Hydraulic traits adjustments and nonstructural carbohydrate dynamics of Haloxylon ammodendron under drought stress

doi:10.17521/cjpe.2022.0276

Abstract

Abstract:

Aims Haloxylon ammodendron is the major dominated species in the Gurbantünggüt Desert, which plays a key role in ecosystem services: such as biodiversity conservation and prevention of dryland degradation. Frequent droughts have a significant impact on the survival of H. ammodendron, thus understanding the drought resistant strategies of H. ammodendron is essential for the sustainability and stability of desert ecosystems. Robust hydraulic system and carbon balance are important parts of the drought resistance mechanism, but the hydraulic threshold for survival of H. ammodendron under drought stress are still unquantified.

Methods We set up a control group and a drought treatment group for adult H. ammodendron, and determined the water status of assimilation twigs, the loss rate of xylem hydraulic conductivity in branches, gas exchange characteristics, nonstructural carbohydrate (NSC) contents and morphological characteristics at upper, lower and middle branches of H. ammodendron. We used one-way ANOVA for each trait among different treatments and heights, linear regression for stomatal sensitivity and principal component analysis for drought resistance of H. ammodendron, respectively.

Important findings (1) The predawn and midday water potential of assimilation twig, assimilation twig water content and branch water content of H. ammodendron decreased under drought stress, but did not affected by the increase of height; P50 and P88 (xylem tension causing 50% and 88% loss of maximum hydraulic conductivity) did not change significantly under drought and with increasing height, and the mean value of P50 was -4.12 MPa and P88 was -7.10 MPa for each height and treatment groups, while the hydraulic safety margin was significantly reduced under drought. (2) The stomatal opening of H. ammodendron was not sensitive to drought stress, and thus drought stress and branch height increase did not significantly affect net photosynthetic rate and stomatal conductance in general. (3) The NSC contents of assimilation twigs and branches did not decrease under drought stress or with increasing branch height; the value of NSC contents in the assimilation twigs and branches were 22.11% and 13.10% higher, compared to the control group. (4) The Huber value of H. ammodendron increased by 73.78% in the drought treatment group compared to the control group; the specific leaf area decreased by 14.60% compared to the control group, but there were no significant difference between the two treatment groups. In conclusion, the hydraulic traits of H. ammodendron were significantly affected by drought stress, but not by the increase of branch height, and there was no hydraulic limitation with increasing branch height. Under drought stress, the risk of simultaneous hydraulic failure of the peripheral branches at the crown edge was high, the hydraulic safety margin (difference between midday assimilation twig water potential and P88) was only 40.85% of that of the control group. Due to the low sensitivity of stomata to water stress, the shrub can maintain the capacity of photosynthetic carbon fixation under drought stress, and even slightly increased NSC contents of the assimilation twigs and branches.

Key words: drought stress, drought resistant strategy, hydraulic trait, nonstructural carbohydrate, tree mortality, Haloxylon ammodendron

CHEN Tu-Qiang, XU Gui-Qing, LIU Shen-Si, LI Yan. Hydraulic traits adjustments and nonstructural carbohydrate dynamics of Haloxylon ammodendron under drought stress[J]. Chin J Plant Ecol, 2023, 47(10): 1407-1421.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2022.0276

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Figures/Tables 12

Fig. 1 Soil water content at different depths in Haloxylon ammodendron sampling plot (mean ± SE). Different uppercase letters indicate significant differences among soil depths of the same treatment (p < 0.05), and different lowercase letters indicate significant differences between treatments of the same soil depth (p < 0.05).

Fig. 2 Percent loss of xylem conductivity for Haloxylon ammodendron. The vertical solid lines indicate the pressure on the xylem (i.e. the water potential of the xylem) for 50% and 88% loss of maximum hydraulic conductivity (P50, P88), respectively; the dashed lines and shaded areas are 95% confidence intervals.

