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Wei-Ling Yuan, Shang-yong Yuan, Xiao-hui Deng, Cai-xia Gan, Lei Cui and Qing-fang Wang

benefit from fertilizer of the cotton. However, few studies have been conducted concerning N management practices for the radish. What are the difference in plant uptake of fertilizer N and root yield among the three splits of radish N application? The

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W. Michael Sullivan, Zhongchun Jiang, Richard J. Hull and Carl D. Sawyer

Intraspecific variation in nitrate absorption by turfgrasses has been studied, but differences in turfgrass root morphology, which may contribute to observed variation, have not been ascertained. This information may benefit breeding programs aimed at improving the ability of turfgrasses to absorb nitrate from low fertility soils. This study quantified root morphological traits of Kentucky bluegrass (Poa pratensis L.) cultivars and their nitrate uptake rates (NUR). Tiller-generated plants were grown in silica sand, mowed weekly, and watered daily with half-strength modified Hoagland's nutrient solution containing 1 mM nitrate. When 5 months old, plants were excavated, and roots washed to remove sand. The plants were then transferred to 120-mL black bottles. After nitrate depletion of the nutrient solution was monitored for 8 consecutive days, the underground portion of each plant was separated into three parts: 1) adventitious roots, 2) fibrous roots, and 3) rhizomes. Measurements of total root length, total surface area, and average diameter were made by a scanning and image analysis system. NURs were calculated from nitrate depletion data and expressed as micromoles per plant per hour. Correlation analyses were performed on these morphological traits and NUR by the Minitab program. NUR was significantly and positively correlated with the total biomass, length, and area of the three underground parts. This was attributable mainly to fibrous roots as indicated by significant and positive correlations between NUR and the total biomass, length, area, and average diameter of fibrous roots. NUR was also positively correlated with the total biomass, length, and area of adventitious roots but negatively correlated with total biomass, area, and average diameter of rhizomes.

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Wei Qiang Yang and Barbara L. Goulart

Aluminum (Al) uptake by and root cation exchange capacity (CEC) of mycorrhizal (M) and nonmycorrhizal (NM) blueberry (Vaccinium corymbosum L.) plants were studied. Root CEC was higher in M plants than in NM plants, but total and root Al contents were higher in NM plants. Leaf Al content was higher in NM than in M plants after 1 and 5 hours of exposure. The aurintriboxylic acid stain for Al indicated the presence of Al in the M symbiont. Despite a larger root system and higher root CEC, regression analysis indicated roots of M plants absorbed less Al in the first 5 hours, suggesting that Al sequestration in the M symbiont is responsible for reduced total Al uptake. Differences in dry matter partitioning between M and NM plants were also observed.

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Qingzhang Xu and Bingru Huang

Roots play important roles in plant responses to environmental changes. The objective of this study was to investigate seasonal changes and cultivar variation in root growth, respiratory activity, nitrogen uptake, and carbon allocation in relation to turf performance for two cultivars of creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.)] under field conditions. Two cultivars, `Penncross' and `L-93', were managed under USGA-specification putting green conditions, with daily irrigation and mowing at a 3-mm height from May to November in 1999 and 2000. Turf quality of both cultivars declined from the highest rating of 7 to 9 in May to 4 to 5 in August and September, and recovered to above 7 in October and November in both years. This corresponded to seasonal changes in root dry weight, dehydrogenase activity, nitrate reductase (NR) activity, carbon allocation to roots, and 15N uptake. Compared to Penncross, L-93 generally maintained better turf quality, as well as higher root dry weight, 15N uptake, NR activity, and carbon allocation during summer months. Previous studies often emphasize the important of a large, extensive root system. The results in the present study demonstrated that root metabolic activities followed the same seasonal pattern and cultivars variation as turf performance, and suggested that decline in root metabolic activities could be contributed to summer decline in turf quality for creeping bentgrass.

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Eran Raveh

Carbohydrates are the energy source for most root activities, including membrane maintenance and osmotic adjustment. Yet, the relationship between root carbohydrate status and selective sodium chloride uptake remains unknown. The following study examined the effects of root carbohydrate starvation due to girdling on sodium and chloride uptake in mature citrus trees. Trees were girdled during the spring or during the autumn, when girdling is known to have more dramatic affects. In spring-girdled trees, 4 days after girdling, root total carbohydrate and starch decreased by 25% and 30%, respectively. The decrease in root carbohydrates was followed by a 20% reduction in root respiration rate. Based on root mineral analysis, spring-girdled trees were characterized by having 42% more sodium and 30% more chloride. The effects of girdling on shoot xylem sap mineral concentration were similar to trends in root mineral status; xylem sap from spring-girdled trees had 43% more sodium and 22% more chloride. Leaf chloride concentration measured 6 months after girdling was 74% higher in girdled trees and reached toxicity levels (0.65% vs. 0.37% dry mass, for girdled and nongirdled trees, respectively). The differences in leaf sodium, however, were nonsignificant (0.14% vs. 0.13% dry mass, for girdled and nongirdled trees, respectively). In autumn-girdled trees, the effects on leaf sodium and chloride concentration were more dramatic. Leaves from autumn-girdled trees (sampled 10 months later) had about two times more sodium and about five times more chloride in comparison to nongirdled trees (0.39 % vs. 0.20% dry mass sodium and 1.02% vs. 0.22% dry mass chloride, respectively). The above results link root carbohydrate status and selective sodium or chloride uptake in citrus trees.

