DOI: 10.5061/dryad.ngf1vhhs2
title: Root morphological responses to population density vary with soil conditions and growth stages

description: How plants cope with increases in population density via root plasticity
 is not well documented, although abiotic environments and plant ontogeny
 may have important roles in determining root response to density. To
 investigate how plant root plasticity in response to density varies with
 soil conditions and growth stages, we conducted a field experiment with an
 annual herbaceous species (Abutilon theophrasti). Plants were grown at
 low, medium and high densities (13.4, 36.0 and 121.0 plants ▪ m-2,
 respectively), under fertile and infertile soil conditions and a series of
 root traits were measured after 30, 50 and 70 d. Root allocation
 increased, decreased or canalized in response to density, depending on
 soil conditions and stages of plant growth, indicating the complex effects
 of population density, including both competitive and facilitative
 effects. Root allocation was promoted by neighbor roots at early stages
 and in abundant resource availability, due to low to moderate belowground
 interactions among smaller plants, leading to facilitation. As plants
 grew, competition intensified and infertile soil aggravated belowground
 competition, leading to decreased root allocation in response to density.
 Root growth may be more likely restricted horizontally rather than
 vertically by the presence of neighbor, suggesting a spatial-orientation
 effect in their responses to density. We emphasized the importance of
 considering effects of abiotic conditions and plant growth stages in
 elucidating the complexity of density effects on root traits.
description: <i>Data
 collection</i> Plants were harvested at 30, 50 and
 70 d of growth, representing developmental stages of early vegetative
 growth, late vegetative or early reproductive growth, and middle to late
 reproductive growth respectively. At each stage, six individual plants
 were randomly chosen from each plot, making a total of 6 replicates × 3
 plots × 3 densities × 2 soils × 3 stages = 324 samplings. For each
 individual plant, the following traits were measured if applicable:
 diameter at the basal of the main root, length and number of lateral roots
 (above or equal to 1 mm in diameter along the main root). Morphological
 root traits were not measured at 30 d of growth due to small sizes of
 plants. Each individual was then separated into roots, stems, petioles,
 leaves, reproductive organs and branches (if any), enveloped respectively,
 and oven-dried at 75 <sup>o</sup>C for
 2 d and weighed. <i>Statistical
 analysis</i> All statistical analyses were
 conducted using SAS statistical software (SAS Institute 9.0 Inc. 2002).
 Biomass traits including shoot mass, root mass, total biomass and
 root:shoot ratio, and morphological traits including main root length,
 main root diameter, lateral root number and lateral root length were
 analyzed. To minimize variance heterogeneity, all data were
 log-transformed before statistical analysis. Three-way ANOVA and ANCOVA
 were used to evaluate overall effects of growth stage, soil conditions and
 population density and their interactions on all traits, with total
 biomass nested in growth stage as a covariate in three-way ANCOVA. Within
 each soil condition at each stage, effects of density were analyzed by
 one-way ANOVAs for total mass, and one-way ANCOVAs for all the other
 traits with total mass as a covariate. For a given trait, it was
 considered to exhibit apparent plasticity whenever plant size (total
 biomass) accounted for significant variation in its response to density,
 and any variation in its expression that was independent of total biomass
 was considered an indication of true plasticity (after removal of size
 effects) (McConnaughay and Coleman 1999, Weiner 2004). Multiple
 comparisons used Least Significant Difference (LSD) method of the General
 Linear Model (GLM) program in one-way ANCOVA, which also produced adjusted
 mean values and standard errors.
description: The data includes two sheets, sheet1 is for traits of root mass,
 shoot mass and root to shoot ratio of all three stages, sheet2 is for root
 morphological traits of the latter two stages. Line 1-5
 for each sheet are original lables for data, can be neglected, and data of
 all blocks has been put together, as effects of blocks were
 not considered.  Line 6-8 are factors considered in
 analyses, and Line 9-13 are values measured, each of which came from one
 individual plant.