Dry Weight Gain Research Articles

Root‐zone temperature affects nutrient uptake and growth of snapdragon

Abstract Nutrient uptake by snapdragon (Antirrhinum majus L. ‘Peoria') was compared at five root‐zone temperatures: 8, 15, 22, 29, and 36°C. Uptake of nitrate (NO3 ‐‐N), ammonium (NH4 +‐N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), boron (B), iron (Fe), manganese (Mn), and zinc (Zn) responded quadratically to increasing root‐zone temperature. Greatest nutrient uptake temperature varied with nutrient but ranged from 15 to 29°C. Uptake of copper (Cu) and molybdenum (Mo) were unaffected by root‐zone temperature. Dry weight gain and stem length also responded quadratically to increasing root‐zone temperature. Optimal temperatures for nutrient uptake and growth were similar, averaging 22°C. These results indicate increasing or maintaining root‐zone temperatures near 22°C maximizes growth and nutrient uptake of snapdragons.

Growth responses and ruminal adaptation of lambs fed crustacean processing wastes

Eighteen Native Louisiana breed (average initial body weight 24 kg) lambs (13 males, five females) were used in two experiments to determine the feeding value of crustacean processing wastes (CW) using either ground dehydrated CW (mixed crayfish and crab; DCW) or fresh, partially comminuted crayfish waste (FCW). In Experiment 1, lambs were fed corn-cottonseed hull based diets (13.5% protein) with either soya-bean meal (CON) or DCW (15% of the diet) as protein sources. The 60 day experiment consisted of a 30 day growth phase immediately preceded and followed by nitrogen (N) metabolism phases (males only). During the second N metabolism phase, a third treatment was included which consisted of lambs (males) completely unadapted to DCW. Ruminal fluid samples (50 ml) were collected at 14 day intervals throughout the 60 day experiment and the in vitro chitin degrading capacity (IVCDC) of the ruminal fluid was determined in 72 h incubations with pure crab chitin. Daily dry matter (DM) intake and body weight gain during the growth phase were similar ( P > 0.05) for lambs fed CON or DCW (1.26 kg vs. 1.44 kg and 263 g vs. 206 g, respectively). Lambs fed DCW had lower ( P < 0.05) body weight gain: DM intake ratio than those fed CON (0.14 vs 0.21, respectively). While changing only marginally in lambs fed CON, ruminal IVCDC increased dramatically in lambs fed DCW (diet × time interaction, P < 0.05) with maximum values occurring by Day 28. In the second N metabolism phase, ruminal NH 3-N measured 4 h after feeding increased dramatically when compared with pre-feeding concentrations in lambs adapted to DCW. In contrast, ruminal NH 3-N concentrations in lambs not adapted to DCW or fed CON were not altered by feeding (time × treatment interaction, P < 0.05). A similar time-dependent trend ( P = 0.13) was observed for plasma urea-N (PUN). Although N balance parameters were not affected ( P > 0.05) by treatment in Experiment 1, blood and ruminal metabolite data suggested that ruminal adaptation may be required to elicit maximum degradation of DCW protein. In Experiment 2, 11 male lambs from Experiment 1 were in a 20 day N metabolism trial. Diets were formulated as described for Experiment 1 with CON or FCW (15% of the diet) as treatments. Only those lambs that had previously received DCW were fed FCW. Apparent N digestion and N retention were greater ( P < 0.05) for lambs fed FCW than for those fed CON. Although PUN in lambs fed CON was not altered by feeding, PUN 4 h after feeding was higher than pre-feeding concentrations in lambs fed FCW (time × treatment interaction, P < 0.05). Data suggested that CW may be incorporated into the diets of growing ruminants to comprise 35–40% of protein intake with positive growth responses. It was further suggested that more than 4 weeks may be needed for full ruminal adaptation to CW. Hence, gradual introduction of CW into ruminant diets may be required before its nutritional benefits are realized.

Photosynthetic Acclimation to Elevated CO2 Occurs in Transformed Tobacco with Decreased Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Content.

