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  • Author or Editor: Jun Liu x
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Far-red photons (700–750 nm) can accelerate crop growth during indoor production through both physiological and morphological processes. A previous study showed that far-red photons can drive photosynthesis with efficiency similar to that of traditionally defined photosynthetically active photons (400–700 nm) if they are provided together with shorter-wavelength photons. Far-red photons also promote leaf and canopy expansion, which can increase light interception and growth. This study aimed to distinguish the contribution of morphological and physiological changes to crop growth induced by substituting red photons with far-red photons. We studied the long-term effects of substituting red photons with far-red photons on canopy light interception and whole-plant photosynthesis. ‘Little Gem’ lettuce (Lactuca sativa) seedlings were grown under four light spectrums of the same total photon flux density (400–750 nm). In addition to a background of a mixture of white and blue photons of 150 μmol⋅m−2⋅s−1, we provided 51 μmol⋅m−2⋅s−1 red photons, far-red photons, or mixtures of red and far-red photons. In the first run, plants were harvested twice. The first harvest was at canopy closure, and the second harvest was when plants reached full size. In the second run, we harvested lettuce plants more frequently to minimize leaf overlap and interplant competition. We found that far-red photon substitution promoted leaf and canopy expansion and increased light interception. The effect of far-red photon substitution on leaf and canopy expansion was stronger in the second run than in the first run, likely because of lower plant density in the second run when plants were harvested more frequently. Far-red photon substitution of red photons decreased the amount of extended photosynthetically active radiation (ePAR) photons (400–750 nm) absorbed by leaves because of the lower leaf absorptance of far-red photons. The greater effect on canopy expansion in the second run of far-red photons substitution was able to exceed the reduction of ePAR photon absorption by leaves; therefore, we observed an increased crop gross photosynthetic rate (Pg) between the second and third harvests during the second run. However, during the first run, lower absorptance of ePAR completely offset the effect of the greater canopy size and light interception, and crop Pg was decreased in the first run before the first harvest. The changes in light interception and crop Pg resulting from far-red photon substitution did not affect dry weight. Far-red photons had photosynthetic activity when applied with a blue and white light mixture, but their efficiency was approximately half that of red photons, potentially because of the lower absorptance of far-red photons. In conclusion, far-red photon substitution of red photons increased canopy size but decreased ePAR photons absorbed by leaves and did not increase the final dry weight. Because far-red light-emitting diodes (LEDs) have higher efficacy for converting electricity into photons, including far-red LEDs in fixtures for sole-source lighting can reduce energy costs without decreasing lettuce yields.

Open Access

Low mobility and solubility reduce the availability of traditional phosphorus (P) fertilizer in red acidic soil. Hydroxyapatite (HAP), especially nano-hydroxyapatite (n-HAP), may be more efficient than P fertilizer because of its nanoparticle characteristics. Camellia oleifera (C. oleifera) is an edible oil tree whose productivity is greatly affected by P fertilizer. During this study, we investigated the migration of different particle sizes of HAP (20 nm, 200 nm, and 80 μm) and their effects on the seedling growth of C. oleifera cultivar Huashuo (HS) cuttings. A column experiment showed that the efflux ratio was negatively correlated with particle size in red acidic soil. The leaching results revealed that the contents of total P and available P in the 20-nm treatment were significantly higher than those in the 200-nm and 80-μm treatments in the deep soil (10–15 cm or 15–20 cm), whereas the application of 20-nm n-HAP caused 13.43% wastage of available P. During the container experiments, 200-nm and 20-nm HAP significantly promoted the growth of the seedlings in terms of seedling height, stem diameter, and biomass. The available P contents in the rhizosphere and nonrhizosphere soils were negatively correlated with the HAP particle sizes. In conclusion, the migration of HAP is inversely correlated with particle size, and HAP improves the P bioavailability in red acidic soil. In summary, 200-nm HAP was the best P fertilizer for the seedlings of HS among the three particle sizes. This study offers preliminary results indicating that 200-nm HAP might be a better P fertilizer compared with other two HAP particle sizes for use in future C. oleifera orchards.

Open Access
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Abstract

Daminozide-sprayed ‘McIntosh’ apples (Malus domestica Borkh.) were stored for 7.5 to 8 months in 19-liter jars with flow-through controlled atmosphere (CA) at 3.3°C. Various combinations of gases were tested in 2 years: 1%, 1.5%, 2%, 2.5%, and 3% O2; 0%, 3%, and 3→5% (3% for one month and then 5%) CO2; and <1 and 500 μl·liter−1 ethylene. High ethylene caused significant softening of apples in 3% O2 + 3% CO2 or 3% O2 + 3→5% CO2 (3 + 3 or 3 + 3→5), but its effect diminished by lowering O2 concentrations. In 1 + 3, the 2 concentrations of ethylene made only a slight difference in fruit firmness in one year and no difference in another year. In <1 μl·liter−1 ethylene, lowering O2 concentrations from 3% to 2% and 1% did not increase fruit firmness, but did reduce rates of ethylene production. A small percentage of apples developed skin injury in 1 + 3 and 1.5 + 3 in one year, and apples of one of 3 jars stored in 1 + 3 developed slight off-flavors in another year. A storage atmosphere of 2 + 3 and <1 μl·liter−1 ethylene, which kept apples firm without injury or off-flavor and with very low rates of ethylene production, may be ideal for low-ethylene CA storage of daminozide-sprayed ‘McIntosh’ apples. Chemical names: butanedioic acid mono (2,2-dimethylhydrazide) (daminozide).

