Different Phenotypic, Photosynthetic, and Physiological Responses to Flooding between Q. nuttallii and Q. palustris

Abstract

Flooding stress is an increasingly serious problem in wetlands, often affecting large areas of crops and timber production areas. The current study aimed to explore the species differences in responses to flooding stress between Q. nuttallii and Q. palustris in an outdoor environment. All the tested plants survived after a 60-day flooding treatment that left 5 cm of water above the soil surface. This suggests that the two species are flood-tolerant, so they can be applied in the construction of riparian protection forests and wetland restoration. Compared with control conditions, flooding treatment significantly decreased seedling height and diameter and the P_n, G_s, T_r, F_v/F_m, ABS/CS_m, TR₀/CS_m, ET₀/CS_m, RE₀/CS_m, IAA, and GA₃ content and significantly increased the content of MDA, H₂O₂, soluble sugars, SOD, POD, ADH, ABA, and JA. Under control conditions, Q. nuttallii showed significantly greater growth and photosynthetic capability than Q. palustris. In contrast, Q. palustris exhibited less inhibition of growth and photosynthesis, oxidative stress levels, and antioxidant enzyme activities than Q. nuttallii under flooding conditions. The findings indicate that Q. palustris has better defense mechanisms against the damage caused by flooding stress than Q. nuttallii. Q. nuttallii was more sensitive and responsive to flooding than Q. palustris.

Keywords: antioxidant defense; flooding stress; physiological response; phytohormone; quercus.

Figure 1

Leaf phenotype and seedling growth under flooding conditions for Q. nuttallii and Q. palustris. (A) Leaf phenotype of Q. nuttallii. (B) Leaf phenotype of Q. palustris. (C) Seedling height growth of Q. nuttallii and Q. palustris. (D) Diameter growth of Q. nuttallii and Q. palustris. The bars show the mean ± SE (n = 3). Mean values with different letters are statistically different at the 5% level.

Figure 2

Leaf color parameters in CIELAB space for Q. nuttallii and Q. palustris before and after flooding treatment. (A) L*, lightness—positive toward white and negative toward black. (B) a*, red–green value—positive toward red and negative toward green. (C) b*, yellow–blue value—positive toward yellow and negative toward blue. (D) a/b, the ratio of red–green value to yellow–blue value. (E) C*, chroma value. (F) ΔE, the overall color difference. Columns with different lowercase letters are statistically different (p < 0.05).

Figure 3

Gas exchange parameters, including P_n, T_r, G_s, C_i, and WUE_i, of Q. nuttallii (A,C,E,G,I) and Q. palustris (B,D,F,H,J) seedlings in the treatment days under flooding stress. (A,B) P_n, maximum net photosynthetic rate. (C,D) T_r, transpiration rate. (E,F) C_i, intercellular CO₂ concentration. (G,H) G_s, stomatal conductance. (I,J) WUE_i, instantaneous water use efficiency. Data are given as means ± SE (n = 3). Columns with different lowercase letters are statistically different (p < 0.05).

Figure 4

Chlorophyll fluorescence parameters including F_v/F_m (A), ABS/CS_m (B), DI₀/CS_m (C), TR₀/CS_m (D), ET₀/CS_m (E), and RE₀/CS_m (F) of Q. nuttallii (left figures) and Q. palustris (right figures) seedlings in the treatment days under flooding stress. Data are given as means ± SD (n = 3). Columns with different lowercase letters are statistically different (p < 0.05).

Figure 5

MDA (A,B), H₂O₂ (C,D), and soluble sugar (E,F) content in Q. nuttallii (A,C,E) and Q. palustris (B,D,F) seedlings in the treatment days under flooding stress. Data are given as means ± SD (n = 3). Polylines with different lowercase letters are statistically different (p < 0.05). The results of t-test that discerning difference between the two treatments was labelled by ‘*’ (p < 0.05) and ‘**’ (p < 0.01) above the letters.

Figure 6

Content of SOD (A,B), POD (C,D), and ADH (E,F) of Q. nuttallii (A,C,E) and Q. palustris (B,D,F) seedlings in the treatment days under flooding stress. Data are given as means ± SD (n = 3). Polylines with different lowercase letters are statistically different (p < 0.05). The results of t-test that discerning difference between the two treatments was labelled by ‘*’ (p < 0.05) and ‘**’ (p < 0.01) above the letters.

Figure 7

Content of IAA (A,B), GA₃ (C,D), ABA (E,F), and JA (G,H) in Q. nuttallii (A,C,E,G) and Q. palustris (B,D,F,H) seedlings in the treatment days under flooding stress. Data are given as means ± SD (n = 3). Polylines with different lowercase letters are statistically different (p < 0.05). The results of t-test that discerning difference between the two treatments was labelled by ‘*’ (p < 0.05) and ‘**’ (p < 0.01) above the letters.

Figure 8

Pearson correlation analysis (A,B) and principal component analysis (C,D) of photosynthetic and physiological parameters of Q. nuttallii (A,C) and Q. palustris (B,D) seedlings in the treatment days under flooding stress on days 0, 20, 40, and 60. The results of the pearson correlation analysis that discerning the difference between the two parameters were labeled by ‘*’ (p < 0.05) and ‘**’ (p < 0.01) above the letters.

Figure 9

The schematic model of the physiological responses of Q. nuttallii and Q. palustris seedlings in different periods under control conditions and flooding stress. (A) The physiological schematic model of Q. nuttallii and Q. palustris under control conditions. (B) The physiological schematic model of Q. nuttallii and Q. palustris under flooding stress. ‘↑’, significantly increased. ‘↓’, significantly decreased. ‘ns’, not significant.