Table 1.
Root traits used to characterize the ability of a plant species to exploit soil resources.
Table 2.
Species name, abbreviation and status in the banana cropping system.
See photos of these plants in S1 File.
Table 3.
Correlations between root traits related to the ability of the species to exploit soil resources.
Fig 1.
Species distributions regarding the relationship between total root-impact density and root exploration zone.
See Table 2 for the species names. (n = 4 replicates for all species except BD (n = 3)).
Fig 2.
Species distributions regarding the relationship between specific root length and root diameter.
See Table 2 for the species names. (n = 4 replicates for all species except BD (n = 3)).
Fig 3.
Principal component analysis on four soil-resource exploitation traits and 21 species (n = 4 replicates for all species except BD (n = 3)).
a Correlation circle between traits; b Representation of weed species (in blue), banana cultivars (in red) and cover plant species (in green) on the first two axes (see Table 2 for the species names). The soil-resource exploitation traits are: SRL for specific root length, DI for total root-impact density, Z for median root exploration zone and D for root diameter. The symbols represent contrasted plant strategies, with a triangle for species with a high DI (total root-impact density), a square for species with a high SRL (specific root length) and a circle for species with high Z (median root exploration zone) and D (root diameter).
Table 4.
Correlations between traits related to the ability to exploit soil resources (vertically) and traits related to the ability to exploit light (horizontally).
Fig 4.
Principal component analysis on four soil-resource exploitation traits and six light exploitation traits and 21 species.
a Correlation circle between traits; b Representation of weed species (in blue), banana cultivars (in red) and cover plant species (in green) on the first two axes (see Table 2 for the species names). The light exploitation traits are: Bma for aboveground dry biomass, SLA for specific leaf area, LARa for aboveground leaf area ratio, H for height and CW for plant crown width. The soil-resource exploitation traits are: SRL for specific root length, DI for total root-impact density, Z for the root exploration zone and D for root diameter. The yellow arrow represents the leaf economic spectrum gradient (according to the SLA direction) and the red arrow represents the root economic spectrum gradient (according to the SRL direction).
Fig 5.
Species distribution according to differences in root-impact density between the cover plant species and the Cavendish banana cultivar (Bcav) in two soil layers (0–20 cm and 40–80 cm).
a Banana root-impact density profile (red line) and root-impact density profile of an ideal cover plant species (blue dashed line) which is complementary to the banana profile, i.e. with a positive Δ0–20 (lower root-impact density than banana) and negative Δ40–80 (higher root-impact density than banana). b Species distribution according Δ0–20 and Δ40–80. The area outlined in red corresponds to the root-impact density profile required for associations with banana. See Table 2 for the species names.
Fig 6.
Comparison of the six potential cover crop species with regard to the four studied root traits: Root exploration zone (Z), root diameter (D), Specific Root Length (SRL) and total root impact Density (DI).
a Crotalaria spectabilis (CS). b Crotalaria zanzibarica (CZ). c Gliricidia sepium (GS). d Mucuna pruriens var. deeringiana. e Vigna unguiculata var. David (N). f Neonotonia wightii (NW). For each trait, values are expressed in proportion to the highest value per trait observed for that trait in the panel of species studied. For each species, when the name of a trait is surrounded by green, then the species is one of the two species (among the six species) with the highest values for this trait. For each species, when the name of a trait is surrounded by red, then the species is one of the two species (among the six species) with the lowest values for this trait. Light exploitation strategy [see 20] of each species is mentioned under its name.