SUPPLEMENTAL TABLES Table S1. Effect of all treatments on final gravimetric soil moisture. F-statistic and p-values provided; significant p-values (p < 0.05) are bolded. Factor F, p Precipitation 7.981,27, 0.008 Microbial treatment 0.542,27, 0.591 Life-stage 3.511,27, 0.072 Precip.* Soil.Treat. 0.292,27, 0.753 Precip.* Life-stage 0.011,27, 0.919 Mic.Treat.*Life-stage 0.172,27, 0.844 Precip.*Mic.Treat.*Life-stage 0.052,27, 0.954 Table S2. Full-model ANOVA results for the effect of precipitation and all microbial treatments (bulk, autoclaved, and rhizosphere) on germinant responses. Chi- square, F-statistic and p-values provided; significant p-values (p < 0.05) are bolded. Germination rate Germinant Germinant total Germinant final Germinant final Days to first (Number of survival biomass (g) Germinant bacterial Germinant final Factor bacterial Inverse germination seeds that (given (given root:shoot community bacterial richness Simpson germinated/ germination) germination) composition pot) 2 2 2 F, p χ , p χ , p F, p F, p R p F, p F, p Precipitation 3.541,50, 0.066 4.30, 0.038 0.06, 0.803 0.841,39, 0.365 8.341,37, 0.006 0.06 <0.001 1.591,14, 0.228 0.031,17, 0.864 Microbial treatment 4.632,51, 0.014 4.79, 0.091 7.06, 0.029 3.982,39, 0.027 0.942,38, 0.398 0.44 <0.001 355.682,15, <0.001 16.472,17, <0.001 Precip.* Microbial 0.682,51, 0.513 1.89, 0.388 2.36, 0.307 10.012,39, <0.001 2.592, 38, 0.088 0.05 0.006 0.702,15, 0.514 0.242,17, 0.789 treatment Ulbrich et al. SUPPLEMENTAL Page 1/15 Table S3. Full-model ANOVA results for the effect of precipitation and all microbial treatments (bulk, autoclaved, and rhizosphere) on seedling responses. Chi- square, F-statistic and p-values provided; significant p-values (p < 0.05) are bolded. Seedling final Seedling final Seedling specific Seedling Seedling final Seedling total Seedling Seedling bacterial bacterial Factor root length rhizosheath bacterial biomass (g) root:shoot survival community Inverse (cm g dry root-1) weight (g) richness composition Simpson 2 2 F, p F, p χ , p F, p F, p R p F, p F, p Precipitation 13.421,80, <0.001 1.441,74, 0.234 NA 5.571,18, 0.030 0.101,21, 0.753 0.06 0.011 5.001,18, 0.038 1.401,18, 0.253 Microbial treatment 4.892,80, 0.010 0.312,74, 0.738 15916,<0.001 0.772,17, 0.478 2.592,21, 0.098 0.59 0.004 67.982,18, <0.001 3.902,18, 0.039 Precip.* Microbial 3.342,80, 0.041 0.492,74, 0.617 NA 4.072, 17, 0.036 0.092,21, 0.912 0.07 0.060 2.342,18, 0.124 2.862,18, 0.084 treatment Ulbrich et al. SUPPLEMENTAL Page 2/15 Table S4. Full model results for all response variables measured on both life-stages; split by microbial presence (bulk vs. autoclaved) and inocula association history (rhizosphere vs. bulk). Chi-square, F-statistic and p-values provided; significant p-values (p < 0.05) are bolded. Survival just Final Bacterial Final Bacterial Bacterial Community Biomass Root:shoot in drought Richness Inv. Simpson Composition 2 2 Factor χ , p F, p F, p F, p F, p R P Precipitation NA 0.351,76 0.,557 6.441,113, <0.001 3.471,20, 0.077 0.101,23, 0.759 0.06 <0.001 Microbial Presence 5.06, 0.024 7.801,76, 0.007 0.462,113, 0.083 685.071,20, <0.001 12.631,23, 0.002 0.48 <0.001 Life-stage 0.68, 0.408 1.66 , 0.202 23.46 , <0.001 13.85 , 0.001 9.52 , 0.005 0.04 0.006 Microbial 1,78 1,113 1,20 1,23 Precip.* Mic.Pres. NA 1.011,78, 0.302 0.632,113, 0.014 1.301,20, 0.268 0.101,23, 0.757 0.03 0.021 Presence Precip.* Life-stage NA 10.191,76, 0.002 2.251,113, 0.007 0.111,20, 0.741 0.201,23, 0.656 0.02 0.148 Mic.Pres.*Life-stage 1.48, 0.223 0.131,76, 0.721 0.472,113, 0.043 0.011,20, 0.938 1.841,23, 0.189 0.05 0.004 Precip.* Mic.Pres.*Life-stage NA 12.811,78, 0.001 2.362,113, <0.001 0.011,20, 0.939 1.491,23, 0.234 0.02 0.174 Precipitation NA 7.191,87, 0.009 2.741,84, 0.102 3.331,24, 0.080 0.931,24, 0.345 0.021 0.001 Microbial Inocula 0.47, 0.494 0.011,85, 0.921 0.821,84, 0.368 4.061,24, 0.055 6.411,24, 0.018 0.08 0.021 Microbial Life-stage 0.34, 0.558 3.831,4, 0.116 16.491,84, <0.001 1.761,24, 0.197 0.301,24, 0.592 0.02 0.503 Association Precip.* Mic.Inoc. NA 0.271,84, 0.606 0.081,84, 0.777 1.191,24, 0.286 2.101,24, 0.160 0.03 0.245 History Precip.* Life-stage NA 0.251,87, 0.620 0.311,84, 0.578 2.451,24, 0.131 0.451,24, 0.510 0.02 0.343 Mic.Inoc.