Abstract
Understanding how mowing height and soil moisture influence drought resistance mechanisms may lead to better management of seashore paspalum. This research was conducted to evaluate the effect of mowing height and soil moisture replacement on drought tolerance strategies in three seashore paspalum cultivars. In a greenhouse, clear polyvinyl chloride (PVC) root tubes were placed in a black PVC sleeve with a bottom cap drilled with holes for drainage. Sod pieces (10 cm in diameter) of seashore paspalum (Paspalum vaginatum Swartz) cultivars Salam, Excalibur, and Adalayd were planted into these tubes after roots were trimmed. In a split-split experimental design, water regimes applied included control [100% of the total evapotranspiration (ET)] as well as 75%, 50%, and 25% of the total ET. Mowing heights were 45.0, 35, and 25 mm. Visual turf quality, maximum root extension (MEM), root length densities (RLD), total nonstructural carbohydrate content (TNC), shoot reducing sugar content (RSC), and proline content were determined. Turf quality decreased linearly with the decrease in irrigation water applied under the three mowing heights with higher slope at 25.0 mm than at either 35.0 or 45.0 mm. 'Salam' turf quality declined only to the unacceptable rating of 5.5 and 4.5 when mowed to 35 and 25 mm, respectively, whereas quality was 6.5 at the mowing height of 45 mm under the water regime of 25% of total ET. 'Excalibur' did not show acceptable turf quality at the 25% treatment, whereas 'Adalayd' did not show such quality at both 50% and 25% water regimes under all mowing heights. Regression analysis indicated a significant negative association between RLD and drought levels at all mowing heights and soil depths. In 'Salam', as drought levels increased from control to 25%, average RLD decreased by 76%, 75%, and 76% at 25-, 35-, and 45-mm mowing heights, respectively, at the top 30 cm of soil in the column. The change was 93%, 85%, and 83% at 25-, 35-, and 45-mm mowing heights, respectively, at the deeper soil (90 to 120 cm). In 'Salam', on average overall water regimes, MRE at 45 mm was approximate to 10% to 17% greater than that of 35-mm mowing height and 28% to 36% greater than that of 25-mm mowing height. The highest root mass (810 mg) was obtained when 'Salam' was mowed to 45 mm and subjected to the drought level of 50% of the total ET. The lowest root mass (320 mg) was obtained when 'Salam' was mowed to 25 mm and the water regime was not limiting. In 'Salam', as drought increased from control to 25% of the total ET, average TNC decreased by 43.5%, 26.0%, and 29.0% and the average TNC decrease in 'Excalibur' shoots was 48.0%, 30.0%, and 32.0%, whereas the decrease in 'Adalayd' was 51.3%, 42.3%, and 35.4% at 25-, 35-, and 45-mm mowing heights, respectively. As drought levels increased from control to 25% of the total ET, average RSC increased by 57.3%, 57.1%, and 53.0% in 'Salam' and by 59.4%, 57.0%, and 51.5% in 'Excalibur' and 61.2%, 58.1%, and 61.0%, in 'Adalayd' at 25-, 35-, and 45-mm mowing height, respectively. When drought increased to 25%, average proline content in shoots increased by 435%, 432%, and 431% in 'Salam'; 404%, 376%, and 324% in 'Excalibur'; and 257%, 278%, and 302% in 'Adalayd', at 25-, 35-, and 45-mm mowing heights. The resistance of paspalum cultivars to moderate to high drought stress can be enhanced by increasing the mowing height that may be related to increased carbon fixation, which favors increased root production.
Proline accumulation could add to the drought tolerance through osmoregulation or by acting as a carbon and nitrogen sink for stress recovery.