Inhibition of net carbon assimilation rates during growth at elevated CO2 was studied in transgenic tobacco (Nicotiana tabacum L.) plants containing zero to two copies of antisense DNA sequences to the small subunit polypeptide (rbcS) gene of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). High- and low-Rubisco tobacco plants were obtained from the selfed progeny of the original line 3 transformant (S.R. Rodermel, M.S. Abbott, L. Bogorad [1988] Cell 55: 673-681). Assimilation rates of high- and low-Rubisco tobacco plants increased 22 and 71%, respectively, when transferred from 35- to 70-Pa CO2 chamber air at 900 [mu]mol m-2 s-1 photon flux density. However, CO2-dependent increases of net carbon assimilation rates of high- and low-Rubisco plants virtually disappeared after 9 d of growth in elevated CO2 chamber air. Total above-ground dry matter production of high- and low-Rubisco plants was 28 and 53% greater, respectively, after 9 d of growth at 70 Pa compared with 35 Pa CO2. Most of this dry weight gain was due to increased specific leaf weight. Rubisco activity, Rubisco protein, and total chlorophyll were lower in both high- and low-Rubisco plants grown in enriched compared with ambient CO2 chamber air. Soluble leaf protein also decreased in response to CO2 enrichment in high- but not in low-Rubisco tobacco plants. Decreased Rubisco activities in CO2-adapted high- and low-Rubisco plants were not attributable to changes in activation state of the enzyme. Carbonic anhydrase activities and subunit levels measured with specific antibodies were similar in high- and low-Rubisco tobacco plants and were unchanged by CO2 enrichment. Collectively, these findings suggested that photosynthetic acclimation to enriched CO2 occurred in tobacco plants either with or without transgenically decreased Rubisco levels and also indicated that the down-regulation of Rubisco in CO2-adapted tobacco plants was related to decreased specific activity of this enzyme.

Influences of soil volume and an elevated CO2 level on growth and CO2 exchange for the Crassulacean acid metabolism plant Opuntia ficus‐indica

Effects of the current (38 Pa) and an elevated (74 Pa) CO2 partial pressure on root and shoot areas, biomass accumulation and daily net CO2 exchange were determined for Opuntia ficus‐indica (L.) Miller, a highly productive Crassulacean acid metabolism species cultivated worldwide. Plants were grown in environmentally controlled rooms for 18 weeks in pots of three soil volumes (2 600, 6 500 and 26 000 cm3), the smallest of which was intended to restrict root growth. For plants in the medium‐sized soil volume, basal cladodes tended to be thicker and areas of main and lateral roots tended to be greater as the CO2 level was doubled. Daughter cladodes tended to be initiated sooner at the current compared with the elevated CO2 level but total areas were similar by 10 weeks. At 10 weeks, daily net CO2 uptake for the three soil volumes averaged 24% higher for plants growing under elevated compared with current CO2 levels, but at 18 weeks only 3% enhancement in uptake occurred. Dry weight gain was enhanced 24% by elevated CO2 during the first 10 weeks but only 8% over 18 weeks. Increasing the soil volume 10‐fold led to a greater stimulation of daily net CO2 uptake and biomass production than did doubling the CO2 level. At 18 weeks, root biomass doubled and shoot biomass nearly doubled as the soil volume was increased 10‐fold; the effects of soil volume tended to be greater for elevated CO2. The amount of cladode nitrogen per unit dry weight decreased as the CO2 level was raised and increased as soil volume increased, the latter suggesting that the effects of soil volume could be due to nitrogen limitations.

Effects of elevated carbon dioxide on three grass species from montane pasture II. Nutrient uptake, allocation and efficiency of use

Agrostis capillaris L. 4 , Festuca vivipara L. and Poa alpina L. were grown in outdoor open-top chambers at either ambient (340 μmol mol -1 ) or elevated (680 μmol mol -1 ) CO 2 for periods from 79 to 189 d. Under these conditions there is increased growth of A. capillaris and P. alpina, but reduced growth of F. vivipara. Nutrient use efficiency, nutrient productivity (total plant dry weight gain per unit of nutrient) and nutrient allocation of all three grass species were measured in an attempt to understand their individual growth responses further and to determine whether altered nutrient-use efficiencies and productivities enable plants exposed to an elevated atmospheric CO 2 environment to overcome potential limitations to growth imposed by soil fertility

