Regrowth dynamics and morpho-physiological characteristics of Plantago lanceolata under different defoliation frequencies and intensities

Abstract

Traditional pastures in temperate regions face limitations such as reduced growth and nutritional quality during the summer season. Plantain (P. lanceolata L.) offers advantages like increased yield and decreased nitrogen losses from grazing ruminants. Effective grazing management is essential for pasture health, and defoliation frequency and intensity play a pivotal role. This study aimed to evaluate plantain's regrowth, yield, and morpho-physiological and chemical responses under different defoliation frequencies and intensities, with the goal of enhancing its management in pastures. The study was conducted in pots within a controlled-environment growth chamber, examining the impact of three defoliation frequencies (based on extended leaf length: 15, 25 and 35 cm) and two defoliation intensities (5 and 8 cm of residual heights) with four replicates (24 pots as experimental units). The variables of interest were morphological characteristics, dry matter (DM) accumulation, herbage chemical composition, growth rate traits, and photosynthetic parameters. Defoliation frequency affected plantain's growth and nutritional composition. More frequent cuts (15 cm) resulted in lower DM yield per cut and lower stem content, while less frequent cuts (35 cm) produced higher values. Defoliation intensity influenced the proportion of leaves and stems in the total DM, with 5 cm cuts favoring leaves. Nutrient content was also affected by defoliation frequency, with less frequent cuts (35 cm) showing lower crude protein concentration and metabolizable energy content but higher neutral detergent fiber and water-soluble carbohydrate concentration. Plantain's growth rate variables were mainly influenced by defoliation frequency, with less frequent cuts promoting faster leaf appearance and growth of new leaves. The basal fluorescence variables and chlorophyll content were affected by cutting frequency, being highest when cut less frequently (35 cm), while no differences were found in the actual quantum efficiency among different defoliation frequencies and intensities. The fraction of light dedicated to non-photochemical quenching was highest when cut less frequently and more intensively. Overall, defoliation at 25 cm of extended leaf length balanced plantain forage quality and regrowth capacity.

Fig 1. Linear electron flow (LEF, μmol m^-2 s^-1) of leaves of plantain (Plantago lanceolata L.) plants cut at three frequencies (15, 25 and 35 cm extended leaf length) and at two intensities (5 and 8 cm).

Floating bar: standard error of the mean/ Least significant difference (p ≤ 0.05) of the interaction effect was 1.236.

Fig 2. Biplot of PCA of plant characteristics.

The principal components (PCs) were calculated with all measured variables of morphological and physiological traits, leaf and stem growth rate of leaves and stems, and nutritional composition. However, loadings are only presented for those variables with loadings greater than 0.20 or less than -0.20 for PC1 (black) or PC2 (dark red). F0Prime: minimum chlorophyll fluorescence (Fo´). FmPrime: maximum chlorophyll fluorescence (Fm´). Fs: steady‐state chlorophyll fluorescence. FvP/FmP: actual quantum efficiency of PSII (Fv′/Fm′). NPQt: total non-photochemical quenching. PHi2: quantum yield of PSII (Φ2). PhiNPQ: fraction of light dedicated to non-photochemical quenching (ΦNPQ). SPAD: relative chlorophyll content.