DOI: 10.5061/dryad.r4xgxd2r3
title: Evidence of local adaptation to aridity but not nitrogen deposition in invasive annuals

description: Rapid adaptation of traits and trait plasticity may contribute to plant
 invasiveness and confer fitness advantages in novel environments resulting
 from global change. The importance of trait differentiation in invasive
 plant populations is well-recognized, particularly in response to climate.
 However, it is largely unknown how invasive plant populations will respond
 evolutionarily to atmospheric nitrogen (N) deposition resulting from air
 pollution, which is a major contributor to invasion success in many
 ecosystems. Using a common garden experiment, a widely used method for
 testing local adaptation, we assessed potential differences in plant
 functional traits and nitrogen plasticity across populations of two
 widespread invasive annuals from sites spanning a range of N deposition
 and aridity throughout southern California. These species exhibited clear
 population-level differences in traits and N responses, but these were
 unrelated to N deposition. Instead, we detected significant relationships
 between several traits and aridity, and populations from more arid sites
 exhibited reduced N plasticity for multiple traits. Multivariate
 plasticity indices also showed a strong negative relationship with aridity
 across populations for both species. However, trait responses to N
 addition also appeared be influenced by species’ drought-coping
 strategies. In Bromus diandrus, a drought-escaping early-season annual
 grass, populations from less arid sites showed increased plasticity in
 shoot growth and more rapid flowering in response to N addition. In
 contrast, Centaurea melitensis, a drought-tolerant late-season forb,
 showed climate-driven shifts in biomass allocation in response to N;
 populations from more arid sites invested more in roots, while populations
 from less arid sites allocated more to leaves. These contrasting N
 responses strongly suggest distinct growth strategies and ecophysiological
 tradeoffs shaped by adaptation to local climate conditions. While elevated
 N availability may indeed promote invasion, climate stress might exert an
 overriding influence on local adaptation of plant invaders in dryland
 ecosystems subject to N deposition.
description: # Evidence of local adaptation to aridity but not nitrogen deposition in
 invasive annuals Dataset DOI:
 [10.5061/dryad.r4xgxd2r3](10.5061/dryad.r4xgxd2r3) ## Description of the
 data and file structure Data collected from a common garden experiment in
 which multiple populations of two invasive plant species, *Bromus
 diandru*s and *Centaurea melitensis*, were grown under high and low
 nitrogen. Plant traits and responses were then related to aridity and
 nitrogen deposition of the source populations. ### Files and variables
 #### File: BRODIA\_data.csv **Description:** Plant trait data for *Bromus
 diandrus* populations grown under high and low nitrogen availability. For
 some plant traits (i.e., Amax, Cond, WUE, SLA, perc_N, CN, and d13C), data
 were collected only on a subset of individuals in each treatment, so these
 columns contain blank cells. ##### Variables | **Variable** |
 **Description** | **Units** | | :------------ |
 :---------------------------------------------- | :-------------------- |
 | `site_number` | Site identification number | unitless | | `rep` |
 Replicate number | unitless | | `Maternal_ID` | Identifier for maternal
 plant source | unitless (ID code) | | `M_seed_ave` | Average mass of
 maternal seeds | g (grams) | | `N` | Nitrogen treatment (high N or low N)
 | unitless (treatment) | | `root` | Root biomass | g (grams) | |
 `Infl_count` | Inflorescence count | count | | `leaf` | Leaf biomass | g
 (grams) | | `repr_mass` | Reproductive biomass (flowers and/or seeds) | g
 (grams) | | `total_mass` | Total plant biomass (root + shoot) | g (grams)
 | | `shoot_mass` | Total above-ground biomass (stem + leaf + repr) | g
 (grams) | | `LMR` | Leaf mass ratio (leaf\_mass / shoot\_mass) | unitless
 (proportion) | | `RMR` | Root mass ratio (root\_mass / total\_mass) |
 unitless (proportion) | | `seed_mass` | Average seed mass | g (grams) | |
 `DTF` | Days to flowering | days | | `Amax` | Maximum photosynthetic rate
 | μmol CO₂ m⁻² s⁻¹ | | `Cond` | Stomatal conductance | mol H₂O m⁻² s⁻¹ | |
 `WUE` | Water use efficiency (Amax / transpiration) | μmol CO₂ / mmol H₂O
 | | `SLA` | Specific leaf area | cm² g⁻¹ | | `perc_N` | Leaf nitrogen
 content | % dry weight | | `CN` | Carbon-to-nitrogen ratio | unitless (C/N
 ratio) | | `d13C` | Carbon isotope discrimination | ‰ (per mil) | ####
 File: CENMEL\_data.csv **Description:** Plant trait data for *Centaurea
 melitensis* populations grown under high and low nitrogen
 availability. For some plant traits (i.e., Amax, Cond, WUE, SLA, perc_N,
 CN, and d13C), data were collected only on a subset of individuals in each
 treatment, so these columns contain blank cells. ##### Variables |
