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Abstract
Cuttings of Ficus benjamina L. and Chrysanthemum × morifolium(Dendranthema grandiflora tzvelev.) were rooted in aero-hydroponics to study the effect of dissolved oxygen concentrations in the range of 8 mg·liter. (ambient saturation) to 0 mg·liter−1. The results of this study indicate that dissolved oxygen is essential to root formation and root growth. Woody (Ficus) and herbaceous (Chrysanthemum) cuttings responded similarly. Lowering the dissolved oxygen concentration increased the time required to form adventitious roots, reduced rooting percentages, reduced numbers of roots formed per cutting, and reduced average root lengths. Comparisons between stirred and unstirred water suggested the development of an area of depleted oxygen concentration (boundary layer) at the stem-water interface on cuttings immersed in unstirred water. Cuttings in water stirred constantly rooted sooner and formed more roots than did those in unstirred water. Maximum rooting occurred in misted (high dissolved oxygen concentrations) sections of cuttings suspended in the aero-hydroponics chambers. Chemical name used: potassium salt of lH-indole-3-butyric acid (K-IBA).
Exudation of organic acids by roots has been implicated in uptake of minerals from soil. Three cultivars within each of two subspecies of summer squash (Cucurbita pepo ssp. ovifera D. S. Decker var. ovifera and C. pepo ssp. pepo var. pepo) were grown in the field. Plants of ssp. pepo had higher concentrations of K, P, and Zn than those of ssp. ovifera. These same cultivars were grown under P sufficient and depleted conditions in hydroponics, to measure exudation of organic acids from roots. When grown in hydroponics, tissues of ssp. ovifera had similar or higher concentrations of nutrients than ssp. pepo. Therefore, differences in tissue composition of field-grown plants are likely due to differences in nutrient uptake ability, not inherent differences in tissue composition between subspecies. Phosphorus nutrition played a significant role in exudation of organic acids into the hydroponics solution. For both subspecies, P depletion resulted in exudation of more citric and succinic acid, and less oxalic and tartaric acid. Under P depletion, ssp. pepo exuded more citric acid than ssp. ovifera. When soil was eluted with solution containing root exudates, the exudates from ssp. pepo eluted more K, Mg, Fe, and Zn than did those from ssp. ovifera. Among subspecies of C. pepo, exudation of organic acids, particularly exudation of citric acid in response to P depletion, is associated with the plant's ability to accumulate more inorganic nutrients when grown in the field.
Strawberries (Fragaria xananassa Duch. .Osogrande.) were grown hydroponically with three NO3-N concentrations (3.75, 7.5, or 15.0 mM) to determine effects of varying concentration on NO3-N uptake and reduction rates, and to relate these processes to growth and fruit yield. Plants were grown for 32 weeks, and NO3-N uptake and nitrate reductase (NR) activities in roots and shoots were measured during vegetative and reproductive growth. In general, NO3-N uptake rates increased as NO3-N concentration in the hydroponics system increased. Tissue NO3-. concentration also increased as external NO3-N concentration increased, reflecting the differences in uptake rates. There was no effect of external NO3-N concentration on NR activities in leaves or roots during either stage of development. Leaf NR activity averaged ~360 nmol NO2 formed/g fresh weight (FW)/h over both developmental stages, while NR activity in roots was much lower, averaging ~115 nmol NO2 formed/g FW/h. Vegetative organ FW, dry weight (DW), and total fruit yield were unaffected by NO3-N concentration. These data suggest that the inability of strawberry to increase growth and fruit yield in response to increasing NO3-N concentrations is not due to limitations in NO3-N uptake rates, but rather to limitations in NO3 - reduction and/or assimilation in both roots and leaves.