*Life-stage 0.09, 0.759 0.871,85, 0.354 0.031,84, 0.870 5.541,24, 0.027 3.011,24, 0.092 0.11 0.006 Precip.* Mic.Inoc.*Life-stage NA 0.001,84, 0.996 0.381,84, 0.540 1.631,24, 0.213 2.541,24, 0.124 0.05 0.062 Ulbrich et al. SUPPLEMENTAL Page 3/15 Table S5. Final bacterial community analyses for microbial presence treatments (autoclaved and bulk microbial treatments only). F-statistic and p-values provided; significant p-values (p < 0.05) are bolded. Bacterial Bacterial Inverse community composition Factor Bacterial richness Simpson (Weighted Unifrac) 2 F, p F, p R p Precipitation 0.271,8, 0.617 0.011,11, 0.934 0.11 0.007 Germinant Microbial presence 175.641,8, <0.001 1.731,11, 0.216 0.40 0.007 Precip.* Mic.Presence 0.0021,8, 0.970 0.291,11, 0.598 0.05 0.020 Precipitation 0.681,9, 0.432 2.281,9, 0.165 0.06 0.013 Seedling Microbial Presence 210.611,9, <0.001 25.111,9, <0.001 0.62 0.027 Precip.* Mic.Presence 0.071,9, 0.799 3.181,9, 0.108 0.06 0.023 Table S6. Soil properties for initial inocula (autoclaved bulk, live bulk, live rhizosphere) and final seedling-associated soils. Microbial biomass carbon and dissolved organic carbon were only assessed on the seedling ambient-exposed soils (n = 5 per microbial treatment). F-statistic and p-values provided; significant p-values (p < 0.05) are bolded. Final soil Final soil dissolved Final microbial Factor Initial nitrate Initial ammonium Final soil nitrate ammonium organic carbon biomass carbon F, p F, p F, p F, p F, p F, p Precipitation NA NA 15.221,17, 0.001 5.361,20, 0.031 NA NA Microbial treatment 0.792,11, 0.477 62.792,11, <0.001 9.122,17, 0.002 16.552,20, <0.001 2.6072,10, 0.123 0.912,10, 0.434 Precip.* Microbial NA NA 4.632,17, 0.025 3.432,20, 0.052 NA NA treatment Ulbrich et al. SUPPLEMENTAL Page 4/15 Table S7. SIMPER results for bacterial OTUS that differ between the seedling-associated live microbial inocula (rhizosphere and bulk) in drought versus ambient conditions with Weighted Unifrac distance metric. OTUs with significantly greater average percent relative abundance in the drought than ambient soils are presented (p < 0.05). Percent dissimilarity explained refers to the amount of community dissimilarity between the ambient- and drought-exposed bacterial communities that a particular OTU explains. Rows organized by taxonomy and unadjusted p-value presented. Percent Avg. % Avg. % dissimilarity rel.abund. rel.abund. Unadjusted OTU explained under drought under ambient Phylum Class Order Family Genus P-value OTU6729 3.75E-05 0.75 0 Acidobacteria Acidobacteria Subgroup_4 UNKONWN Blastocatella 0.023 OTU1520 0.000125 2.5 0 Actinobacteria Acidimicrobiia Acidimicrobiales UNKNOWN UNKNOWN 0.025 OTU851 0.000356 9.5 3.125 Actinobacteria Acidimicrobiia Acidimicrobiales UNKNOWN UNKNOWN 0.012 OTU13605 0.000109 2.375 0.25 Actinobacteria Actinobacteria Corynebacteriales Mycobacteriaceae UNKNOWN 0.01 OTU1903 0.000303 7.5 2.25 Actinobacteria Actinobacteria Corynebacteriales Nocardiaceae Smaragdicoccus 0.023 OTU494 0.000109 2.375 0.375 Actinobacteria Actinobacteria Frankiales Acidothermaceae Acidothermus 0.012 OTU272 0.000264 6.75 2.125 Actinobacteria Actinobacteria Frankiales Frankiaceae UNKNOWN 0.018 OTU6546 0.000481 10.875 1.25 Actinobacteria Actinobacteria Frankiales UNKNOWN UNKNOWN 0.002 OTU3122 0.000548 15.375 5.25 Actinobacteria Actinobacteria Frankiales UNKNOWN UNKNOWN 0.013 OTU13146 0.000306 9.75 4.25 Actinobacteria Actinobacteria Kineosporiales Kineosporiaceae UNKNOWN 0.018 OTU768 0.000433 11.625 3.625 Actinobacteria Actinobacteria Propionibacteriales Nocardioidaceae Aeromicrobium 0.007 OTU80 0.000853 36.375 23.375 Actinobacteria Actinobacteria Pseudonocardiales Pseudonocardiaceae Pseudonocardia 0.048 OTU810 0.00035 10.125 3.625 Actinobacteria Actinobacteria Streptomycetales Streptomycetaceae Streptomyces 0.009 OTU478 0.000356 10 4.375 Actinobacteria Thermoleophilia Gaiellales Gaiellaceae Gaiella 0.035 OTU6042 9.38E-05 1.875 0 Actinobacteria Thermoleophilia Solirubrobacterales 0319-6M6 UNKNOWN 0.005 OTU1155 0.000767 20.875 5.625 Actinobacteria Thermoleophilia Solirubrobacterales 0319-6M6 UNKNOWN 0.002 OTU294 0.001058 32.875 15.75 Actinobacteria Thermoleophilia Solirubrobacterales 288-2 UNKNOWN 0.033 OTU2691 0.000177 4.125 1.375 Actinobacteria Thermoleophilia Solirubrobacterales 480-2 UNKNOWN 0.036 Ulbrich et al.