‘Chardonnay’ functional trait variation in relation to soil bulk density
All leaf traits measured here, with the exception of LLCP, varied significantly across planting rows (Table S1). Photosynthesis andΦ varied most widely across the ‘Chardonnay’ vines and leaves evaluated here (CV=25.6-43.2), and all of these traits related to C assimilation rates declined significantly with soil compaction. Specifically, sampling row identity explained 45.4% and 64.8% of the variation in A area andA mass, respectively (Table 1). In turn, both declined significantly with higher bulk density (p <0.01 in the mixed model slope term), with soil compaction explaining 31.3% and 40.3% of the variation in A area andA mass, respectively (Figure 1A-B, Table S2). Similarly, 42.9% of the variation in leaf Φ was explained by sampling row identity (Table 1), and this trait was negatively correlated with soil bulk density (mixed model slope term p =0.01, marginal r 2=0.243; Figure 1F, Table S2). Although 19.3% and 26.0% of the variability inR area and R mass was attributable to sampling row identity (Table 1), and these traits differed significantly across rows (Table S1), neither of these traits was statistically correlated with soil bulk density when individual plant identity was accounted for in our mixed models (Figure 1D-E, Table S2). Across our dataset, LLCP was also not correlated with soil bulk density (marginal r 2=0.03), and sampling row explained <1% of the variation in this trait (Figure 1C).
Soil bulk density had a strong and statistically significant influence on LMA and leaf area, with planting row identity explaining 62.9% and 30.3% of the variation in these traits, respectively (Table 1). Both traits were significantly correlated to bulk density (mixed model slopep≤ 0.01, Figure 1, Table S2). Generally, ‘Chardonnay’ leaves were smaller in terms of leaf area and expressed a higher LMA in areas of higher soil compaction: leaf area varied by a factor of three across our dataset (CV=25.3), ranging from 44.0-153.9 cm2 and declining significantly as bulk density increased, while LMA varied nearly 2-fold (range 63.5-111.2 g m-2, CV=12.2) and increased significantly with higher bulk density (Figure 1G-H, Tables 1 and 2). Leaf dry mass did vary from 0.28-1.26 g across our dataset (CV=28.1), though this variation was weakly explained by planting row (15.5% variation explained) and was not related to soil bulk density (Figure 1I, Table S2). Therefore, statistically significant increases in LMA across a bulk density gradient were attributable to declines in leaf area, and not increases in leaf mass.
Compared to other suites of traits, leaf chemical traits including C and N concentrations were less variable across ‘Chardonnay’ leaves (CV=1.8 and 10.4, respectively). However, consistent with declines in photosynthesis and leaf Φ that occurred in relation to bulk density, leaf N concentrations also declined significantly as bulk density increased (mixed model slope p =0.04, marginalr 2=0.241; Figure 1K, Table S2). Across all leaves, N concentrations ranged from 1.9-2.9% with sampling row explaining over half of the variation in this trait (Table 1). Leaf C also declined significantly with greater bulk density (mixed model slopep≤ 0.04, marginal r 2=0.41, respectively; Figure 1J, Table S2). Sampling row explained 54 and 56% of the variability in leaf N and C, respectively (Table 1).