Table 1.
Botanical family, taxonomic status, leaf functional traits values, crop growth rate (CGR) and crop N acquisition rate (CNR) of the 36 taxa studied.
Table 2.
Pearson’s correlations between crop growth rate (CGR) and crop N acquisition (CNR) of cover crop species (n = 36) and leaf functional traits: specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen content (LNC) and leaf area (LA).
Fig 1.
Relationships between crop growth rate (CGR) and leaf functional trait values: (a) leaf dry matter content (LDMC), (b) leaf area (LA); and relationships between crop N acquisition rate (CNR) and leaf functional trait values: (c) leaf dry matter content (LDMC), (c) leaf area (LA).
The significance of differences was assessed by Student’s t-tests. Values of traits and CGRs are means of both experimental sites.
Fig 2.
Generalized linear models based on significant leaf traits (P<0.05) as input variables to fit a) crop growth rate (CGR) and b) crop nitrogen acquisition rate (CNR).
The equation of the CGR model is: CGR = 4.8E-2*SLA + 1.5E-2* LA and that for CNR is: CNR = 63 + 0.4*LA+ 1.5*SLA − 0.3*LDMC, where LDMC is leaf dry matter content (mg g-1), LA is leaf area (cm2), and SLA is specific leaf area (m2 kg-1).
Fig 3.
Principal component analysis (PCA) based on four functional traits measured on 36 cover crop species.
(a) Correlation circle between SLA (specific leaf area), LDMC (leaf dry matter content), LNC (leaf nitrogen content) and LA (leaf area) and loadings; coordinates position of CGR (crop growth rate) and CNR (crop nitrogen acquisition rate); (b) Botanical families and cover crop species position along the first two axes of the PCA; A: Asteraceae; B: Brassicaceae; F: Fabaceae; H: Hydrophyllaceae; P: Polygonaceae; PC3: C3 Poaceae; PC4: C4 Poaceae.
Fig 4.
Position of cover crop species along grass and herbs of the Leaf Economic Spectrum (LES) (Wright et al. [17]) based on specific leaf area (SLA) and leaf nitrogen content (LNC) axes (the latter logarithmic).
Fig 5.
Cover crop species position compared to the relationship between leaf dry matter content (LDMC) and specific leaf area (SLA) established for 1392 grass, forbs and succulents wild species (S1 Text).
Fig 6.
Cover crop species position on Grime’s CSR triangle (Pierce et al. [24]).
C: competition, S: stress-tolerance, R: ruderality. Letters correspond to species identification (Table 1).
Table 3.
Leaf trait values of cover crop species obtained in the present study compared to trait values of congeneric wild species obtained from the TRY plant-trait database (Kattge et al. [34] and S2 Text).