RESUMO
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.
Assuntos
Folhas de Planta , Solo , Chile , Fenótipo , Floresta ÚmidaRESUMO
BACKGROUND AND AIMS: Ecologists are increasingly using plant functional traits to predict community assembly, but few studies have linked functional traits to species' responses to fine-scale resource gradients. In this study, it was tested whether saplings of woody species partition fine-scale gradients in light availability based on their leaf mass per area (LMA) in three temperate rain forests and one Mediterranean forest in southern Chile. METHODS: LMA was measured under field conditions of all woody species contained in approx. 60 plots of 2 m2 in each site, and light availability, computed as the gap light index (GLI), was determined. For each site, species' pairwise differences in mean LMA (Δ LMA) and abundance-weighted mean GLI (Δ light response) of 2 m2 plots were calculated and it was tested whether they were positively related using Mantel tests, i.e. if species with different LMA values differed in their response to light availability. Additionally linear models were fitted to the relationship between plot-level mean LMA and GLI across plots for each site. KEY RESULTS: A positive and significant relationship was found between species' pairwise differences in mean LMA and differences in light response across species for all temperate rain forests, but not for the Mediterranean forest. The results also indicated a significant positive interspecific link between LMA and light availability for all forests. This is in contrast to what is traditionally reported and to expectations from the leaf economics spectrum. CONCLUSIONS: In environments subjected to light limitation, interspecific differences in a leaf trait (LMA) can explain the fine-scale partitioning of light availability gradients by woody plant species. This niche partitioning potentially facilitates species coexistence at the within-community level. The high frequency of evergreen shade-intolerant species in these forests may explain the positive correlation between light availability and LMA.
Assuntos
Ecossistema , Folhas de Planta/anatomia & histologia , Floresta Úmida , Luz Solar , Adaptação Fisiológica , Folhas de Planta/fisiologia , Plantas/anatomia & histologiaRESUMO
A basic assumption of the trait-based approach in plant ecology is that differences in functional trait values are greater between species than within species. We questioned this assumption by assessing (1) the relative extent of inter- and intraspecific leaf trait variation throughout a complete growing season (phenological variation) in a group of deciduous and evergreen woody species, and (2) whether species rankings based on leaf traits were maintained across the growing season. We analysed leaf mass per area (LMA) and leaf nutrient concentrations (C, N, P), including the C:N and N:P ratios. Intraspecific trait variation (ITV) due to phenology was significantly greater than interspecific variation for leaf N concentration on a mass basis (Nm; 68.90 %) and for the leaf C:N ratio (60.60 %), whereas interspecific variation was significantly higher than ITV for LMA (62.30 %) and for leaf C concentration on a mass (Cm) and area (Ca) basis (Cm 70.40 %; Ca 65.30 %). ITV was particularly low for LMA (<20 %). Species rankings were highly modified by phenology for a number of leaf traits (Pm, N:P ratio) but were relatively well conserved throughout the growing season for others (LMA, Nm). Patterns of ITV across the growing season differed significantly between deciduous and evergreen species for all traits except leaf P but did not vary between native and exotic species. Overall, our results show that intraspecific phenological variation in leaf traits may be similar to or greater than interspecific variation and that temporal patterns of ITV vary considerably among traits and species, especially for leaf nutrient concentrations, factors which can potentially affect quantitative interspecific relationships.