Defoliation Intensity Affects Bahiagrass Nutritive Value Through Increases in Proportion of Non-Degraded Leaf Tissue Components

Abstract

Understanding relationships between defoliation intensity, tissue components, and forage nutritive value is important to predict plant and animal responses. In bahiagrass (Paspalum notatum Flügge), the proportion and organisation of non-degraded leaf tissues affect nutritive value, yet these relationships remain understudied. We examined the effects of defoliation intensity (4-, 8-, and 12-cm stubble heights) on canopy structure, leaf length, tissue composition, and nutritive value in decumbent-growing (‘3Fpen8’) and upright-growing (‘Hybrid 93’) bahiagrasses, in a replicated study (n = 4) in Gainesville, Florida, USA. Responses were measured after 3-week regrowth periods during mid-summer, late summer, and early fall in 2022 and 2023. Increasing stubble height from 4 to 12 cm increased leaf blade length in 3Fpen8 (18.7–23.2 cm) and Hybrid 93 (22.7–29.7 cm). During late summer and early fall, each additional centimetre in leaf length increased the proportion of non-degraded vascular tissue and ‘girder structure’ (sclerenchyma + vascular tissue), respectively, by 0.23%–0.34% and 0.15%–0.27% in 3Fpen8 and 0.12% and 0.08%–0.11% in Hybrid 93. Leaf length affected nutritive value indirectly through non-degraded tissues; a one-unit decrease in girder structure increased Hybrid 93 digestibility by 7.5 g kg⁻¹ in late summer, when digestibility was lowest (412 g kg⁻¹). Likewise, a one-unit reduction in vascular tissue in early fall increased crude protein by ~6 g kg⁻¹ and reduced acid detergent fibre by ~9 g kg⁻¹ in both grasses. These findings suggest that greater defoliation intensity between late summer and early fall may minimise observed increases in non-degradable tissues in bahiagrass.