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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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E. G. Rhoden, P. J. Ndolo and G. W. Carver

A greenhouse study was conducted to investigate the ability of sweetpotato (Ipomoea batatas), cv. `Centennial', `Rojo Blanco', `Georgia Jet' and `TI-82-155', fibrous roots to accumulate N, P, K, Ca and Mg. Sweetpotato plants were grown in a fritted clay medium and harvested 42 and 82 days after planting. Fibrous roots comprised 22 to 28.1% and 3.9 to 11.1% of the plant dry weight at 42 and 82 days after planting, respectively. There was no difference in the average root length/cm depth of soil among the four sweetpotato cultivars at day 42. While there was no difference in average root length among `Centennial', `Rojo Blanco' and `TI-82-155', these cultivars were significantly different from `Georgia Jet' at day 82. For the four cultivars, there were no significant differences in N, P, K, Mg and Ca Uptake at day 42, but each cultivar absorbed significantly more of each element 82 days after planting. `Georgia Jet' absorbed significantly more of the nutrients measured than the other cultivars, resulting in the highest dry matter yield. The data show that the efficient uptake and utilization of nutrients by sweetpotato are related to the amount of fibrous roots present.

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H.C. Wien, P.L. Minotti and V.P. Grubinger

Tomato (Lycopersicon esculentum Mill.) plants grown on polyethylene (PE) mulch in New York State frequently have more branches and increased mineral nutrient uptake and yield than plants not mulched. In four field experiments conducted on a silt loam soil, clear PE mulch stimulated root extension shortly after transplanting. One week after transplanting, roots were significantly longer for mulched than for unmulched plants in all four experiments, whereas aboveground dry matter differences did not become significant until 14 days after transplanting in two of four trials. Mulching increased branching, hastened flowering on basal branches, and increased concentration of major nutrients in the aboveground parts. In the field, stimulation of aboveground growth due to mulch might be brought about by warming of the stem by air escaping from the planting hole in the mulch. However, an experiment with black, white, or clear mulch, in which the planting hole was either left uncovered or covered with soil, showed no effect of hole closure on branching even though air temperature near the stem was increased when holes were left uncovered. The results taken together imply that the increased aboveground growth observed with mulching is a consequence of enhanced root growth and nutrient uptake.

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Hamish Tulloch, Doug Waterer and Dan Polonenko

Root zone inoculation with P-solubilizing Penicillium bilaji (PB) has increased P uptake and yields of several field crops. We examined the influence of applying 0 - 5 × 105 C.F.U./plant of PB to geranium and petunia grown in the greenhouse in a low P soil amended with rock P. All rates of inoculation increased growth and enhanced flowering of both crops. A second study examined the interaction between PB and rock P amendments in poinsettia. Inoculation with PB accelerated growth through to pinching as did addition of rock P to the media. The combined PB + rock P treatment enhanced bract development resulting in better red color at market time. These results suggest that PB inoculation can enhance growth and/or improve P use efficiency in greenhouse crops.

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Wei Qiang Yang and Barbara L. Goulart

Aluminum (Al) uptake and root cation exchange capacity (CEC) of mycorrhizal (M) and non-mycorrhizal (NM) blueberry plants (Vaccinium corymbosum L.) were studied. Mycorrhizal roots took up more Al than non-mycorrhizal roots over a 48-h period. Different patterns of Al uptake occurred between M and NM roots. The M roots contained more Al at hour 1, followed by a deep decrease at hour 3, and then increased gradually. However, Al uptake in NM roots increased with time. Foliar Al analysis indicated that Al concentration increased with time in both M and NM plants, but a significant increase of foliar Al concentration during the first 3-h period was not observed in M plants. The results suggested that the rate of Al transport and the redistribution of foliar Al were different in M and NM plants. The higher Al concentration in M roots may be due to the higher CEC in M roots and vice versa. Further, the CEC of M roots was decreased by the respiration inhibitor (CN-) treatment while the CEC of NM roots was not, suggesting that CEC in M roots is related to respiration.