DOI: 10.5061/dryad.q2bvq840f
title: Dominant species determine drought effects on grassland multifunctionality

description: Extreme drought often diminishes ecosystem multifunctionality in
 grasslands, but the potential mechanisms behind these responses are
 conflicting. The diversity hypothesis posits that diverse species
 promote grassland multifunctionality through compensatory interactions,
 while the mass-ratio hypothesis suggests that the traits of dominant
 species control multifunctionality. It remains unknown whether either or
 both underpin multifunctionality responses to extreme drought. Here we
 experimentally imposed an extreme two-year drought in two
 C3-dominated grasslands and analyzed 11 individual grassland
 functions (e.g., productivity, soil and plant nutrient
 pools) along with 17 community diversity and trait
 metrics (e.g., species diversity, functional diversity,
 phylogenetic diversity and community-weighted mean traits).
 Using structural equation modeling, we separated the effects of
 these community-based mechanisms on the drought sensitivity of grassland
 multifunctionality. Experimental drought had both direct and
 indirect negative effects on multifunctionality. Diversity metrics did not
 influence multifunctionality. However, multifunctionality was positively
 associated with several community mean traits linked to resource
 acquisition (e.g., plant height and leaf nitrogen content) and
 negatively associated with traits related to resource conservation (e.g.,
 leaf dry matter content and leaf carbon content). Drought shifted traits
 towards resource conservation, leading to reduced multifunctionality.
 Synthesis. These findings indicate that the mass-ratio effect,
 rather than complementarity, drives grassland multifunctionality,
 highlighting the importance of community-weighted traits in strongly
 dominated communities under drought. Together, These
 insights deepen our mechanistic understanding of drought effects on
 grassland multifunctionality and underpin strategies for
 sustainable grassland management and conservation.
description: # Data for: Dominant species determine drought effects on grassland
 multifunctionality Dataset DOI: 10.5061/dryad.q2bvq840f ## Description of
 the data and file structure We provide two datasets in CSV format
 (Biodiversity_index.csv; Multifunctionality_and_functions.csv), containing
 data on grassland multifunctionality, 11 individual grassland functions,
 and 17 community diversity and trait metrics from 2021 and 2022 (results
 averaged across EFS and NHG sites). Moreover, all missing values in the
 data are represented as “null.” We also provide the code (code_for_R.zip)
 and the data used for calculations (Data_for_R.zip), which demonstrate all
 computational steps, statistical analyses, and graphing procedures
 performed in R_4.2.0. Finally, we include the figures (figures.zip),
 containing PDF versions of all figures presented in the Manuscript and
 Supporting Information. Dominant species determine drought effects on
 grassland multifunctionality ### Files and variables ## File:
 code_for_R.zip **Description:** It demonstrates all computational steps,
 statistical analyses, and graphing procedures performed in R_4.2.0.
 **Caculation.R:** Calculation of biodiversity indicators and
 multifunctionality. It includes: 1. Species diversity (H-index, D-index,
 J-index, SR); 2. Functional diversity (FRic, FEve, FDiv, FDis) and CWM
 traits; 3. Phylogenetic diversity(PD, MPD, MNTD); 4. Calculation of
 Multifunctionality(the averaging approach and the cluster-threshold
 approach); 5. Calculate the correlation between MFt, MFa, and other
 functions. **Statistical analysis.R:** All statistical analyses conducted
 in Section 2.4, “Statistical Analyses,” of the manuscript. It includes: 1.
 Liner mixed-effects(lme) results for the interaction among drought, site
 and year on all factors(Table S2); 2. The statistical results of Figure 1;
 3. The statistical results of Figure 2; 4. The statistical results of
 Figure 3; 5. The statistical results of Table S3 and Figure 4. **Main
 figures plotted.R:** R code used to generate all figures in the manuscript
 and Manuscript and Supporting Information. It includes: 1. Figure 1; 2.
 Figure 2; 3. Figure S1; 4. Figure S2; 5. Figure S5. ## File:
 Data_for_R.zip **Description:** This document contains all the raw data
 required for the aforementioned R execution and computational procedures.
 This section contains a total of 12 CSV files and 2 txt files. It
 includes: **2021EFS.csv, 2021NHG.csv, 2022EFS.csv, 2022NHG.csv:** raw data
 required for species diversity (H-index, D-index, J-index, SR) in the file
 “Caculation.R”. **Notes:** none of these four datasets involve units.
 Variables: * Site:EFS and NHG * Treatment:drought and control *
 Block:randomized complete block design was used, with six blocks per site
 * Year:2021 and 2022 **basic data_biomass.csv:** raw data required for
 Functional diversity (FRic, FEve, FDiv, FDis) and CWM traits in the file
 “Caculation.R”; Variables: * Site:EFS and NHG * Treatment:drought and
