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Two warm-season bedding plant species, zinnia (Zinnia elegans) and vinca (Catharanthus roseus), were used to determine if phosphorus (P) supply should be adjusted with light supply, and if deficiency and/or oversupply symptoms were apparent at different P rates when growth rates were altered by light levels. An additional goal was to determine the influence of P and light on overall P uptake efficiencies and water use efficiencies. Plants were grown in a greenhouse with or without shade over portions of the bench and supplied 0.1, 0.2, 0.5, 1, 2, or 4 mm P along with complete nutrient solution as needed with no leaching fraction. Optimum plant growth and flower development rate occurred at a P supply of 0.5 mm regardless of the light supply. Plant growth was greatly reduced by P supply below 0.5 mm regardless of shade conditions. Tissue P concentration was not influenced by light, but overall P content (mg P per plant) was higher when plants were grown without shading as a result of larger plants in higher light environments. The appearance or severity of deficiency symptoms also was not influenced by light. Water use efficiency was maximized when growth was not limited by P supply (at or above 0.5 mm). One hundred percent recovery of applied P was obtained at the 0.5 mm P supply in vinca, whereas recovery was less at the same P supply in zinnia. These results indicate no benefit for plant growth and flowering to P supply above 0.5 mm and illustrate how P content is demand-driven. However, there was no induction or delay of nutrient stress symptoms as a result of different plant growth rates in the different light differences environments.

Greenhouses that are well sealed can result in carbon dioxide (CO₂) drawdown and suppressed plant growth. While growers can add supplemental CO₂, it is unknown how supplemental CO₂ fits within the framework of sustainable crop production in greenhouses. In this study, supplemental CO₂ was used in combination with reduced temperatures to evaluate the productivity of ‘Grand Rapids’ lettuce (Latuca sativa) compared with a traditionally maintained, warmer, and well-insulated greenhouse without supplemental CO₂ at a commercial facility. Simulations using Virtual Grower software based on identical greenhouses compared fuel use and carbon (C) consumed because of heating and CO₂ supplementation. Models were verified with measurements in a well-sealed commercial greenhouse; CO₂ quickly decreased to below 300 ppm in a nonsupplemented greenhouse containing plants. Supplemental CO₂ boosted total leaf number and mass of lettuce even though temperatures were maintained 3 °F lower in elevated CO₂ than in the traditional management scenario. Maintaining a cooler greenhouse but adding CO₂ decreased total carbon (C) consumed (by combined fuel use and CO₂ supplementation) by 7% during the 3-month season that required a well-sealed greenhouse. Additionally, fuel savings because of lower temperature set points paid for the cost of adding CO₂. The use of CO₂ enrichment should be considered as a tool in sustainable systems when its use can counteract the plant growth and development reductions brought on by lowered temperatures.

A major source of power consumption in controlled-environment crop production is plant-growth lighting. Methods developed to minimize this source of power consumption will reduce the negative environmental impact of crop production through more-efficient management of non-renewable resources. One such method uses “intracanopy lighting,” in which the plants are allowed to grow through multiple levels of low-intensity lamps to irradiate the understory that normally is shaded when traditional overhead lighting is used. Early results with cowpea (Vigna unguiculata L. Walp `IT87D-941-1') indicate a significant reduction in net power consumption within a given growth area or volume while enhancing the harvest index (HI = percent edible biomass). Incorporation of mylar reflectors and manipulation of lamp geometries for more-efficient use of available photosynthetically active radiation, while maintaining low power consumption are the focus of present experiments. Photosynthetic rates by leaves of different ages and positions within the canopy are measured as a way of determining lighting efficiency. The productivity parameters HI, edible yield rate (EYR = gDW × m^–2 × day^–1), yield efficiency rate (YER = gDW edible × m^–2 × day^–1 [gDW non-edible]^-1), energy conversion efficiency (ECE = EYR × [kW·h]^–1), and energy partition efficiency (EPE = YER × [kW·h]^–1) express the costs of edible biomass production in terms of the spatial, temporal, energetic, and non-edible biomass penalties. [Research supported in part by NASA grant NAGW-2329.]

