convenient and effective alternative to traditional split-nitrogen (N) fertilization, can ensure a sufficient late-season N supply to increase maize yield. However, the effects of MCU ratios on maize root development, post-silking growth, and grain-filling process remain poorly understood. In this study, 3-year field experiments were conducted on sandy and clay soils in Northeast China, to evaluate maize yield responses to different MCU ratios (from 0% to 60% at 15% intervals). Four key treatments, i.e., N omission (N0), MCU0%, MCU30%, and MCU60%, were then selected to investigate root traits, post-silking plant growth and N uptake, grain-filling parameters, and their relationships with grain yields. Across different soils and years, grain yields showed a parabolic curve with increasing MCU ratios, with the highest yields obtained in MCU30%. On average, MCU30% increased grain yield by 22.3% and 11.7% on sandy and clay soils, respectively, relative to MCU0%. The appropriate early-N supply in MCU30% promoted root growth by allocating more dry matter (DM) to roots, while increasing total root length by producing more and longer crown roots, as well as higher lateral root length. The well-developed roots in MCU30% increased post-silking plant N uptake under sufficient late-N supply, thereby delayed leaf senescence and improved DM production for grain-filling, ultimately increased kernel weight and grain yield. Compared to MCU30%, MCU60% showed similar growth and yield performances on clay soil. In contrast, MCU60% performed notably worse on sandy soil due to limited CRU-N release at early period under inherently lower soil moisture and fertility levels. Our measurements and correlation analysis support the conclusion that MCU30% effectively sustain leaf longevity and increase post-silking DM by optimizing root growth and morphology under an optimal N supply pattern during maize growing season, thus improving grain-filling and final yield. The results advance our understanding of how MCU method affects maize post-silking growth and yield formation, providing important insights for optimizing crop N management by regulating root development, especially on lower fertility soils. • Higher yield in MCU30% was driven by increased post-silking DM and improved grain-filling rate. • Compared to MCU30%, maize plants in MCU60% performed equally on clay soil, but worse on sandy soil. • MCU30% increased root length by producing more, longer crown roots while elongating lateral roots. • The well-developed root enhanced post-silking N uptake and reduced vegetative-N mobilization. [ABSTRACT FROM AUTHOR]

To understand the physiological mechanisms involved in xanthine metabolism during salt priming for improving low-temperature tolerance, salt priming (SP), xanthine dehydrogenase inhibitor (XOI), exogenous allantoin (EA), and back-supplemented EA (XOI + EA) treatments were given and the low-temperature tolerance of sugar beet was tested. Under low-temperature stress, salt priming promoted the growth of sugar beet leaves and increased the maximum quantum efficiency of PS II (Fv/Fm). However, during salt priming, either XOI or EA treatment alone increased the content of reactive oxygen species (ROS), such as superoxide anion and hydrogen peroxide, in the leaves under low-temperature stress. XOI treatment increased allantoinase activity with its gene (BvallB) expression under low-temperature stress. Compared to the XOI treatment, the EA treatment alone and the XOI + EA treatment increased the activities of antioxidant enzymes. At low temperatures, the sucrose content and the activity of key carbohydrate enzymes (AGPase, Cylnv, and FK) were significantly reduced by XOI compared to the changes under salt priming. XOI also stimulated the expression of protein phosphatase 2C and sucrose non-fermenting1-related protein kinase (BvSNRK2). The results of a correlation network analysis showed that BvallB was positively correlated with malondialdehyde, D-Fructose-6-phosphate, and D-Glucose-6-phosphate, and negatively correlated with BvPOX42 , BvSNRK2 , dehydroascorbate reductase, and catalase. These results suggested that salt-induced xanthine metabolism modulated ROS metabolism, photosynthetic carbon assimilation, and carbohydrate metabolism, thus enhancing low-temperature tolerance in sugar beet. Additionally, xanthine and allantoin were found to play key roles in plant stress resistance. • Salt priming improves low temperature tolerance by xanthine metabolism. • Xanthine metabolism induced ROS and ABA signaling under low temperature stress. • Salt-induced xanthine metabolism regulates carbohydrate and nitrogen metabolite levels. • The effect of xanthine on low temperature tolerance was not completely replaced by allantoin. [ABSTRACT FROM AUTHOR]