Aboveground-trait variations in 11 (sub)alpine plants along a 1000-m elevation gradient in tropical Mexico

Abstract

With the aim to explore how plants acclimate to elevation changes in the understudied (sub)alpine tropics we tested two hypotheses along a 1000-m elevation gradient in Mexico: (H1) due to a severe increase in abiotic constraints at higher elevations, the functional traits of the plant species will converge toward more resource conservation, and (H2) the specific growth forms and biogeographic origins present in the (sub)alpine tropics may influence the interspecific trait variation along the gradient. We measured five aboveground functional traits: specific leaf area (SLA), leaf dry-matter content (LDMC), leaf thickness, leaf area and plant height, of 11 species representing fourPowered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation growth forms: rosette, tussock grass, shrub and tree the soil microclimate. Microclimatic data revealed a steep decrease in soil water content at higher elevations. Across all species and all individuals, SLA, plant height and leaf area decreased with elevation whereas LDMC and leaf thickness increased, all of which revealing adjustments towards resource conservation in line with H1. Consistently with H2, the functional traits of the growth forms that were characteristic of tropical alpine regions (tussock grasses and erect shrubs) were less sensitive to changes in elevation compared to more generalist growth forms such as forbs. Also, within the growth form "rosette" the functional traits of species of tropical biogeographic origin changed with elevation whereas those of Holarctic origin did not. Our Mexican data indicate a convergence of plant traits toward improved resource conservation at higher elevations, which may be influenced partially by the growth form and the biogeographical origin of plant species.

Environmental variation drives the decoupling of leaf and root traits within species along an elevation gradient

“…Whereas root trait patterns were highly idiosyncratic between elevations, leaf traits generally varied as hypothesized, with plants having lower SLA and denser and thicker leaves at higher elevations. Similar and largely consistent intraspecific relationships between leaf traits and elevation were also observed for the majority of species by Cruz-Maldonado et al, (2021) and Kichenin et al, (2013). Albert et al, (2010) however, reported more diverse intraspecific leaf trait patterns across 15 species along a 300 -1000 m gradient in the French Alps.…”

“…Collected plants (herbaceous species) or branches (woody species) with leaves attached were stored cooled in moist plastic bags during the field work and were rehydrated overnight in water at 4°C until further analysis (Cruz-Maldonado et al 2021). Within 24 h of collection in the field, we selected between 5 and 25 healthy, fully expanded leaves without petioles from each individual.…”

Water and nutrient availability exert selection on reproductive phenology

“…The observed pattern of selection for increased height at flowering in B. stricta, a highly selfing plant, is likely not mediated by pollinators. Instead, we propose that the genetic cline of declining height with elevation in this and other studies (Gairola et al, 2008;Wadgymar et al, 2017a;Cruz-Maldonado et al, 2021) is driven by strong selection for early reproduction at high-elevation locations associated with short growing seasons and genetic trade-offs between height and timing of flowering (Bemmels and Anderson, 2019). We did not manipulate the length of the growing season or vary conditions temporally across the season and thus cannot directly evaluate how these agents of selection influence trait evolution.…”

Microclimatic Warming Leads to a Decrease in Species and Growth Form Diversity: Insights From a Tropical Alpine Grassland

“…Given the gradual change in species and growth form diversity as elevation increases, we expected changes in growth form diversity. For example, we expected an increase in graminoid and shrub species because their growth form might be more resilient to changes in microclimatic conditions or, in the case of shrubs, higher temperatures result in favorable conditions for them (Harte and Shaw, 1995;Cruz-Maldonado et al, 2021;Lasso et al, 2021). While there has not been a clear trend for AGB under warming conditions, we expected an increase in AGB due to the previously mentioned increase in shrubs and graminoids that may contribute more biomass per square meter than other growth forms.…”