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  • Author or Editor: Raymond M. Wheeler x
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Abstract

Greenhouse tomatoes (Lycopersicon esculentum Mill. cv. Tropic) subjected to 10 seconds of gentle water spraying each day were inhibited up to 40% in plant height, compared to unsprayed controls or plants wet each day with a water mist. Manual shaking of the stems for 10 seconds each day produced reduction in stem elongation similar to the spraying. Spraying or shaking also slightly reduced fresh weights and yields.

Open Access

The effect of photoperiod (PP) on net carbon assimilation rate (Anet) and starch accumulation in newly mature canopy leaves of `Norland' potato (Solanum tuberosum L.) was determined under high (412 ∝mol·m-2·s-1) and low (263 ∝mol·m-2·s-1) photosynthetic photon flux (PPF) conditions. The Anet decreased from 13.9 to 11.6 and 9.3 μmol·m-2·s-1, and leaf starch increased from 70 to 129 and 118 mg·g-1 drymass (DM) as photoperiod (PP) was increased from 12/12 to 18/6, and 24/0, respectively. Longer PP had a greater effect with high PPF conditions than with low PPF treatments, with high PPF showing greater decline in Anet. Photoperiod did not affect either the CO2 compensation point (50 μmol·mol-1) or CO2 saturation point (1100-1200 μmol·mol-1) for Anet. These results show an apparent limit to the amount of starch that can be stored (≈15% DM) in potato leaves. An apparent feedback mechanism exists for regulating Anet under high PPF, high CO2, and long PP, but there was no correlation between Anet and starch concentration in individual leaves. This suggests that maximum Anet cannot be sustained with elevated CO2 conditions under long PP (≥12 hours) and high PPF conditions. If a physiological limit exists for the fixation and transport of carbon, then increasing photoperiod and light intensity under high CO2 conditions is not the most appropriate means to maximize the yield of potatoes.

Free access

The National Aeronautics and Space Administration (NASA) has been conducting controlled environment research with potatoes (Solanum tuberosum L.) in recirculating nutrient film technique (NFT)-hydroponic systems as a human life support component during long-duration spaceflight. Standard nutrient solution management approaches include constant pH regulation with nitric acid (HNO3) and daily adjustment of electrical conductivity (EC) equivalent to half-strength modified Hoagland's solution, where nitrate (NO3-) is the sole nitrogen (N) source. Although tuber yields have been excellent with such an approach, N use efficiency indices are expected to be low relative to tuber biomass production. Furthermore, the high amount of N used in NFT-hydroponics, typically results in high inedible biomass, which conflicts with the need to minimize system mass, volume, and expenditure of resources for long-duration missions. More effective strategies of N fertilization need to be developed to more closely match N supply with demand of the crop. Hence, the primary objective of this study was to identify the optimal N management regime and plant N requirement to achieve high yields and to avoid inefficient use of N and excess inedible biomass production. In separate 84-day cropping experiments, three N management protocols were tested. Treatments which decreased NO3 --N supply indirectly through lowering nutrient solution EC (Expt. I), or disabling pH control, and/or supplying NH4 +-N (Expt. III) did not significantly benefit tuber yield, but did influence N use efficiency indices. When supplied with an external 7.5 mm NO-3 --N for the first 42 days after planting (DAP), lowered to 1.0 mm NO3 -N during the final 42 days (Expt. II), plants were able to achieve yields on par with plants which received constant 7.5 mm NO3 --N (control). By abruptly decreasing N supply at tuber initiation in Expt. II, less N was taken up and accumulated by plants compared to those which received high constant N (control). However, proportionately more plant accumulated N was used (N use efficiency) to produce tuber biomass when N supply was abruptly lowered at tuber initiation in Expt. II. Hence, a hydroponic nutrient solution N management system may be modified to elicit greater plant N-use while maintaining overall high tuber yield as opposed to achieving high tuber yields through excess N supply and shoot growth.

