DOI: 10.5061/dryad.31zcrjdkh
title: Plastic responses to hot temperatures homogenize riparian leaf litter, speed decomposition, and reduce detritivores

description: Efforts to maintain the function of critical ecosystems under climate
 change often begin with foundation species. In the southwestern US,
 cottonwood trees support diverse communities in riparian ecosystems that
 are threatened by rising temperatures. Genetic variation within
 cottonwoods shapes communities and ecosystems, but these effects may be
 modified by phenotypic plasticity, where genotype traits change in
 response to environmental conditions. Here, we investigated plasticity in
 Fremont cottonwood (Populus fremontii) leaf litter traits as well as the
 consequences of plasticity for riparian ecosystems. We used three common
 gardens each planted with genotypes from six genetically divergent
 populations spanning a 12oC temperature gradient, and a decomposition
 experiment in a common stream environment. We found that leaf litter area,
 specific leaf area, and carbon to nitrogen ratio (C:N) were determined by
 interactions between genetics and growing environment, as was the
 subsequent rate of litter decomposition. Most of the genetic variation in
 leaf litter traits appeared among rather than within source populations
 with distinct climate histories. Source populations from hotter climates
 generally produced litter that decomposed more quickly, but plasticity
 varied the magnitude of this effect. We also found that hotter growing
 conditions reduced the variation in litter traits produced across
 genotypes, homogenizing the litter inputs to riparian ecosystems. All
 genotypes in the hottest garden produced comparatively small leaves that
 decomposed quickly and supported lower abundances of aquatic
 invertebrates, whereas the same genotypes in the coldest garden produced
 litter with distinct morphologies and decomposition rates. Our results
 suggest that plastic responses to climate stress may constrict the
 expression of genetic variation in predictable ways that impact
 communities and ecosystems. Understanding these interactions between
 genetic and environmental variation is critical to our ability to plan for
 the role of foundation species when managing and restoring riparian
 ecosystems in a warming world.
description: # Plastic responses to hot temperatures homogenize riparian leaf litter,
 speed decomposition, and reduce detritivores
 [https://doi.org/10.5061/dryad.31zcrjdkh](https://doi.org/10.5061/dryad.31zcrjdkh) ## Description of the data and file structure **Dataset 1: Tree Level Trait Data (.csv)** This file lists information about each tree (Garden, Population, Genotype) and the trait values (Leaf Area, SLA, C:N) for that tree. It also includes the total weight of litter from that tree that was included in the litter packs for that genotype from that garden. This was used to calculate weighted averages for each trait in each litter pack. **Dataset 2: Source Population Climate Data (.csv)** This file lists GPS coordinates, elevation, and climate variables for all 16 populations grown in the common gardens. These data were used to construct the climate PCA, which was then used to test for relationships between home climate and the magnitude of phenotypic plasticity in the six populations we studied (KKH-OPI, JLA-JAK, PSA-SON, CAF-AUG, SCT-MEX, LBW-BIL). The climate variables are from Wang et al. (2012) and are abbreviated as follows: Mean annual temperature (MAT) Temperature difference between warmest and coldest months (TD) Annual heat-to-moisture index (AHM) Summer heat-to-moisture index (SHM) Degree-days above 18oC (DDa18) Extreme maximum temperature over a 30-year normal (EXT) Reference atmospheric evaporative demand (Eref) Wang, T., A. Hamann, D. L. Spittlehouse, and T. Q. Murdock. 2012. ClimateWNA-high-resolution spatial climate data for western North America. Journal of Applied Meteorology and Climatology 51:16–29. **Dataset 3: Litter Pack Decomposition Rates (.csv)** This file lists decomposition data for each of the 310 litter packs. This includes information about the litter source (Garden, Population, and Genotype), as well as information about the litter traits and decomposition rates. The litter traits for each leaf pack (Leaf Area, SLA, C:N) are weighted averages of the tree-level trait measurements contributing to that pack. Decomposition rate (k) is estimated using the final ash free dry mass (AFDM) of each pack, which was measured directly, and the initial AFDM, which was estimated from initial dry mass using a regression derived from handling packs. Also included is the length of the in-stream decomposition period (Days in Creek) and the random grouping by length of rebar (Rebar Group). **Dataset 4: Invertebrate Communities (.csv)** This file lists the abundances of each of 13 orders of invertebrates in each of the litter packs assayed for community composition, along with the information about the litter source (Garden, Population, and Genotype). Community assays focused on a subset of tree populations from across the climate range (KKH-OPI, PSA-SON, SCT-MEX, LBW-BIL).