Open Access

Centipedegrass [Eremochloa ophiuroides (Munro) Hack] is a native grass of China, and information on soil adaptation ranges, including acid soils, among centipedegrass cultivars is limited. Therefore, objectives of this study were 1) to conduct a preliminary evaluation of relative aluminum tolerance of 48 centipedegrass accessions plus a cultivar, TifBlair, and a common centipedegrass under aluminum (Al) stress (0 and 1500 μM Al) by using a solution culture method; and 2) to determine Al effects on nutrient uptake between resistant-group and sensitive-group accessions among the 50 accessions and cultivars. Differences were found among accessions and cultivars, and the CV of relative root weight, relative shoot weight, and relative total weight were 39.9%, 32.9%, and 33.6%, respectively. After growing 28 days in an acid subsoil, the resistant-group accessions showed much better growth than the sensitive-group accessions. The Al concentrations in roots and shoots of the two groups of accessions were increased under Al treatment, but most absorbed Al remained in roots with greater Al absorption among the sensitive group compared with the resistant group. The concentrations of phosphorus (P), magnesium (Mg), calcium (Ca), and potassium (K) in the two groups were reduced under Al stress with reductions of 59.3%, 54.8%, 47.9%, and 41.3% in shoots and reductions of 8.70%, 52.5%, 43.2%, and 34.4% in roots, respectively. Under Al stress, differences in P, Mg, and Ca concentrations were found between the two groups; however, differences were not found for K. The resistant-group accessions maintained higher concentrations of Mg and Ca than the sensitive group.

Free access

Differential thermal analysis (DTA) has great potential as a quick and convenient cold hardiness determination method in plants. It measures freezing events inside of plant samples by detecting exotherm(s) produced when water changes from liquid to solid phase. DTA is highly sensitive to the experimental conditions and it has been reported to be ineffective among different fruit crops after acclimation of floral buds has occurred. The objective of this project was to establish DTA as a rapid and accurate method to predict peach floral bud cold hardiness from acclimation to deacclimation as compared with the traditional standard artificial freezing test. Floral buds of ‘Elberta’ and ‘Flavorich’ peach cultivars were subjected to DTA and artificial freezing tests throughout the winters of 2015–16 and 2016–17. Before deacclimation, two distinct exotherms, low-temperature exotherms (LTE) and high-temperature exotherms (HTE), were normally detected from floral bud DTA analyses. After deacclimation, DTA tests yielded only a few LTEs. However, incubation of floral buds at −2 °C overnight before the cooling process of DTA tests yielded an increased number of LTEs for both seasons in comparison with samples directly run using DTA without incubation. Similarly, after deacclimation started, the temperature in which LTE occurred was correlated (r = 0.59–0.86) with LT50 (lethal temperature that damaged 50% of floral buds) when DTA samples were treated overnight at −2 °C. In our study, pretreatment of floral buds at −2 °C overcame the inability of DTA to detect LTEs after deacclimation, which improved the ability and reliability of DTA to detect LTEs for more than 50% of the buds used per date per cultivar. DTA is a promising method to predict cold hardiness of peach plants.

Free access

Aluminum ion (Al3+) toxicity is a major factor limiting plant production on acid soils. Species of zoysiagrass (Zoysia Willd.) are grown for lawn, turf, and soil conservation, especially in temperate zones. Herein, 46 zoysiagrass accessions obtained from eight provinces in China were evaluated for Al resistance using small-scale liquid culture. Each accession was grown in triplicate in nutrient solutions with 1500 μm AlCl3·6H2O (experimental) or without exposure to Al (control). The mean dry weights of the roots, shoots, and total bodies of the accessions relative to those of the nontreated controls were calculated after 60 days, and showed considerable diversity. Overall, the cv for the shoot, root, and total weights of the Al-treated accessions relative to the nontreated controls were 45.78%, 56.67%, and 42.84%, respectively. A cluster analysis based on Al resistance and subordinate function values revealed that 12 of the 46 zoysiagrass accessions (26.09%) were resistant to Al, 9 (19.57%) were moderately resistant, and 25 (54.35%) were sensitive to Al stress. These 46 zoysiagrass accessions from China have great potential for horticultural breeding and development, and for research into mechanisms that underlie Al resistance.

