English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

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 (gS) 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. Nitrogen is a key component of most organic compounds found in plants, including proteins, amino acids, nucleic acids, and secondary metabolites (Marschner, 1995) and accounts for 3% of plant biomass on a dry mass basis. Plant N demand is often higher than that of other nutrients and N deficiency symptoms are frequently reported, resulting in reduced growth and marketability of plant material. Plant N requirements are species-dependent and may vary within plant parts and the developmental phase. At optimum supplementation, N stimulates growth, delays senescence, modifies plant morphology, increases protein synthesis, and chloroplast formation as well as the concentration of chlorophylls, carotenoids, vitamins, and lipids in leaves (Marschner, 1995). However, suboptimal or excess N levels may result in reduced growth. Nitrate (NO3 ) and NH4 + are the main sources of inorganic N absorbed by roots of higher plants. The uptake of either NO3 – or NH4 + affects physiological and metabolic processes as a result of the difference in ion charge (Gerendás et al., 1997) and the proportion of carbohydrates used for plant growth or N metabolism. In that, NH4 + assimilation demands lower energy inputs because its oxidative state eliminates the need for reduction (Marschner, 1995). However, toxicity may develop in plants that receive high concentrations/proportions of NH4 + because it is reduced to ammonia (NH3), which is deleterious for plant growth even at low concentrations (Gerendás et al., 1997). Ammonium toxicity has been attributed to reduced proton extrusion at low external pH, acidification of the cytosol, and growing media (Walch-Liu et al., 2000), reduced content of sugars in the roots, and induced deficiency of cations, particularly K (Marschner, 1995). Potassium is a highly abundant cation in plants and has a significant effect on N nutrition. Potassium affects NO3 – uptake by being a counteranion for NO3 – translocation from the root to the shoot (Marschner, 1995). Potassium is also related to NH4 + because they share several similarities: charge type, diameter of hydrated ion, and effect on the electrical potential of cell membrane. High K concentrations, within the luxury consumption zone, have also been reported to have an antagonistic effect on the uptake of other cations such as calcium (Ca), magnesium (Mg), sodium, and NH4 + (Marschner, 1995). The objective of the present study was to delineate the response of Capsicum annuum L. cv. Dársena (bell pepper) plants, a species widely cultivated in protected agricultural and soilless systems in México, to varying proportions of NH4 + combined with increasing concentrations of K in the nutrient solution. Materials and Methods Cultural conditions and plant material. The study was conducted under greenhouse conditions in north México (lat. 25 27 N, long. 101 02# W, 1610 m above sea level) starting in the Fall to Winter of 2009 and ending in spring to summer of 2010. Average maximum/minimum temperatures were 22/ 10 C for the fall to winter and 28/15 C for the spring to summer. Minimum/maximum relative humidity for the experimental duration averaged 45%/75%. Average photosynthetically active radiation (PAR) measured at solar noon was 460 mmol·m·s for the fall to winter and 501 mmol·m·s for the spring to summer. Thirty-three-day old bell pepper plants (15 cm height) were transplanted (18 Sept. 2009) into rigid plastic 20.3-cm pots, one Received for publication 7 Aug. 2013. Accepted for publication 5 Oct. 2013. To whom reprint request should be addressed; e-mail luisalonso.valdez@uaaan.mx. 1530 HORTSCIENCE VOL. 48(12) DECEMBER 2013 plant per container, and filled with 12 L sphagnum peatmoss (Sun Gro Horticulture Inc., Bellevue, WA) (pH 6.3). Plants were trellised with two stems and density was maintained at three one-plant containers