Commercial recommendations exist for using short-term salt-shocks on tomato (Lycopersicon esculentum Mill.) to improve fruit quality. Six experiments were conducted to 1) assess the influence of nutrient concentration and short-term salt-shocks on fruit quality and yield and 2) identify a vegetative predictor of subsequent fruit quality. The first objective was addressed in three nutrient film technique (NFT) experiments (Expts. 1-3). Four treatments were applied: two maintained constant at two baseline concentrations (0.25X and 1X-commercial level) and two provided salt-shock periods of 30 min, twice daily. There were no effects of baseline concentration or salt-shocks on total number and weight of marketable fruit. Fruit quality was better at the 1X baseline concentration as observed by higher titratable acidity (Expt. 2), higher percent dry matter (Expts. 2 and 3), higher soluble solids concentration (Expt. 2), and lower pH (Expts. 2 and 3), however, weight per marketable fruit was lower (Expt. 2). Salt-shocks had little effect on fruit quality, refuting its commercial potential. Salt-shocks decreased fruit pH (Expts. 1 and 3). However, titratable acidity increased at the 0.25X level and decreased at the 1X level (Expt. 3). In Expt. 2, but not in Expt. 3, citrate concentration in the fifth leaf from the apex of young vegetative plants was correlated with subsequent fruit quality. Three additional experiments in static hydroponics with vegetative plants showed no significant differences in leaf citrate levels due to a single, short-term salt-shock. Thus, citrate is not a good predictor of fruit quality.
Effects of N level (15 to 30 mm), time of N increase (14 to 28 days after planting), and planting density (1163 to 2093 plants/m2) were determined for crop yield responses of dwarf, rapid-cycling brassica (Brassica napus L., CrGC 5-2, Genome: ACaacc). Crops were grown in solid-matrix hydroponic systems and under controlled-environment conditions, including nonsupplemented (ambient) or elevated CO2 concentrations (998 ± 12 μmol·mol-1). The highest seed yield rate obtained (4.4 g·m-2·day-1) occurred with the lowest N level (15 mm) applied at the latest treatment time (day 28). In all trials, CO2 enrichment reduced seed yield rate and harvest index by delaying the onset of flowering and senescence and stimulating vegetative shoot growth. The highest shoot biomass accumulation rate (55.5 g·m-2·day-1) occurred with the highest N level (30 mm) applied at the earliest time (day 14). Seed oil content was not significantly affected by CO2 enrichment. Maximum seed oil content (30% to 34%, dry weight basis) was obtained using the lowest N level (15 mm) initiated at the latest treatment time (day 28). In general, an increase in seed oil content was accompanied by a decrease in seed protein. Seed carbohydrate, moisture, and ash contents did not vary significantly in response to experimental treatments. Effects of N level and time of N increase were consistently significant for most crop responses. Planting density was significant only under elevated CO2 conditions.
An artificial neural network (NN) and a statistical regression model were developed to predict canopy photosynthetic rates (Pn) for `Waldman's Green' leaf lettuce (Latuca sativa L.). All data used to develop and test the models were collected for crop stands grown hydroponically and under controlled-environment conditions. In the NN and regression models, canopy Pn was predicted as a function of three independent variables: shootzone CO2 concentration (600 to 1500 mmol·mol-1), photosynthetic photon flux (PPF) (600 to 1100 μmol·m-2·s-1), and canopy age (10 to 20 days after planting). The models were used to determine the combinations of CO2 and PPF setpoints required each day to maintain maximum canopy Pn. The statistical model (a third-order polynomial) predicted Pn more accurately than the simple NN (a three-layer, fully connected net). Over an 11-day validation period, average percent difference between predicted and actual Pn was 12.3% and 24.6% for the statistical and NN models, respectively. Both models lost considerable accuracy when used to determine relatively long-range Pn predictions (≥6 days into the future).
Boron deficiency in fresh-market tomatoes (Lycopersicon esculentum Mill.) is a widespread problem that reduces yield and fruit quality but is often not recognized by growers. Tomatoes were grown in field and hydroponic culture to compare the effects of foliar and soil applied B on plant growth, fruit yield, fruit quality, and tissue nutrient levels. Regardless of application method, B was associated with increased tomato growth and the concentration of K, Ca, and B in plant tissue. Boron application was associated with increased N uptake by tomato in field culture, but not under hydroponic culture. In field culture, foliar and/or soil applied B similarly increased fresh-market tomato plant and root dry weight, uptake, and tissue concentrations of N, Ca, K, and B, and improved fruit set, total yields, marketable yields, fruit shelf life, and fruit firmness. The similar growth and yield responses of tomato to foliar and root B application suggests that B is translocated in the phloem in tomatoes. Fruit from plants receiving foliar or root applied B contained more B, and K than fruit from plants not receiving B, indicating that B was translocated from leaves to fruit and is an important factor in the management of K nutrition in tomato.
