Leaf Economics traits in relation to crop domestication syndromes
Studies reporting differences in the LES traits relationships in crops
vs. wild plants have supported inferences and hypotheses surrounding the
unintended consequences of artificial selection (e.g. Milla et al.,
2015; Roucou et al., 2018). Perhaps most consistent with hypotheses
related to artificial selection is our find that in comparison to wild
plants, ‘Chardonnay’ expressed a steeper increase inA mass and R mass per unit
increase in leaf N. Specifically, based on our SMA models fits (Table
S2), across the range of leaf N values in ‘Chardonnay’ observed here
(1.9-2.9%), predicted A mass increased by
~84.3% (from 0.06-0.38 μ mol CO2g-1 s-1) andR mass increases by ~ 71.8% (from
0.008 to 0.028 μ mol CO2 g-1s-1). Comparatively, in wild plants from the GLOPNET
dataset this same increase in leaf N from 1.9 to 2.9% corresponds to
only a 47.0% predicted increase in A mass (from
0.138 to 0.264 μ mol CO2 g-1s-1) and 42.2% increase inR mass (from 0.028 to 0.048 μ mol
CO2 g-1 s-1). Higher
photosynthetic rates for a given value or increase in leaf N
concentrations have been similarly detected in rice (Xiong & Flexas,
2018), and may reflect conscious or unconscious artificial selection for
more rapid growth responses to N availability in crops vs. wild plants.
However, this is not universal among crops. Certain crops, namely
coffee, show significantly lower increases inA mass with greater leaf N (Martin & Isaac, 2021;
Martin et al., 2017), while others including soy expressA mass-leaf N relationships that are statistically
indistinguishable from those in wild plants (Hayes et al., 2019). In
sum, the growing literature to which we contribute with our study
indicates that LES trait relationships are a unique and idiosyncratic
feature of crop domestication syndromes.
In this regard, a novel contribution from our work here is the
integration of R into studies evaluating intraspecific or
intragenotypic LES in crops. Specifically, previous studies evaluating
crop trait (co-)variation in comparison to non-domesticated wild plants
have not included R in their analyses (Hayes et al., 2019; Martin
et al., 2017; Milla, Morente-López, Alonso-Rodrigo, Martín-Robles, &
Stuart Chapin III, 2014; Roucou et al., 2018; Xiong & Flexas, 2018),
despite this trait representing a key trade-off along the LES (P.B.
Reich et al., 1998; I. J. Wright et al., 2004). The LES trait
relationships in ‘Chardonnay’ that included R masswere qualitatively unique, in that none of these bivariate datasets and
SMA models intersected the global LES defined by wild plants (Figure 2C,
D, and E). Instead, at a given value of A mass,
LMA, or leaf N, in nearly all of the leaves measured here (i.e., 43 or
45 leaves), ‘Chardonnay’ R mass was consistently
lower than average vs. R mass in wild plants. This
indicates that domestication has favoured vines that express leaves with
a low rate of C loss at a given rate of structural or chemical
investment in C assimilation.
These results have two possible explanations: 1) even the lowest bulk
density/compaction values at our study site still restrict physiological
functioning; and/or 2) lower R mass for a given
value of A mass, leaf N, or LMA is a signature of
domestication in Vitis vinifera varieties. Since the primary
targets of grape domestication are related to yield, quality, growth
form, and harvestability (Keller, 2020), our findings point to an
unintended consequence of domestication related to plant C economy.
Expanding our work across a wider range of ‘Chardonnay’ growing sites
(particularly where bulk density is lower) and grape varieties is
therefore central in testing either proposed explanation.
One unexpected finding in our analysis here, were patterns of leaf C
variation. Although not a primary focus of our analysis, since it is not
considered a primary trait forming the LES (I. J. Wright et al., 2004),
we found that this trait covaried in an unexpected pattern along the
intragenotype LES in ‘Chardonnay’. Specifically, we detected a
statistically significant positive relationship between leaf C andA mass, R mass, and leaf N,
and a significant negative relationship between leaf C and LMA (Table
S5). Furthermore, when incorporated into an additional PCA, leaf C
covaried across the first PCA axis positively withA mass, leaf N, and negatively with LMA (Table
S6). Therefore in our dataset, leaf C covaries along LES traits such
that higher leaf C values reflect a resource acquisitive trait syndrome.
This finding is counter to studies of certain other domesticated plants
where leaf C is by in large positively related to leaf construction
costs, leaf dry matter content, and LMA (Gagliardi et al., 2015; Martin
et al., 2017). In ‘Chardonnay’, coordination of leaf C along an
intragenotype LES likely owes to the selection for C loading in leaves
and plants in the form of sugars and starches (Keller, 2020).