 control * Block:randomized complete block design was used, with six blocks
 per site * Year:2021 and 2022 * Latin name:Latin names of plant species *
 Biomass(g/m2):Dry weight of plants per square meter in grassland
 communities * LNC(mg/g):leaf nitrogen content * LCC(mg/g):leaf carbon
 content * LPC(mg/g):leaf phosphorus content * MPH(cm):maximum plant height
 * LDMC(mg/g):leaf dry matter content * SLA(cm2/g):specific leaf area
 **PD_abun.csv and PD_species.txt:** raw data required for Phylogenetic
 diversity (PD, MPD, MNTD) in the file “Caculation.R” PD_abun.csv records
 species cover data, and PD_species.txt represents phylogenetic
 relationships among species (i.e., the phylogenetic tree). 
 **Notes:** none of these two datasets involve units. **calculation of
 multifunctionality.csv and calculation of multifunctionality.txt:** raw
 data required for Calculation of Multifunctionality (the averaging
 approach and the cluster-threshold approach) in the file “Caculation.R”;
 Variables: * Site:EFS and NHG * Treatment:drought and control *
 Block:randomized complete block design was used, with six blocks per site
 * Year:2021 and 2022 * N_pool(g/m2):aboveground plant nitrogen pool *
 C_pool(g/m2):aboveground plant carbon pool * STP(g/kg):soil total
 phosphorus content * SAP(g/kg):soil available phosphorus content *
 STN(g/kg):soil total nitrogen content * STC(g/kg):soil total carbon
 content * C/N(unitless):soil carbon:nitrogen ratio *
 ANPP(g/m2):aboveground net primary productivity * BNPP(g/m2):belowground
 net primary productivity * MBC(g/kg):soil microbial biomass carbon content
 * MBN(g/kg):soil microbial biomass nitrogen content **functions and
 MFt.csv:** raw data required for The statistical results of Figure 1 in
 the file “Statistical analysis.R” and Figure 1 in the file “Main figures
 plotted.R” Variables: * Treatment:drought and control * Block:randomized
 complete block design was used, with six blocks per site * Year:2021 and
 2022 * MFt(unitless):grassland multifunctionality * ANPP(g/m2):aboveground
 net primary productivity * BNPP(g/m2):belowground net primary productivity
 * APCP(g/m2):aboveground plant carbon pool * APNP(g/m2):aboveground plant
 nitrogen pool * STC(g/kg):soil total carbon content * STN(g/kg):soil total
 nitrogen content * STP(g/kg):soil total phosphorus content *
 SAP(g/kg):soil available phosphorus content * C_N(unitless):soil
 carbon:nitrogen ratio * MBC(g/kg):soil microbial biomass carbon content *
 MBN(g/kg):soil microbial biomass nitrogen content **biodiversity and
 MFt.csv:** raw data required for The statistical results of Figure 2,
 Figure 3, Talbe S3 and Figure 4 in the file “Statistical analysis.R”
 and Figure 2, Figure 3 and Figure S5 in the file “Main figures plotted.R”
 Variables: * Treatment:drought and control * Block:randomized complete
 block design was used, with six blocks per site * Year:2021 and 2022 *
 H(unitless):Shannon-Wiener diversity index * D(unitless):Simpson’s
 dominance index * J(unitless):Pielou evenness index * S(unitless):species
 richness * FEve(unitless):functional evenness * FDiv(unitless):functional
 divergence * CWM.LN(mg/g):leaf nitrogen content * CWM.LC(mg/g):leaf carbon
 content * CWM.LP(mg/g):leaf phosphorus content * CWM.H(cm):maximum plant
 height * CWM.LDMC(mg/g):leaf dry matter content * CWM.SLA(cm2/g):specific
 leaf area * PD(unitless):phylogenetic diversity * MPD(unitless):mean
 pairwise distance * MNTD(unitless):mean nearest taxon distance *
 MFt(unitless):grassland multifunctionality * FRic(unitless):functional
 richness * FDis(unitless):functional dispersion * SWC(unitless):soil water
 content **Table S2_1.csv and Table S2_2.csv:** raw data required for Liner
 mixed-effects(lme) results for the interaction among drought, site and
 year on all factors(Table S2) in the file “Statistical analysis.R”.
 Variables and abbreviations are the same as above.
 **data_precipitation.csv:** raw data required for Figure S1 in the file
 “Main figures plotted.R” Variables: * Year:For 50 consecutive years, from
 1972 to 2022 * Mouth:January through December each year *
 Precipitation(mm):Average monthly precipitation(mm) ## File: figures.zip
 **Description:** It contains PDF versions of all figures presented in the
 Manuscript and Supporting Information. Specifically includes: 1.
 **Figure_1.pdf**; **Description:** Experimental drought effects on
 individual grassland function and multifunctionality at two study sites
 combined (mean ± SE). The horizontal bars represent the 95% confidence
 interval. Statistical significance is depicted as * *P* &lt;0.05, **
 *P*&lt;0.01, and *** *P*&lt;0.001. **Abbreviations: **
 ANPP(g/m2), aboveground net primary productivity; BNPP(g/m2), belowground
 net primary productivity; APCP(g/m2), aboveground plant carbon pool;
 APNP(g/m2), aboveground plant nitrogen pool; TC(g/kg), soil total carbon
 content; TN(g/kg), soil total nitrogen content; TP(g/kg), soil total
 phosphorus content; AP(g/kg), soil available phosphorus content; C:N
 ratio(unitless), soil carbon:nitrogen ratio; MBC(g/kg), soil microbial
 biomass carbon content; MBN(g/kg), soil microbial biomass nitrogen
 content. 
 
