Differential Regulation of Amino Acids and Nitrogen for Drought Tolerance and Poststress Recovery in Creeping Bentgrass

Abstract

Effects of amino acids and nitrogen on plant regrowth or recovery from drought stress remain largely unknown. The objectives of this study were to examine how gamma-aminobutyric acid (GABA) or proline, alone and in combination, or inorganic nitrogen [ammonium nitrate (NN)] may differentially affect turf performance during drought stress and rewatering, and to determine which specific endogenous amino acids regulated by GABA, proline, or NN priming were associated with plant tolerance to drought stress and postdrought recuperation in cool-season grass species. Creeping bentgrass (Agrostis stolonifera cv. Penncross) planted in porous ceramic fritted clay medium were exposed to well-watered conditions or drought stress by withholding irrigation for 21 days in growth chambers. Plants were treated with water (untreated control), GABA, or proline alone and in combination, or NN through foliar spray before drought stress and every 7 days during the 21-day stress period. For postdrought recovery, at 21 days of drought treatment, plants were rewatered for 14 days to return soil water content to prestress levels. Plants treated with GABA or proline alone or in combination maintained higher turf quality (TQ), dark green color index (DGCI), and stolon length by 21 days of drought stress, whereas proline-treated plants also maintained higher leaf relative water content (RWC) during drought as well as longer stolon length during rewatering. Plants treated with NN maintained higher TQ and leaf RWC during drought and had improved percent canopy cover, DGCI, and stolon length during postdrought rewatering. Accumulation of endogenous amino acids under drought stress, including proline and alanine, for proline-treated creeping bentgrass may have contributed to the enhancement of drought tolerance and postdrought regrowth. Nitrogen-enhanced accumulation of GABA, proline, and glutamic acid may have played a role in active amino acid assimilation and subsequent postdrought regrowth. Results from this study indicate that GABA or proline were mainly effective in promoting the tolerance of creeping bentgrass to drought stress while inorganic NN was effective in promoting rapid postdrought recovery and regrowth potential through the activation of amino acid metabolism. Endogenous amino acids, including GABA, proline, alanine, and glutamic acid, may be used as biomarkers to select for drought-tolerant plants and biostimulant components for improvement of drought stress tolerance and poststress recovery in cool-season turfgrass species.