title: Root growth dynamics linked to above-ground growth in walnut (Juglans regia).
abstract: OBJECTIVE
  Examination of plant growth below ground is relatively scant compared with that above ground, and is needed to understand whole-plant responses to the environment. This study examines whether the seasonal timing of fine root growth and the spatial distribution of this growth through the soil profile varies in response to canopy manipulation and soil temperature.
  
  
  METHODS
  Plasticity in the seasonal timing and vertical distribution of root production in response to canopy and soil water manipulation was analysed in field-grown walnut (Juglans regia 'Chandler') using minirhizotron techniques.
  
  
  RESULTS
  Root production in walnuts followed a unimodal curve, with one marked flush of root growth starting in mid-May, with a peak in mid-June. Root production declined later in the season, corresponding to increased soil temperature, as well as to the period of major carbohydrate allocation to reproduction. Canopy and soil moisture manipulation did not influence the timing of root production, but did influence the vertical distribution of roots through the soil profile. Water deficit appeared to promote root production in deeper soil layers for mining soil water. Canopy removal appeared to promote shallow root production.
  
  
  CONCLUSIONS
  The findings of this study add to growing evidence that root growth in many ecosystems follows a unimodal curve with one marked flush of root growth in coordination with the initial leaf flush of the season. Root vertical distribution appeared to have greater plasticity than timing of root production in this system, with temperature and/or carbohydrate competition constraining the timing of root growth. Effects on root distribution can have serious impacts on trees, with shallow rooting having negative impacts in years with limited soil water or positive impacts in years with wet springs, and deep rooting having positive impacts on soil water mining from deeper soil layers but negative impacts in years with wet springs.
authors.affiliation: University of California, Department of Plant Sciences, One Shields Avenue, Davis, CA 95616, USA and USDA-ARS Water Management Research Unit, 2150 Centre Avenue, Bldg D, Suite 320, Fort Collins, CO 80526, USA mlcontador@ucdavis.edu.
authors.forename: Maria Loreto
authors.initials: ML
authors.lastname: Contador
authors.affiliation: University of California, Department of Plant Sciences, One Shields Avenue, Davis, CA 95616, USA and USDA-ARS Water Management Research Unit, 2150 Centre Avenue, Bldg D, Suite 320, Fort Collins, CO 80526, USA.
authors.forename: Louise H
authors.initials: LH
authors.lastname: Comas
authors.affiliation: University of California, Department of Plant Sciences, One Shields Avenue, Davis, CA 95616, USA and USDA-ARS Water Management Research Unit, 2150 Centre Avenue, Bldg D, Suite 320, Fort Collins, CO 80526, USA.
authors.forename: Samuel G
authors.initials: SG
authors.lastname: Metcalf
authors.affiliation: University of California, Department of Plant Sciences, One Shields Avenue, Davis, CA 95616, USA and USDA-ARS Water Management Research Unit, 2150 Centre Avenue, Bldg D, Suite 320, Fort Collins, CO 80526, USA.
authors.forename: William L
authors.initials: WL
authors.lastname: Stewart
authors.affiliation: University of California, Department of Plant Sciences, One Shields Avenue, Davis, CA 95616, USA and USDA-ARS Water Management Research Unit, 2150 Centre Avenue, Bldg D, Suite 320, Fort Collins, CO 80526, USA.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Porris Gomez
authors.affiliation: University of California, Department of Plant Sciences, One Shields Avenue, Davis, CA 95616, USA and USDA-ARS Water Management Research Unit, 2150 Centre Avenue, Bldg D, Suite 320, Fort Collins, CO 80526, USA.
authors.forename: Claudia
authors.initials: C
authors.lastname: Negron
authors.affiliation: University of California, Department of Plant Sciences, One Shields Avenue, Davis, CA 95616, USA and USDA-ARS Water Management Research Unit, 2150 Centre Avenue, Bldg D, Suite 320, Fort Collins, CO 80526, USA.
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Lampinen
mesh_terms: D000388:Air; D031324:Juglans / Q000254:growth & development*; D018517:Plant Roots / Q000254:growth & development*; D012621:Seasons; D012987:Soil; D013194:Staining and Labeling; D013696:Temperature; D014197:Trees / Q000254:growth & development
chemical_list: D012987:Soil
keywords: Canopy removal; Juglans regia; pruning; rhizotron; root dynamics; root production; root vertical distribution; walnut; water deficit