Inhibitions of cotton seedling growth by volatile ketones emitted by cover crop residues

Low-input, sustainable agriculture (LISA) systems can include soil incorporation of residues of weeds and legume cover crop species. However, both seed germination and seedling growth of crops, including cotton (Gossypium hirsutum L.), are inhibited by volatile organic compounds emitted by these residues during decomposition. A cotton seedling-growth assay was used to demonstrate that C4 through C9 ketones released by decomposing legume residues significantly inhibited root and shoot elongation, root and shoot fresh and dry weight gain, and cotyledon expansion. Seedling root and shoot water relationships were relatively insensitive to those components of plant residue volatile emissions. Concentration (0.0, 0.5, 1.0, 1.5, or 2.0μM/cm(3) sterile greenhouse soil mix) and root-zone temperature (20 or 30°C) altered the activity of the more inhibitory ketones. Molecular weight (carbon chain length), carbon chain branching, and position of the carbonyl group also influenced ketone inhibitory activity.

ROOT ZONE CUPRIC HYDROXIDE TREATMENT ENHANCES SUBSEQUENT GROWTH OF TOMATO, BUT NOT PEPPER, TRANSPLANTS

`Sunny' tomato (Lycopersicon esculentum Mill.) and `Jupiter' pepper (Capsicum annuum L), seeds were sown in TODD 100A flats (Speedling, Inc.) treated with 100 g/liter cupric hydroxide applied to the root cell surfaces in a latex based carrier (Spin Out, Griffin Corp., Valdosta GA). Total root numbers were not affected by cupric hydroxide but initial root dry weight of 33-day-old tomato plants was reduced 30% by the treatment. Two-weeks after transplanting to sand-culture in the greenhouse, total root dry weight of treated transplants was 4% greater than that of untreated tomato transplants. The rate of shoot dry weight gain of treated transplants over 12 days of sand culture was slightly greater than that of untreated transplants. However, roots of 45-day-old pepper transplants were slower to recover from the copper damage. Initial root dry weight of treated plants was reduced 32% relative to controls. After two weeks of sand culture, root dry weight of treated plants was still 22% less than controls. Shoot growth of pepper transplants was unaffected. Root development inside the plug was particularly lacking indicating reductions in lateral root branching.

Effects on growth and respiration due to the ingestion of the rapeseed meal glucosinolates in young larvae of Tenebrio molitor

1. 1. We investigated the effects of the ingestion of naturally occurring glucosinolates in rapeseed meal on growth rate, metabolic efficiency and respiratory rate in larvae of the yellow mealworm, Tenebrio molitor L. 2. 2. In our feeding studies, larvae were reared on one of seven different diets, including a whole ground wheat control diet and rapeseed meal from six rapeseed varieties. Dry weight gain of larvae and dry food assimilated were measured after 4 weeks of rearing, and the conversion of food into insect biomass was determined. The results may be explained by variations in the glucosinolates content of the diets. 3. 3. The effect of glucosinolates on food consumption, larval growth, expired carbon dioxide, oxygen uptake and respiratory quotient were studied. 4. 4. Glucosinolates did not reduce food assimilation or growth after 1 day of experimentation, but they caused some inhibition of respiratory exchanges and increased the RQ ratio.

MECHANICAL CONDITIONING OF GREENHOUSE-GROWN TRANSPLANTS

Since chemical growth retardants are no longer labelled for use on vegetable transplants, mechanical conditioning provides an alternative method of controlling excessive stem elongation under greenhouse conditions. Mechanical conditioning includes brushing or shaking treatments that physically impact or displace the plant and generally reduce plant growth, increase stem and petiole strength, and improve overall plant quality. The resulting transplants have less breakage during postharvest handling, may be more stress tolerant, and are faster to establish in the field. However, only minor effects on crop yield have been identified. Brushing reduced broccoli transplant size, but improved shoot dry weight gain during field establishment but had no effect on head yield. Brushing is a labor intensive practice for large-scale operations. Current attempts to mechanize brushing require that the plants are uniform in height and treatment tolerant. Additional research in non-contact treatments like shaking or vibration of benches is necessary. The effects of the treatments on stress tolerance and predisposition to disease need to be clarified.

