Effects of stem photosynthesis on hydraulic traits and leaf photosynthesis in Calligonum arborescens under drought stress

doi:10.17521/cjpe.2023.0386

Abstract

Abstract:

Aims Stem photosynthesis plays a crucial role in maintaining the carbon balance in plants. By exploring the impact of stem photosynthesis on hydraulic traits and leaf gas exchange in desert woody plants during a long period of drought, we aimed to gain deeper insights into the remarkable drought resistance capabilities of these plants in extreme environments.

Methods Aluminum foil was used to shade the stems of two-year-old Calligonum arborescensseedlings planted in 15-L pots at the beginning of the 2022 growing season under the rain shelter of Fukang desert station. The stems of a control group were exposed to normal light levels. After 0, 15 and 30 d of drought, the stem/leaf photosynthesis rate, hydraulic parameters, and non-structural carbohydrates (NSC) contents were measured in the shading and control groups.

Important findings Our main results showed that: (1) Stem photosynthetic rate of C. arborescens ranged from 1.0 to 2.0 μmol·m^-2·s^-1, and was not significantly affected by the duration of the drought. Stem photosynthetic rates were 1.42, 1.28 and 1.21 μmol·m^-2·s^-1 after 0, 15 and 30 d of drought, respectively. (2) The specific hydraulic conductivity, leaf/stem water content, leaf water potential, and leaf photosynthetic rate decreased significantly over the dry period in the shading group but declined more slowly in the control group. (3) After 15 d without water, the percentage loss of conductivity, was significantly reduced in the control seedlings and the NSC contents of leaf and stem were significantly increased. Following 30 d of drought, the number and cross-sectional area of embolized vessels decreased significantly, by 33.8% and 22.8%, respectively, in the control seedlings. (4) In the same drought duration, leaf photosynthetic rate in the control group was significantly higher than that of the shading group, increasing 2.3 and 3.2 μmol·m^-2·s^-1 after 15 and 30 d of drought, respectively. Our results indicate that stem photosynthesis can improve the drought resistance of desert plants and provide a theoretical foundation for understanding the strategies and mechanisms used by desert plants to survive under drought conditions, which are important when considering projected climate change scenarios.

Key words: stem photosynthesis, non-structural carbohydrates, percentage loss of conductivity, micro-CT, leaf photosynthesis

LI Min-Qing, ZHOU Xiao-Ming, WANG Shuang-Long, CHEN Li-Dan, LI Cong-Juan, LIU Ran. Effects of stem photosynthesis on hydraulic traits and leaf photosynthesis in Calligonum arborescens under drought stress[J]. Chin J Plant Ecol, 2024, 48(11): 1524-1535.

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Figures/Tables 12

Fig. 1 Stem photosynthetic rate (Ps) of Calligonum arborescens under drought duration (mean ± SD, n = 5). Same lowercase letters indicates no significant differences between treatments (p > 0.05).

Table 1 Stem respiration rate and stem respiration rate refixation ratio under drought conditions (mean ± SD, n = 5)

干旱时间 Drought time (d)	P_s(μmol·m^-2·s^-1)	R_s(μmol·m^-2·s^-1)	R_d(%)
0	1.45 ± 0.29^a	2.64 ± 0.33^a	55.6 ± 12.9^a
15	1.28 ± 0.17^a	2.09 ± 0.25^a	62.4 ± 14.1^a
30	1.21 ± 0.33^a	1.19 ± 0.29^b	100.9 ± 10.4^b

Fig. 2 Percentage loss of conductivity (PLC) and specific hydraulic conductivity (Ks) under drought conditions (mean ± SD, n = 5). Different uppercase or lowercase letters represent the significant difference between the drought time of control or shading. * indicates the significant difference between the control and shading for the same drought time at the p < 0.05 level.

Fig. 3 Micro-CT scan of the vessels after 30 d of drought treatment. A, 2D cross-section of young stem treated of control. B, 2D cross-section of young stem treated of shading. C, Number of vessels statistics and embolized vessels number ratio (mean ± SD). D, Cross-sectional area statistics of vessels and embolized vessels cross-sectional area ratio (mean ± SD). Different lowercase letters represent the significant difference of control and shading in C and D (p < 0.05).

