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Thomas J. Tworkoski and D. Michael Glenn

Competitive effects of different grass species were evaluated on growth, yield, leaf N, and leaf water potential of 8-year-old peach [Prunus persica (L.) Batsch.] trees and on weed abundance. Two cultivars (`Loring' on Lovell rootstock and `Redhaven' on Halford rootstock) of peach trees were planted in separate orchards in 1987. Nine orchard floor treatments were installed beneath the peach trees in 1995: Festuca arundinacea Schreber (tall fescue); Lolium perenne L., var. Manhattan II (perennial ryegrass); Lolium perenne L., var. Linn; Agrostis gigantea Roth (red top); Dactylis glomerata L. (orchardgrass); Phleum pratense L. (timothy); Bromus carinatus Hook. and Arn. (brome); weedy control; and herbicide weed control (simazine, glyphosate). In general, grasses reduced vegetative growth and yield in both cultivars. Orchardgrass was one of the most competitive species and reduced vertical water sprout length by 15% to 27% and lateral shoot length on fruit-bearing branches by 19% to 30% compared with herbicide treatments. Orchardgrass reduced yield by 37% and 24% in `Loring' and `Redhaven', respectively. All grasses were not equally competitive; `Linn' perennial ryegrass did not significantly reduce growth or yield in `Redhaven'. Control treatments with weeds also did not differ from herbicide treatments in peach tree growth and yield. Grass and weed ground covers consistently reduced peach tree leaf N by at least 10%, compared to herbicide treatment, possibly due to reduced root growth. `Redhaven' root density in the top 10 cm of soil was ≈12 cm·cm-3 in herbicide strips vs. 1 cm·cm-3 in weedy or ground-covered strips. Peach leaf water potential was not affected by grass and weeds. Weed weights were significantly reduced by all grasses compared with weedy control. The results indicate that peach cultivars respond differently to grass competition, but the relative competitiveness of each grass species was similar for both cultivars. Grass competition reduced growth, yield, and pruning weights of mature peach trees, but the reduction in vegetative growth did not significantly reduce pruning time per tree. Grasses that are less inhibitory to peach yield may be useful for weed management in orchards.

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Matt Kelting, J. Roger Harris, Jody Fanelli, and Bonnie Appleton

Application of biostimulants, humate-based products marketed as aids to plant establishment, may increase early post-transplant root growth and water uptake of landscape trees. We tested three distinct types of biostimulants on root growth and sapflow of balled and burlapped red maple (Acer rubrum L. `Franksred') trees. Treatments included: humate, 1) as a wettable powder formulation, applied as a soil drench; 2) as a liquid formulation to which various purported root growth—promoting additives had been added, also applied as a soil drench; 3) as a dry granular formulation, applied as a topdress; and 4) a nontreated control. Root growth was monitored through single-tree rhizotrons, and sap flow was measured with a heat balance sapflow system. Roots were first observed in the rhizotron windows 38 days after planting. No biostimulant-treated trees had more root length than nontreated controls, and the two soil drench treatments had the lowest root length throughout the 20 weeks of post-transplant observation. All biostimulants increased sapflow.

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Pilar Andreu, Arancha Arbeloa, Pilar Lorente, and Juan A. Marín

the root response to salt stress are important, mainly in fruit tree species, where the plant characteristics make these studies difficult. Besides root growth, we studied the starch content of the root tissues, because starch formation and

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W. Roland Leatherwood, D. Mason Pharr, Lisa O. Dean, and John D. Williamson

under a 12-h photoperiod of 150 μmol·m −2 ·s −1 provided by white fluorescent lights. To allow accurate measurement of root length, plates were incubated vertically to ensure geotropic root growth. Because time to emergence and radical elongation varied

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Thomas E. Marler

An aeroponics system was used to determine root growth of Citrus aurantifolia Swingle following removal from containers. Rooted cuttings were planted in 0.46-liter containers in a 1 sand: 1 perlite medium, and watered daily and fertilized with a complete nutrient solution weekly. The plants were grown in the containers until root growth had filled the container volume. A sample of plants was removed from the bench after 86, 146, or 210 days in container production. Plants were bare-rooted and the existing root system dyed with methylene blue, and placed in the aeroponics system. The plants were maintained in the aeroponics system for 50 days, then were harvested and the roots separated into pre-existing roots and new roots. Two dimensional area and dry weight of roots were measured. Relative new root growth of plants that were maintained 210 days in the containers was less than that of plants that were removed from containers earlier. The data indicate that maintaining plants in containers for extended periods of time may reduce root regeneration following removal from containers.

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Ben van Hooijdonk, David Woolley, Ian Warrington, and Stuart Tustin

limits root growth and/or cytokinin biosynthesis and consequently the amount of root-produced cytokinin supplied to the scion in the xylem vasculature. In support of this hypothesis, cytokinins were identified in the xylem sap of apple trees ( Jones, 1973

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Marjorie Reyes-Diaz, Miren Alberdi, and Maria de la Luz Mora

, 2002 ; Delhaize and Ryan, 1995 ). Many reports indicate that acidification generates an increase in Al concentration as Al 3+ in the soil solution ( Jarvis, 1987 ). This results in root growth reduction ( Mora et al., 2004 , 2005 ; Tamás et al

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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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S.S. Snapp and C. Shennan

Roots respond first to edaphic stresses, yet little is known about root response to stress in mature, soil-grown plants. We investigated the effects of salinity and phytophthora root rot on root growth and senescence in tomato (Lycopersicon esculentum Mill.). Using minirhizotron- and rhizotron-based methodologies, we quantified intraspecific differences in root-system response to salinity and inoculation. Genotype susceptibility to salt-induced disease was related to root vulnerability to salt. `UC82B' was vulnerable to infection by Phytophthora parasitica when subjected to salt stress and produced thinner roots and ≈50% higher root-senescence rates compared to the phytophthora root rot-resistant `CX8303'. Root growth at the peripheral regions of the `CX8303' root system was inhibited by salinity, but otherwise root dynamics were not affected by salinity or inoculation. Overall, roots from the central root system and roots from the periphery responded differently to salt stress. Monitoring the diameters of new initiated roots indicated the vulnerability of a stressed root system to disease and early senescence.

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Tyler C. Hoskins, James S. Owen Jr., and Alex X. Niemiera

the container profile; and 2) to determine the subsequent effect of root growth on water movement. Materials and Methods Experimental design. The experiment was a four (sampling interval) × three (height of sensor placement in container profile