Effects of sunflower residues and tillage on winter wheat

Wheat ( Triticum aestivum L.) and sunflower ( Helianthus annuus L.) offer oppurtunities for double-cropping but little is known about possible effects of sunflower residues on wheat in a cropping sequence. In this study, we have investigated effects of sunflower extracts and residues on wheat germination, growth and yield. Wheat germination in a soilless medium was not affected by aqueous extracts of sunflower residues; however, stem and leaf extracts (1:10 dilution) of dried sunflower tissues did inhibit dry-weight gain of 5-day-old wheat seedlings by 20–40%. In greenhouse studies, ground leaves or forage-chopped shoots, when surface-applied, promoted wheat growth. Wheat tissue had significantly greater N in wheat grown with ground leaf residues. Forty-day-old wheat grown in pots with incorporated, chopped sunflower residues had only one-third the dry weight of plants with the same amount of residue on the soil surface. Chopped sunflower residues equivalent to 6.9 Mg/ha suppressed weed numbers by 50% if incorporated, and ground leaf material surface-applied at 15 Mg/ha reduced weed populations by approximately 75% when compared to residue-free treatments. In a split-plot study, wheat was grown following sunflower or fallow. The plot splits were managed as either no-till (residues on surface) or conventionally tilled (residues incorporated). Wheat grain yields were higher in the no-till treatments (5.2 Mg/ha) than in the conventionally tilled treatments (4.9 Mg/ha). Residue applications rates did not affect grain yields. Overall, the results suggest that sunflower residues can inhibit early wheat and weed growth and that incorporation of residues may reduce grain yields, but no-till production of wheat following sunflower appears viable.

Drought, Paclobutrazol, Abscisic Acid, and Gibberellic Acid as Alternatives to Daminozide in Tomato Transplant Production

`Floradade' tomato (Lycopersicon esculentum Mill.) transplants treated with foliar sprays of paclobutrazol at 0, 14, 30, 60, or 90 ppm exhibited reductions in stem length, leaf area, and plant dry weight in a cubic response pattern. Gibberellic acid (GA) drenches, at 10, 100, or 250 ppm, increased stem length, leaf area, and plant dry weight. Daminozide (2500 or 5000 ppm) sprays reduced leaf area and dry weight, but 5000 ppm had no effect on stem length. Abscisic acid drenches, at 275, 660, or 1320 ppm, did not affect final plant size. In subsequent experiments to produce transplants for field evaluation, plants treated with paclobutrazol sprays at 90 (1987) and 14 or 60 ppm (1988) had smaller leaf area, stem length, and shoot dry weight than untreated plants. In 1987,90 ppm paclobutrazol reduced stem shear strength, while 2500 ppm daminozide increased stem strength relative to controls. In 1988, 2500 ppm daminozide increased transplant growth while 660 ppm abscisic acid had no effect. Paclobutrazol (14 ppm) and drought improved field establishment of transplants as measured by shoot dry weight gain after field planting. In 1988, total fruit yield was reduced by 60 ppm paclobutrazol and GA. Although fruit size was unaffected by treatments, fruit number was reduced by GA. Chemical names used: butanedioic acid mono (2,2-dimethylhydrazide) (daminozide); B-[(4-chlorophenyl)methyl]-α -(1,1-dimethylethyl) -N-1,2,4-triazole-1-ethanol (paclobutrazol).

