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Nanoparticles have been widely used in agriculture, but few studies have reported the effect of silicon dioxide nanoparticles (SiO2NPs) application on rice growth. This study is the first to investigate the effect of SiO2NPs on rice under the interaction of light and nitrogen. This study aimed to investigate the effects of SiO2NPs on the growth, antioxidant response, and nitrogen metabolism of rice seedlings under different light and nitrogen conditions. Two fragrant rice cultivars, Meixiangzhan 2 and 19 Xiang, were grown under four SiO2NPs concentrations (SiO2NPs at 0 mg L−1, 50 mg L−1, 100 mg L−1, and 500 mg L−1) and four light and nitrogen levels. The results showed that the application of SiO2NPs significantly affected root and shoot length, total fresh weight, dry weight, and some physiological parameters. The application of SiO2NPs resulted in changes in growth and physiological parameters, which varied with different light and nitrogen levels. The total dry weight significantly increased after the application of SiO2NPs at 50 mg L-1 under normal light and nitrogen conditions by 28.95% and 15.81% for Meixiangzhan 2 and 19 Xiang, respectively. In addition, the application of SiO2NPs modified the superoxide dismutase activity, nitrate reductase activity, soluble protein content, and hydrogen peroxide content under different light and nitrogen conditions. The correlation between the investigated parameters under the application of SiO2NPs at different light and nitrogen levels was assessed. Overall, this study suggested that the application of SiO2NPs alleviates light stress and nitrogen deficiency stress by regulating soluble protein content, nitrite reductase activity and the antioxidant reaction system, thus promoting rice growth. This study provides theoretical support for the application of nano-fertilizer technology and SiO2NPs to alleviate low light stress in rice. [ABSTRACT FROM AUTHOR]

Rice yield and nitrogen use efficiency will be affected by different nitrogen (N) application rate. However, previous studies were limited on different nitrogen fertilization rate under deep placement. In order to study the effect of different nitrogen fertilization rate on grain yield, nitrogen use efficiency and its physiological traits under deep placement in mechanical pot-seedling transplanting rice, the field experiment was conducted with two rice varieties Meixiangzhan-2 (MXZ-2) and Y-liangyou 1378 (YLY-1378) from July to November of 2021. And a radioisotope N15 tracer experiment was conducted. There were five fertilizer treatments used as basal fertilizer: all N-fertilizer were deeply applied with application rates of 150 kg ha−1 by machine (T1); all N-fertilizer were deeply applied at a 10% reduction (135 kg ha−1) by machine (T2); all N-fertilizer were deeply applied at a 15% reduction (127.5 kg ha−1) by machine (T3); all N-fertilizer were manually surface broadcast with application rates of 150 kg ha−1 (T4) and blank treatment was designed without N-fertilizer (T0). The results showed that 31.20 and 26.42% higher grain yield, 63.09 and 58.52% higher nitrogen recovery efficiency, and 121.58 and 121.04% higher nitrogen agronomic efficiency in T1 and T2 than T4 for MXZ-2 and YLY-1378, respectively. Nitrogen derived from fertilizer in T1 and T2 was enhanced by 43.72 and 26.96% than T4 for MXZ-2, 49.54 and 32.97% for YLY-1378, respectively. Nitrogen residual rate of T1 and T2 was increased by 26.59 and 46.36% than T4 for MXZ-2, 8.62 and 20.24% for YLY-1378, respectively. The increase in NUE was due to the increase in nitrogen metabolism enzyme activity including nitrate reductase (NR), glutamine synthetase (GS) and glutamate synhthase (GOGAT) promoted by deep N-fertilization. The total chlorophyll content, leaf area index (LAI) and total aboveground biomass (TAB) under T1 and T2 were also enhanced compared with T4. There was also no significant difference on grain yield or NUE between T1 and T2. Hence, basal nitrogen fertilizer with 135 kg N ha− 1 under deep placement is an efficient method to increase grain yield and nitrogen use efficiency in mechanical pot-seedling transplanting rice in South China. [ABSTRACT FROM AUTHOR]