Free access

Reduced atmospheric pressures may be used to minimize mass and engineering requirements for plant growth habitats used in some extraterrestrial applications. A chamber with high vacuum capability and thermal control at Kennedy Space Center was used to measure water loss of lettuce plants at reduced atmospheric pressures. A test stand with three, high-pressure sodium vapor lamps was used to determine short-term plant responses to reduced pressure. Initial experiments with lettuce showed that a pressure of 10 kPa (≈0.1 atm) resulted in a 6.1-fold increase in the rate of water loss compared to water loss at ambient pressure. However, due to low relative humidity, plants wilted after 30 minutes exposure to 10 kPa. A follow-up experiment in which relative humidity was controlled between 70% and 85%, demonstrated that water loss was directly proportional to the vapor pressure gradient, regardless of atmospheric pressure in the pressure range of 10 to 101 kPa. However, the response was curvilinear, suggesting effects on the pathway resistance. Results indicate that plant growth at atmospheric pressures of 5 to 10 kPa should be achievable. Further work will necessitate better relative humidity control and carbon dioxide control in order to separate vapor pressure deficit effects from diffusion effects.

Free access

Ethylene production by 10 or 20 m2 stands of wheat, soybean, lettuce, potato, and tomato was monitored throughout growth and development in an atmospherically closed plant chamber. Chamber ethylene levels varied among species and rose during periods of canopy expansion and rapid growth for all species. Following this, ethylene levels either declined during seed fill and maturation for wheat and soybean, or remained relatively constant for potato and tomato (during flowering and early fruit development). Lettuce plants were harvested during rapid growth and peak ethylene production. Chamber ethylene levels increased rapidly during tomato ripening, reaching concentrations about 10 times that measured during vegetative growth. The highest ethylene production rates during vegetative growth ranged from 1.6 to 2.5 nmol·m-2·d-1 during rapid growth of lettuce and wheat stands, or about 0.3 to 0.5 nmol·g-1 fresh weight per hour. Estimates of stand ethylene production during tomato ripening showed that rates reached 43 nmol·m-2·d-1 in one study and 93 nmol·m-2·d-1 in a second study with higher lighting, or about 50× that of the rate during vegetative growth of tomato. In a related test with potato, the photoperiod was extended from 12 to 24 hours (continuous light) at 58 days after planting (to increase tuber yield), but this change in the environment caused a sharp increase in ethylene production from the basal rate of 0.4 to 6.2 nmol·m-2·d-1. Following this, the photoperiod was changed back to 12 h at 61 days and ethylene levels decreased. The results suggest three separate categories of ethylene production were observed with whole stands of plants: 1) production during rapid vegetative growth, 2) production during climacteric fruit ripening, and 3) production from environmental stress.

Free access

A system and methodology were developed for the nondestructive qualitative and quantitative analysis of volatile emissions from hydroponically grown `Waldmann's Green' leaf lettuce (Lactuca sativa L.). Photosynthetic photon flux (PPF), photoperiod, and temperature were automatically controlled and monitored in a growth chamber modified for the collection of plant volatiles. The lipoxygenase pathway products (Z)-3-hexenal, (Z)-3-hexenol, and (Z)-3-hexenyl acetate were emitted by lettuce plants after the transition from the light period to the dark period. The volatile collection system developed in this study enabled measurements of volatiles emitted by intact plants, from planting to harvest, under controlled environmental conditions.

Free access

To investigate the effects of environment on plant volatile emissions, `Waldmann's Green' leaf lettuce was cultivated under different levels of photosynthetic photon flux (PPF), photoperiod, and temperature. A modified growth chamber was used to sample plant volatile emissions nondestructively, over time, and under controlled conditions. Total volatile emission rates were significantly higher from lettuce cultivated under PPF of 360 or 200 μmol·m-2·s-1 compared to 105 μmol·m-2·s-1, and significantly higher under a 16-h photoperiod than an 8-h photoperiod. No differences were detected among emission rates from different temperature treatments. In controlled environments, emissions could be regulated by adjusting environmental conditions accordingly.

Free access

Abstract

Polyurethane foam plugs commonly are used as collars or supports to grow plants in solution culture. Despite their utility, these foam plugs can be quite toxic to plants, particularly to small seedlings. We have observed tissue injury in tests using plugs to support lettuce, red beet, and potato plants in solution culture. Typically, the injury is initiated on the hypocotyl or stem tissue in direct contact with the foam, and appears within 30 hr as a brownish discoloration on the tissue surface. This discoloration can be followed by complete collapse of affected tissue and eventual death of the seedling. When injury does not progress beyond surface browning, the seedling survives but growth is slowed. In this paper, we report on different treatments that can be used to remove the toxicity of these plugs so they can be used in plant research.

Open Access