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The relative coolness-to-touch of light-emitting diodes (LEDs) has enabled commercial implementation of intracanopy lighting (ICL) in the greenhouse. Intracanopy lighting, which refers to the strategy of lighting along the side or from within the foliar canopy, can increase canopy photosynthetic activity, but physiological and productivity responses of high-wire greenhouse tomato (Solanum lycopersicum) to intracanopy supplemental lighting (SL) still are not yet fully understood. Two consecutive production experiments were conducted across seasons in a glass-glazed greenhouse located in a midnorthern, continental climate [lat. 40°N (West Lafayette, IN)]. Plants were grown from winter-to-summer [increasing solar daily light integral (DLI)] and from summer-to-winter (decreasing solar DLI) to compare three SL strategies for high-wire tomato production across changing solar DLIs: top lighting with high-pressure sodium lamps (HPS) vs. intracanopy LED vertical towers vs. hybrid SL (HPS + horizontal ICL-LEDs). A control treatment also was included for which no SL was provided. Supplemental DLI for each experimental period was adjusted monthly, to complement seasonal changes in sunlight, aiming to approach a target total DLI of 25 mol·m‒2·d‒1 during fruit set. Harvest parameters (total fruit fresh weight, number of fruit harvested, and average cluster fresh weight), tissue temperature, chlorophyll fluorescence, and stomatal conductance (gS) were unaffected by SL treatment in both experiments. Among the physiological parameters evaluated, CO2 assimilation measured under light-saturating conditions, light-limited quantum-use efficiency, and maximum gross CO2 assimilation (Amax) proved to be good indicators of how ICL reduces the top-to-bottom decline in leaf photosynthetic activity otherwise measured with top lighting only (HPS-SL or solar). Although SL generally increased fruit yield relative to control, lack of SL treatment differences among harvest parameters indicates that higher crop photosynthetic activity did not increase fruit yield. Compared with control, intracanopy SL increased yield to the same extent as top SL, but the remaining photoassimilate from ICL most likely was partitioned to maintain nonharvested, vegetative plant parts as well.

Obtaining uniform mechano-dwarfing of Arabidopsis thaliana (L.) Heynh. seedlings within dense plantings is problematic. Alternative forms of mechano-stimulation were applied to seedlings in effort to obtain uniform growth reduction compared with undisturbed controls in both greenhouse and controlled growth environments. Arabidopsis grown under low photosynthetic photon flux (PPF) artificial light grew upright with limited leaf expansion, which enhanced mechano-responsiveness compared to that of rosette-growing plants under filtered sunlight or high PPF artificial light. Hypocotyls of seedlings grown at PPFs >60 μmol·m-2·s-1 elongated less and had 6% less sensitivity to mechanical stress than seedlings grown at PPFs -2·s-1. Fluorescent lamps alone (F) or fluorescent plus incandescent (F+I) lamps were compared for seedling responses to mechanical stress. Under F lighting, hypocotyl elongation was reduced 25% to 40% by twice-daily brush or plate treatments, and brushed seedlings exhibited more growth reduction than did plate treatments. Seedlings grown under F+I lamps exhibited similar stress-induced growth reduction compared to seedlings grown under F only, but stressed F+I seedlings lodged to a greater extent due to excessive hypocotyl elongation. Temperature-response studies using standardized F-only lighting indicated increased hypocotyl elongation but decreased leaf expansion, and decreased mechano-responsivity to brushing over the temperature range from 20 to 28 °C. Daylength studies indicated similar degrees of mechano-inhibition of hypocotyl elongation over the daylength range of 12, 16, 20, and 24 hours, whereas fresh weight of stressed seedling shoots declined compared to controls. A combination of environmental growth parameters that give repeatable, visual mechanical dwarfing of Arabidopsis include low-PPF fluorescent lighting from 55 to 60 μmol·m-2·s-1, ambient temperatures from 22 to 25 °C, and twice-daily brush treatments.