 **Variable** | **Description** | **Units** | | :----------------- |
 :---------------------------------------------------------- |
 :-------------------- | | site\_number | Site identification number (see
 site\_data.csv) | unitless | | rep | Replicate number | unitless | |
 Maternal\_ID | Identifier for maternal plant source | unitless (ID code) |
 | M\_seed\_ave | Average mass of maternal seeds | g (grams) | | N |
 Nitrogen treatment (high N or low N) | unitless (treatment) | | root\_mass
 | Root biomass | g (grams) | | stem\_mass | Stem biomass | g (grams) | |
 leaf\_mass | Leaf biomass | g (grams) | | repr\_mass | Reproductive
 biomass (flowers/seeds) | g (grams) | | flower# | Number of flowers
 produced | count | | seeds\_per\_flower | Average number of seeds per
 flower | count | | total\_seed\_mass | Total seed mass produced | g
 (grams) | | mean\_seed\_mass | Average mass per seed | g (grams) | |
 total\_mass | Total above- and below-ground biomass | g (grams) | |
 shoot\_mass | Total above-ground biomass (stem + leaf + repr) | g (grams)
 | | LMR | Leaf mass ratio (leaf\_mass / shoot\_mass) | unitless
 (proportion) | | RMR | Root mass ratio (root\_mass / total\_mass) |
 unitless (proportion) | | DTF | Days to flowering | days | | Amax |
 Maximum photosynthetic rate | μmol CO₂ m⁻² s⁻¹ | | Cond | Stomatal
 conductance | mol H₂O m⁻² s⁻¹ | | WUE | Water use efficiency (Amax /
 transpiration) | μmol CO₂ / mol H₂O | | SLA | Specific leaf area | cm² g⁻¹
 | | perc\_N | Leaf nitrogen content | % dry weight | | CN |
 Carbon-to-nitrogen ratio | unitless (C/N ratio) | | d13C | Stable carbon
 isotope ratio (carbon isotope discrimination) | ‰ (per mil) | #### File:
 site\_data.csv **Description:** Site-level data for the locations from
 which seed of each species was collected for plant growth trials in the
 common garden experiment. ##### Variables | **Variable** | **Description**
 | **Units** | | :---------------- |
 :------------------------------------------------------------------ |
 :------------------------- | | site | Site identification number |
 unitless | | site\_name | Name of the site | text | | lat | Latitude of
 the site | decimal degrees (°N) | | lng | Longitude of the site | decimal
 degrees (°W) | | CMAQ\_2002 | Modeled nitrogen deposition from CMAQ for
 the year 2002 | kg N ha⁻¹ yr⁻¹ | | CMAQ\_2017 | Modeled nitrogen
 deposition from CMAQ for the year 2017 | kg N ha⁻¹ yr⁻¹ | | average\_Ndep
 | Average nitrogen deposition across years (e.g., 2002 and 2017) | kg N
 ha⁻¹ yr⁻¹ | | elev | Elevation of the site | meters above sea level (m) |
 | mean\_annual\_ppt | Mean annual precipitation | mm yr⁻¹ | | map\_CV |
 Coefficient of variation in mean annual precipitation | unitless | |
 mean\_tmax | Mean maximum temperature (annual or seasonal, depending on
 dataset) | °C | | aridity\_index | Aridity index | unitless (index) | ##
 Software All statistical analyses and data visualization were conducted
 using open-source software in **R** (R Core Team 2013), version **4.1.0**,
 within the **RStudio** environment. Analyses were performed on a standard
 desktop computing setup. To view and reproduce the data analyses, users
 will need to install R and RStudio, both of which are freely available at
 [https://www.r-project.org](https://www.r-project.org) and
 [https://www.rstudio.com](https://www.rstudio.com), respectively. The
 following R packages were used in the analysis: * **`psych`**: for
 principal component analysis (PCA) and data exploration * **`ggplot2`**:
 for data visualization * **`dplyr`**, **`tidyr`**: for data wrangling and
 transformation * **`car`**: for model diagnostics and ANOVA tools *
 **`stats`** (base): for `aov`, `lm`, and `anova` functions used in model
 fitting * **Custom functions** were written for calculating plasticity
 indices such as log response ratios and the multivariate plasticity index
 (MVPi) following the method of Pennacchi et al. (2021) Pennacchi, J. P.,
 J. M. S. Lira, M. Rodrigues, F. H. S. Garcia, A. M. d. C. Mendonça, and J.
 P. R. A. D. Barbosa. 2021. A systemic approach to the quantification of
 the phenotypic plasticity of plant physiological traits: the multivariate
 plasticity index. Journal of Experimental Botany **72**:1864-1878. ##
 Access information Climate data were acquired from the Oregon State
 University **PRISM Group**'s online tool
 ([https://prism.oregonstate.edu/](https://prism.oregonstate.edu/)). All
 data retrieved from this website or otherwise provided on the website may
 be freely reproduced and distributed for non-commercial purposes PRISM
 Group, Oregon State University,
 [https://prism.oregonstate.edu](https://prism.oregonstate.edu), data
 accessed August 2020. Nitrogen deposition data were acquired from the
 Environmental Protection Agency's **Community Multiscale Air
 Quality** model. These data are publicly available. Benish, S. E., J. O.
 Bash, K. M. Foley, K. W. Appel, C. Hogrefe, R. Gilliam, and G. Pouliot.
 2022. Long-term Regional Trends of Nitrogen and Sulfur Deposition in the
 United States from 2002 to 2017. Atmospheric Chemistry and Physics
 Discussions:1-27.