ROOT CHARACTERISTICS OF WARM SEASON TURFGRASS SPECIES UNDER LIMITED SOIL WATER AND VARYING MOWING HEIGHTS By BISHOW PRAKASH POUDEL DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2016 © 2016 Bishow P. Poudel Dedicated to my family and all the earthquake victims of Nepal ACKNOWLEDGMENTS I would like to thank my advisers Dr. Diane Rowland and Dr. Kevin Kenworthy and the supervisory committee for their continuous support and help throughout the program. My sincere acknowledgement goes to Andy Schreffler for his help with root images collections throughout the study period. Sincere thanks goes to Dr. Patricio Munoz and James Colee for their help with statistical analysis. Similarly I would also like to acknowledge my lab mates, colleague and friends for their help and support. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 7 LIST OF FIGURES ........................................................................................................ 12 LIST OF ABBREVIATIONS ........................................................................................... 14 ABSTRACT ................................................................................................................... 15 CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW ..................................................... 17 U.S. Turfgrass Industry ........................................................................................... 17 Warm-Season Turfgrass Species ........................................................................... 18 St. Augustinegrass .................................................................................................. 19 Bermudagrass ........................................................................................................ 20 Zoysiagrass ............................................................................................................ 21 Water Stress Physiology for Warm-Season Turfgrass ............................................ 21 Water Stress Resistance Mechanisms ................................................................... 22 Water Stress and Turfgrass Performance Ranking ................................................ 23 Turfgrass Root Architecture and Drought Responses............................................. 26 Approaches to Study Turfgrass Root Architecture .................................................. 30 Goals and Objectives .............................................................................................. 32 2 ROOTING CHARACTERISTICS OF WARM SEASON TURFGRASS SPECIES UNDER LIMITED SOIL WATER DURING GREENHOUSE DRY DOWN ............... 34 Introduction ............................................................................................................. 34 Materials and Methods............................................................................................ 36 Statistical Analysis .................................................................................................. 39 Results .................................................................................................................... 41 Evidence of Dry Down Progression .................................................................. 41 Comparisons Among Genera During DD and WW at Two Depths (0-30, 30- 90 cm): the Traits of TRL, TRSA, ARD and FRL ........................................... 43 Comparing Genotypes within Species During DD ............................................ 44 Discriminate Analysis: Testing Combinations of Root Traits ............................ 47 Stepwise Regression Analysis ......................................................................... 48 Discussion .............................................................................................................. 49 Summary ................................................................................................................ 53 3 ROOTING CHARACTERISTICS OF WARM SEASON TURFGRASS SPECIES UNDER LIMITED SOIL MOISTURE DURING FIELD DRY DOWN ........................ 72 5 Introduction ............................................................................................................. 72 Materials and Methods............................................................................................ 77 Statistical Analysis .................................................................................................. 79 Results .................................................................................................................... 81 Evidence of Dry Down ...................................................................................... 81 Across Species During Periods of DD (day 1, 7, 14, 21): at 0-30 and 30-90 cm ................................................................................................................. 81 Genotypes within Species ................................................................................ 82 Discriminate Analysis .............................................................................................. 83 Across Species at the End of DD (day 21) ....................................................... 83 Genotypes within Species (day 21) .................................................................. 84 Stepwise Regression Analysis to Quantify Relevant Root Traits at the End of DD (day 21) ......................................................................................................... 86 Stepwise Regression Analysis to Determine if the Root Traits Deemed Most Useful at the End of DD (day 21) Can be Obtained During Day 1 (WW) ............. 86 Discussion .............................................................................................................. 87 Summary ................................................................................................................ 94 4 AN IN SITU STUDY ON ROOTING DYNAMICS OF ST. AUGUSTINE AND BERMUDAGRASS AS AFFECTED BY MOWING HEIGHTS ............................... 113 Introduction ........................................................................................................... 113 Materials and Methods.......................................................................................... 117 Statistical Analysis ................................................................................................ 118 Results .................................................................................................................. 120 Floratam ......................................................................................................... 120 Tifway ............................................................................................................. 123 Discussion ............................................................................................................ 125 Summary .............................................................................................................. 131 5 CONCLUSION ...................................................................................................... 146 APPENDIX A GREENHOUSE GENOTYPE COMPARISON ...................................................... 149 B FIELD STUDY GENOTYPE COMPARISON ........................................................ 152 C MULTIVARIATE ANALYSIS OF VARIANCE ACROSS GENOTYPE FOR GREENHOUSE AND FIELD STUDIES ................................................................ 155 LIST OF REFERENCES ............................................................................................. 160 BIOGRAPHICAL SKETCH .......................................................................................... 171 6 LIST OF TABLES Table page 2-1 Analysis of Variance F-statistics for time domain reflectometer (TDR) of four warm season turfgrass species at two soil depths (15, 60 cm) for the dry down (DD) treatment tubes. ............................................................................... 55 2-2 Average values for time domain reflectometry (TDR) readings (reflective of volumetric soil moisture), of four warm season turfgrass species at 15 and 60 cm depths for dry down (DD) tubes. ................................................................... 55 2-3 Analysis of Variance F-statistics of species for turf quality (TQ) and leaf firing (LF) at beginning (TQ1, LF1) and end of dry down (TQ11 and LF11). ............... 56 2-4 Species averages for turf quality (TQ1, TQ11) and leaf firing (LF1, LF11) at the beginning and at the end of greenhouse DD. ............................................... 56 2-5 Analysis of variance F-statistics for total root length (TRL), total root surface area (TRSA), average root diameter (ARD), fine root length (FRL) and root proportion (RP) across species and root depths for DD and WW tubes in. ........ 57 2-6 Average values across 2012 and 2013 for total root length (TRL), total root surface area (TRSA), average root diameter (ARD), fine root length (FRL) and root proportion (RP) at 0-30 and 30-90 cm depths for the DD tubes. .......... 58 2-7 Average values in 2012 and 2013 for total root length (TRL), total root surface are (TRSA), average root diameter (ARD),