Response of seed germination and seedling growth of perennial ryegrass (Lolium perenne L.) to drought, salinity, and pH in Karst regions

Abstract

Seed germination and seedling growth are crucial for the successful establishment and reproduction of plants in heterogeneous environments, especially in the ecologically fragile karst regions. Despite the ecological importance of perennial ryegrass (Lolium perenne L.) as a forage resource and its role in mitigating rocky desertification, studies addressing the effects of karst-specific environmental factors on its early growth stages are limited. This study is the first to simulate karst soil conditions to evaluate the impacts of drought (0-0.53 MPa), salinity (0-150 mM), and pH (pH 3-9) on seed germination and seedling growth of perennial ryegrass. The results showed that under different drought stresses, water potentials ranging from 0 to - 0.32 MPa had no significant effect on seed germination. However, water potentials of - 0.06 MPa and - 0.17 MPa significantly promoted root and shoot growth, as well as increased biomass. In the salt stress experiment, CaCl₂ concentrations of 5-10 mM favored seed germination; specifically, 5 mM CaCl₂ increased the germination rate to 96.5%, and root and shoot lengths exceeded those of the control. pH levels ranging from 3 to 9 had little effect on germination, but extremely acidic conditions (pH 3) significantly inhibited root and shoot elongation. Therefore, optimal growth conditions were determined to be drought stress from 0 to - 0.17 MPa, calcium salt stress from 0 to 25 mM, and a pH of 4 to 9. These findings identify optimal growth conditions for perennial ryegrass, providing a scientific basis for seed cultivation, pasture management, and ecological restoration in karst regions. Our study contributes to the understanding of plant responses to environmental stresses in karst systems and supports sustainable agricultural and conservation practices.

Keywords: Lolium perenne L.; CaCl2; Drought; Karst areas; Seed germination; pH.

Fig. 1

Effects of different treatments on the germination of perennial ryegrass seeds (mean ± SE; n = 4). (A) Effects of PEG-6000 treatments on germination potential and germination rate. (B) Effects of CaCl₂ treatments on germination potential and germination rate. (C) Effects of pH treatments on germination potential and germination rate. (D) Effects of PEG-6000 treatments on germination index and vitality index. (E) Effects of CaCl₂ treatments on germination index and vitality index. (F) Effects of pH treatments on germination index and vitality index. Different lowercase letters indicate significant differences among treatments at P ≤ 0.05 level.

Fig. 2

Effects of different treatments on the growth of perennial ryegrass seedlings (mean ± SE; n = 4). (A) Effects of PEG-6000 treatments on root and shoot lengths. (B) Effects of CaCl₂ treatments on root and shoot lengths. (C) Effects of pH treatments on root and shoot lengths. (D) Effects of PEG-6000 treatments on root length inhibition rate and shoot length inhibition rate. (E) Effects of CaCl₂ treatments on root length inhibition rate and shoot length inhibition rate. (F) Effects of pH treatments on root length inhibition rate and shoot length inhibition rate. Different lowercase letters indicate significant differences among treatments at P ≤ 0.05 level.

Fig. 3

Effects of different treatments on the biomass accumulation of perennial ryegrass seedlings (mean ± SE; n = 4). (A) Effects of PEG-6000 treatments on root fresh weight and shoot fresh weight. (B) Effects of CaCl2 treatments on root fresh weight and shoot fresh weight. (C) Effects of pH treatments on root fresh weight and shoot fresh weight. (D) Effects of PEG-6000 treatments on root dry weight and shoot dry weight. (E) Effects of CaCl2 treatments on root dry weight and shoot dry weight. (F) Effects of pH treatments on root dry weight and shoot dry weight. Different lowercase letters indicate significant differences among treatments at P ≤ 0.05 level.

Fig. 4

Pearson correlation analysis of seed germination parameters, seedling morphological indicators, and seedling biomass indicators under PEG-6000 stress. Significance levels: **P ≤ 0.01 (highly significant), *P ≤ 0.05 (significant).

Fig. 5

Pearson correlation analysis of seed germination parameters, seedling morphological indicators, and seedling biomass indicators under CaCl₂ stress. Significance levels: **P ≤ 0.01 (highly significant), *P ≤ 0.05 (significant).

Fig. 6

Pearson correlation analysis of seed germination parameters, seedling morphological indicators, and seedling biomass indicators under pH stress. Significance levels: **P ≤ 0.01 (highly significant), *P ≤ 0.05 (significant).