 2. **Figure_2.pdf**; **Description:** Experimental drought effects on
 community-weighted mean (CWM) traits and community diversity at two study
 sites combined. Results are presented as a response ratio
 (drought/control). Circle colors indicate different types of variables:
 species diversity (pink), functional diversity (yellow), CWM traits
 (green), and phylogenetic diversity (blue). The horizontal bars represent
 the 95% confidence interval. Statistical significance is depicted as * *P*
 &lt;0.05 and ** *P*&lt;0.01. **Abbreviations: **
 H-index(unitless), Shannon-Wiener diversity index; D-index(unitless),
 Simpson’s dominance index; J-index(unitless), Pielou evenness index;
 SR(unitless), species richness; FEve(unitless), functional evenness;
 FDiv(unitless), functional divergence; LNC(mg/g), leaf nitrogen content;
 LCC(mg/g), leaf carbon content; LPC(mg/g), leaf phosphorus content;
 MPH(cm), maximum plant height; LDMC(mg/g), leaf dry matter content;
 SLA(cm2/g), specific leaf area; PD(unitless), phylogenetic diversity;
 MPD(unitless), mean pairwise distance; MNTD(unitless), mean nearest taxon
 distance. 
 
 3. **Figure_3.pdf**; **Description:** Relationships between grassland
 multifunctionality and community-weighted mean (CWM) traits and community
 diversity under extreme drought at two study sites combined. Solid line
 represents a significant linear relationship, with the light area showing
 the 95% confidence interval. **Abbreviations** are consistent with those
 in Figure_2 above. 
 
 4. **Figure_4.pdf**; **Description:** Structural equation model
 illustrating the effect of extreme drought on multifunctionality mediated
 by four composite indices representing species diversity, functional
 diversity, phylogenetic diversity, and community‐weighted mean (CWM)
 traits across grassland sites. Blue and red arrows reflect positive and
 negative relationships, while solid and dashed arrows reflect significant
 and insignificant effects, respectively. Statistical significance is
 depicted as * *P* &lt;0.05, ** *P*&lt;0.01, and *** *P*&lt;0.001;
 standardized path coefficients are shown along the paths. Marginal
 *R^2^*^ ^values (*R^2^~m~*) and conditional *R^2^*^ ^(*R^2^~c~*) values
 are given.  
 
