DOI: 10.5061/dryad.pzgmsbct6
title: Stress alters the role of silicon in controlling plant water movement

description: One function of plant Si is ameliorating stress, including drought and
 salinity stress, which can induce active Si uptake in addition to passive
 uptake via transpiration. However, the interactions and feedbacks between
 stress, water movement, and Si uptake remain unknown. To examine this gap,
 we compiled papers reporting transpiration and/or stomatal conductance of
 plants exposed to stresses while varying Si availability. Our
 meta-analysis (34 studies, excluding rice) showed that stress alters the
 role of Si in controlling water movement across diverse plant groups.
 Increased Si availability significantly increased water movement in
 stressed plants, particularly stomatal conductance (p&lt;0.001, k=84)
 in plants exposed to salinity (p&lt;0.05, k=20) and drought
 (p&lt;0.05, k=45) stress. This signal of increased conductance was
 most apparent in C4 plants (p&lt;0.001, k=41) and Poales
 (p&lt;0.001, k=47). These findings have implications for plants under
 increasing water and salinity stress, particularly for Poales, where
 survival in affected ecosystems could be mediated by soil Si availability,
 and in agricultural systems, supplying Si to water-stressed plants could
 increase productivity.  Intriguingly, Si addition to unstressed
 plants had no consistent impact on water movement, with reduction of water
 movement with Si addition to unstressed plants in 50% of studies, mostly
 those involving non-Poales species. This is an important first broad-scale
 Si cost quantification, as the costs of Si for plants have remained
 stubbornly mysterious, hampering evolutionary and functional understanding
 of plant Si use.
description: We systematically identified papers testing or reporting the
 impact of Si availability on plant conductance and transpiration by
 searching the Web of Science database, for TOPIC: (silicon OR silica) AND
 TOPIC: (transpiration OR stomatal conductance) AND TOPIC: (plant OR leaf
 OR leaf OR foliar) and NOT TOPIC (rice) in November 2021. We excluded rice
 from our analyses. We extracted values for stomatal conductance and
 transpiration, for experiments in which plants were grown with and without
 Si addition (+/- Si) and with or without stress (+/- stress) applied to
 the plants. We converted reported water movement values to stomatal
 conductance (mmol H<sub>2</sub>O m<sup>2</sup>
 s<sup>-1</sup>) and transpiration rate (mol
 H<sub>2</sub>O m<sup>2</sup>
 s<sup>-1</sup>) as appropriate, and all measures of variance
 to standard deviations. We used the ‘metafor’ package
 (Viechtbauer, 2010) in R (R Core Team, 2022) to calculate the effect size
 (Hedges’ D) of the impact of silicon addition on one response (e.g.
 conductance or transpiration) at a time for individual studies. This
 effect size measure compares two means using a pooled standard deviation
 and bias correction and is a measure of the number of standard deviations
 by which the means differ (Hedges & Olkin, 1985). We considered
 stress and unstressed treatments separately. The effect sizes calculated
 from individual studies were then used to conduct our analyses. The raw
 effect sizes, prior to analysis, are reported here.   
 Viechtbauer, W. (2010). Conducting Meta-analyses in R with the
 metafor package. Journal of Statistical Software, 36(3), 1–48.
 R Core Team (2022). R: A language and environment for
 statistical computing. Foundation for Statistical Computing, Vienna,
 Austria. https://www.R-project.org/.
description: # Stress alters the role of silicon in controlling plant water movement
 [https://doi.org/10.5061/dryad.pzgmsbct6](https://doi.org/10.5061/dryad.pzgmsbct6) We asked questions about the impact of silicon supply on water movement in plants, and if stress impacted this relationship. To do this we converted the results of multiple studies into effect sizes that could then be quantitatively combined in a meta-analysis. All effect sizes report a comparison for a given response measure (conductance and transpiration separately) between plants supplied vs not supplied with silicon, and we considered stressed and unstressed plants separately. Our meta-analysis (34 studies) showed that stress alters the role of Si in controlling water movement across diverse plant groups. Increased Si availability significantly increased water movement in stressed plants, particularly stomatal conductance (p&lt;0.001, k=84) in plants exposed to salinity (p&lt;0.05, k=20) and drought (p&lt;0.05, k=45) stress. This signal of increased conductance was most apparent in C4 plants (p&lt;0.001, k=41) and *Poales* (p&lt;0.001, k=47). The effect sizes extracted from multiple studies, then used to conduct our analyses, are reported here. ## Description of the data and file structure The title of each .csv file indicates whether it contains effect sizes for transpiration or conductance, and for stressed or unstressed plants. Each file reports the effect size (Hedges D and a measure of variance) comparing plants supplied with vs not supplied with silicon in an experiment, collated from published studies. All .csv files have the same headings, which are described in more detail below.    Title: source paper title REF\_ID: a numerical value for each paper that allowed easy identification of data from the same paper to factor into analyses  Authors: source paper authors Source.Title: source journal name Publication.Year: source publication year DOI: source doi, where known Species: species of plant used in the comparison Stress: type of stress applied (e.g. drought, salinity) in the study. If these plants are in the unstressed files, the plants are in the control treatment to compare to this stress, but stress has not be applied here Order: taxonomic order of species of plant Oder2: Order re-classified as Poales or non-Poales C3C4: photosynthetic pathway of species (C3 or C4) Response\_Measure: transpiration or conductance N: number of replicates in the study Hedges\_D: effect size of the experimental outcome of the study comparing plants supplied with silicon vs those not supplied with silicon. Effect sizes are for one response (e.g. conductance or transpiration) which is indicated in the Response\_Measure column and file names. Whether stressed or unstressed plant treatments were selected is indicated in file name. This effect size measure compares two means using a pooled standard deviation and bias correction and is a measure of the number of standard deviations by which the means differ (Hedges & Olkin, 1985). HedgesD\_var: The standard deviation value of the above.