Free access

Platycladus orientalis is one of the main species used in afforestation projects in the arid mountains of north and northwest China, meaning that the species has high ecological and economic value. Studying its genetic diversity and obtaining a core germplasm base and genetic fingerprint data are important for the screening, development, and utilization of the species. This can provide the core materials for the preservation and evaluation and mining of germplasm resources and can provide superior gene resources for breeding programs. In this study, the genetic diversity among 104 P. orientalis germplasm resources was examined using simple sequence repeat (SSR) markers, and a core germplasm containing 31 accessions was constructed that represents the most genetic diversity of P. orientalis accessions. Each of 20 pairs of primers showed polymorphism, and 117 alleles were identified. The average number of alleles at each locus was six, and the mean effective allele number was 2.607. The average Shannon’s information index was 0.983, and the average polymorphism information content was 0.445. There is thus a significant amount of genetic variation within P. orientalis germplasm, yielding a rich genetic diversity. The constructed core germplasm accounted for 30% of the original germplasm. There was no significant difference in genetic diversity between the core germplasm and the original germplasm resources, indicating that the obtained core germplasm resources could fully represent the original germplasm. Using 17 SSR primers with high polymorphism, the DNA fingerprints of 104 P. orientalis germplasm resources were constructed. The results showed that 98 had specific DNA fingerprints. The results of this study provide a valuable basis for the collection, preservation, and utilization of P. orientalis germplasm resources, and the methods adopted in this study have important reference value for the construction of core germplasm of other perennial woody plants.

Open Access

To understand the soil nutrient status of pear orchards in Beijing, we investigated their fertilization situation, including the fertilizer type, amount, and period. Furthermore, soil samples were collected at a depth of 0 to 40 cm to determine the contents of soil nitrogen, phosphorus, and potassium. The status of nutrient profits and losses was analyzed. The results showed that 50% of the pear orchards received organic fertilizer as a single nutrient source, and 35.7% of the pear orchards received a combined application of organic fertilizer and chemical fertilizer. Most pear orchards received organic fertilizer in autumn, but the application of chemical fertilizer occurred mainly before germination and during fruit expansion. The average nutrient input to the investigated pear orchards was 569.6 kg/ha for N, 855.0 kg/ha for P2O5, and 448.1 kg/ha for K2O, and the corresponding proportion of organic fertilizer was 76.9%, 88.0%, and 85.8%, respectively. However, the pear orchards had surpluses of nitrogen, phosphorus, and potassium, with average surplus amounts as high as 445.5, 794.3, and 321.4 kg/ha, respectively. Among all pear orchards surveyed, 93.33% faced environmental risks and 37.04% faced leaching risks. The average content of soil phosphorus was 2.23 times its critical value, and 64.29% of the studied pear orchards exceeded the critical value. Most pear orchards had surplus potassium, with 26.92% exceeding 500 kg/ha. This study provides a basis for soil improvement, high-quality production of fruits, and efficient utilization of pear orchards in Beijing.

Open Access

Camellia oleifera Abel. is one of four major woody oil plants in the world. The objective of the current study was to evaluate the effect of different plant growth regulators (PGRs) and concentrations on direct organogenesis using cotyledonary nodes, hypocotyls, and radicle explants. High induction frequency of adventitious shoots were obtained from cotyledonary nodes, hypocotyls, and radicle explants (85.2%, 73.6%, and 41.0%, respectively) when cultured on half-strength Murashige and Skoog (1/2 MS) medium containing 2.0 mg·L−1 6-benzylaminopurine (BA) and 0.1 mg·L−1 indole-3-acetic acid (IAA). Microshoots from cotyledonary nodes, hypocotyls, and radicle explants were then transferred to 1/2 MS medium containing 2.0 mg·L−1 BA and 0.05 mg·L−1 indole-3-butyric acid (IBA) for shoot multiplication, resulting in 6.9 shoots per explant. The shoots were transferred to Woody Plant Medium (WPM) supplemented with various α-naphthalene acetic acid (NAA) and gibberellic acid (GA3) for shoot elongation. The mean length of shoots and the number of leaves per shoot were 3.7 and 6.6 cm, respectively, in WPM supplemented with 0.5 mg·L−1 NAA and 3.0 mg·L−1 GA3. The highest rooting of shoots (90.2%) or the number of roots per shoot (7.2) was obtained when elongated microshoots were transferred to 1/2 MS medium supplemented with 3.5% perlite, 1.0 mg·L−1 IBA and 2.0 mg·L−1 NAA. The rooted plantlets were successfully acclimatized in the greenhouse with a survival rate of 90.0%. The in vitro plant regeneration procedure described in this study is beneficial for mass propagation and improvement of C. oleifera through genetic engineering.

Free access