Response of maize and rice to 9-?-L(+) adenosine applied under different environmental conditions

The increase in growth, determined by dry weight gain, of rice (Oryza sativa L.) and maize (Zea mays L.) caused by foliar applications of 9-β-L(+) adenosine, a putative second messenger elicited by triacontanol, was studied under different environmental conditions. Maize seedlings cultured in the greenhouse under approximately 100 μmol m−2s−1 of light prior to treatment with L(+) adenosine did not respond unless they received supplemental light (250–300 μmol m−2s−1) after treatment. Exposure of rice seedlings growing for 16 h at 150 μmol m−2s−1 to short periods of 450 μmol m−2s−1 (< than 20 min) had no effect on the positive response of rice to L(+) adenosine; however, exposure for 60 min or more increased the growth of rice and obviated the effect of L(+) adenosine. Rice seedlings treated with L(+) adenosine at different times during the day responded only when treated 9 to 12h after initiation of the photoperiod. Normal growing temperatures under different light intensities had little or no direct effect on the response of plants to L(+) adenosine.

Growth and 14C-Photosynthate Allocation in Citrus Nursery Trees Subjected to One of Three Bud-forcing Methods

Three commercially employed treatments to force scion bud growth were compared using greenhouse-grown `Carrizo' citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.] seedlings budded with `Hamlin' orange [Citrus sinensis (L.) Osb.]. Scion buds were forced either by 1) cutting off (removing the rootstock shoot above the bud union); 2) lopping (cutting half-way through the rootstock shoot above the bud union and breaking over the rootstock stem); or 3) bending (bending the rootstock shoot to its base and tying it in position). Plants were harvested, dried, and weighed at various times after scion shoot emergence. Plants on which rootstock shoots remained attached (lopping or bending) had the largest scion leaf area and gained the most scion and whole-plant dry weight. Bending rootstock shoots also resulted in a longer scion, more leaves, and higher root dry weight than did removal of rootstock shoots by cutting off. Few differences in overall growth were observed among trees retaining their rootstock shoots after two scion growth flushes. Removal of rootstock shoots after the first scion growth flush reduced leaf area and dry weight gain of the second scion growth flush; however, it did not affect total scion leaf area or dry weight. Analysis of 14C-photosynthate transfer from labeled rootstock leaves showed that bending allowed the greatest movement of labeled assimilates to other plant parts during the 24 hours after 14CO2 fixation. Radiolabeled photosynthates from rootstock leaves were partitioned primarily to shoots during scion growth flushes and to roots during periods between growth flushes.

Growth criteria of two common cyanobacteria isolated from Egyptian flooded soil, as influenced by some pesticides

Higher rates of the two organophosphorus Insecticides (dimethoate and dursban) induced severe drop in the dry weight gain of Nostoc muscorum and Anabaena oryzae. The fungicide karathane seemed to be inhibitory to the growth of Anabaena whereas all levels of the fungicide, except the two higher stimulated the growth of Nostoc. Trifluralin at all levels inhibited the growth of both organisms. However the magnitude of inhibition was always more pronounced in Anabaena. The lowest concentrations of dursban and dimethoate favored chlorophyll a synthesis in the cells of both cyanobacteria. Contrary to chlorophyll, total carotenoid accumulation was significantly suppressed. Moderate and higher doses of karathane and trifluralin increased chlorophyll a biosynthesis in Nostoc and to lesser extent in Anabaena, a phenomenon that was accompanied by significant increase in total carotenoid content. Glucose uptake by both organisms from media was accelerated following adminestration of all pesticides, an effect that was intensified with further increase in concentrations. Dimethoate and dursban favored the total carbohydrate accumulation in the cells of both organisms, whereas karathane and trifluralin accentuated the process, more prominently in Nostoc.

Modification of Yield and Chlorophyll Content in Leaf Lettuce by HPS Radiation and Nitrogen Treatments