Fig. 4 Starch and soluble sugar contents in root, stem and leaf under drought conditions (mean ± SD, n = 5). Different uppercase or lower case letters represent the significant difference between the drought time of control or shading. * and ** indicate the significant difference between the control and shading for the same drought time at the p < 0.05 and p < 0.01 level.

Fig. 5 Predawn water potential (Ψpd) and midday water potential (Ψmd) under drought conditions (mean ± SD, n = 5). Different uppercase or lowercase letters represent significant difference between the drought time of control or shading (p < 0.05). * and ** indicate the significant difference between the control and shading for the same drought time at the p < 0.05 and p < 0.01 level.

Table 2 Absolute and relative water content of stem and leaf under drought conditions (mean ± SD)

干旱时间 Drought time (d)	对照 Treatment	AWC_l	AWC_s	RWC_l	RWC_s
0	对照 Control	3.14 ± 0.42^a	0.81 ± 0.06^a	0.93 ± 0.04^a	0.71 ± 0.01^a
0	遮光 Shading	3.03 ± 0.41^a	0.80 ± 0.05^a	0.90 ± 0.05^a	0.72 ± 0.04^a
15	对照 Control	2.70 ± 0.34^a	0.81 ±0.04^a	0.78 ± 0.05^a	0.68 ± 0.07^a
15	遮光 Shading	2.64 ± 0.24^a	0.72 ± 0.05^b	0.76 ± 0.05^a	0.61 ± 0.04^a
30	对照 Control	1.88 ± 0.27^a	0.61 ± 0.03^a	0.73 ± 0.05^a	0.63 ± 0.03^a
30	遮光 Shading	1.22 ± 0.36^b	0.54 ± 0.03^b	0.55 ± 0.03^b	0.45 ± 0.07^b

Fig. 6 Leaf photosynthetic rate (Pl), transpiration rate (Tr) and leaf stomatal conductance (gs) under drought conditions (mean ± SD, n = 5). Different uppercase or lowercase letters represent the significant difference between the drought time of control or shading (p < 0.05). * and ** indicate the significant difference between the control and shading for the same drought time at the p < 0.05 and p < 0.01 level.

Fig. 7 Conceptual diagram illustrating stem photosynthesis of Calligonum arborescens resistance drought stress. The unit of leaf photosynthesis is μmol·m-2·s-1, and the unit of non-structural carbohydrate content is mg·g-1. TD0, initial drought; TD15, after 15 d of drought; TD30, after 30 d of drought. The proportion of TD15 and TD30 decline is relative to TD0. PLC, percentage loss of conductivity; NSC, non-structural carbohydrates.

TD15, after 15 d of drought; TD30, after 30 d of drought.

Isat, saturation light intensity; Rd, ratio of stem photosynthetic rate to stem release CO2 rate.

Supplement III Non-structure carbohydrate content in leaf, stem and root (NSCl, NSCs, NSCr) under drought conditions of Calligonum arborescens (mean ± SD, n = 5).

干旱天数 Drought time (d)	处理 Treatment	NSC_l	NSC_s	NSC_r
0	对照组Control	119.3 ± 9.6^a	90.8 ± 6.8^a	108.6 ± 8.9^a
	遮光组Shading	111.0 ± 5.9^a	87.0 ± 7.5^a	113.2 ± 15.2^a
15	对照组Control	94.3 ± 10.5^a	106.9 ± 7.0^a	103.1 ± 12.9^a
	遮光组Shading	76.5 ± 2.5^b	73.7 ± 4.0^b	107.6 ± 13.6^a
30	对照组Control	83.1 ± 6.0^a	117.3 ± 9.7^a	96.0 ± 5.5^a
	遮光组Shading	63.9 ± 6.1^b	88.6 ± 8.0^b	79.1 ± 7.1^b

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