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  • Author or Editor: Ana María Castillo-González x
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Nitrogen and potassium changes in poinsettia `Supjibi Red' were evaluated at four stages: vegetative growth, inductive stage, bract development and flowering. Nitrogen doses were 100, 200, 300, 400, and 500 mg·L-1 and those of potassium were: 175, 250, 325, and 400 mg·L-1, which were applied constantly with irrigation. Plants were grown in 7-inch pots with tezontle as the substrate. A completly random experimental design with nine treatments and 10 replicates was used. Short photoperiod was applied from 61 days after transplant, covering plants for 14 hours from 7 pm on. Samples for nitrogen and potassium evaluations were taken from recently grown-up leaves at 25, 50, 75, 100 and 125 days after transplant. Nitrogen absorption increased up to 75 days after transplant; treatments with 400 and 500 mg·L-1 of nitrogen induced the highest foliar levels 2.44% and 2.6%, respectively. In the following sampling dates, nitrogen decreased for all treatments. Potassium content decreased as plants developed; highest levels were obtained 25 days after transplant. The 325 and 400 mg·L-1

K treatments induced the highest concentrations in leaves 7.04% and 7.02%, respectively. Thus, it is confirmed that nitrogen is required throughout vegetative growth, and potassium just in the initial stage of vegetative growth.

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The uptake of nitrogen (N) in nitrate or ammonium (NH4 +) form affects physiological and metabolic processes and toxicity may develop in plants receiving high concentrations of NH4 +. The objective of the present study was to delineate the response of bell pepper plants to varying proportions of NH4 + combined with increasing concentrations of potassium (K) in the nutrient solution. Bell pepper plants were tolerant to moderate proportions of NH4 + (25% or less or 50% or less); however, higher proportions resulted in growth reduction. The application of higher K concentrations in the nutrient solution did not ameliorate the growth on vegetative plant parts; however, when K was increased to 9 mm, the yield was sustained even when 50% of total N was in the NH4 + form. Decreased shoot:root ratio and harvest index indicated that biomass accumulation was affected more in the shoot than in the root and in the fruit than in the shoot, respectively. There was a lower concentration of NH4 + in the roots compared with leaves, suggesting that the higher K concentration that resulted from the increased K in the nutrient solution was associated with NH4 + translocation through the xylem. A decrease in calcium and magnesium detected in leaves suggests an antagonistic relationship with NH4 + and K in the nutrient solution, which was correlated with the acidification of the growing medium. Higher yields when K was at 9 mm may be the result of the high photosynthetic rate and stomatal conductance (g S) detected in plants fertigated with 25% of total N as NH4 + and the higher leaf water potential when the proportion of NH4 + was 50%. The biochemical composition of fruits was affected because both high NH4 + and increased K resulted in higher ethylene production, lipid peroxidation, superoxide dismutase activity, and carotenoids.

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Irrigation water high in alkalinity can severely compromise the growth and marketability of ornamental plants. In the present study we investigated the response of lisianthus to increased calcium (Ca) when irrigated with solutions containing high levels of bicarbonate (HCO3 )-induced alkalinity. Alkalinity in irrigation water reduced the growth of lisianthus; however, plants supplemented with an increased concentration of Ca at alkalinity levels from 4 to 7 meq·L−1 of HCO3 exhibited improved growth and dry mass (DM) accumulation or were not detrimentally affected, demonstrating that Ca contributes to the increase of the tolerance of lisianthus to alkalinity. Supplementary Ca did maintain a high stomatal conductance (g S) and transpiration rate when alkalinity was at 4 meq·L−1, which explained the lower water potential in young leaves. Plants irrigated with solutions containing supplementary Ca had higher total DM, which was associated with a higher g S; however, when conductance was higher than 0.280 cm·s−1, like in plants with no supplementary Ca, DM tended to decrease. At a typical Ca concentration, there was a disruption on stomata functioning as g S and transpiration rate increased, which was associated with a reduction in shoot potassium (K). Calcium ameliorated the uptake of K when alkalinity was 4 meq·L−1 by allowing a less marked reduction in shoot K concentration. Chlorophyll was reduced by increasing alkalinity as a result of a decrease in shoot iron (Fe); however, supplementary Ca also contributed in increasing plant tolerance to alkalinity at 4 meq·L−1 by sustaining a high shoot Fe concentration. Supplementary Ca increased catalase and peroxidase activities, indicating that lisianthus responded to the stress by enhancing the activity of these enzymes to reduce oxidative damage.

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The domestication of wild orchids for commercial production is a new endeavor, which may represent a sustainable alternative to the collection/harvest from natural populations of threatened or endangered orchid species. In the present study, the growth and nutrition of vegetative plants of Laelia anceps Lindl. as affected by three components of the growing medium (peat, volcanic rock, and/or horticultural grade charcoal) and the nutrient solution concentration, measured as osmotic potential (ψS), were assessed using mixture experiments methodology. Leaf dry mass (DM) was the highest when plants were irrigated with nutrient solutions of –0.076 MPa. The lower leaf DM at lower or higher ψS was influenced by the medium because plants grown in 100% volcanic rock exhibited no effect, whereas plants grown in either 100% charcoal or 100% peat had a marked reduction. Regardless of the ψS of the nutrient solution, the highest leaf DM was observed in mixtures of two components containing charcoal and peat at high proportions. Dry mass of pseudobulbs and roots was highest in plants irrigated with solutions of –0.051 MPa, especially in mixtures with charcoal or 100% peat. Decreasing the ψS of the nutrient solution resulted in increased shoot nitrogen (N) and potassium (K) concentrations and decreased concentration of phosphorus (P), calcium (Ca), magnesium (Mg), boron (B), manganese (Mn), zinc (Zn), and copper (Cu). Increasing charcoal proportion in the growing media resulted in increased plant iron (Fe) and Cu concentration. However, increasing volcanic rock reduced plant P and K and increased Mn concentration. A higher proportion of peat was correlated with a decrease in plant Fe concentration. Leaf DM fit models on which macronutrient:micronutrient or micronutrient:micronutrient ratios were calculated, suggesting that nutrient imbalance may be responsible for a plant’s responses. The coefficients with the higher values included a micronutrient:micronutrient ratio, suggesting that an extremely fine balance in the uptake of a given micronutrient in relation to other micro- or macronutrient is of major importance for adequate growth of Laelia.

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