This study evaluated the potential of high photosynthetic photon flux (PPF) from high-pressure sodium (HPS) lamps, alone or in combination with metal halide (MH) plus quartz iodide (QI) incandescent lamps, to support lettuce growth, with or without N supplementation. Varying exposures to radiation from combined HPS, MH, and QI lamps influenced dry weight gain and photosynthetic pigment content of hydroponically grown Black-Seeded Simpson' lettuce (Lactuca sativa L.) seedlings. Cumulative leaf dry weight declined with increasing exposure, up to 20 hours per day, to 660 micromoles m-2 s-1 of photosynthetically active radiation (PAR) from HPS lamps concomitant with constant 20 hours per day of 400 micromoles m-2 s-1 from MH + QI lamps. Leaves progressively yellowed with increasing exposure to radiation from the three-lamp combination, corresponding to lower specific chlorophyll content but not to specific carotenoid content. Lettuce grown under 20-hour photoperiods of 400, 473, or 668 micromoles m-2 s-1 from HPS radiation alone had the highest leaf dry weight at a PPF of 473 micromoles m-2 s-1. Chlorophyll, but not carotenoid specific content, decreased with each incremental increase in PPF from HPS lamps. Doubling the level of N in nutrient solution and supplying it as a combination of NH4+ and NO3- partially ameliorated adverse effects of high PPF on growth and pigment content relative to treatments using single-strength N as NO3-.

Stability of salt tolerance at the cell level after regeneration of plants from a salt tolerant tobacco cell line

Plants were regenerated from both the wild type and a stable NaCI‐tolerant line of tobacco cells (Nicotiana tabacum/gossii). The regeneration process was much more difficult in the case of the NaCI‐tolerant line and was only successful in the absence of NaCI. These plants differed morphologically from those regenerated from the wild type cell line, exhibiting abnormally short internodes, small leaves and reduced growth. Cell suspension cultures derived from plants regenerated from the stable NaCI‐tolerant line retained a high level of tolerance to salt. The NaCI‐concentration required to reduce fresh and dry weight gain by 50% was about twice that observed in the case of the cells obtained from wild type plants.The results presented here, together with those of Watad et al. (1985), indicate that resistance to salt is operating and stable at the cellular level before and after plant regeneration. When the regenerated plants were grown in increasing levels of salt their growth response was not clearly different from that of the plants regenerated from the wild type cell line. However, the survival of plants on high concentrations of NaCI tended to be higher in the case of plants regenerated from the NaCI‐tolerant cell line.

The Effect of Brushing on the Growth and Quality of Field-grown Root Crops

Shoots of field-grown plants of European radish (Raphanus sativus L. `Comet'), Japanese radish (daikon) (R. sativus L. `Mino-wase'), and Asian turnip (Brassica rapa L. `Hinona') were brushed twice daily, 40 cycles (back-and-forth strokes equal one cycle), for 8 (short-term) or 13, 21, or 14 days (long-term), respectively. European turnip (B. rapa L. `Hikari-kabu') plants were grown in a raised bed in an uncovered plastic house and were brushed for 9 or 21 days. Short-term brushing reduced root dry weight and the root: shoot dry weight ratio (R: S) of European radish, whereas the treatment increased these measurements for Asian turnip and European turnip. Short-term brushing had no effect on growth of Japanese radish plants, but increased root dry weight gain by both turnip cultivars, thereby increasing their R: S ratios. Lung-term brushing reduced root dry weight gain and the R: S ratio of European radish and root dry weight of Asian turnip but had no effect on these measurements for the other crops. Long-term brushing reduced cracking of European radish roots, thereby resulting in a higher proportion of oblong (medium quality) roots. Consequently, the percentage of marketable-quality roots of European radish was increased by brushing. Lung-term brushing increased the percentage of medium-sized roots of Asian turnip at the expense of large-sized roots. Brushing had no effect on root quality of European turnip.

Growth Yields and Maintenance Coefficients of Unadapted and NaCl-Adapted Tobacco Cells Grown in Semicontinuous Culture

Comparison of carbon utilization between unadapted and NaCl (428 millimolar) adapted tobacco (Nicotiana tabacum L.) cells under substrate limited growth conditions was facilitated using semicontinuous culture. Growth yields (Y(g)) and maintenance coefficients (m) of unadapted and NaCl adapted cells were similar, indicating that the efficiency of carbon utilization for growth was not altered as a result of salt adaptation and that no additional metabolic costs were associated with growth of adapted cells in the presence of a high concentration (428 millimolar) of NaCl. The Y(g) (0.588 grams organic dry weight gain per gram sugar uptake) and m values (0.117 grams sugar uptake per gram organic dry weight per day) were comparable in spite of substantial physiological and biochemical differences that exist between unadapted and NaCl adapted cells. Apparently, a metabolic homeostasis governs biomass production of cells before and after adaptation to salinity.