Traditional overhead lighting of dense crop stands in controlled environments favors development of upper leaf layers to maximize interception of light incident at the top of the foliar canopy. The resultant mutual shading of lower leaves in the understory of the canopy can severely limit productivity and yield of planophile crops. Intracanopy lighting alleviated the effects of mutual shading in dense, vegetative stands of cowpea [Vigna unguiculata (L.) Walp ssp. unguiculata] growing in a controlled environment by sustaining irradiance within the understory throughout development of this edible-foliage crop. For an overhead lighting system, photosynthetic photon flux (PPF) in the understory was reduced to 1% of its initial value by 35 days of growth. PPF in an intracanopy-lighted stand remained within 30 μmol·m-2·s-1 of initial values throughout the 50-day cropping period. Spectral distribution of radiation within the intracanopy-lighted stand also remained relatively constant throughout canopy development. In the overhead-lighted stand, violet and blue radiation in the understory decreased as much as 60% from initial values. Stability of the radiation environment within the intracanopy-lighted stand delayed leaf senescence 27 days beyond when interior leaves of the overhead-lighted canopy began to turn yellow on day 16. The intracanopy-lighted stand produced twice as much edible biomass per unit electrical energy consumed by lamps as for the overhead-lighted system. The treatment differences were due to the continuous presence of understory irradiation when using intracanopy lighting but not when using overhead lighting, and they underscore the importance of the entire foliar canopy in realizing the full productivity potential of dense crop stands in controlled environments.

A copolymer acrylamide acrylate gel was investigated as the sole root matrix for dark-grown seedlings of soybean (Glycine max Merr. `Century 84'). Increasing Ca2+ in the hydrating solution of the hydrogel from 1 to 10 mm decreased its water-holding capacity from 97 to 46 mL·g-1, yet water potential of the medium remained high, sufficient for normal plant growth at all Ca2+ concentrations tested. Elongation rate of dark-grown soybean seedlings over a 54-hour period was 0.9, 1.5, and 1.8 mm·h-1 with 1.0, 2.5, or 5.0 mm Ca2+, respectively, but did not increase with further increases in Ca2+ concentration. Further study revealed that Na+ was released from the hydrogel medium and was taken up by the seedlings as Ca2+ increased in the medium. In dry hypocotyl tissue, sodium content correlated negatively with calcium content. Despite the presence of Na+ in the hydrogel, seedling growth was normal when adequate Ca2+ was added in the hydrating solution. Acrylamide hydrogels hold good potential as a sole growth matrix for short-term experiments with dark-grown seedlings without irrigation.

Photoperiod and harvest scenario of cowpea (Vigna unguiculata L. Walp) canopies were manipulated to optimize productivity for use in future controlled ecological life-support systems. Productivity was measured by edible yield rate (EYR: g·m-2·day-1), shoot harvest index (SHI: g edible biomass·[g total shoot dry weight]), and yield-efficiency rate (YER: g edible biomass·m-2·day-1per [g nonedible shoot dry weight]). Breeding lines `IT84S-2246' (S-2246) and `IT82D-889' (D-889) were grown in a greenhouse under 8-, 12-, or 24-h photoperiods. S-2246 was short-day and D-889 was day-neutral for flowering. Under each photoperiod, cowpeas were harvested either for leaves only, seeds only, or leaves plus seeds (mixed harvest). Photoperiod did not affect EYR of either breeding line for any harvest scenario tested. Averaged over both breeding lines, seed harvest gave the highest EYR at 6.7 g·m-2·day-1. The highest SHI (65%) and YER (94 mg·m-2·day-1·g-1) were achieved for leaf-only harvest of D-889 under an 8-h photoperiod. For leaf-only harvest of S-2246, both SHI and YER increased with increasing photoperiod, but declined for seed-only and mixed harvests. However, photoperiod had no effect on SHI or YER for D-889 for any harvest scenario. A second experiment utilized the short-day cowpea breeding line `IT89KD-288' (D-288) and the day-neutral breeding line `IT87D-941-1' (D-941) to compare yield parameters using photoperiod extension under differing lamp types. This experiment confirmed the photoperiod responses of D-889 and S-2246 to a mixed-harvest scenario and indicated that daylength extension with higher irradiance from high pressure sodium lamps further suppressed EYR, SHI, and YER of the short-day breeding line D-288.

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.

