The Leaf Economics Spectrum (LES) is a framework for understanding the causes and consequences of differences in the comparative ecophysiology, morphology, and biochemistry of plants (Wright et al. 2004). On one end of the LES, are species expressing “resource acquiring” trait syndromes that include high maximum leaf-level photosynthesis (A) and dark respiration (R) rates, high leaf nitrogen (N) concentrations, and low leaf mass per unit area (LMA). The other end of the LES is defined by plants expressing the opposite suite of trait values, which represent “resource conserving” trait syndromes (Wright et al. 2004). Variability in traits along the LES underpin differences in how plant species respond to environmental conditions and change (e.g. Wright et al. 2005), and are central in driving relationships between plant species composition and ecosystem functioning (e.g. Reich et al. 2014). Correlations and trade-offs among LES traits detected across thousands of plant species, both within and across biomes (Reich et al. 1999; Reich et al. 1997; Thomas et al. 2020), have also informed our understanding of the evolutionary and environmental factors that constrain leaf form and function (Donovan et al. 2011; Reich et al. 2003; Shipley et al. 2006).
The original formulation and early research on the LES, focused trait differences across plant species or communities (Reich et al. 1997; Wright et al. 2004). However more recently, meta-analyses have argued and shown that variation within species constitutes a considerable proportion (e.g., ~ 29% of LMA and leaf N) of total LES trait variation within plant communities (Albert et al. 2010; Fajardo and Siefert 2018; Siefert et al. 2015). Extending from this work, studies have now begun focusing on evaluating how plants of the same species differ in their LES traits, with conspecific plants commonly differing from one another along an intraspecific LES (Hayes et al. 2019; Martin et al. 2017; Niinemets 2015). Moreover, in unmanaged systems, the within-species variation that exists in certain LES traits has also been found to be a significant correlate of ecosystem structure, function, and responses to environmental change (Laforest-Lapointe et al. 2014; Mitchell et al. 2021; Siefert and Ritchie 2016; see also Westerband et al. 2021 and references therein).
Research on LES trait variation and relationships within species also informs an understanding of how and why the functional ecology of crops varies in managed agroecosystems. Specifically, studies have shown that individuals of the same crop species or genotype express wide variation in their LES traits, often along an intraspecific or intragenotypic Leaf Economics Spectrum. This includes studies detecting within species or genotype LESs that exists in several of the world’s most common crops including soy (Hayes et al. 2019), rice (Xiong and Flexas 2018), coffee (Gagliardi et al. 2015; Martin et al. 2017), wheat (Roucou et al. 2018), and maize (Martin et al. 2018). Across these studies, intraspecific or intragenotypic LES trait variation in crops was a statistical correlate of agroecosystem functions including yield (Gagliardi et al. 2015; Hayes et al. 2019), photosynthetic N-use efficiency (Xiong and Flexas 2018), tissue decomposition (Coleman et al. 2020), N2-fixing structures (Martin et al. 2019), and soil microbial diversity (Fulthorpe et al. 2019).
Studies on crops have also helped elucidate the factors that cause plants to differentiate along a given intraspecific or intragenotypic LES, which to date includes temperature and precipitation regimes (Martin et al. 2018), soil nutrient availability (Buchanan et al. 2019), plant ontogenetic stages (Hayes et al. 2019) or size (Martin and Isaac 2021), or light (Gagliardi et al. 2015). Results differ across crops and spatial scales, though generally studies have found plants of the same crop move towards the resource conserving end of a within-species- or -genotype LES (i.e., plants expressing low A, low leaf N, high LMA) under the following: 1) hot and dry environments (Martin et al. 2017); 2) shaded conditions, such as those in agroforestry systems (Gagliardi et al. 2015); and 3) following reproductive onset (Hayes et al. 2019; Martin and Isaac 2021). While these studies are instructive, there remain important factors that may also lead to differences in crop traits along an intraspecific or intragenotypic LES that have yet to be explored.