Fuel prices have fluctuated wildly in the last several years, and faced with unpredictable or rising fuel costs, growers often lower temperature set points to decrease fuel use. However, plant growth and development are influenced by lower temperatures and may actually cause increases in fuel use as a result of longer production times. Alternative strategies to efficient crop production are needed. Fertility, light, and CO₂ are other environmental factors that can be manipulated within a greenhouse but how all three interact together on growth and development are surprisingly not well known. Petunia ×hybrida Vilm. were grown in controlled environments in a 2 × 2 × 2 factorial study investigating how light, fertility, and CO₂ influence growth and development, including shoot partitioning, nutrient uptake, and carbohydrate concentration. Generally, light enhanced flowering, both mass and fraction of total biomass, whereas increased fertility was detrimental to the proportion of biomass allocated to flowers. The influence of CO₂ was complex with high CO₂ suppressing flowering and enhancing leaf growth, but only midway through the 7-week experiment. Carbohydrate concentration remained high in elevated CO₂, even when light and fertility were not limiting. This suggests a sink limitation, so even in high light and fertility, crop response to enhanced CO₂ was low. Although CO₂ had no size effect late in growth, CO₂ suppressed nutrient concentrations. Together, these data suggest strategies that growers may have in controlling their crop growth and development and indicate that enhanced growth (leaf and steam mass) may be at the detriment of development (flowering mass and allocation).

Intensive, deep-batch, hydroponic systems that use float beds (FBs) are used extensively by the tobacco industry to produce transplants. FBs and a modified FB system with separate drying and flooding stages called ebb-and-flood (EF) beds were used to grow 12 diverse horticultural crops to maturity. Beds were filled with 570 L of water with 114 mg·L⁻¹ N and 143 mg·L⁻¹ K or 66 mg·L⁻¹ N and 83 mg·L⁻¹ K in 1994 and 1995, respectively. The EF beds were flooded for 6 hours, then drained for a 6-hour dry stage each 12 hours in 1994, and flooded for 1 hour and dried for 5 hours each 6-hour period in 1995 from May through August. Although both systems were suitable for producing Chinese water spinach (Ipomoea aquatica Forssk.—see footnote in Table 1), vegetable amaranth (Amaranthus tricolor L.), zinnia (Zinnia elegans Jacq.), and sweet basil (Ocimum basilicum L.), the EF system provided greater control over water availability and higher oxygen concentration in the root zone.

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.

Copper (Cu) is an essential micronutrient for plants and is the a.i. in pesticides for some pathogens and algae. Elevated doses of Cu can cause toxicity in plants. While silicon (Si) is reported to alleviate the toxicity of some heavy metals, its role in reducing the symptoms induced by excess Cu is unclear. Therefore, the role of Si in plant response to Cu stress was investigated in arabidopsis [Arabidopsis thaliana (L.) Heyn.]. Based on plant symptoms (a reduction of leaf chlorosis as well as increased shoot and root biomass) and a reduction of phenylalanine ammonia lyase [PAL (EC 4.3.1.5), a stress-induced enzyme] activity in the shoot, Si was found to alleviate copper stress. Real-time reverse transcriptase-polymerase chain reaction analyses indicated that the RNA levels of two arabidopsis copper transporter genes, copper transporter 1 (COPT1) and heavy metal ATPase subunit 5 (HMA5) were induced by high levels of Cu, but were significantly decreased when Si levels were also elevated. Taken together, our findings indicate that Si addition can improve the resistance of arabidopsis to Cu stress, and this improvement operates on multiple levels, ranging from physiological changes to alterations of gene expression.