 5. **Figure_S1.pdf**; **Description:** Experimental drought shelter setup
 (a). The main figure shows the precipitation and probability density
 curves during the growing season (May to August) over the past 50 years
 (1972–2022). The precipitation data for the Control and experimental
 drought treatments from 2021 to 2022 are plotted on the probability
 density curves. The inset figure in the upper right illustrates the
 effects of drought on soil water content over two years (2021–2022). 
 
 6. **Figure_S2.pdf**; **Description:** Determination of functional
 clusters for calculating multifunctionality. (a) Elbow method used to
 identify the optimal number of grassland ecosystem function clusters. (b)
 Cluster membership and eigenvalues (x-axis) for each ecosystem function. 
 **Abbreviations:** ANPP(g/m2), aboveground net primary productivity;
 BNPP(g/m2), belowground net primary productivity; APCP(g/m2), aboveground
 plant carbon pool;  APNP(g/m2), aboveground plant nitrogen pool;
 STC(g/kg), soil total carbon content; STN(g/kg), soil total
 nitrogen content; STP(g/kg), soil total phosphorus content; SAP(g/kg),
 soil available phosphorus content; C/N(unitless), soil carbon:nitrogen
 ratio;  MBC(g/kg), soil microbial biomass carbon content; MBN(g/kg), soil
 microbial biomass nitrogen content. 
 
 7. **Figure_S3.pdf**; **Description:** Pearson correlation matrix between
 cluster-threshold multifunctionality (MFt), average multifunctionality
 (MFa), and individual ecosystem functions. Different colors represent
 different aspects of ecosystem functions.  **Abbreviations** are
 consistent with those in Figure_1 above. 
 
 8. **Figure_S4.pdf**; **Description:** Relationships between
 grassland multifunctionality and (a) functional richness (FRic), (b)
 functional dispersion (FDis) under extreme drought at both sites. 
 
 9. **Figure_S5.pdf**. **Description:** Results of the effects of
 experimental drought on (a) species-specific mean biomass and (b) relative
 abundance compared to Control (we averaged the values of biomass per year
 at both sites). 
 
 ## File: Multifunctionality_and_functions.csv **Description:** It
 contains data on grassland multifunctionality and 11 individual grassland
 functions from 2021 and 2022 (results averaged across EFS and NHG sites).
 Variables: * Treatment:drought and control * Block:randomized complete
 block design was used, with six blocks per site * Year:2021 and 2022 *
 Multifunctionality(unitless):grassland multifunctionality *
 ANPP(g/m2):aboveground net primary productivity * BNPP(g/m2):belowground
 net primary productivity * APCP(g/m2):aboveground plant carbon pool *
 APNP(g/m2):aboveground plant nitrogen pool * TC(g/kg):soil total carbon
 content * TN(g/kg):soil total nitrogen content * TP(g/kg):soil total
 phosphorus content * AP(g/kg):soil available phosphorus content * C:N
 ratio(unitless):soil carbon:nitrogen ratio * MBC(g/kg):soil microbial
 biomass carbon content * MBN(g/kg):soil microbial biomass nitrogen content
 ## File: Biodiversity_index.csv **Description:** It contains data on 17
 community diversity and trait metrics from 2021 and 2022 (results averaged
 across EFS and NHG sites). Variables: * Treatment:drought and control *
 Block:randomized complete block design was used, with six blocks per site
 * Year:2021 and 2022 * H-index(unitless):Shannon-Wiener diversity index *
 D-index(unitless):Simpson’s dominance index * J-index(unitless):Pielou
 evenness index * SR(unitless):species richness * FEve(unitless):functional
 evenness * FDiv(unitless):functional divergence * LNC(mg/g):leaf nitrogen
 content * LCC(mg/g):leaf carbon content * LPC(mg/g):leaf phosphorus
 content * MPH(cm):maximum plant height * LDMC(mg/g):leaf dry matter
 content * SLA(cm2/g):specific leaf area * PD(unitless):phylogenetic
 diversity * MPD(unitless):mean pairwise distance * MNTD(unitless):mean
 nearest taxon distance * FRic(unitless):functional richness *
 FDis(unitless):functional dispersion ## Code/software All calculations
 (biodiversity indicators and multifunctionality), statistical analyses
 (interactive effects, general mixed-effects models, principal component
 analysis and piecewise structural equation models), and figure generation
 in this study were performed in R 4.2.0, and we have provided all the
 code.