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

Abstract

Plant functional traits can provide a more mechanistic understanding of community responses to global change and effects on ecosystem functions. In particular, nitrogen enrichment shifts trait composition by promoting dominance of fast growing, acquisitive plants (with high specific leaf area [SLA] and low leaf dry matter content [LDMC]), and such fast species have higher aboveground biomass production. Changes in mean trait values can be due to a shift in species identity, a shift in species relative abundance and/or a shift in intraspecific trait values. However, we do not know the relative importance of these three shifts in determining responses to global change and effects on function. We quantified the relative importance of composition, abundance and intraspecific shifts in driving variation in SLA and LDMC. We collected leaf samples in a large grassland experiment, which factorially manipulates functional composition (slow vs. fast species), plant species richness, nitrogen enrichment and foliar fungal pathogen removal. We fitted structural equation models to test the relative importance of abundance shifts, intraspecific shifts and sown trait composition in contributing to overall variation in community weighted mean traits and aboveground and belowground biomass production. We found that intraspecific shifts were as important as abundance shifts in determining community weighted mean traits, and even had large effects relative to a wide initial gradient in 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. Belowground biomass was reduced by SLA and increased by LDMC, while aboveground biomass increased in communities dominated by high SLA species. However, despite large intraspecific trait shifts, intraspecific variation in these traits had no effect on above or belowground biomass production. Our results add to a growing body of literature showing large intraspecific trait variation and emphasise the importance of using field sampled data to determine community composition. However, they also show that intraspecific variation does not affect ecosystem functioning and therefore trait response-effect relationships may differ between vs. within species.

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.…”

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).…”

Change in functional trait diversity mediates the effects of nutrient addition on grassland stability

“…Unexpectedly, we found overall weak diversity-mediated indirect effects on stability. A few other studies also show that traits are poor predictors for ecosystem properties including productivity and its stability (van der Plas et al ., 2020; Pichon et al ., 2022). These weak effects may be due to the following three reasons.…”

“…Nutrient addition may promote fast communities through shifting intraspecific traits related to fast growth, promoting fast-growing species, or both (Lepš et al ., 2011; Siefert & Ritchie, 2016; Tatarko & Knops, 2018; Zhou et al ., 2018; Pichon et al ., 2022). Additionally, nutrient addition may decrease all stability facets investigated here by decreasing the diversity of slow-fast trait that represents leaf economic spectrum and species richness.…”