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Lorna C. Wilkins and William R. Graves

Development of half-sib Gleditsia triacanthos inermis Willd. (honey locust) seedlings was studied during exposure to osmotic and high root temperature stress. Seven days after seed scarification, seedlings of uniform fresh weight were transferred to static hydroponic culture vessels in a growth chamber. Three days later, vessel solutions were replaced with polyethylene glycol 8000-amended solutions with osmotic potentials (ψπ) of -0.05, -0.10, or -0.20 MPa at 23C. Within each ψπ treatment, root temperature was increased from ambient (23C) to 35C for 0, 6, 12, or 24 hr day-1 for 20 days. Root and shoot dry weights decreased with increasing exposure to 35C among seedlings in the -0.05 MPa solution and decreased for seedlings in -0.10 and -0.20 MPa solutions in all temperature regimes. Epicotyl expansion tended to decrease with decreasing ψπ and increasing exposure to 35C. However, for plants in the -0.20 MPa solution, epicotyl length was greatest when roots were exposed to 35C for 6 hr day-1.

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John E. Erwin and Gerard Engelen-Eigles

Interaction between simulated shipping and rooting temperature and harvest year was studied on Lilium longiflorum. Bulb dormancy and maturity appear to be separate phenomenon and are affected by temperature differently. Shoot emergence (an indicator of release from dormancy) was hastened by 10 °C shipping and 10 to 20 °C rooting temperatures in both years. Flower induction was affected differently by simulated shipping and rooting temperatures during 1992 and 1993, indicating that bulb maturity differed between the 2 years. Final leaf and flower number decreased because of shipping or rooting temperature, but only when bulbs were mature and received cool temperatures (<16 °C) before a 6-week vernalization treatment. Immature bulbs (at harvest) are unresponsive to vernalizing shipping and rooting temperatures. Prevernalization handling temperature and vernalization treatment length should vary with year based on degree of bulb maturity to achieve consistency in final morphology. Internode length is associated more with the time elongation is suppressed after dormancy is broken than with flower induction (where internode length increases as the length of time elongation is suppressed after breaking of dormancy increases).

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Juan M. Ruiz, Joaquín Hernández, Nicolas Castilla and Luis Romero

Potato (Solanum tuberosum L.) `Spunta' plants were grown with the root zone covered by different types of polyethylene plastic mulches. The plastic mulches used were transparent, white, co-extruded black and white, and black. As a control, plants were grown without plastic mulch. The parameters analyzed were soil temperature, root concentration of K and Ca, and enzymatic activities of ATPase and pyruvate kinase (PK), measured as basal and in the presence of K+ and Ca2+. The physical characteristics of the plastic mulches directly influenced soil and root temperatures in potato plants. In addition, the concentration of cations in the roots (particularly Ca2+) and basal ATPase activity were affected by soil temperature, whereas basal PK was not affected by soil temperature. The use of co-extruded black and white plastic mulch improved the nutritional status of Ca in the roots of potato plants. Finally, the basal ATPase and PK activities in the presence of K+ and Ca2+ were related with the root levels of these cations.

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Martin P.N. Gent and Vincent Malerba

The soil within a greenhouse was heated by blowing hot air from a forced-air heater through drainage pipes buried beneath raised beds. This warmed the soil from 50F (10C) to 68F (20C) after 1 week of heating in mid-March. Soil in unheated beds did not warm to this temperature until May. The yield of tomato (Lycopersicon esculentum Mill.) planted in heated beds was higher than in unheated beds by 16% over the season in 1992, and by 14% as of early July 1993. The weight fraction of highest-quality fruit also were 11% greater in 1993. This simple method of soil heating involved negligible additional expense

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Helen C. Thompson, Robert W. Langhans, Arend-Jan Both and Louis D. Albright

`Ostinata' Butterhead lettuce (Lactuca sativa L.) was used to study lettuce production at varied shoot (air) and root (pond) temperatures. A floating hydroponic system was used to study the influence of pond temperature on lettuce growth for 35 days. Pond water temperature setpoints of 17, 24, and 31 °C were used at air temperatures of 17/12, 24/19, and 31/26 °C (day/night). Pond temperature affected plant dry mass, and air temperature significantly affected growth over time. Maximum dry mass was produced at the 24/24 °C (air/pond temperature) treatment. Final dry mass at the 31/24 °C treatment did not differ significantly from the 24/24 °C treatment. The 24 °C pond treatment maintained market quality lettuce head production in 31 °C air. Using optimal pond temperature, lettuce production was deemed acceptable at a variety of air temperatures outside the normal range, and particularly at high air temperatures.

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Luisa Dalla Costa, Nicola Tomasi, Stefano Gottardi, Francesco Iacuzzo, Giovanni Cortella, Lara Manzocco, Roberto Pinton, Tanja Mimmo and Stefano Cesco

− (+81%), 35 SO 4 2− (+16%), and Fe (+15%). Conversely, a further warming of root temperature (T25) caused a drastic limitation of NO 3 − and SO 4 2− acquisition, halving their uptake rates. Similarly, a remarkable reduction was recorded for Fe uptake

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Bingru Huang and Qingzhang Xu