Direct seeding of rice is an efficient and labor-saving planting method. Deep sowing during direct seeding may benefit rice, although it will influence seed germination and seedling establishment. In a pot experiment, thirty rice varieties were grown under two different sowing depths (0 cm and 2.5 cm) under dry-seeded conditions, and the germination rate and seedling establishment parameters were measured. The results showed that the seed germination rate and seedling emergence rate were higher than 90% at the 0 cm sowing depth, while under deep sowing, the seed germination rate, and seedling emergence rate were 77.70% and 50.97%, respectively. Rice varieties with seedling establishment rates > 80% and better growth under deep-sowing conditions were identified. In addition, variety, sowing depth, and their interaction significantly affected seedling establishment parameters. Parameters, such as the seed germination rate, seedling emergence rate, prophyll leaf length, first leaf sheath length, and first leaf length, which are highly related to sowing depth, were analyzed. The seedling rate was significantly positively associated with the seed germination rate, mesocotyl length, root length, root fresh weight, shoot fresh weight, and total fresh weight under deep sowing. An approach for screening rice varieties with tolerance to deep sowing is proposed. [ABSTRACT FROM AUTHOR]

Different fertilization methods will affect rice yield and its growth. To address the influence of different fertilization methods on yield, photosynthetic intensity, and nitrogen synthetase enzymatic activities for hill direct-seeded rice, the field trials were conducted using two different rice varieties Yuxiangyouzhan and Wufengyou 615 in 2018 and 2019. There were four fertilizer application treatments at the rate of 150 kg N ha−1 in hill direct-seeded rice: All the fertilizer deep application as a disposable basal fertilizer by machine (T1); deep application of mechanized decrement fertilizers, i.e. 50% of all fertilizers into 10 cm depth of soil as basal by machine, whilst 25% of fertilizers at tillering stage and 25% of the fertilizer in the panicle initiation (PI) stage were artificially sown on the soil surface (T2), respectively; farmers' manually traditional surface broadcast, i.e. 40% of the fertilizers as the basal fertilizer, whilst 30% of fertilizers was applied at tillering and PI stage (T3), respectively, and the control treatment is no fertilization (T0). The result showed that grain yield of Yuxiangyouzhan and Wufengyou 615 for T2 was increased by 25.79 and 11.98%, compared with T3, respectively. The rate of photosynthetic, water use efficiency and stomatal conductance for T2 treatment was 35.86, 27.32, and 56.87% higher than that for T0 treatment, respectively. It was also found that T2 had the highest chlorophyll and carotenoids during the heading stage (HS). We also observed that glutamine systhetase (GS) and glutamate synhthase (GOGAT) activities of T2 were higher than T3 at mid-tillering stage for both rice varieties, respectively. Among all treatments at the HS, Wufengyou 615 had the largest leaf area index and total above-ground biomass. Hence, the present study revealed that 50% of total amount of fertilization as basal fertilization deep placement with the rest of fertilization as topdressing more benefited the rice growth and produced more grain yield. [ABSTRACT FROM AUTHOR]

Water (W) and nitrogen (N) management at tillering stage could largely affect aroma biosynthesis in fragrant rice. In the present study, three rice cultivars, i.e., Basmati, Nongxiang 18, and Yungengyou 14, were applied with three N levels, i.e., 0, 30, and 60 kg N ha−1 regarded as N0, N1, and N2, respectively, and three water levels, i.e., well-watered treatment with water layer of 4–6 cm, 0 kPa (W1), soil water potential of ‒10 kPa (W2), and soil water potential of ‒20 kPa (W3), were applied at tillering stage during 2012 and 2013 under field conditions. Results depicted that application of N fertilizer and less irrigation water at tillering stage increased head milled rice yield and 2 acetyle-1-pyrroline (2AP) content in grain. The N2 and W3 treatments were found effective regarding grain yield and aroma improvements than other levels of nitrogen and water. The head milled rice yield (HMRY) in Nongxiang 18 and Yungengyou 14 was remained than Basmati during both years, whereas the trend for HMRY and 2AP content in mature grain was found as W1 < W2 < W3 and N1 < N2 < N3 for water and nitrogen treatments, respectively. Moreover, the 2AP, 1-pyrroline-5-carboxylic acid content, and pyrroline-5-carboxylic acid synthetase activity were significantly associated with the grain 2AP content at MS. Overall, additional N application at tillering stage with intermittent irrigation could improve rice yield and aroma of fragrant rice. [ABSTRACT FROM AUTHOR]

