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Cui-ping Hua, Zhong-kui Xie, Zhi-jiang Wu, Yu-bao Zhang, Zhi-hong Guo, Yang Qiu, Le Wang, and Ya-jun Wang

100 × 100 cm, and there were 36 bulbs per plot. All plots were adjacent to each other to eliminate the variation of soil properties caused by spatial differences. There were three replicate plots in every site. We collected rhizosphere soil from four

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M.L. Elliott, E.A. Guertal, and H.D. Skipper

The rhizospheres of creeping bentgrass (Agrostis palustris Huds.) and hybrid bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy) putting greens were sampled quarterly for 4 years. Six bacterial groups, including total aerobic bacteria, fluorescent pseudomonads, actinomycetes, Gram-negative bacteria, Gram-positive bacteria, and heat-tolerant bacteria, were enumerated. The putting greens were located in four geographic locations (bentgrass in Alabama and North Carolina; bermudagrass in Florida and South Carolina) and were maintained according to local maintenance practices. Significant effects were observed for sampling date, turfgrass species and location, with most variation due to either turfgrass species or location. Bentgrass roots had significantly greater numbers of fluorescent pseudomonads than bermudagrass roots, while bermudagrass roots had significantly greater numbers of Gram-positive bacteria, actinomycetes and heat-tolerant bacteria. The North Carolina or South Carolina locations always had the greatest number of bacteria in each bacterial group. For most sampling dates in all four locations and both turfgrass species, there was a minimum, per gram dry root, of 107 CFUs enumerated on the total aerobic bacterial medium and a minimum of 105 CFUs enumerated on the actinomycete bacterial medium. Thus, it appears that in the southeastern U.S. there are large numbers of culturable bacteria in putting green rhizospheres that are relatively stable over time and geographic location.

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Lurline Marsh, Dyremple Marsh, and Raymond Baptiste

Pigeonpea [Cajanus cajan (L.) Millsp.] and cowpea [Vigna unguiculata (L.) Walp.] seeds were inoculated with broth cultures of Rhizobium strains 3278, 3458, and 3472 at a population of ≈9.5 × 10 g viable cells/ml. They were planted at three air temperature regimes: 20/10C, 30/20C, and 38/25C (day/night), which generated variable rhizosphere temperatures of 17/6C, 26/15C, and 33/20C, respectively. Seeds and/or seedling roots were sampled at 3, 7, 11, and 15 days after planting and Rhizobium survival was enumerated as viable cells on agar media. Only strain 3458 in association with pigeonpea genotype ICPL8304 had a higher population at day 15 than that at the earlier sample dates. The duration of the strains in the rhizosphere, rather than temperature, influenced population changes. No strain showed a consistent increase in cell numbers from inoculation to 15 days after planting. There was no clear pattern of population changes for any strain within or across temperatures, hence it was difficult to identify any strain as having superior growth habits over another.

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Shufu Dong and Huairui Shu

Malus hupehensis Reld apple rootstock seedlings and the rhizobox technique were used in this study. The seeds were collected from healthy mature trees at the Wanshougong Forest Farm in Shandong, China, stratified at 0 to 2 °C for 60 days, sown into growing medium with 1/3 loam soil+1/3 silt sand+1/3 compost manure, grown until the three-leaf stage, and then transplanted into rhizoboxes with four plants in each box. The rhizoboxes were inserted into the ground with the top of the boxes levelled with the soil surface. After the root mattress formed in the center of the box, plants were harvested by carefully dividing each box into rhizoplane, rhizosphere, and bulk soil, and mineral nutrients in each part were analyzed. The relationships were tested between the rhizoplane, rhizosphere, and bulk soil for each nutrent. Significant correlations were found for NH + 4, NO 3, K, Mg, Zn, and Cu in the rhizoplane, rhizosphere, and bulk soil. There were significant relationships for P and Ca between the rhizoplane and rhizophere, but not between the rhizoplane or rhizosphere and bulk soil. Fe in the rhizoplane closely related to Fe in the rhizosphere but not to Fe in bulk soil. No correlation was found between the rhizoplane and either rhizosphere or bulk soil, but close correlation existed between rhizosphere and bulk soil for Mn.

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Lesley A. Judd, Brian E. Jackson, and William C. Fonteno

measurement technique. The name rhizometer stems from rhizo, meaning rhizosphere, and - ometer or - meter , from the term porometer and an instrument used in scientific measuring. The rationale of this apparatus was to measure both the physical properties

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Amy N. Wright, Robert D. Wright, Brian E. Jackson, and Jake A. Browder

