Increased Stem Height Research Articles

Effects of shading and humus fertility on growth, competition, and ectomycorrhizal colonization of boreal forest tree seedlings

We performed a pot experiment to study the effects of varying levels of vegetation shade and humus fertility, simulating natural conditions of the boreal forest, on growth, interspecific competition, and ectomycorrhizal colonization of seedlings of three coexisting tree species: Pinus sylvestris L., Picea abies (L.) Karst., and Betula pendula Roth. In contrast to late-successional Picea abies, early-successional species Pinus sylvestris and particularly B. pendula responded to shade with an increase in stem height and with some changes in biomass, especially in the high-fertility humus. Humus fertility had greater effects on biomass of seedlings than did shade treatments. Interspecific competition among pairwise combinations of the three species was greatest in the high-fertility humus, but was not affected by shade. Betula pendula was the strongest competitor among species; it was not affected by the presence of coexisting species and strongly suppressed coniferous seedlings, especially in the high-fertility humus. Generally, ectomycorrhizal colonization was not affected by shade treatments, but was highest in the low-fertility humus. These results show that effects of light, humus fertility, and presence of neighbours are species specific, and these differences are important for the competitive and recruitment abilities of seedlings of coexisting tree species and ultimately for the species composition of developing forests.

Screening of willow species for resistance to heavy metals: Comparison of performance in a hydroponics system and field trials

The aim of this study was to ascertain whether metal resistance in willow (Salix) clones grown in a hydroponics screening test correlated with data from the same clones grown independently in a field trial. If so, results from a short‐term, glasshouse‐based system could be extrapolated to the field, allowing rapid identification of willows suitable for planting in metal‐contaminated substrates without necessitating long‐term field trials. Principal Components Analysis was used to show groups of clones and to assess the relative importance of the parameters measured in both the hydroponics system and the field; including plant response factors such as increase in stem height, as well as metal concentrations in plant tissues. The clones tested fell into two distinct groups. Salix viminalis clones and the basket willow Black Maul (S. triandra) were less resistant to elevated concentrations of heavy metals than a group of hardier clones, including S. burjatica ’Germany,’ S.x dasyclados, S. Candida and S. spaethii. The more resistant clones produced more biomass in the glasshouse and field, and had higher metal concentrations in the wood. The less resistant clones had greater concentrations of Cu and Ni in the bark, and produced less biomass in the glasshouse and field. Significant relationships were found between the response of the same clones grown the in short‐term glasshouse hydroponics system and in the field.

Interactive effects of lateral shade and wind on stem allometry, biomass allocation, and mechanical stability in Abutilon theophrasti (Malvaceae)

The effects of lateral shade and wind on stem allometry, whole-plant biomass allocation, and mechanical stability were examined for Abutilon theophrasti in a fully factorial glasshouse experiment. Lateral shade from neighboring plants increased stem height by 33% relative to control plants grown individually, despite a decrease in plant dry mass. Intermittent wind decreased stem height by 18% in unshaded plants, but by only 3% in shaded plants. Surprisingly, both lateral shade and wind caused decreases in stem diameter, even with diameter controlled for height, resulting in low diameter : height ratios in wind-treated plants relative to untreated plants. Under shade, wind-treated plants had higher root allocation than untreated plants, which allowed wind-treated shade plants to compensate for a low diameter : height ratio. This did not occur in the absence of shade, where stem tissue density and root allocation of wind-treated plants did not exceed that of untreated plants. Nevertheless, wind-treated plants experienced low drag relative to untreated plants due to a lower leaf area. Consequently, stem deflections of wind-treated plants did not exceed those of untreated plants at any given windspeed. Our results document a complex interaction between shade and wind on plant morphology and suggest that the nature of this interaction is generally that lateral shade acts to reduce or eliminate thigmomorphogenic responses.

Vessel-element dimensions and frequency within the most current growth increment along the length of Eucalyptus globulus stems

The mean number of vessels per unit area in the outer most growth increment at six percentage heights in individual trees, viewed in transverse section, showed an increasing trend from basal to apical regions. The highest frequency of vessels occurred at 90% of total tree height (23.58 mm–2) while the lowest frequency (9.99 mm–2) was recorded at 15% of total tree height from the base. Vessel elements were largest at 15% of total tree height and proceeded to decrease in size with increased stem height. Average radial measurements ranged between 111.27 µm and 160.0 µm while average tangential measurements ranged between 76.30 µm and 112.80 µm. There was variation seen at each percentage height between collection dates (i.e. individual trees); however, the trend of increasing vessel frequency from basal to apical regions existed regardless of between-tree variation in dimensions. Vessel-element dimensions showed a similar, but inverse trend to vessel-element frequency with the largest vessel elements located at 15% of total tree height and the smallest vessel elements located at 90% of total tree height.

