Intraspecific trait variation and the leaf economics spectrum across resource gradients and levels of organization

Abstract

Understanding patterns of functional trait variation across environmental gradients offers an opportunity to increase inference in the mechanistic causes of plant community assembly. The leaf economics spectrum (LES) predicts global tradeoffs in leaf traits and trait-environment relationships, but few studies have examined whether these predictions hold across different levels of organization, particularly within species. Here, we asked (1) whether the main assumptions of the LES (expected trait relationships and shifts in trait values across resource gradients) hold at the intraspecific level, and (2) how within-species trait correlations scale up to interspecific or among-community levels. We worked with leaf traits of saplings of woody species growing across light and soil N and P availability gradients in temperate rainforests of southern Chile. We found that ITV accounted for a large proportion of community-level variation in leaf traits (e.g., LMA and leaf P) and played an important role in driving community-level shifts in leaf traits across environmental gradients. Additionally, intraspecific leaf trait relationships were generally consistent with interspecific and community-level trait relationships and with LES predictions-e.g., a strong negative intraspecific LMA-leaf N correlation-although, most trait relationships varied significantly among species, suggesting idiosyncrasies in the LES at the intraspecific level.

The interplay among intraspecific leaf trait variation, niche breadth and species abundance along light and soil nutrient gradients

“…Specifically, species that occurred across a wide range of light environments had high ITV in leaf N concentration, and species broadly distributed along the soil P availability gradient had high ITV in leaf N and P. Importantly, we found these positive relationships between niche breadth and ITV by comparing species’ ITV measured across a common set of environments. Research conducted in these southern hemisphere cool temperate rainforests thus far (Lusk , Fajardo and Siefert , Peltzer and Wardle ) has commonly focused on light availability as the limiting factor, especially, for regeneration, but here we show that soil N and P availability had a strong positive relationship with leaf trait variation, indicating that multiple environmental filters drive regeneration dynamics (see also Lusk and Laughlin , Fajardo and Siefert ). Although some studies have found that N is the most limiting nutrient in soils of temperate rainforests in southern Chile (Huygens et al ), the volcanic origin of these soils makes them very poor in available P for plants (large amount of allophane and sesquioxide in the soil, which have a high phosphate‐fixing capacity, making P not readily available for plants) (Fajardo and Piper ).…”

“…In temperate rainforests of southern Chile, where as many as 25 woody species per hectare can co‐occur within forest communities, species can be found in a variety of local environmental conditions, from deep shade to tree‐fall canopy gaps (Veblen 1985, Lusk , Fajardo and Siefert , ), and from spots with poor to rich nutrient availability. Given these apparent strong environmental gradients, we expected that species achieving high local abundance would be those that could tolerate a wide range of environments by adjusting their trait values to local conditions (Darwin 1859, Sides et al ).…”

“…We selected four second‐growth, temperate rainforests for our study (Fig. 1) (Fajardo and Siefert , ). The first site was Exploradores (EXP, 46°29′S, 73°12′W, 75 m above sea level), where the forest is on moraine deposits of glacial erosion originating from the Exploradores Glacier (Aniya et al ).…”

“…To relate patterns of ITV to species’ niche breadth along these gradients, we focused on four leaf traits – leaf area (cm 2 ), leaf mass per area (LMA, g m −2 ), leaf nitrogen (N) and phosphorus (P, mg g −1 ) concentrations. These traits are intimately related to light and soil nutrient availability – and therefore carbon investment and ultimately carbon economy (Wright et al , Fajardo and Siefert ) – corresponding to different plant strategies of resource acquisition and utilization (Poorter et al ). Thus, trait–environment relationships can be interpreted in terms of physiological tradeoffs related to resource availability.…”

A scale‐dependent framework for trade‐offs, syndromes, and specialization in organismal biology

“…As with all such largescale patterns, the question emerges of how it evolved, and whether within-species patterns are consistent with across-species patterns. These studies have largely taken a phenotypic approach assessing within vs. between species trait associations, typically via field sampling within and between plant communities (Funk and Cornwell 2013, Niinemets 2015, Fajardo and Siefert 2018. The authors concluded that constraints are thus unlikely the driver of the LES, but rather selection for and against particular trait combinations is more likely responsible for the pattern across species.…”