The use of copper (Cu) in agriculture is widespread as a pesticide, and it is present in high concentrations in certain types of manures. As the use of Cu continues and manure management is incorporated into sustainable systems, the likelihood of Cu toxicity increases. Supplemental silicon has been used to successfully counteract potential micronutrient toxicity. There is currently considerable debate regarding the value of including silicon (Si) as a nutrient in fertility programs and as such, it is not part of a typical management practice in floriculture crop production in the United States. We investigated the potential for Si to ameliorate the effects of Cu toxicity in both a Si-accumulating [zinnia (Zinnia elegans)] and a Si-non-accumulating [snapdragon (Antirrhinum majus)] species. Using visible stress indicators and dry weight analysis, it initially appeared that Si was a significant benefit to only zinnia under Cu toxicity. Enzymatic assays and elemental analysis of leaves, stems, and roots revealed that both species responded to supplemental Si, showing evidence of reduced stress and nutrient concentrations more similar to healthy, control plants than plants exposed to Cu toxicity. Although there appear to be differences in the extent of Si-mediated amelioration of Cu toxicity between these two plants, both responded to supplemental Si. This adds to the growing body of evidence that all plants likely have Si-mediated responses to stress, and its inclusion into fertility programs should be more broadly considered than current practices.

In protected environments, temperature is often regulated to produce ornamental crops for specific market dates. Temperature primarily controls plant developmental rate and thus production time, but it can also interact with light quantity to affect crop quality attributes such as flower number, branching, and biomass accumulation. We quantified how mean daily temperature (MDT) between 14 and 26 °C influenced quality characteristics of 15 common bedding plant crops. American marigold (Tagetes erecta), cup flower (Nierembergia caerulea), diascia (Diascia barberae), flowering tobacco (Nicotiana alata), geranium (Pelargonium ×hortorum), globe amaranth (Gomphrena globosa), heliotrope (Heliotropium arborescens), nemesia (Nemesia foetans), New Guinea impatiens (Impatiens hawkeri), osteospermum (Osteospermum ecklonis), pot marigold (Calendula officinalis), snapdragon (Antirrhinum majus), stock (Matthiola incana), and torenia (Torenia fournieri) were grown under two mean daily light integrals (9.0 and 18.0 mol·m⁻²·d⁻¹) in five environmentally controlled greenhouse compartments with a 16-h photoperiod. As MDT increased from 14 to 26 °C, flower or inflorescence number decreased for nearly all crops. In six crops, flower or inflorescence size decreased as MDT increased, whereas in five crops, there was an initial increase in flower size with an increase in MDT and then a subsequent decrease at MDT greater than 20 °C. In 10 of the crops, shoot weight at flowering decreased linearly or quadratically with an increase in MDT. Branch number was inversely related with MDT in eight crops and was positively correlated with an increase in flower number. We conclude that in a majority of the crops studied, plant quality decreased as the MDT increased, which can at least partially be attributed to earlier flowering at the higher MDTs. Therefore, there is often a tradeoff between faster crop timing and higher plant quality, especially for plants with a low estimated base temperature (T_min) for development.

Growers tend to over fertilize their plants as a way to minimize the likelihood of encountering nutrient deficiencies that would reduce the quality of their plants. Much of the nutrition literature focuses on the nutritional extremes namely of toxicity and deficiency. Once plants get to this stage, little can be done to correct the problem. Characteristics of plant performance in super-optimal conditions, yet below toxic levels, is less well known, and needs to be developed to help growers identify problems in their production practices before they impact sales. New Guinea Impatiens were grown over a wide range of N, K, and B levels, from 15% to 400% full strength Hoagland's solution for each nutrient after establishing transplanted rooted cuttings in a peat: perlite soilless media. Plants were grown for four weeks during treatment, during which time the flowers were pinched. After only 2 weeks of treatment, plants with 200% and 400% N were significantly shorter than control plants and plants with 15% N. Reflectance measurements and photographs were made twice a week. At the end of the four weeks, plant tissue was analyzed for form of N, root development and structure, and leaf area. Tissue samples were also analyzed with SEM and energy dispersive X-ray analysis to determine changes in nutrient location and tissue structure. This data provides insight into the nutrition economy of plants in general, tests the use of reflectance spectrometry as a method of detecting super-optimal fertilizer concentrations, and will help growers optimize their fertilization requirements to reduce production costs yet maintain high plant quality.