The mechanics of Norway spruce [ Piceaabies (L.) Karst]: mechanical properties of standing trees from different thinning regimes

In the first part, the authors discuss the mechanical stability of dominant and suppressed Norway spruce trees ( Picea abies) grown under differing thinning regimes with a focus on the stem shape and the mechanical properties of the standing tree. In the second part, they concentrate on the variation of the modulus of elasticity of green wood (MOE fresh) and the density within the stem to analyse the effect of the underlying patterns in variation of these wood properties on the mechanics of the entire stem. At the standing-tree level, the investigations comprised a morphological description and static bending tests on the trees to measure flexural stiffness and structural Young’s modulus of the stem. Discs sampled from different stem heights were examined to distinguish between different tissues (cortex, wood, pith) and wood types (adult, adolescent, juvenile), and to measure quantitatively their contribution to the axial second moment of area of the stem. An analysis of the variation of density and MOE fresh within the stem was carried out on small wood samples cut out of stem sections taken from the same height as the stem discs. The flexural stiffness of the trees is mainly influenced by stem radius, resulting in a higher flexural stiffness for thicker trees. Independently from the stem dimensions, the structural Young’s modulus was slightly higher for the suppressed trees within each site. In an individual tree the structural Young’s modulus decreases with increasing stem height. The cross-sectional analyses of wood type proportions and their characterisation by density and MOE fresh showed that the distribution of adult, adolescent and juvenile wood within the stem affects the structural Young’s modulus and the flexural stiffness of the stem. Finally, a method is presented that allows a re-calculation of the mechanical bending properties of the entire standing trees using MOE and axial second moments of area of the different wood types. Our results suggest that further modelling of mechanical behaviour of trees might be possible taking into account the composite nature of conifer stems.

Rate and time of GA 4/7 treatment affect vegetative growth and flowering in a genetic line of Aquilegia × hybrida Sims

Aquilegia `Rose-White' flowered from seed in about five months without vernalization. GA 4/7 treatment increased stem height, induced earlier flowering, and increased the number of flowers/plant. Each of these responses, however, was dependent upon both rate (10, 25, or 50 ppm) and timing of application (4-, 8-, or 12-leaf stage). Treatment at the 4-leaf stage resulted in earlier flowering at all rates, had no effect on stem height, but reduced the number of flowers/plant and total leaf area. Treatment at the 8-leaf stage induced earlier flowering at all rates, and increased both the number of flowers/plant and plant height (50 ppm), but had no effect on total leaf area. Treatment at the 12-leaf stage had no effect on time of flowering, but increased the number of flowers/plant, plant height (50 ppm) and total leaf area, at all rates. A rate of 50 ppm at the 8-leaf stage is the optimal treatment resulting in earlier flowering with increased plant height and number of flowers/plant.

Internal oxygen levels decrease during the growing season and with increasing stem height

The oxygen levels in the sapwood of Norway spruce [Picea abies Karst. (L.)] trees were measured by GC-MS (gas chromatography – mass spectrometry) as stem growth progressed during the growing season. The measurements were made on 30-year-old, 13–15 m high, trees growing on three plots which were irrigated, left undisturbed or subjected to drought. The oxygen measurements were done at 1.5, 4 and 8 m above the ground. The internal oxygen levels dropped to about 5% of the level in air in irrigated trees, 1–3% in control trees and to below 1% in trees subject to drought between mid-July and mid-August. In the trees subjected to drought there where no differences in internal oxygen concentrations between the positions on the tree during the growing season except for a faster increase back to ambient concentration occurring in late August in the 1.5 m position. In trees growing on the two other plots the internal oxygen concentration was higher near the ground than at 4 or 8 m above ground during July and August. At all other dates there were no differences between the positions. The results indicate that there is an oxygen gradient with levels decreasing acropetally, giving indirect support to the hypothesis that oxygen is supplied to the growing stem in the transpiration stream.

