EFFECTS OF RADIATION AND CARBON-DIOXIDE LEVEL ON YIELD, GAS EXCHANGE, AND GROWTH OF 'WALDMANN'S GREEN' LETTUCE IN MINITRON II CHAMBERS (PPF, TRIACONTANOL)
Abstract
Minitron II growth chambers, together with their environmental control system, were developed to provide a means of controlling the growth environment of a small canopy of plants. Atmospheric composition of CO(,2) in these chambers can be maintained by means of a computer-assisted mass flow control system. Effects of three levels of incandescent (In) combined with fluorescent (Fl) radiation were tested for 8 days on growth and canopy gas exchange by 'Waldmann's Green' leaf lettuce (Lactuca sativa L.) in Minitron II chambers. Dry matter production and leaf area each were 12 to 17% greater for plants grown in 84/16% than in 16/84% In:Fl irradiance output throughout treatment, whereas relative growth rate (RGR) and photosynthesis (Pn) were only increased for the high-In regime the first four days of treatment. Transferring lettuce from an 84% In environment from 0 to 4 days to 50% In from days 4 to 8 increased plant dry weight, leaf area, RGR, and net assimilation rate (NAR) compared to those under continuous 84% In. Growth and Pn of 'Waldmann's Green' was not different between 84% In + 16% Fl relative to 100% metal halide (MH) radiation under a photosynthetic photon flux (PPF) of 392 (mu)mol s('-1) m('-2) from 11 to 19 days from seeding. Elevating PPF increased leaf dry weight, NAR, and RGR from 0 to 4 days of treatment, but from days 4 to 8 decreased RGR, NAR, and Pn. When CO(,2) was enriched from ambient to 1000 (mu)l l('-1) at a moderate PPF of 450 (mu)mol s('-1)m('-2), leaf fresh weight increased 39%, leaf dry weight 75%, and RGR 20%. Further yield increases were attained by increasing CO(,2) from 1000 to 1500 (mu)l l('-1) at high PPF. After 4 days, growth, RGR, NAR, and Pn were greater and dark respiration less at 1500 than at 2000 (mu)l l('-1) CO(,2) under high PPF. However, from 4 to 8 days, RGR increased and absolute growth was comparable at 2000 or 1500 (mu)l l('-1) CO(,2). Triacontanol (TRIA) was applied as a foliar spray at 4 and 8 days after seeding. TRIA increased plant fresh and dry weight, leaf area, and RGR 12 to 37% relative to plants sprayed with water. (Abstract shortened with permission of author.)
Degree
Ph.D.
Subject Area
Plant propagation
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