Seedlings of tomato (Lycopersicon esculentum Mill. cv. Rutgers) were agitated periodically on a gyratory shaker. Shaking plants at 175 rpm for 5 minutes once daily during the winter reduced leaf area, stem length, and water content and dry weight of both leaves and stems. This treatment was ineffective when applied during the summer. Five- to 20-minute treatments applied 2 or 3 times daily reduced growth during either season, but were more effective during winter. Responses were independent of the time of day at which treatment took place. Leaf area, stem length, water content of leaves and stems, leaf dry weight, and specific stem water content were reduced progressively relative to undisturbed controls as the shaking rate increased from 125 to 175 rpm during the winter. Leaf area, specific leaf water content, and specific stem water content were reduced by shaking at 44% of full summer sunlight, but not at 31% or 17%. Shaking enhanced specific stem weight only at 44% light, whereas stem length was reduced most by shaking at 17% light. Differences in relative plant response to shaking between summer and winter remained even when seasonal differences in solar flux density were minimized by use of shadecloth during the summer.

Growth in stem length, shoot fresh weight, and leaf surface area of sunflower (Helianthus annuus L.) plants was inhibited by periodic shaking (seismo-stress) or rubbing (thigmo-stress), and by drought-stress treatments. Mechanical- and drought-stress treatment of intact plants reduced xylem exudation from detopped plants. This reduction was accompanied by a reduction in root dry weight only in the case of the drought-stress treatment. Exudate from thigmo-stressed plants contained a broad band of extractable inhibitors some of which co-chromatographed with abscisic acid (ABA). ABA-like substances were not detected in exudate from tall or dwarf controls. Enhanced cytokinin (CK)-like substances were detected in exudate collected from seismo-stressed plants. Shoot tip extracts from thigmostressed plants contained no detectable gibberellin (GA)-like substances, whereas those extracts from unstressed controls contained multiple zones of GA-like activity. Extracts of plant parts most disturbed by a given mechanical treatment yielded no detectable GA-like substances. This study provides evidence that, in addition to auxin and ethylene, other endogenous hormones, particularly GA-like substances, are influenced by mechanical stress in sunflower.

The design and operation of a system is described in which small plants can be grown under controlled environment conditions. Important features of this “Minitron” system include precise control of temperature and CO2 concentration in a flowing atmosphere. Plants can be grown either hydroponically or in solid root support medium. For either culture method, nutrient solution or water is added from an external reservoir, altering neither atmospheric composition nor temperature equilibrium within a closed Minitron chamber.

Seedlings of tomato (Lycopersicon esculentum Mill cv. Rutgers) grown in a greenhouse under conditions of limiting light intensity developed weak stems. Periodic gyratory shaking retarded axial and lateral growth of stems and petioles while strengthening these tissues. Hypocotyls and first internodes excised from shaken plants had greater moduli of elasticity and of rupture and ultimate shear strength than did similar sections cut from undisturbed controls. Threshold of deformation (rigidity) was greatest for stems of shaken plants. The cellulose fraction of stem fiber increased concomitant with elastic strength of shaken tomato seedlings.

Eggplant (Solanum melongena L. var. esculentum ‘Burpee's Black Beauty’) and soybean [Glycine max (L.) Merr. ‘Wells II’] seedlings were assigned to a greenhouse or a windless or windy outdoor environment. Plants within each environment received either periodic seismic (shaking) or thigmic (flexing or rubbing) treatments, or were left undisturbed. Productivity (dry weight) and dimensional (leaf area and stem length) growth parameters generally were reduced more by mechanical stress in the greenhouse (soybean) or outdoor-windless environment (eggplant) than in the outdoor windy environment. Outdoor exposure enhanced both stem and leaf specific weights, whereas mechanical stress enhanced only leaf specific weight. Although both forms of controlled mechanical stress tended to reduce node and internode diameters of soybean, outdoor exposure increased stem diameter.

Growth of Lycopersicon esculentum Mill, and Pisum sativum L. was dwarfed by various forms of mechanical stimulation including shaking, flexing, and rubbing of the plant axis. The general effect of gently shaking a tomato plant once or twice daily was a reduction in node and leaf number, shortening of internodes, nodal swelling, epinasty of leaves, deep greening of new leaves, and increased lateral branch development. It is suggested that the term “seismomorphogenesis” appropriately describes mechanical stress effects on plant growth such as result from wind action.