Growth and yield of 3 hybrid papayas (Carica papaya L.) under mulched and bare ground conditions

At Yarwun (151.3˚E, 23.75˚S), Australia, papaya Hybrid 29 yielded twice as much fruit as Hybrid 11 and 30% more than Hybrid 13. The plots mulched with coarse grass hay yielded 50% more fruit than the plots with bare ground. The highest yielding treatment, Hybrid 29 + mulch, averaged the equivalent of 81 t/ha.year over the 16.5-month harvest period. The yields were achieved in spite of inadequate water supply due to drought and the loss of 877 plants from 1441 plant positions (4 plants per position) due to the 3 phytoplasma diseases; dieback, yellow crinkle and mosaic. Hybrid 29 produced higher yields than the other hybrids by flowering early on shorter plants with thicker stems and setting more fruit that commenced lower down on the stem. Hybrid 13 was intermediate in size and the amount of fruit setting between Hybrid 29 and Hybrid 11 but was the slowest to flower and set fruit. Hybrid 11 had the thinnest and tallest stems, flowered at an intermediate time between the other 2 hybrids and produced fewer flowers and fruit resulting in the lowest yield. Mulching increased stem height and thickness, promoted earlier flowering and increased fruit set, yield and average fruit weight

270 Root, Stem, and Fruit Growth of `Tainung 1' Papaya Plants following Defoliation

The influence of plant size on recovery following defoliation of `Tainung 1' papaya was used to study the role of respiratory sink size relative to photosynthetic surface area and the carbohydrate pool size available for remobilization. Defoliated (D) plants at three different ages: oldest, 24 weeks posttransplant (PT), supporting ≈8 weeks of fruit set; intermediate, 10 weeks PT, ≈2 weeks from initial flowering; and youngest, 4 weeks PT, were compared to an equal number of control plants. The oldest plants abscised all fruit <5.5 cm in diameter as a result of defoliation. Increase in stem height and basal circumference ceased on all plants and increase in fruit circumference ceased on the oldest plants following defoliation. Increase in stem height of D plants began again 3 weeks postdefoliation (PD) and returned to that of control plants by 6 weeks PD. Increase in basal circumference of D plants began again 6 weeks PD. Root density was observed on observation windows, and fine roots completely disappeared within 1 week PD. Root density returned to that of control plants by 6 weeks for the youngest and intermediate plants and by 8 weeks for the oldest plants. Increase in fruit circumference of pre-existing fruit for the oldest D plants never returned to that for control plants. These plants began setting fruit again ≈8 weeks PD. Defoliation delayed initial flowering of the intermediate plants 6.5 weeks and of the youngest plants ≈2 weeks. Thus, the greatest impact of defoliation on reproductive growth occurred with the two oldest age groups.

Black alder (Alnus Glutinosa (L.) Gaertn.) trees mediate methane and nitrous oxide emission from the soil to the atmosphere

Three-year-old seedlings of black alder (Alnus glutinosa (L.) Gaertn.), a common European wetland tree species, were grown in native soil taken from an alder swamp. Fluxes of methane (CH4) and nitrous oxide (N2O) between the tree stem and the atmosphere were determined under controlled conditions. Both CH4 and N2O were emitted through the bark of the stem into the atmosphere when the root zone exhibited ‘higher-than-ambient’ CH4 and N2O gas mixing ratios. Flooding of the soil caused a decreased N2O emission but an increased CH4 efflux from the stem. Immediately after flooding of the soil, N2O was emitted from the seedlings' bark at a rate of 350 μmol N2O m-2 h-1 whereas CH4 flux could not be detected. After more than 40 days of flooding CH4 fluxes up to 3750 μmol CH4 m-2 h-1 from the stem were measured, while N2O emission had decreased below the limit of detection. Gas efflux decreased with increasing stem height and correlated with gas mixing ratios in the soil, indicating diffusion through the aerenchyma as the major path of gas transport. From these results it is assumed that woody species with aerenchyma can serve as conduits for soil-derived trace gases into the atmosphere, to date only shown for herbaceous plants. This, yet unidentified, ‘woody plant pathway’ contributes to the total greenhouse gas source strength of wetlands.

