Seedlings of Cucumis sativus (cucumber), Tagetes patula (marigold), Viola tricolor (pansy), Pelargonium × hortorum (geranium), and Impatiens wallerana (impatiens) were germinated on towels soaked with either deionized water, nutrient control solutions, or humic acid solutions. Root fresh weight and root dry weights were higher for all seedlings germinated on towels soaked with humic acid as compared to seedlings germinated on towels soaked with deionized water or nutrient control solutions. Lateral root number and total lateral root length were higher for cucumber, marigold, pansy, and geranium seedlings germinated on towels soaked with humic acid than those germinated on towels soaked with deionized water or nutrient control solutions. Root fresh and dry weights were higher for impatiens, Begonia semperflorens (begonia), marigold, and geranium seedlings germinated in a sphagnum peat: vermiculite (80:20, %v/v) substrate drenched with humic acid as compared to seedlings germinated in substrate drenched with deionized water or nutrient control solutions. Foliar sprays of humic acid also resulted in increased root fresh and dry weights while foliar application of nutrient control solutions either had no effect or reduced root fresh and dry weights.
Nitrogen greatly impacts plant growth and development. The objective of this study was to characterize growth, nitrogen use, and gene expression of perennial ryegrass (Lolium perenne) in response to increasing nitrogen supplies. Perennial ryegrass (cv. Inspire) was grown in sand culture and irrigated with a half-Hoagland solution amended with 0, 0.5, 1.0, 2.5, 5.0, and 7.5 mm nitrogen. Leaf tissues were harvested at 10 days (first cutting) and 20 days (second cutting) and roots were harvested at 20 days. The relatively higher N supply (2.0–7.5 mm) resulted in a larger amount of leaf fresh and dry weight but lower root fresh and dry weight, especially for the second cutting. Root:leaf ratio was higher under low N, but lower under the high N treatment. Leaf N content was relatively higher under 2.5, 5, and 7.5 mm N than under the other three treatments, while 2.5 mm N exhibited relatively higher leaf carbon content for both cuttings. Leaf C:N ratio and leaf nitrogen use efficiency (LNUE) decreased with increasing N supplies for the first cutting but were higher under low N (0–1.0 mm) for both cuttings. Leaf C:N ratio and LNUE did not differ among low N and LNUE also remained unchanged among high N for the second cutting. Root N content increased, but the root C:N ratio and root N use efficiency (RNUE) decreased with increasing N supplies, especially under 2.5, 5.0, and 7.5 mm N. Low (0.5 mm), moderate (2.5 mm), and high (7.5 mm) N were chosen to examine the expression level of NR encoding nitrate reductase and GS1b encoding glutamine synthetase. Treatment of 0.5 mm N had higher expression levels of leaf NR than other two treatments for both cuttings and a higher level of leaf GS for the second cutting. Expression of NR in the roots did not vary among treatments but the expression of GS increased under 2.5 and 7.5 mm, compared with the 0.5 mm N. Differential leaf and root growth and physiological responses to low N (0 to 1 mm) and to moderate to high N (2.5 to 7.5 mm) could be used for examining the natural variation of N use in diverse perennial ryegrass populations.
The aim of this study was to quantitatively investigate the impacts of nitrogen on growth dynamics and yield, so as to facilitate the optimization of nitrogen management for muskmelon crop in plastic greenhouse. For this purpose, four experiments with different levels of nitrogen treatment and planting dates on muskmelon (Cucumis melo L. ‘Nanhaimi’ and ‘Xizhoumi 25’) were conducted in plastic greenhouse located at Sanya from Nov. 2012 to Sept. 2014. The quantitative relationship between leaf nitrogen content and growth dynamics and yield of muskmelon was determined and incorporated into a photosynthesis-driven crop growth model (SUCROS). Independent experimental data were used to validate the model. The critical leaf nitrogen content at flowering stage for muskmelon ‘Nanhaimi’ and ‘Xizhoumi 25’ were 19.8 and 21.0 mg·g−1. The coefficient of determination (r2) and the relative root-mean-squared error (rRMSE) between the predicted and measured value of growth dynamics and yield were, respectively, 0.91 and 10.8% for leaf area index (LAI), 0.90 and 19.6% for dry weight of shoot (DWSH), 0.76 and 30.3%, 0.82 and 21.1%, and 0.92 and 11.9% for dry weight of leaf (DWL), stem (DWST), and fruit (DWF), 0.91 and 17.3%, 0.89 and 13.9%, 0.86 and 27.8%, and 0.88 and 20.6% for soluble sugar content (SU), soluble protein content (PR), vitamin C content (VC), and soluble solids content (SO) of fruit, and 0.90 and 10.1% for fresh weight of fruit (FWF). The model could be used for the optimization of nitrogen management for muskmelon production in plastic greenhouse. Further calibration and test would be needed during the application of the model in wider range of conditions and muskmelon cultivars.