Rhizosphere pH preferences vary for species and can dramatically influence root growth rates. Research was conducted to determine the effect of root zone pH on the root growth of BuxusmicrophyllaSieb. & Zucc. `Green Beauty' (boxwood) and KalmialatifoliaL. `Olympic Wedding' (mountain laurel). Boxwood plants removed from 3.8-L containers and mountain laurel plants removed from 19-L containers were situated in the center of separate Horhizotrons™. The key design feature of the Horhizotron is four wedge-shaped quadrants (filled with substrate) that extend away from the root ball. Each quadrant is constructed from glass panes that allow the measurement of roots along the glass as they grow out from the root ball into the substrate. For this experiment, each quadrant surrounding a plant was filled with a pine bark substrate amended per m3 (yd3) with 0.9 kg Micromax (Scotts-Sierra, Marysville, Ohio) and 0, 1.2, 2.4, or 3.6 kg dolomitic limestone. All plants received 50 g of 15N–3.9P–9.8K Osmocote Plus (Scotts-Sierra), distributed evenly over the surface of the root ball and all quadrants. Plants were grown from May to Aug. 2003 in a greenhouse. Root lengths were measured about once per week throughout the experiment. Root length increased linearly over time for all species in all substrates. Rate of root growth of boxwood was highest in pine bark amended with 3.6 kg·m3 lime and lowest in unamended pine bark. Rate of root growth of mountain laurel was lowest in pine bark amended with 3.6 kg·m3 lime. Results support the preference of mountain laurel and boxwood for acidic and alkaline soil pH environments, respectively.

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B.L. Goulart, K. Demchak, and W.Q. Yang

Previous experiments in the laboratory and the field have suggested that location of mycorrhizal infection within the rhizosphere of blueberry plants may depend on cultural practices that are being used. Furthermore, we have observed that rapidly growing roots, whether in solution culture or within petri dishes, appear to be less likely to become infected when inoculated. A preliminary experiment found higher levels of mycorrhizal infection in roots growing at a 5-cm depth of soil compared to roots growing just under the mulch layer. To further test this hypothesis, an experiment was designed to evaluate the infection intensity of highbush blueberry plants (Vaccinium corymbosum L.) at different locations within the rhizosphere on plants growing under varying cultural practices. Cultural practices included mulching (mulch vs. no mulch) and nitrogen level (0 and 120 g ammonium sulfate/plant). Four-year-old `Bluecrop' highbush blueberry plants subjected to these treatments were arranged in a complete factorial design with six replications at the Russell E. Larson Agricultural Research Center at Rock Springs, Pa. Mycorrhizal infection intensity was evaluated from roots sampled nondestructively using a 2.5 cm soil corer at the interface of the mulch and soil, and at soil depths of 3 and 15 cm from two locations 15 cm from the crown of each plant. Results will be discussed.

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Wan-Yi Yen, Yao-Chien Alex Chang, and Yin-Tung Wang

., 2007 ). Other than anchoring the plant and absorbing water and nutrients, roots also release organic and inorganic substances to alter the rhizosphere. The tendency to secrete such substances and the type of substances released are affected by a number

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Georgios Psarras, Ian A. Merwin, Alan N. Lakso, and John A. Ray

A 2-year field study of `Mutsu' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] on `Malling 9' (M.9) rootstock was conducted to observe root growth in situ, and compare patterns of root growth, root maturation and turnover rates, and soil-root respiration. Rhizosphere respiration was monitored with a portable chamber connected to an infrared gas analyzer; root emergence, browning, and turnover rates were measured by direct observation through minirhizotron tubes inserted in the root zone. Negligible root growth was observed before the onset of shoot growth in mid-May. In both years, a main peak of new root emergence in late June and early July coincided partially with major phases of shoot and fruit growth. A smaller peak of root emergence during August to September 1997 consisted primarily of new roots at 20 to 45 cm soil depths. Most roots remained <1 mm in diameter and developed in the upper 25 cm soil profile; no roots were observed at any time below 50 cm, due to a compacted soil layer at that depth. The cumulative survivorship of new roots was 38% in 1996 and 64% in 1997, and 50% of emergent white roots turned brown or senesced within 26 days in 1996 and 19 days in 1997. Root turnover rates were highest in mid-August both years. Rhizosphere respiration was correlated (r 2 = 0.36 and 0.59, P = 0.01 and 0.004) with soil temperatures in 1996 and 1997, with Q10 values of 2.3 in both years. The Q10 for root-dependent respiration (the difference between soil only and combined soil-root respiration) in 1997 was 3.1, indicating that roots were more sensitive than soil microflora to soil temperature. The temporal overlap of high rates of shoot, root and fruit growth from late May to mid-July suggests this is a critical period for resource allocations and competition in temperate zone apple trees.

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Amy N. Wright and Robert D. Wright

Root growth following transplanting allows a plant to exploit water and nutrient resources in the soil backfill (landscape) or container substrate and thus is a critical factor for transplant survival. The Horhizotron, a horizontal root growth measurement instrument, has been developed and evaluated for use in measuring root growth under a variety of root environments. The design of the Horhizotron includes four wedge-shaped glass quadrants that extend away from a plant's root ball allowing measurement of roots as they grow out from the original root ball. The substrate in each quadrant can be modified in order to evaluate the effect of substrate or root environment on root growth. Materials used for construction were lightweight, durable, easy to assemble, and readily available from full service building supply stores. Units were suitable for use on a greenhouse bench or outdoors in contact with the ground. Horhizotrons provided a simple, nondestructive method to measure root growth over time under a wide range of rhizosphere conditions.