Effects of far-red light on the growth, mycorrhizas and mineral nutrition of Scots pine seedlings

The effects of supplementary far-red sidelight on the formation of mycorrhizas and on the accumulation and allocation of dry weight and mineral nutrients were studied in Scots pine (Pinus sylvestris L.) seedlings. Starting one week after germination the seedlings were subjected to two different light quality regimes: control and simulated sparse-canopy conditions (FR+). In the FR+ regime, light reflected by neighbouring plants was simulated by means of supplementary far-red light sources, which reduced the horizontal red/far-red photon ratio (R:FR) without affecting PAR. Seedlings were harvested after three months of treatment. FR+ increased stem height and decreased the total dry weight of seedlings. Dry weight allocation to needles was not affected, whereas dry weight allocation to roots was reduced and that to stems was increased in FR+ treated seedlings. The total number of short root tips and developing mycorrhizas per seedling were lower in FR+ than in control plants. Most short roots were developing mycorrhizas, while non-mycorrhizal short roots and mycorrhizas with mantle or external mycelium were very scarce. Changes in the allocation of nutrients in general followed the changes in dry weight allocation, and changes in nutrient content followed those in total dry weight. However, mismatches among these changes resulted in significant changes in nutrient concentrations in some organs: the concentrations of nitrogen and potassium in needles and the concentration of nitrogen in stems were higher in FR+ than in control seedlings. Changes in biomass and nutrient allocation under low R:FR may promote rapid height growth during early development in stands of Scots pine seedlings, but concomitant reductions in growth of the root system and mycorrhizas may negatively affect tree performance over the long term.

Growth and photosynthetic responses of four Virginia Piedmont tree species to shade.

To determine the effects of shade on biomass, carbon allocation patterns and photosynthetic response, seedlings of loblolly pine (Pinus taeda L.), white pine (Pinus strobus L.), red maple (Acer rubrum L.), and yellow-poplar (Liriodendron tulipifera L.) were grown without shade or in shade treatments providing a 79 or 89% reduction of full sunlight for two growing seasons. The shade treatments resulted in less total biomass for all species, with loblolly pine showing the greatest shade-induced growth reduction. Yellow-poplar was the only species to show increased stem height growth in the 89% shade treatment. The shade treatments increased specific leaf area of all species. Quantum efficiency, dark respiration and light compensation point were generally not affected by the shade treatments. Quantum efficiency, dark respiration, maximum photosynthesis and light compensation point did not change consistently between the first and second growing seasons. We conclude that differences in shade tolerance among these species are not the result of changes in the photosynthetic mechanism in response to shade.

Elevated CO 2 and hybrid poplar: a detailed investigation of root and shoot growth and physiology of Populus euramericana, ‘Primo’

Exposure of the hybrid poplar clone ‘Primo’ ( Populus deltoidex × Populus nigra) to 580 μl 1 −1 carbon dioxide for just 68 days significantly ( P ≤ 0.05) increased stem height by 13% compared with trees grown in ambient CO 2 concentrations. The stem diameter was significantly ( P ≤ 0.05) increased and both total biomass and woody stem biomass also showed higher values (38% and 31% increases respectively) in elevated CO 2. Trees in elevated CO 2 had more leaves and a greater total leaf area, whilst the specific leaf area was decreased in elevated CO 2 on four out of five occasions and was significantly ( P ≤ 0.05) lower after 68 days, an effect indicating that leaves were thicker and/or heavier. Rates of photosynthesis ( A) measured after 49 and 67 days of exposure revealed that trees in the elevated CO 2 treatment had lower values of A when measured at either 350 or 580 μl 1 −1 CO 2. Sequential harvests at intervals during the study in which the root and shoot components were analysed separately allowed the construction of root:shoot ratios and allometric coefficients; there was no significant effect on the allometric coefficient and the root:shoot ratio was significantly increased on only one occasion. However, measurements of the ‘apparent’ root length suggested that root lengths were greater in the CO 2 treatment. There was a significant increase in the number of fine root tips visible down the surface of specially designed rooting tubes ( P ≤ 0.05), indicating more fine roots or an increase in fine root branching. The growth rates of individual fine or large roots over 24 h were unaffected, again suggesting that increases in biomass may be due to more root segments rather than longer individual roots. Root water relations were also examined and showed a tendency towards solute accumulation and increases in turgor pressure ( P) and effective turgor ( P e) at times when root growth was stimulated, although these were not consistent. Cell wall plasticity of the tips of large roots was significantly ( P ≤ 0.01) reduced in elevated CO 2, possibly indicating a greater tendency to divert resources to the formation of root branches. The results of the study are discussed in the light of the possible consequences of changes in poplar growth and physiology for forestry practice in an increased CO 2 environment.