Tomato accessions PI 128644 (Lycopersicon peruvianum var. dentatum Mill.) and PI 406966 (L. esculentum Mill.) were identified in preliminary screening trials as being relatively nonresistant and resistant to root-zone flooding, respectively. A comparative study of these accessions was undertaken to examine adaptive responses to inundation. Root and shoot growth of both accessions were inhibited by 120 hr of flooding. Aerobic respiratory capacity of secondary roots of both accessions decreased to a similar extent after 24 hr of inundation. Flooding did not significantly affect anaerobic root respiration rate of either accession. Stomatal conductance decreased after 24 hr of flooding for both accessions, with some recovery by PI 406966 after 168 hr of treatment, coinciding with development of adventitious roots on lower stems. Few adventitious roots formed on flooded PI 128644 plants. Leaf water potential of both accessions initially increased as a result of flooding, but declined to near control level by 120 hr of treatment. Total phenol content of PI 128644 roots decreased with 72 hr of flooding, while that of PI 406966 roots was not significantly affected. Factors underlying the greater resistance of PI 406966 to flooding remain unclear, but may include a lower root respiratory requirement for O2 and greater ability to sequester or eliminate toxic substances during inundation.

Red maple (Acer rubrum L.) and baldcypress (Taxodium distichum (L.) Rich.) seedlings were very tolerant of extended flooding, whereas shoots of sugar maple (Acer saccharum Marsh) seedlings experienced desiccation after 8 days of flooding, and leaf death after 14 days. Shoot desiccation occurred after 14 days of flooding. Roots of all 3 species utilized O2 with similar efficiency prior to flood stress. However, the respiratory capacity of sugar maple roots declined substantially during the first 8 days of flooding, and more gradually from 8 to 22 days, at 21, 5, or 0.5% O2. Red maple roots declined gradually in respiratory capacity over the entire flooding period at 21 and 5%, but not at 0.5% O2. After an initial sharp decline, baldcypress roots gradually regained capability to utilize O2 from 8 to 22 days of flooding at all 3 levels of O2. When tested at 21% O2, both red maple and baldcypress roots had 2- to 3-fold higher respiratory capacities than did sugar maple roots after 22 days of flooding. Presoaking root sections from flooded red and sugar maple in a sucrose solution mildly stimulated respiration rates measured at 21% O2, but did not fully restore respiratory capacity lost by flooding either species.

Effects of cyanide (as KCN) and/or salicylhydroxamic acid (SHAM) on respiratory rates (QO2) of excised tree roots were evaluated before and after flooding intact plants. CN, an inhibitor of cytochrome oxidase, stimulated QO2 in flood-intolerant sugar maple (Acer saccharum Marsh.) and Japanese yew (Taxus cuspidata Sieb. and Zucc.), but not in flood-tolerant red maple (Acer rub rum L.), and inhibited QO2 in very flood-tolerant baldcypress (Taxodium distichum (L.) Rich). Eight days of flooding eliminated CN-stimulation of QO2 in sugar maple. SHAM, an inhibitor of the alternative oxidase, had little effect on QO2 of any species when used alone, but greatly inhibited QO2 of all species when combined with KCN, indicating the presence of substantial amounts of both respiratory pathways in flood-tolerant and intolerant species, as well as the ability of electrons to flow from one pathway to another when one is blocked by a specific inhibitor. Flooding reduced root respiration capacity in all species, affecting intolerant species the most and tolerant the least. The exception was QO2 of dormant Taxus roots, which was not inhibited by flooding. CN-sensitive QO2 was lost from roots of intolerant species in particular, and to a lesser extent from more tolerant species. A limiting leveL of O2 (0.5%) suppressed SHAM-sensitive QO2 more than CN-sensitive QO2 indicating a greater affinity for O2 by the CN-sensitive path-way. The evidence is consistent with a model for relative flood tolerance based upon differential damage to the aerobic respiratory mechanism.