Intraspecific trait changes have large impacts on community functional composition but do not affect ecosystem function

Abstract

Plant functional traits can provide a mechanistic understanding of community responses to global change and of community effects on ecosystem functions. Nitrogen enrichment typically shifts trait composition by promoting the dominance of acquisitive plants (high specific leaf area [SLA] and low leaf dry matter content [LDMC]), translating into high biomass production. Changes in mean trait values can be due to shifts in species identity, relative abundances and/or intraspecific trait values. However, we do not know the relative importance of these shifts in determining trait responses to environmental changes, or trait effects on ecosystem functioning, such as biomass production. We quantified the relative importance of species composition, abundance and intraspecific shifts in driving variation in SLA and LDMC, and how these shifts affected above‐ and below‐ground biomass. We measured traits in a grassland experiment manipulating nitrogen fertilisation, plant species richness, foliar fungal pathogen removal and sown functional composition (slow vs. fast species). We fitted structural equation models to test the importance of abundance and intraspecific shifts in determining (a) responses of functional composition to treatments and (b) effects on above‐ and below‐ground biomass. We found that species intraspecific shifts were as important as abundance shifts in determining the overall change in functional composition (community weighted mean trait values), and even had large effects compared to substantial initial variation in sown trait composition. Intraspecific trait shifts resulted in convergence towards intermediate SLA in diverse communities; although convergence was reduced by nitrogen addition and enhanced by pathogen removal. In contrast, large intraspecific shifts in LDMC were not influenced by the treatments. However, despite large responses, intraspecific trait shifts had no effect on above‐ or below‐ground biomass. Only interspecific trait variation affected functioning: below‐ground biomass was reduced by SLA and increased by LDMC, while above‐ground biomass was increased by SLA. Synthesis. Our results add to a growing body of literature showing large intraspecific trait variation and emphasise the importance of using field collected data to determine community functional composition. However, they also show that intraspecific variation does not necessarily affect ecosystem functioning and therefore response–effect trait relationships may differ between versus within species.

Nitrogen addition and warming modulate the pathogen impact on plant biomass by shifting intraspecific functional traits and reducing species richness

“…Meanwhile, these results also highlight the importance of intraspecific trait variations. Recent studies showed that intraspecific trait variations might be equal or greater than interspecific variations in determining community responses to biotic and abiotic environmental changes (Jessen et al, 2020;Pichon et al, 2022;Wang et al, 2022;Wilfahrt et al, 2020). Consistent with these studies, we found that the fungicide effect on plant community biomass was more related to intraspecific trait variations, rather than trait changes induced by abundance shifts (Figure 5).…”

“…Due to local adaptation or phenotypic plasticity, functional traits of plant individuals within one species can vary in response to environmental changes (Albert et al, 2011;Messier et al, 2010;Violle et al, 2012). Generally, nitrogen addition can increase plant individuals' height, leaf chlorophyll content, SLA and decrease LDMC, which are related to fast growth in resource-rich conditions (Pichon et al, 2022;Wang et al, 2022;Wilfahrt et al, 2020). However, these intraspecific trait variations may increase the pathogen effect on plants because developing these fast-growing traits often comes at the cost of reduced defense against natural enemies (Coley et al, 1985;Herms & Mattson, 1992;Züst & Agrawal, 2017).…”

Intraspecific trait variation and changing life-history strategies explain host community disease risk along a temperature gradient

“…Our results suggest that patterns of disease can be strongly influenced by inter-and intraspecific variation in SLA, but relationships between SLA and biotic interactions are being increasingly recognized as multidirectional: not only can host pace-of-life influence biotic interactions but biotic interactions can reciprocally influence intraspecific variation in host pace-of-life. For example, across 101 species embedded in alpine communities, SLA decreased with increasing herbivory [101], within eight common tundra plant species, SLA increased when mammalian herbivory was excluded [102], and across 20 species in a biodiversity manipulation, fungicide application reduced SLA within species [103]. Together with the results of this study, these experimental results highlight the potential for important feedbacks between ITV and disease risk in host communities experiencing climate change.…”

Impact of Selected Environmental Factors on Variation in Leaf and Branch Traits on Endangered Karst Woody Plants of Southwest China

“…Studies on plant traits from the individual to the global scale have found that intraspecific and interspecific trait variation within functional groups and communities, and that between communities can strongly reflect the response of different species to limited resource competition and changes in environmental factors [3]. Interspecific variation and intraspecific trait variation are important factors affecting species coexistence and community composition [10,11].…”