Predicting intraspecific trait variation among California's grasses

Abstract

Plant species can show considerable morphological and functional variation along environmental gradients. This intraspecific trait variation (ITV) can have important consequences for community assembly, biotic interactions, ecosystem functions and responses to global change. However, directly measuring ITV across many species and wide geographic areas is often infeasible. Thus, a method to predict spatial variation in a species’ functional traits could be valuable. We measured specific leaf area (SLA), height and leaf area (LA) of grasses across California, covering 59 species at 230 sampling locations. We asked how these traits change along climate gradients within each species and used machine learning to predict local trait values for any species at any location based on phylogenetic position, local climate and that species’ mean traits. We then examined how much these local predictions alter patterns of assemblage‐level trait variation across the state. Most species exhibited higher SLA and grew taller at higher temperatures and produced larger leaves in drier conditions. The random forests predicted spatial variation in functional traits very accurately, with correlations up to 0.97. Because trait records were spatially biased towards warmer areas, and these areas tend to have higher SLA individuals within each species, species means of SLA were upwardly biased. As a result, using species means over‐estimates SLA in the cooler regions of the state. Our results also suggest that height may be substantially under‐predicted in the warmest areas. Synthesis. Using only species mean traits to characterize the functional composition of communities risks introducing substantial error into trait‐based estimates of ecosystem properties including decomposition rates or NPP. The high performance of random forests in predicting local trait values provides a way forward for estimating high‐resolution patterns of ITV without a massive data collection effort.

Adjustments in physiological and morphological traits suggest drought‐induced competitive release of some California plants

“…Diplacus aurantiacus and S . pulchra had higher SLA during drought, which is unexpected based on classic leaf economic spectrum theory (Wright et al, 2004 ), but consistent with other research for plants in California (Sandel et al, 2021 ; Welles & Funk, 2021 ). Higher SLA is related to resource acquisitive strategies (Funk et al, 2008 ; Wright et al, 2004 ) and possibly underlies drought escape (Kooyers, 2015 ), especially for plants in semi‐arid environments.…”

“…Strategies such as drought escape, avoidance, and tolerance are coordinated by physiological and morphological traits, and can be used to further understand plant responses to global change (Kooyers, 2015;Levitt, 1980). Drought tolerance and escape are more consistent with the classic leaf economic spectrum theory, while drought avoidance coordinates characteristics not typical of the leaf economic spectrum (Kooyers, 2015;Sandel et al, 2021;Volaire, 2018;Wright et al, 2004). Drought tolerance is more common for woody species with conservative traits (Ingram & Bartels, 1996;Volaire, 2018).…”

“…Lupinus nanus had lower leaf area and SLA, but higher VLA and lobedness in competition, which could indicate its sensitivity to competition. A combination of these traits could help increase retention of resources under high demand when contending with competition (Sack & Scoffoni, 2013 ; Sandel et al, 2021 ). Higher VLA could facilitate transport of water, photosynthates, and assimilated N (Sack & Scoffoni, 2013 ), while increased lobedness (Luong et al, 2021 ) and decreased SLA and leaf area (Pérez‐Harguindeguy et al, 2016 ) can facilitate reduced transpirational water loss.…”

“…Pretreatment leaf characteristics and biomass were used to confirm there was no grouping effect prior to experimental treatments ( p all > .05). SLA is related to photosynthetic ability, palatability, leaf life span, and growth rates (Sandel et al, 2021 ; Wright et al, 2004 ). SLA often decreases in response to drought but increases due to competition (Wright et al, 2004 ).…”

Effects of abiotic environment on invertebrate herbivory depend on plant community context in a montane grassland

“…1 black arrow). Specifically, the effects of temperature on plant quality (e.g., plant defense, palatability, tissue nutrients), growth rates, or phenology can vary considerably among taxa from different clades or functional groups (Herz et al 2017;Roybal & Butterfield 2019;Kuppler et al 2020;Hamann et al 2021;Sanczuk et al 2021;Sandel et al 2021) (but see Midolo et al 2019). Variation in how taxa within a community respond to changing temperature could result in thermal mismatch between the plant community and insect herbivores, and alter the role of phylogenetic or functional diversity in driving herbivory across temperature regimes.…”