Temporal Dynamics of Physiological Integration Intensity in Zoysia japonica Under Heterogeneous Stress of Cadmium or/and Phenanthrene

Abstract

Heavy metals (HMs) or/and polycyclic aromatic hydrocarbons (PAHs) stress have significant adverse effects on the photosynthetic function and SPAD values of plants. Physiological integration is the typical feature of clonal plants, which can mitigate the adverse effects on ramets under heterogeneous stress. However, the sustainability of physiological integration between clones over prolonged stress durations, the dynamics of integration intensity and potential differences under various stress types remain unclear. This study examined the effects of three different heterogeneous stresses-cadmium (Cd), phenanthrene (Phe), and a combination of Cd and Phe (Cd + Phe) on the physiological integration of Zoysia japonica at different time points. The results indicate that physiological integration significantly enhances SPAD value, net photosynthetic rate (P_N), stomatal conductance (Cond), intercellular CO₂ concentration (C_i), transpiration rate (Tr), and water use efficiency (WUE). However, the physiological integration intensity diminishes with prolonged stress exposure. In addition, among different stress types, the initial integration intensity was highest under the highest toxicity conditions, it decreased most rapidly, resulting in the lowest integration intensity during the later stages of stress. To sum up, this study highlights the role of physiological integration in maintaining the photosynthetic function of clonal plants under heterogeneous stress and elucidates the temporal changes in integration intensity under different stress conditions.

Keywords: HMs; PAHs; clonal plant; photosynthetic parameters; physiological integration intensity.

Figure 1

Photosynthetic parameters and SPAD values in connected and severed Z. japonica ramets under Cd heterogeneous stress at different times. SPAD value (A), P_N (B), Cond (C), C_i (D), Tr (E), and WUE (F). Values are mean ± SD for n = 9. Bars with different letters are statistically different at p < 0.05, as determined by the LSD test.

Figure 2

Photosynthetic parameters and SPAD value in connected and severed Z. japonica ramets under Phe heterogeneous stress at different times. SPAD value (A), P_N (B), Cond (C), C_i (D), Tr (E), and WUE (F). Values are mean ± SD for n = 9. Bars with different letters are statistically different at p < 0.05, as determined by the LSD test.

Figure 3

Photosynthetic parameters and SPAD value in connected and severed Z. japonica ramets under Cd and Phe heterogeneous stress at different times. SPAD value (A), P_N (B), Cond (C), C_i (D), Tr (E), and WUE (F). Values are mean ± SD for n = 9. Bars with different letters are statistically different at p < 0.05, as determined by the LSD test.

Figure 4

Physiological integration intensity of SPAD value, P_N, Cond, C_i, Tr, and WUE of Z. japonica ramets under Cd or/and Phe heterogeneous stress at different times. The values are calculated from the average of the relevant indicators.

Figure 5

Connected and severed Z. japonica ramets under Cd or/and Phe heterogeneous treatments. C: Ramets remained connected (rhizomes intact); S: Ramets were severed (rhizomes cut). Cd+, Phe+, and Cd-Phe+: means the pot was treated with Cd, Phe, and Cd combined with Phe, respectively; Cd-, Phe-, and Cd-Phe-: means the pot was left untreated. Untreated, no contaminants were added to either pot.