Drought stress substantially influences the growth and development of many crops. The present study was conducted to investigate the effects of exogenous selenium on the growth, photosynthesis and antioxidant response of fragrant rice seedlings under drought stress. In a pot experiment, fragrant rice seedlings were subjected to drought stress (soil water potential was controlled at − 0.025 ± 5 MPa) and foliar application of selenium (Se) at 0, 10, 30, and 50 μmol L−1. Rice seedlings not exposed to drought stress and Se were used as control. Exposure of fragrant rice seedlings to drought stress resulted in significant (P < 0.05) decrease in fresh weight, dry weight, plant height and stem diameter relative to the control. Total chlorophyll, chlorophyll a, chlorophyll b and carotenoid were 20.54–27.24%, 20.82–26.83%, 19.45–29.07% and 21.49–29.17% lower with drought stress treatment compared to CK. Drought stress also significantly (P < 0.05) decreased net photosynthetic rate and soluble protein content. However, Se treatments (30 and 50 μmol L−1) substantially improved fresh weight and dry weight of fragrant rice seedlings under drought stress. Net photosynthetic rate, activities of antioxidant enzymes (GPX, SOD and CAT) and soluble protein content in rice seedlings under drought stress improved due to Se treatment. Higher transcript levels of antioxidant-related genes (GPX1, GPX4, CATA and CATC) were also observed with Se treatment. [ABSTRACT FROM AUTHOR]

Deep placement of nitrogen (N) fertilizer has become one of the effective management practices for increasing crop yield and improving N recovery efficiency (NRE). However, it is unclear how different N fertilization depths affect grain yield, nitrogen use efficiency, and root characteristics in direct-seeded rice (DSR) in South China. Here, we conducted stainless steel-box experiment to evaluate the effects of different N fertilization depths at four fertilization depths (0, 4, 8, and 12 cm, written as D0, D4, D8, and D12, respectively) with a conventional ammonium bicarbonate fertilizer (TN = 17.7%) (150 kg N ha−1) and a control (no N fertilizer applied, CK) on grain yield, NRE, and root characteristics of DSR. The results indicated that both D8 and D12 significantly increased grain yields by 72.91 and 81.84%, respectively, compared with CK. The highest nitrogen agronomic efficiency (NAE) and NRE were found under D12 treatment, which were increased by 165.42 and 129.45% compared to D0, respectively. We also found that deep placement of N fertilizer (both D8 and D12) could also promote rice root growth such as larger root length, root superficial area, and thicker root diameter. Furthermore, nitrate reductase (NR), glutamine synthetase (GOGAT), and glutamine synthetase (GS) activities of flag leaves at the heading stage were also increased. The result shows that both 8 and 12 cm are relatively reasonable fertilization depths depended on adopted rice varieties when ammonia bicarbonate fertilizer is used in DSR production. [ABSTRACT FROM AUTHOR]

The influences of γ-aminobutyric acid (GABA) and nitrogen on grain yield, yield-related traits, plant growth, grain–leaf ratio and NSC contents in different fragrant rice genotypes are not fully understood. A pot experiment was conducted with four nitrogen rates, i.e. 0, 0.87, 1.75, and 2.61 g pot−1, two GABA levels, i.e. 0 and 250 mg L−1, and three fragrant rice cultivars, i.e. Yuxiangyouzhan, Yungengyou 14 and Basmati. Results depicted that GABA treatment significantly increased the mean grain yield by 11.84% as a consequence of the increment of grain weight, spikelet per pot, grain weight per leaf area, stem sheath dry weight at HS, panicle dry weight at HS, panicle dry weight at MS and total dry weight at MS. Besides, significant effects of nitrogen and cultivar on yield and yield-related traits and some rice growth parameters were observed. Moreover, significant positive correlation relationships between yield and panicle number per pot, leaf area and dry weight for all the cultivars were observed. GABA application could alleviate the effects of nitrogen on grain yield in fragrant rice. These results suggest that GABA is feasible to increase grain yield and improve rice plant growth for fragrant rice varieties grown under different nitrogen conditions. [ABSTRACT FROM AUTHOR]