This study was designed to compare and determine root growth and nutritional responses of creeping bentgrass cultivars that differ in heat tolerance to deferential, supraoptimal shoot and root temperatures. Shoots and roots of `Penncross' (heat sensitive) and `L-93' (heat tolerant) were exposed to four differential air/soil temperature regimes (20/20-control, 20/35, 35/20, and 35/35 °C) in water baths and growth chambers. Exposing roots to supraoptimal root temperature (35 °C) while maintaining shoots at normal temperature (20 °C), or at 35 °C in particular, reduced root fresh weight, root number, the content of N, P, and K in shoots and roots, and accelerated root death for both cultivars. High root temperature had a greater detrimental effects on root growth and nutrient accumulation than high shoot temperature for both cultivars. Reducing root temperature at supraoptimal shoot temperature improved root growth, reduced root mortality, and increased N, P, and K content in shoots and roots. Among the three nutrient elements, K was the most sensitive to changes in root temperature. L-93 generally maintained higher root fresh weight and number, and N, P, K content in shoots and roots, particularly K in roots, under high root (20/35 °C) or shoot/root (35/35 °C) temperatures. The results indicated that root growth and nutrient accumulation, particularly K, played an important role in creeping bentgrass tolerance to heat stress imposed to shoots by high air temperature or to roots by high soil temperatures. Reducing root temperature under supraoptimal ambient temperatures enhanced root growth and nutrient relations, and thus could lead to the improved shoot growth in cool-season grasses as reported previously.

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Yong-Zhan Ma and Martin P.N. Gent

Do root temperatures warm during the day and cool during the night benefit plant growth? Tomato (Lycopersicon esculentum Mill.) seedlings were grown at a constant 20C air temperature but with varied root temperature, either 28/12C or 12/28C day/night for 8 days. Eight seedlings were grown in troughs in continuously flowing nutrient solution containing 200 μM \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(^{14}\mathrm{NO}_{3}^{-}\) \end{document} excess amounts of other mineral elements. The flow rate was 0.6 liters/day per trough on the first day, when plants weighed 20 mg, and increased with plant size. After 8 days, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(^{15}\mathrm{NO}_{3}^{-}\) \end{document} was provided for 12 h when roots were warm, and eight plants were harvested at the end of labeling or 12 h later. During the treatments, weight per plant increased more in leaves, 3.5 to 44 mg, than roots, 4.3 to 19 mg, and least for stem, 12 to 30 mg. The whole-plant relative growth rate did not differ among treatments, 0.17 to 0.19/day, but was less than for plants grown at a constant 20C root temperature, 0.22/day. Uptake of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(^{14}\mathrm{NO}_{3}^{-}\) \end{document} from the media and exudation from the stem of decapitated plants were greater when roots were warm than when roots were cold, regardless of light. After labeling for 12 h at the warm root temperature, 15N enrichment in plant tissues was greater with roots warm during the day, 0.20, 0.15, and 0.16, than in those with roots warm during the night, 0.16, 0.11, and 0.10, for roots, stems, and leaves, respectively. Enrichment with roots warm during the day was 22%, 33%, and 62% greater, for roots, stems, and leaves, respectively, than with roots warm during the night. However, uptake of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} at night by roots that were warm during the night was sufficient so that plants grown at out-of-phase root temperature grew as fast as plants grown at in-phase root temperature. Research supported in part by grant 93-37100-9101 from the NRI Competitive Grants Program/USDA.

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Moreno Toselli, James A. Flore and Bruno Marangoni

Low root-zone temperature is one of the potential causes of low rate of plant nutrient uptake in spring. In this period, fruit trees are frequently supplied with nitrogen and a delay in root absorption could lead to an increase of nitrate leaching. In this study we assessed the effect of low root temperature on kinetic of nitrogen absorption of apple trees. One-year-old rooted cuttings of `Mark' apple rootstocks were subjected to two root temperature: 8 ± 1°C (LT) and 23 ± 1°C (HT). Four days after treatment imposition, the potted plants were supplied with 20 mg of N as NH4N03, enriched with 10 atom% of 15N. One, 2, 4, and 8 days after fertilization, tree root system was inserted into a Sholander bomb where a 0.325-Mpa pressure was applied to collect the xylem sap from the stem cross section. The sap exudation rate was always depressed by low root temperature. Nitrogen flow through the xylem vessel was highest in HT plants the day after fertilization (10-fold higher than LT), then decreased constantly. In LT plants, N flow was low the first and the second day after fertilization then reached the maximum 4 days after fertilization, when it was significantly higher than in HT plants. The amount of fertilizer-N found in leaves reflected the different movement rate of N observed in the two treatments. In HT trees fertilizer-N reached a plateau 2 days after fertilization, while in LT it linearly increased over time. This results suggest that root zone temperature of 8°C, although causes a delay (2–4 days) in nitrogen uptake, does not represent a serious limiting factor for N nutrition of tested apple trees.

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Kunihisa Morinaga

Relationship between root system and shoot pruning was studied by three different pruning times (February, June, and August) and intensity (heavy, medium, and light) using satsuma mandarin trees (Citrus unshiu Marc.). Root weight, respiratory rate of fine root, and CO2 concentration in root zone were measured on the 90th day after starting each pruning treatment. The weight of fine root was more severely influenced by pruning intensity than by pruning time. Fine root of heavy pruned trees showed lower respiratory rate than those of medium- and light-pruned trees. Heavy-pruned trees showed the highest CO2 concentration level in root zone. Influence of high root temperature on root respiration was investigated using `Kyoho' grape (Vitis vinifera L. × V. Iabrusca L.), kiwifruit (Actinidia deliciosa), and satsuma mandarin trees. Respiratory rate of grape root increased more rapidly than those of mandarin and kiwifruit under high root temperature. Respiratory rate of mandarin root given immersion treatment in stagnated water began to decrease significantly at the 70th hour after starting the treatment. Photosynthesis of the trees decreased by 85% at the same time.