DIFFERENTIAL SHADE TOLERANCE OF SEVEN WARM SEASON TURFGRASS SPECIES: GROWTH, TURF PERFORMANCE, CHLOROPHYLL CONTENT AND NET PHOTOSYNTHESIS UNDER GRADED SHADE

Abstract

Shade from trees and built structures is a major constraint to turf establishment and persistence in landscapes. Seven warm-season turfgrasses viz., St. Augustine grass, bermudagrass, Manila zoysiagrass, bahiagrass, seashore paspalum, centipedegrass and carpet grass were evaluated under four nominal shade levels (0, 25, 50 and 75%) in a completely randomised design (CRD) with a 7 × 4 factorial arrangement and three replications (84 plots). Shoot and root biomass, root:shoot ratio, turf quality (1-9), turf density (1-5), total chlorophyll, chlorophyll a:b ratio and net photosynthetic rate (Pn) were recorded. Species, shade and the species × shade interaction were significant (P < 0.001) for all traits. Measured photosynthetically active radiation (PAR) was reduced by 31.5, 53.8 and 71.9% under the nominal 25, 50 and 75% shade levels, respectively. Across species, shoot dry weight declined from 11.74 g 100 cm⁻² in full sun to 5.08 g 100 cm⁻² at 75% shade, and Pn from 7.61 to 4.25 µmol CO2 m⁻² s⁻¹. At 75% shade, St. Augustine grass retained 75% of its full-sun shoot dry weight, 91% of root dry weight and 101% of turf quality, and bahiagrass retained 55%, 85% and 95%, respectively, and recorded the highest Pn (10.49 µmol CO2 m⁻² s⁻¹). Bermudagrass was the most shade-sensitive showing retention of 62% turf quality and density (and 41% of full-sun values retained), whereas centipedegrass and carpet grass lost more than 75% of shoot biomass while largely retaining visual quality ratings (87-98%). Manila zoysiagrass showed an atypical peak in growth at 25% shade. St. Augustine grass and bahiagrass were the most shade-adapted species under the conditions tested, and bermudagrass the least.