Leaf water content contributes to global leaf trait relationships

Abstract

Leaf functional traits are important indicators of plant growth and ecosystem dynamics. Despite a wealth of knowledge about leaf trait relationships, a mechanistic understanding of how biotic and abiotic factors quantitatively influence leaf trait variation and scaling is still incomplete. We propose that leaf water content (LWC) inherently affects other leaf traits, although its role has been largely neglected. Here, we present a modification of a previously validated model based on metabolic theory and use an extensive global leaf trait dataset to test it. Analyses show that mass-based photosynthetic capacity and specific leaf area increase nonlinearly with LWC, as predicted by the model. When the effects of temperature and LWC are controlled, the numerical values for the leaf area-mass scaling exponents converge onto 1.0 across plant functional groups, ecosystem types, and latitudinal zones. The data also indicate that leaf water mass is a better predictor of whole-leaf photosynthesis and leaf area than whole-leaf nitrogen and phosphorus masses. Our findings highlight a comprehensive theory that can quantitatively predict some global patterns from the leaf economics spectrum.

Contrasting leaf thickness & saturated water content explain diverse structural/physiological properties of arid species

“…(1999a,c) who proposed it as general rule but it cannot apply to leaf succulents where increased water storage capacity is clearly associated with increased z. Our values for A / Q would force the slope of 0.97, obtained by Wang et al (2022) for several thousand species worldwide, to fall convexly to a mean of 0.05 (Table 1) as Q increased.…”

“…The overall pattern from Fig. 3 compared with the equivalent figure in Wang et al (2022) is that the inclusion of succulents makes the quest for a universal curve quite futile and does not do justice to the rich structural variation in leaf structure that actually exists in nature.…”

“…Since its contribution to leaf volume varied by 50% in our species, Q m and Q v were completely uncorrelated. This means that using Q m as a surrogate for Q v or D v , as undertaken in some functional ecology studies (Weiher et al ., 1999, Wang et al (2022), could be quite misleading. Thus, it is difficult to advocate substituting Q m (or D m ) for Q v (or D v ) on theoretical grounds as they lack a structural basis (the presence of air is ignored).…”

“…Since Wang et al (2022) demonstrated a significant relationship between SLA and Q / D for thousands of species that did not appear to include leaf succulents, we decided to compare Q / D with SLA ( A / D ), whose slope produces Q / A – our preferred index of succulence, with data sets that include succulents: ours, Vendramini et al (2002) and Grubb et al (2015). This provided 34 species that the researchers considered to be succulents, and 69 non-succulents.…”

“…At one level, there are attempts to relate leaf structure to their environment (Lamont et al ., 2002; Wright & Westoby 2002; Grubb et al 2015). At another, the aim is to identify the basic components of leaf structure and see how they vary between species and each other (Niinemets, 1999; Pyankov et al ., 1999; Roderick et al ., 1999b; Wang et al 2022). Few of these studies have included leaf succulents.…”