Zinc (Zn) is an important microelement for rice and plays a key role in many physiological processes. This study assessed the physio-biochemical responses involved in biosynthesis of 2-acety-1-pyrroline (2-AP), which is a key compound in the aroma of fragrant rice, in four different fragrant rice varieties, i.e., Meixiangzhan-2, Xiangyaxiangzhan, Ruanhuayou-134, and Yunjingyou. Four concentrations (0, 0.50, 1.00 and 2.00 g L−1) of zinc chloride were applied to fragrant rice foliage at the heading stage and named CK, Zn1, Zn2 and Zn3, respectively. Our results showed that compared with CK, the Zn1, Zn2 and Zn3 treatments all significantly increased the 2-AP concentration in mature grains of the four fragrant rice genotypes. Furthermore, exogenous application of Zn not only enhanced the activities of enzymes, including proline dehydrogenase (PDH), △1-pyrroline-5-carboxylic acid synthetase (P5CS), and diamine oxidase (DAO), which are involved in 2-AP biosynthesis, but also improved the contents of the related precursors, such as Δ1-pyrroline, proline and pyrroline-5-carboxylic acid (P5C). In addition, compared to the CK treatment, the Zn2 treatment markedly increased the net photosynthetic rate of fragrant rice during the grain filling stage and increased the seed-setting rate, 1000-grain weight and grain yield in all fragrant rice genotypes. Foliar application of Zn also markedly increased the grain Zn content. In general, 1.00 g L−1 seemed to be the most suitable application concentration because the highest 2-AP content and grain weight were recorded with this treatment. [ABSTRACT FROM AUTHOR]

Lead (Pb) is a highly toxic metal that damages normal plant metabolism and often results in reduced crop growth and yield. To measure whether or not ultrasonic seed (US) treatment alleviates Pb stress in rice, the seeds of two rice cultivars, i.e., Guangyan1 and Huahang31, were exposed to 30 min of ultrasonic vibration and then the seedlings were transplanted to Pb-contaminated soil. Results revealed that the Pb contents in roots, stems, leaves, panicles (at heading), and brown rice (at maturity) were lower in US treatment than control (CK; without US treatment); the trend for accumulation of Pb in different plant parts was recorded as: root ˃ stems ˃ leaves ˃ panicles ˃ brown rice in both rice cultivars. Overall, the Pb contents in the brown rice of Huahang31 were higher than those in Guangyan1. Moreover, the contents of proline and soluble protein as well as the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) were significantly higher while the malondialdehyde (MDA) contents were significantly reduced in US treatment compared to CK. The effective panicle number, seed set percentage, grains per panicle, 1000-grain weight, and grain yield were increased by 8.9%, 5.3%, 6.8%, 4.4%, and 26.6% in Guangyan1 and 3.2%, 5.7%, 5.7%, 5.0%, and 24.2% in Huahang31, respectively in US treatment compared to CK. Hence, seed treatment with ultrasonic waves could improve rice performance and reduce brown rice Pb accumulation under Pb-polluted soils. [ABSTRACT FROM AUTHOR]

The effect of light and water on aromatic rice remain largely unclear. A pot experiment was conducted to investigate the influences of light-water treatments (CK: natural light and well-watered conditions, WS: natural light and water-stressed conditions, LL: low light and well-watered conditions, LL-WS: low light and water-stressed treatment) on yield and 2-acetyl-1-pyrroline (2AP) formation in aromatic rice. Compared with CK, the light-water treatments decreased grain yield (10.32–39.19%) due to reductions in the filled grain percentage and total dry weight, in the regulation of biomass distribution, and in the attributes of gas exchange and antioxidant response parameters. The 2AP content in grains increased in the LL treatment (5.08–16.32%) but decreased in the WS treatment compared with that in CK. The changes in 2AP were associated with changes in 2AP formation-related traits and element content. Low light and water stress led to yield declines in aromatic rice, but low light alleviated the decrease in 2AP content caused by water stress. [ABSTRACT FROM AUTHOR]

