Table 2.
Pearson correlation coefficient (r) between pairs of traits among phylogenetically independent contrasts (PICs) analysed separately for each root order (first to fifth order), and by root functional classes, i.e. absorptive (average of first to third order) vs. transport (average of fourth to fifth root order)
| n v | Lx (m3 s–1 MPa–1 cm–2) | t | d | (t/d)2 | RAD (mm) | Develop | Rings | Colonization | |
|---|---|---|---|---|---|---|---|---|---|
| First order | |||||||||
| Shade tolerance | –0.45 | 0.56 | –0.21 | 0.29 | –0.41 | 0.62* | – | – | 0.16 |
| n v | 0.03 | 0.58* | 0.32 | 0.56 | –0.18 | – | – | –0.65** | |
| Lx (m3 s–1 MPa–1 cm–2) | –0.05 | 0.62* | –0.34 | 0.37 | – | – | –0.26 | ||
| t | 0.57# | 0.93† | 0 | – | – | –0.60* | |||
| d | 0.24 | 0.46 | – | – | –0.20 | ||||
| (t/d)2 | –0.22 | – | – | –0.63* | |||||
| RAD (mm) | – | – | 0.23 | ||||||
| Develop | – | – | |||||||
| Rings | – | ||||||||
| Second order | |||||||||
| Shade tolerance | –0.21 | 0.75** | 0.68** | 0.84*** | –0.51 | 0.61* | 0.18 | – | 0.6* |
| n v | 0 | –0.19 | –0.05 | –0.03 | –0.37 | 0.04 | – | 0.18 | |
| Lx (m3 s–1 MPa–1 cm–2) | 0.31 | 0.96† | –0.85*** | 0.14 | 0.68** | – | 0.54* | ||
| t | 0.42 | 0.13 | 0.73** | –0.07 | – | 0.40 | |||
| d | –0.84*** | 0.35 | 0.54 | – | 0.68** | ||||
| (t/d)2 | 0.01 | –0.60* | – | –0.49 | |||||
| RAD (mm) | –0.40 | – | 0.24 | ||||||
| Develop | – | – | |||||||
| Rings | – | ||||||||
| Third order | |||||||||
| Shade tolerance | . | 0.14 | 0.15 | 0.54 | –0.59* | 0.56 | 0.46 | 0.55 | ‡ |
| n v | § | § | § | § | § | § | § | § | |
| Lx (m3 s–1 MPa–1 cm–2) | 0.29 | 0.84*** | –0.46 | 0.03 | 0.17 | –0.15 | ‡ | ||
| t | 0.48 | 0.45 | 0.57* | –0.33 | –0.54 | ‡ | |||
| d | –0.53 | 0.53 | 0.20 | –0.05 | ‡ | ||||
| (t/d)2 | –0.1 | –0.54 | –0.60** | ‡ | |||||
| RAD (mm) | –0.12 | –0.12 | ‡ | ||||||
| Develop | 0.66** | ‡ | |||||||
| Rings | ‡ | ||||||||
| Fourth order | |||||||||
| Shade tolerance | –0.16 | 0.60* | 0.48 | 0.59* | –0.04 | 0.35 | – | 0.66** | – |
| n v | 0.28 | 0.09 | –0.57* | 0.45 | –0.07 | – | –0.39 | – | |
| Lx (m3 s–1 MPa–1 cm–2) | 0.25 | 0.46 | –0.66* | –0.17 | – | 0.86*** | – | ||
| t | 0.40 | 0.56 | 0.81*** | – | 0.12 | – | |||
| d | –0.42 | 0.69** | – | 0.54 | – | ||||
| (t/d)2 | 0.16 | – | –0.54 | – | |||||
| RAD (mm) | – | 0.05 | – | ||||||
| Develop | 0.06 | – | |||||||
| Rings | – | ||||||||
| Fifth order | |||||||||
| Shade tolerance | 0.18 | –0.14 | –0.12 | 0.28 | –0.42 | 0.28 | – | 0.71** | – |
| n v | –0.42 | 0.21 | –0.09 | 0.50 | 0.3 | – | –0.12 | – | |
| Lx (m3 s–1 MPa–1 cm–2) | 0.50 | 0.49 | –0.16 | 0.21 | – | –0.01 | – | ||
| t | 0.70** | 0.33 | 0.75** | – | 0.12 | – | |||
| d | –0.33 | 0.91† | – | 0.60* | – | ||||
| (t/d)2 | –0.10 | – | –0.55 | – | |||||
| RAD (mm) | – | 0.52 | – | ||||||
| Develop | – | – | |||||||
| Rings | – | ||||||||
| Absorptive | |||||||||
| Shade tolerance | –0.34 | 0.83† | 0.16 | 0.89*** | –0.53 | 0.62* | 0.72** | ¶ | 0.27 |
| n v | –0.42 | 0.09 | –0.35 | 0.33 | –0.13 | –0.42 | ¶ | –0.58* | |
| Lx (m3 s–1 MPa–1 cm–2) | –0.17 | 0.84*** | –0.76** | 0.30 | 0.94† | ¶ | 0.64** | ||
| t | 0.24 | 0.72** | 0.53 | –0.35 | ¶ | –0.31 | |||
| d | –0.48 | 0.71** | 0.68** | ¶ | 0.53 | ||||
| (t/d)2 | –0.05 | –0.82*** | ¶ | –0.59* | |||||
| RAD (mm) | 0.21 | ¶ | 0.05 | ||||||
| Develop | ¶ | – | |||||||
| Rings | – | ||||||||
| Transport | |||||||||
| Shade tolerance | 0.13 | –0.18 | 0.06 | 0.37 | –0.28 | 0.32 | –0.02 | 0.74** | – |
| n v | –0.36 | 0.25 | –0.22 | 0.56 | 0.21 | –0.14 | –0.25 | – | |
| Lx (m3 s–1 MPa–1 cm–2) | 0.44 | 0.50 | –0.26 | 0.24 | 0.30 | –0.12 | – | ||
| t | 0.65* | 0.29 | 0.81*** | 0.17 | 0.06 | – | |||
| d | –0.42 | 0.87*** | 0.39 | 0.58* | – | ||||
| (t/d)2 | –0.07 | –0.68** | –0.54 | – | |||||
| RAD (mm) | 0.31 | 0.40 | – | ||||||
| Develop | 0.16 | – | |||||||
| Rings | – |
Traits included the number of conduits (nv), root-specific hydraulic conductance (Lx), thickness of individual conduit walls (t), hydraulic weighted mean conduit (lumen) diameter (d), the critical tension for conduit collapse (t/d)2, root average diameter (RAD), proportion of the sample under secondary development (Develop), number of growth rings (Rings) and mycorrhizal colonization (Colonization).
Statistical significance is indicated by *P < 0.1, **P < 0.05, ***P < 0.01 and †P < 0.001
– Indicates that analyses were not run. For example, first-order roots do not undergo secondary development, and thus do not form growth rings and periderm. All species had fourth- and fifth-order roots with secondary development, thus this trait was the same among all species so analyses were not run.
‡There was only colonization on third-order roots of Q. alba so analyses were not run.
¶Analyses were not run because only two species (P. virginiana and A. saccharum) formed rings on third-order roots.
§Analyses of nv in third-order roots were excluded because these analyses did not pass assumptions for the statistical tests.