ONTOGENY AND PALEOECOLOGY OF THE MIDDLE PENNSYLVANIAN ARBORESCENT LYCOPOD BOTHRODENDRON PUNCTATUM, BOTHRODENDRACEAE (WESTERN MIDDLE ANTHRACITE FIELD, SHAMOKIN QUADRANGLE, PENNSYLVANIA)

Study of an in situ Bothrodendron punctatum community in a strip mine in Bear Valley, Shamokin Quadrangle, Pennsylvania, provides new insights into the ontogeny of Middle Pennsylvanian arborescent lycopods and into the ecological and environmental characteristics of lycopod‐dominated clastic‐swamp communities. Bothrodendron punctatum began growth as a monocaulous stem. The first branches developed when the stem attained a minimum height of 5 m. Lateral branches bore terminal cones and were determinate and deciduous. They grew to a maximum length of 1 m, and became smaller and more closely spaced with increasing stem height. The branch scars were not disrupted by secondary stem growth indicating that the branches stayed attached until the stem attained its determinate growth limit. The plant grew to a height of 25 m. Though B. punctatum is an uncommon component of Euramerican floras, the plant could become locally dominant under favorable environmental and edaphic conditions. The upper canopy was formed by B. punctatum and contained emergents of Lepidodendron aculeatum and a Sigillaria species. The understory contained pteridosperms and rare Calamites. Bothrodendron punctatum seems to have preferred environments transitional between clastic and peat swamp conditions. It was sensitive to local inhomogeneity in microhabitat characteristics, as well as to regional climatic fluctuations (drought stress). Both these variables produce specifically attributable effects on branch size and separation trends.

Effects of Carbon Dioxide Enrichment on the Growth and Morphology of Kudzu (Pueraria lobata)

Kudzu (Pueraria lobataOhwi # PUELO) was grown from seeds in controlled-environment chambers at 350, 675, or 1000μl·1−1CO2. Biomass and leaf area production, morphological characteristics, and growth analysis components were determined at 14, 24, 45, and 60 days after emergence. At 60 days, plants grown at 1000μl·1−1CO2had 51% more biomass, 58% longer stems, and 50% more branches than plants grown at 350μl·1−1CO2. Plants grown at 675μl·1−1CO2were intermediate. Growth analysis components indicated that CO2enrichment increased growth by compounding effects due to increased net assimilation rates and increased leaf area duration. Relative growth rates were not significantly affected. The large CO2-induced increase in stem height versus stem diameter is in marked contrast to previously reported responses of woody erect growth forms. Possible ecological implications for competitive abilities are discussed.

BIOMASS AND PHOTOSYNTHESIS RESPONSES OF ROUGH LEMON (Citrus jambhiri Lush.) TO GROWTH REGULATORS

Four-month-old plants of rough lemon (Citrus jambhiri Lush.) were sprayed, once a week, for 7 consecutive weeks with 100-μM concentrations of abscisic acid (ABA), benzyladenine (BA), gibberellic acid (GA3), naphthaleneacetic acid (NAA), and paclobutrazol (PP333). Leaf photosynthetic rates, photosynthetic carboxylating enzymes, and biomass partitioning were determined for individual treatments. Growth of rough lemon was influenced more with sprays of PP333 and GA3 than with ABA, BA, and NAA. PP333 sprays resulted in about 25, 30, and 33% reductions in both plant height and total plant weight, leaf biomass, and leaf area, respectively. The GA3 treatment, which caused 43 and 38% reductions in leaf biomass and leaf area, respectively, induced increased stem height and thickness, resulting in 48% more stem dry weight. There were no apparent differences in leaf photosynthetic rates and activities of ribulose bisphosphate carboxylase between control plants and plants treated with the growth regulators. The activities of phosphoenolpyruvate carboxylase, however, were depressed from 45 to 60% for the BA, GA3, NAA, and PP333 treatments. This suggests that organic acid metabolism in rough lemon leaves would be affected during repeated sprays of growth regulators.Key words: Plant growth, chemical retardants, carbon assimilation, RuBP carboxylase, PEP carboxylase

Effect of flooding on growth, stem anatomy, and ethylene production of Pinushalepensis seedlings