Soil compaction is a major characteristic of land degradation worldwide, and a primary contributor to reductions in agricultural productivity and sustainability (Colombi and Keller 2019; Hamza and Anderson 2005; Nawaz et al. 2013). In some instances, increased soil compaction results in higher rates of A, growth, and yield (Morales et al. 2018). Though more often, growth and yield reductions in plants under compaction occur as the cumulative consequence of reductions in root growth, which in turn limit water and nutrient uptake; compaction also triggers complex plant signalling pathways, which ultimately reduce leaf-level A via stomatal and non-stomatal factors (Colombi and Keller 2019; Kozlowski 1999; Lipiec and Stępniewski 1995; Morales et al. 2018; Sadras et al. 2005). Existing literature therefore supports the untested hypothesis that soil compaction drives trait covariation and/ or trade-offs along an intraspecific or intragenotypic LES. Specifically, when soil compaction gradients exist within a site, plants in high compaction should express resource conserving LES traits (i.e., low A, leaf N, and R, along with high LMA), while those in low compaction areas should express the opposite suite of traits.
Existing work on crops has also focused only on a subset of the six traits included in the original LES formulation. Specifically, studies on coffee (Gagliardi et al. 2015; Martin et al. 2019), soy (Hayes et al. 2019), and rice (Xiong and Flexas 2018) have largely analyzed how three LES traits—A, LMA or SLA, and leaf N—covary or trade-off within crop species or genotypes. For instance, Martin et al. (2017) found lower A for a given leaf N in coffee vs. wild plants, and based on this finding hypothesized that either artificial selection for caffeine, or luxury consumption of N-based compounds from soil amendments, has altered LES trait relationships in that crop. Conversely, Xiong and Flexas (2018) found that rice expressed a higher A for a given leaf N vs. wild rice plants, supporting the hypothesis that artificial selection has resulted in higher photosynthetic nitrogen-use efficiency in that crop. Other studies have found that while crops such as soy, wheat, and maize occupy the extreme resource-acquiring end of the LES (Martin et al. 2018; Milla et al. 2015), domestication has not necessarily altered the slope or strength of bivariate trait relationships among A, LMA, or leaf N (Hayes et al. 2019).
While these and other findings have informed our understanding of how artificial selection influences plant trait syndromes, certain LES traits—namely leaf R—have largely been omitted from these and other analyses on crop trait syndromes. Leaf R is among the six core traits forming the LES, which exists among plant species globally, being significantly correlated (r2 = 0.34–0.60) to all other LES traits (Wright et al. 2004). The relationship between R and other traits along the global LES, reflect evolved physiological, biochemical, and structural trade-offs in plants: the physiological cost of R, in terms of plant carbon (C) metabolism, increases with greater leaf N and A and declines with increasing LMA (Reich et al. 1998; Wright et al. 2006; Wright et al. 2004). The incorporation of R into any LES is therefore central, as it reflects a quantifiable physiological cost of resource acquisition.
In crops, reducing R while maintaining plant growth and yield is one of several goals of selection programs, with research on tomato (Nunes-Nesi et al. 2005), canola (Hauben et al. 2009), cucumber (Juszczuk et al. 2007), and rye grass (Wilson and Jones 1982) showing that reductions in plant C losses via R, due to artificial selection were related to higher yields. Therefore, one might expect that artificial selection may have altered the shape (i.e., the intercept and slope) and strength of the relationship between leaf R and other LES traits in crops vs. wild plants. Moreover, changes in crop leaf R have been evaluated in responses to soil nutrient amendments, irrigation, and growing temperatures, though relationships between leaf R and soil compaction are less commonly assessed (Amthor 2012). Since, 1) croplands now cover at least ~ 12.2–17.1 million km2 of Earth’s ice-free land (Ramankutty et al. 2008), and 2) compaction is a central feature on an estimated 68 million ha of soils on the world’s arable lands (Colombi and Keller 2019; Hamza and Anderson 2005), then 3) understanding how R, and its relationship to other LES traits in crops, is influenced by compaction is particularly important for refining Earth System models (Atkin et al. 2015).
Here, we explored how LES traits vary in ‘Chardonnay’ (Vitis vinifera var. ‘Chardonnay’), one of the world’s most commercially important, widespread, and rapidly expanding winegrape varieties (Aryal and Anderson 2013). We evaluated LES and related traits on individual ‘Chardonnay’ vines that exist across a soil compaction gradient, to address the following questions: 1) Is intra-genotype variation in Chardonnay LES traits related to soil compaction? If so, then 2) does soil compaction lead to ‘Chardonnay’ leaves and vines differentiating from one another along an intragenotype LES? Finally, we assess 3) whether or not the shape of a potential intra-genotype LES in Chardonnay differs from the LES detected across plants globally?