per m for the experiment duration. Senescent leaves were removed periodically throughout the study period. Nutrient solutions. Nutrient solutions with 13 mM total N were prepared with varying proportions of NH4 : 0% (control), 25%, 50%, and 75% (the remainder was completed with N in the NO3 – form) and three concentrations of K: 6 (control), 9, and 12 mM. Phosphorus (P), Ca, Mg, and micronutrients were supplied at Hoagland’s nutrient solution concentration (Hoagland and Arnon, 1938). The pH ranged from 5.5 to 6.0 and electrical conductivity from 2.2 to 3.3 dS·m. An automated fertigation system was used for application of the nutrient solutions, consisting of a drip irrigation system (144 L·h) and one emitter per pot dispensing 1 L·h. During the vegetative phase (fall to winter), three 2-h irrigations were applied per week. In the reproductive phase (spring to summer), 3.5-h irrigations were applied on a daily basis. Leaching fraction was maintained at 30% throughout the experiment. Assessment of plant growth. At experiment termination, a sample of the growing media was taken at 10-cm depth from each container. Media samples were air-dried, thoroughly mixed with distilled water (1:2 v/v), allowed to equilibrate (60 min), and then filtered (Whatman Grade 1; 11 mm). Filtrate pH was determined (Model 430, WinLab potentiometer; Barloworld Scientific, U.K.). Plants were harvested and separated into roots, leaves, stems, and fruits. Vegetative plant parts were bagged and placed in an oven at 70 C for 72 h before measuring dry mass (DM). Total yield was measured by harvesting fruits that met market quality when ripe ( 50% of fruit exterior had turned red) throughout the study period. Photosynthetic parameters, transpiration rate, and leaf water potential. Photosynthetic rate, gS, transpiration rate (LI-6200; LI-COR, Inc., Lincoln, NE), and water potential (Yw) (Scholander Pressure Chamber; Soil Moisture Equipment Corp., Santa Barbara, CA) of young fully developed leaves (perpendicular to solar radiation) were measured at approximately solar noon (at four different times, at 2-week intervals throughout the experiment) during the reproductive phase. Average PAR, air CO2 concentration, and air temperature during the measurements of photosynthetic parameters were 475 mmol·m·s, 362 ppm, and 26.5 C, respectively. Such environmental conditions for measurements of photosynthetic parameters and leaf Yw were maintained constant in all the samplings performed; therefore, statistical analysis of data was conducted on the average of the measurements for each replication. Nutrient status. Concentration of N forms (NO3 -N, NH4 -N, and total N) and K were determined in young roots and leaves sampled during the summer. Samples were rinsed (twice) in distilled water, bagged, and dried (75 C for 72 h); dried material was ground to pass a 40-mesh screen (Tekmar, Model A-10; Cole-Parmer Instrument, Chicago, IL). Nitrate and NH4 + concentration were determined following Cataldo’s (Cataldo et al., 1975) and Nessler’s method (Krug et al., 1979). Total N was determined with the Kjeldhal procedure. Phosphorus, Ca, and Mg were determined in leaf tissues digested Table 1. Growing medium pH and leaf growth parameters in bell pepper (Capsicum annuum L.) in response to increasing proportion of ammonium (NH4 ) and potassium (K) concentration in the nutrient solution. NH4 + proportion (%) Medium pH Leaf area (cm) Leaf dry mass (g/plant) Specific leaf area (mg·cm) K concn (mM) K concn (mM) K concn (mM) K concn (mM) 6 9 12 6 9 12 6 9 12 6 9 12 0 6.20 6.35 6.33 10,410 9,626 9,345 126 131 132 12.1 13.7 14.1 25 5.75 5.75 5.80 9,550 9,195 9,111 156 135 127 16.7 14.8 14.0 50 5.10 5.08 5.00 6,965 7,994 7,737 130 135 117 19.5 17.1 15.3 75 4.83 4.83 4.80 5,330 4,910 4,648 111 102 105 21.2 24.0 23.6 Trend C* Q* C* L*** L*** Q* Q* Q** L* L** L* Q* Main effects NH4 + P < 0.001 P < 0.001 P < 0.001 P < 0.001

Supplementary Potassium Sustains Fruit Yield in Bell Pepper under High Ammonium Nutrition