Flooding of soil for 43 days greatly altered growth and stem anatomy and increased ethylene production by stems of 10-month-old Pinushalepensis seedlings. Flooding reduced the dry weight increment of seedlings primarily as a result of decay of roots and, to a lesser extent, inhibition of growth of roots and needles. Flooding did not influence height growth of seedlings but increased stem diameter, largely because of an increase in bark thickness at all stem heights and stem hypertrophy associated with proliferation of phloem parenchyma cells and an increased amount of intercellular space in the phloem. The effects of flooding on xylem increment varied appreciably with stem height. In the submerged portion of the stem, flooding greatly reduced the number of tracheids laid down per radial file. Flooding also slightly reduced the number of tracheids produced in the portion of the stem just above the water level. In the upper stem, however, flooding had little effect on xylem increment and on tracheid production for the first 29 days but increased both thereafter. Flooding also induced formation of short, thick-walled, rounded tracheids resembling those in compression wood. However, these tracheids developed an S3 wall layer, which is absent in well-developed compression wood. Flooding also increased the number of longitudinal resin ducts as well as the number and size of the xylem rays. The basic density of stem segments was lower in flooded than in unflooded seedlings, largely because of the high proportion of parenchyma cells and more intercellular spaces in the wood and bark of flooded seedlings. Flooding greatly increased production of 1-amino-cyclopropane-1-carboxylic acid by roots and ethylene by stems. The capacity for production of ethylene increased faster in stem segments just above the water line than in submerged portions of stems. However, the capacity for ethylene production as a flooding response declined progressively with increase in stem height above the basal whorl of branches. The data indicated an important regulatory role of ethylene in altering growth and stem anatomy of woody plants.

Some Effects of Humidity on the Growth and Development of Cirsium arvense

Seedlings of Canada thistle Cirsium arvense (L.) Scop. were grown in sand culture under controlled conditions at low (30%-50%) and high (90%-100%) relative humidity (RH). High RH increased stem height by 50% and shoot and root dry weights by 50% and 80%, respectively, but had no significant effect on root bud growth. When the root buds were released from correlative inhibition by removal of the main shoot, increasing the RH from ca. 50% to 100% significantly increased their rate of emergence and resulted in a twofold increase in the length and dry weight of emergent shoots after 7 days of growth. At low RH, growth of the root buds was significantly inhibited not only by mature leaves but also by mature stem tissue. The root buds were released from the stem-induced inhibition by keeping the stem at a high RH. These results, and supporting evidence from previous investigations with other species, indicate that the correlative inhibition of root buds is caused primarily by competition for water between the r...

Título en español

Un experimento en un suelo Coto arcilloso (un Oxisol) se llevó a cabo en la Subestación Experimental Agrícola de Isabela para determinar los efectos de cuatro niveles (0, 57, 170 y 340 kg/ha) de N y cuatro (0, 2.3, 4.5 y 6.8 kg/ha) de B en el crecimiento y rendimiento del papayo P.R. 7-65. Estos niveles se compararon en un diseño factorial 4 x 4. Los tratamientos se iniciaron cuando las plantas tenían 3 meses a partir del transplante (5 meses desde el semillero). Desde el trasplante hasta el comienzo de los tratamientos, las plantas se abonaron con un análisis completo de N-P-K. Las cantidades de fósforo y potasio no se alteraron durante el experimento. Se recolectaron los siguientes datos: altura y diámetro de las plantas. Aunque el boro tendió a ejercer un mayor efecto que el nitrógeno, los pesos verde y seco de los pecíolos aumentaron consistentemente a medida que se aumentaron los niveles de nitrógeno y boro; el número y el peso de las frutas en las plantas hembras y hermafroditas aumentaron consistentemente pero en forma leve. Los datos demuestran que entre 57 y 170 kg/ha de N y 4.5 kg/ha de B aplicados cada 6 semanas a un suelo Coto arcilloso (Oxisol) como el de Isabela es suficiente para obtener un buen crecimiento de las plantas y un buen rendimiento de frutas.

Dual Minimum Temperature Forcing of ‘Ace’, ‘Croft’, ‘Harson’, and ‘Nellie White’ Easter Lilies, (Lilium longiflorum, Thunb.) using Southern-grown Bulbs

Abstract Southern-grown bulbs of ‘Ace’, ‘Croft’, ‘Harson’, and ‘Nellie White’ Easter lily were naturally cooled and greenhouse-forced with either constant minimum thermostat settings of 16.7 to 15.6°C or with thermostat settings lowered to 7.8 to 4.4° for 8 hours during the night to obtain a dual minimum night temperature regime. The actual greenhouse temperatures varied with outdoor temperatures. Average minimum temperatures obtained with constant and dual thermostat settings were 17.0 to 15.4° and 10.7 to 9.9°, respectively. With constant minimum temperature, 20 to 22 days less time was required to force ‘Harson’ as compared to ‘Ace’, ‘Croft’, and ‘Nellie White’. Dual night temperatures delayed flowering of the cultivars tested 9 to 13 days with a slight increase in flower number and a substantial increase in stem height. Although forcing time was increased with dual minimum temperatures, about 50% reduction in fuel usage was obtained.