It was highlighted that the original article (Mo et al. 2019) contained an error in Fig. 1f which revealed the biosynthesis pathway of 2AP. This Correction article shows the correct Fig. 1 and incorrect Fig. 1. The original article has been updated. [ABSTRACT FROM AUTHOR]

Background: Water (W) and nitrogen (N) management generally cause regulations in the 2-acetyl-1-pyrroline (2AP) accumulation in fragrant rice; nevertheless, the feasibility of such management strategies at booting stage in improving 2AP accumulation has not been examined in details. Methods: Field experiments were conducted in the early season (March–July) and repeated in the late season (July–November) in 2013. The treatments were applied urea (90 kg ha− 1), calcium super phosphate (90 kg ha− 1) and potassium chloride (195 kg ha− 1) as basal fertilizer, and urea (65 kg ha− 1) at tillering stage. Three N levels i.e., 0 kg N ha− 1 (N1), 30 kg N ha− 1 (N2), and 60 kg N ha− 1 (N3) and three water levels i.e., W1 treatment (well-watered treatment with water layer of 2–4 cm), W2 treatment (soil water potential was − 15 ± 5 kPa), and W3 treatment (soil water potential was − 25 ± 5 kPa) at booting stage was set up for three rice varieties i.e., Nongxiang 18, Yungengyou 14 and Basmati. The grain yield, head milled rice yield, 2AP contents and the biochemical parameters related to 2AP formation were investigated. Results: Result indicated that W and N dynamics regulated the grain yield, head milled rice yield, and 2AP contents in brown rice across three varieties. The N2 and N3 treatment significantly increased the 2AP contents in brown rice by 9.54% and 11.95%, and 8.88% and 32.54% in the early and the late season, respectively; improved grain yield and head milled rice yield. The W3 treatment improved grain yield, head milled rice yield and 2AP content. Significant W and N interaction effect on 2AP content in brown rice was detected, where the W3 N3 treatment showed the strongest interaction regarding improvement of 2AP contents in brown rice. The 2AP accumulation and its related biochemical parameters and their relationships in different plant tissues at different growth stages under W and N treatments had also been assessed. The 2AP content, P5C content and DAO activity during grain filling periods was highly related to the 2AP content in brown rice. Conclusion: This study revealed that the 60 kg N ha− 1 coupled with − 25 ± 5 kPa treatment showed the best positive effects on yield and aroma in fragrant rice, suggested that water and nitrogen management at booting stage can improve grain yield and fragrance in fragrant rice. However, further study to evaluate the metabolic and molecular basis of 2AP accumulation in fragrant rice is needed. [ABSTRACT FROM AUTHOR]

Temperature is one of the critical factors affecting rice growth and yield production. This study investigated the effects of rhizosphere temperature at the tillering stage on the growth, physiological parameters and gas exchange attributes of two rice cultivars, i.e., the super rice cultivar Yuxiangyouzhan and the non-super rice cultivar Xiangyaxiangzhan, under hydroponic conditions. Three rhizosphere temperature treatments, i.e., a low-rhizosphere-temperature treatment (LT, nutrient solution at 17.5 ± 1.5 °C), an ambient-temperature treatment (AT, nutrient solution at 27.5 ± 1.5 °C), and a high-rhizosphere-temperature treatment (HT, nutrient solution at 37.5 ± 1.5 °C), were applied in this study. The results showed significant differences in most of the rice growth and physiological and gas exchange parameters as a result of cultivar and rhizosphere temperature as well as their interaction. In addition, the marked reduction in total dry weight was positively correlated with a notable reduction in plant morphological parameters, such as the fresh and dry weight of the leaves and stem sheaths, and changes in gas exchange parameters. Moreover, antioxidant reactions were active in response to high and low rhizosphere temperatures, which varied in different plant tissues. These results suggested that the super and non-super rice were sensitive to high and low rhizosphere temperatures, respectively. [ABSTRACT FROM AUTHOR]