Root Restriction as a Factor in Photosynthetic Acclimation of Cotton Seedlings Grown in Elevated Carbon Dioxide

Interactive effects of root restriction and atmospheric CO(2) enrichment on plant growth, photosynthetic capacity, and carbohydrate partitioning were studied in cotton seedlings (Gossypium hirsutum L.) grown for 28 days in three atmospheric CO(2) partial pressures (270, 350, and 650 microbars) and two pot sizes (0.38 and 1.75 liters). Some plants were transplanted from small pots into large pots after 20 days. Reduction of root biomass resulting from growth in small pots was accompanied by decreased shoot biomass and leaf area. When root growth was less restricted, plants exposed to higher CO(2) partial pressures produced more shoot and root biomass than plants exposed to lower levels of CO(2). In small pots, whole plant biomass and leaf area of plants grown in 270 and 350 microbars of CO(2) were not significantly different. Plants grown in small pots in 650 microbars of CO(2) produced greater total biomass than plants grown in 350 microbars, but the dry weight gain was found to be primarily an accumulation of leaf starch. Reduced photosynthetic capacity of plants grown at elevated levels of CO(2) was clearly associated with inadequate rooting volume. Reductions in net photosynthesis were not associated with decreased stomatal conductance. Reduced carboxylation efficiency in response to CO(2) enrichment occurred only when root growth was restricted suggesting that ribulose-1,5-bisphosphate carboxylase/oxygenase activity may be responsive to plant source-sink balance rather than to CO(2) concentration as a single factor. When root-restricted plants were transplanted into large pots, carboxylation efficiency and ribulose-1,5-bisphosphate regeneration capacity increased indicating that acclimation of photosynthesis was reversible. Reductions in photosynthetic capacity as root growth was progressively restricted suggest sink-limited feedback inhibition as a possible mechanism for regulating net photosynthesis of plants grown in elevated CO(2).

Growth Retardants Affect Landscape Performance of Zinnia, Impatiens, and Marigold

Various spray rates of paclobutrazol, 5000 ppm daminozide, 200 ppm ancymidol, or drought imposition (visible wilt symptoms for up to 2 hours daily) were applied to three bedding plant species to determine effects on growth in the greenhouse and the subsequent growth and performance of treated plants in the landscape. Seedlings of Zinnia efegans Jacq. `Peter Pan Scarlet' responded to all growth retardants (paclobutrazol at 40 and 90 ppm) and the drought treatment in the greenhouse. However, zinnias treated with paclobutrazol or ancymidol still exhibited reductions in plant height 5 and 7 weeks after transplanting to the landscape, and in plant quality (subjective rating of plant appearance with emphasis on flower cover) at 5 weeks after transplanting. Daminozide or drought controlled zinnia growth in the greenhouse but had no carry-over effect in the landscape. Stem elongation of Impatiens wallerana Hook `Accent Red' seedlings was moderately controlled by 20 ppm paclobutrazol in the greenhouse. There were no other treatment effects in the greenhouse. Paclobutrazol (20 ppm) reduced final plant height and quality (7 weeks postplanting). Treatment with daminozide or drought reduced plant width and quality after 5 and 7 weeks in the landscape. Ancymidol had no effect on landscape performance of impatiens. Shoot dry weight gain and stem elongation of Tagetes erects L. `Papaya Crush' seedlings were reduced by ancymidol or 40 ppm paclobutrazol in the greenhouse. Shoot dry weight gain of marigold seedlings was inhibited during the first week of landscape establishment by prior treatment with daminozide, ancymidol, or drought. Final plant height and width in the landscape were not affected by any treatment; however, 40 ppm paclobutrazol, daminozide, or ancymidol decreased final plant quality. Chemical names used: α -cyclopropylα -(4-methoxyphenyl) -5-pyrimidinemethanol (ancymidol); butanedioic acid mono(2,2-dimethylhydrazide) (daminozide); β -[(4-chlorophenyl) methyl] - β - (1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).