The ionic Ca content of expressed apple juice conceivably could be used to estimate the total calcium content of fruit flesh. To evaluate this method, samples of 2 strains of ‘Delicious’ apple (Malus domestica Borkh.) were analyzed at 2- to 3-week intervals, from 4 weeks after full-bloom until full-maturity. Ionic Ca in the juice (juice Ca) was analyzed with a selective electrode, total Ca in the flesh (flesh Ca) with a plasma emission spectrophotometer. The correlation coefficient between calcium concentration in flesh vs. juice was very low during the early stages of fruit development, but increased to +0.758 (significant at P<0.0l) for samples collected 5, 3, and 0 weeks prior to fruit maturity. The correlation was generally significant at P<0.01 when all sampling dates were used (r = 0.734 for ‘Miller Spur’, +0.928 for ‘Starking’, and +0.831 for both strains). The calcium concentration in juice samples taken within 35 days of physiological fruit maturity paralleled the calcium concentration in the flesh on any given date, but was not a reliable predictor of flesh Ca concentration in fruit harvested 2 to 3 weeks thereafter.
Photosynthetic physiology of Dendrobium nobile, Dendrobium pendulum, Dendrobium chrysotoxum, and Dendrobium densiflorum was studied. A bimodal diurnal variation of the net photosynthetic rate (Pn) was observed in the four Dendrobium species with the first peak [5.09 to 6.06 μmol (CO2) per m−2·s−1] ≈1100 hr and the second peak [3.83 to 4.58 μmol (CO2) per m−2·s−1] at 1500 hr. No CO2 fixation was observed at night. For all four Dendrobium species, the light compensation point (LCP) was 5 to 10 μmol·m−2·s−1, light saturation point (LSP) ranged from 800 to 1000 μmol·m−2·s−1, apparent quantum yield (AQY) was 0.02, and CO2 compensation points (CCP) and saturation point (CSP) were 60 to 85 μmol·mol−1 and 800 to 1000 μmol·mol−1, respectively. Carboxylation efficiency (CE) values ranged from 0.011 to 0.020. The optimum temperature for photosynthesis was between 26 and 30 °C. The measurement of Pn seasonal variation indicated that July to August had the higher Pn for Dendrobium species. Additionally, the chlorophyll a/b (Chl a/b) ratios of the leaves were 2.77 to 2.89. Measurement of key enzymes in the photosynthetic pathway indicated relatively high Ribulose-1,5-bisphosphate carboxylase (RuBPCase) and glycolate oxidase (GO) activities but very low phosphoenolpyruvate carboxylase (PEPCase) activities. It suggested that these four Dendrobium species are typical semishade C3 plants.
Ferric chelate reductase (FRO) is a critical enzyme for iron absorption in strategy I plants, reducing Fe3+ to Fe2+. To identify FRO family genes in the local Citrus junos cultivar Ziyang Xiangcheng and to reveal their expression model, the citrus (Citrus sp.) genome was searched for homologies of the published sequence CjFRO1. Five FROs were found, including CjFRO1; these were named CjFRO2, CjFRO3, CjFRO4, and CjFRO5, respectively, and cloned via reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) PCR. The deduced amino acid sequences of five CjFROs contained flavin adenine dinucleotide (FAD)-binding motifs, nicotinamide adenine dinucleotide (NAD)-binding motifs, and 6–10 transmembrane domains, with isoelectric points between 6.73 and 9.46, and molecular weights between 67.2 and 79.9 kD. CjFRO1 and CjFRO2 were predominantly found in the aboveground parts of C. junos, with CjFRO1 highly expressed in leaves, and CjFRO2 largely expressed in stems and leaves. CjFRO3 was less expressed in roots, stems, and leaves. CjFRO4 and CjFRO5 were predominately found in roots. Under iron-deficient conditions, CjFRO4 was significantly and specifically increased in the roots of C. junos, whereas CjFRO1 was upregulated in the roots and leaves.