Nutrient uptake by New Guinea impatiens (Impatiens X hb.) `Equinox' was measured in a growth chamber under various combinations of light [photosynthetic photon flux (PPF)], air temperature, and nutrient solution concentration. Nitrate-N, P, K, Ca, and Mg ions were evaluated individually by measuring depletion of each nutrient from a constant-volume solution over 9 hours with constant environmental conditions. Individual nutrient uptake was not correlated to concurrent daily temperature environment, and only K and Mg showed a correlation with PPF. Uptake rates of N, P, K, Ca, and Mg increased significantly with increasing nutrient solution concentration. Estimated net assimilation rates of nutrients, based on measured shoot tissue concentrations of each nutrient and assuming that uptake occurred continuously at a rate proportional to canopy area, were correlated to average measured uptake rates for N, Ca, and Mg and were not correlated to average uptake rates for P and K. Although nutrient demand from plant growth may determine rates of nutrient uptake necessary over longer periods of time, short-term uptake was not related directly to daily fluctuations in environmental factors.
Cloudy days cause an abrupt reduction in daily photosynthetic photon flux (PPF), but we have a poor understanding of how plants acclimate to this change. We used a unique 10-chamber, steady-state, gas-exchange system to continuously measure daily photosynthesis and night respiration of populations of a starch accumulator [tomato (Lycopersicon esculentum Mill. cv. Micro-Tina)] and a sucrose accumulator [lettuce (Lactuca sativa L. cv. Grand Rapids)] over 42 days. All measurements were done at elevated CO2 (1200 μmol·mol-1) to avoid any CO2 limitations and included both shoots and roots. We integrated photosynthesis and respiration measurements separately to determine daily net carbon gain and carbon use efficiency (CUE) as the ratio of daily net C gain to total day-time C fixed over the 42-day period. After 16 to 20 days of growth in constant PPF, plants in some chambers were subjected to an abrupt PPF reduction to simulate shade or a series of cloudy days. The immediate effect and the long term acclimation rate were assessed from canopy quantum yield and carbon use efficiency. The effect of shade on carbon use efficiency and acclimation was much slower than predicted by widely used growth models. It took 12 days for tomato populations to recover their original CUE and lettuce CUE never completely acclimated. Tomatoes, the starch accumulator, acclimated to low light more rapidly than lettuce, the sucrose accumulator. Plant growth models should be modified to include the photosynthesis/respiration imbalance and resulting inefficiency of carbon gain associated with changing PPF conditions on cloudy days.
Abstract
Cultivars of greenhouse tomato (Lycopersicon esculentum Mill.) were grown in the greenhouse and in growth chambers to study the effects of root and air temperature on flowering and yield. A low air temperature of 19° (day)/14°C (night), during the fall crop, caused no reduction in yield when compared with the commonly used 22°/17° air temperature. A 13°/8° air temperature during the spring crop drastically reduced yield compared with the 19°/14°C air temperature. Flowering of ‘Ohio MR-13’ in growth chambers was delayed significantly at air temperatures of 24°/8° compared to 24°/17°, but the flowering of ‘Vendor’ was unaffected by air temperature treatments. Marketable yield of ‘Vendor’ was significantly higher at 24°/8° compared to the 24°/17° treatment, while the marketable yield of ‘Ohio MR-13’ was unaffected. At a constant, day air temperature of 24°, the amount of small fruit decreased as night air temperature was lowered from 17° to 8° and maturity was delayed as night air temperature was lowered from 14° to 8°. The effect of low air temperature on flowering and yield of tomatoes was large and could not be offset by increasing root temperatures. At air temperatures of 24°/17°, 24°/14°, and 24°/8°, marketable yields were affected adversely by the absence of root thermoperiodicity (day to night root temperature variation).