Table 1 Xylem water potential for 50% and 88% loss of maximum hydraulic conductivity (P50, P88) in upper, middle and lower branches of control and drought-treated Haloxylon ammodendron (mean ± SE)

	P50 (MPa)			P88 (MPa)
	下部 Bottom	中部 Middle	上部 Upper	下部 Bottom	中部 Middle	上部 Upper
对照组 Control	-4.35 ± 0.10^Aa	-4.13 ± 0.33^Aa	-3.98 ± 0.17^Aa	-7.67 ± 0.26^Aa	-7.02 ± 0.56^Aa	-7.10 ± 0.07^Aa
干旱组 Drought	-4.15 ± 0.17^Aa	-3.82 ± 0.16^Aa	-4.27 ± 0.14^Aa	-7.03 ± 0.21^Aa	-6.88 ± 0.24^Aa	-6.86 ± 0.09^Aa

Fig. 3 Predawn assimilation twig water potential, midday assimilation twig water potential, twig water content and branch water content among different heights of Haloxylon ammodendron in control and drought treatment groups (mean ± SE). P50 and P88 are the xylem water potentials for 50% and 88% loss of maximum hydraulic conductivity, respectively. Different uppercase letters indicate significant differences among different heights of the same treatment (p < 0.05) and different lowercase letters indicate significant differences between different treatments of the same height (p < 0.05).

Fig. 4 Hydraulic safety margin among different heights of Haloxylon ammodendron in control and drought treatment groups (mean ± SE). HSM50 and HSM88 are the difference between the midday assimilation twig water potential and the xylem water potential for 50% and 88% loss of maximum hydraulic conductivity, respectively. Different uppercase letters indicate significant differences among different heights of the same treatment (p < 0.05) and different lowercase letters indicate significant differences between different treatments of the same height (p < 0.05).

Fig. 5 Net photosynthetic rate and stomatal conductance among different heights of Haloxylon ammodendron in control and drought treatment groups (mean ± SE). Different uppercase letters indicate significant differences among different heights of the same treatment (p < 0.05) and different lowercase letters indicate significant differences between different treatments of the same height (p < 0.05).

Fig. 6 Response of Haloxylon ammodendron stomatal conductance to vapor pressure deficit. The shaded area are 95% confidence intervals.

Fig. 7 Nonstructural carbohydrate (NSC) content of assimilation twigs and branches among different heights of Haloxylon ammodendron in control and drought treatment groups (mean ± SE). Different uppercase letters indicate significant differences among different heights of the same treatment (p < 0.05) and different lowercase letters indicate significant differences between different treatments of the same height (p < 0.05).

Table 2 Soluble sugar and starch contents of assimilation twigs and branches among different heights of Haloxylon ammodendron in control and drought treatment groups (mean ± SE)

处理 Treatment	高度 Height	同化枝 Assiassimilation twig		枝条 Branch
处理 Treatment	高度 Height	可溶性糖 Soluble sugar (%)	淀粉 Starch (%)	可溶性糖 Soluble sugar (%)	淀粉 Starch (%)
对照 Control	下部 Bottom	2.48 ± 0.45^Ab	3.61 ± 0.62^Aa	2.62 ± 0.70^Aa	1.41 ± 0.17^Aa
	中部 Middle	2.57 ± 0.14^Ab	3.13 ± 0.30^Aa	2.21 ± 0.39^Ab	1.75 ± 0.28^Aa
	上部 Upper	2.83 ± 0.24^Ab	3.57 ± 0.59^Aa	2.22 ± 0.20^Ab	1.71 ± 0.29^Aa
干旱 Drought	下部 Bottom	3.81 ± 0.37^Aa	3.72 ± 0.56^Aa	3.01 ± 0.27^Aa	1.56 ± 0.07^Aa
	中部 Middle	3.48 ± 0.58^Aa	3.12 ± 0.59^Aa	3.01 ± 0.14^Aa	1.34 ± 0.33^Aa
	上部 Upper	4.43 ± 0.49^Aa	3.65 ± 0.71^Aa	3.03 ± 0.19^Aa	1.53 ± 0.13^Aa

Fig. 8 Relationship between branch xylem hydraulic conductivity loss rate and nonstructural carbohydrate (NSC) content of Haloxylon ammodendron in drought treatment group.

Fig. 9 Huber value and specific leaf area among different heights of Haloxylon ammodendron in control and drought treatment groups (mean ± SE). Different uppercase letters indicate significant differences among different heights of the same treatment (p < 0.05) and different lowercase letters indicate significant differences between different treatments of the same height (p < 0.05).

Fig. 10 Principal component (PC) analysis of each trait of drought resistance strategies for Haloxylon ammodendron. ns, no significant difference; ***, p < 0.001. Ψmd, midday assimilation twig water potential; Ψpd, predawn assimilation twig water potential; B.NSC, nonstructural carbohydrate content of branch; BWC, branch water content; gs, stomatal conductance; HSM50, Ψmd - P50; HSM88, Ψmd - P88; HV, Huber value; L.NSC, nonstructural carbohydrate content of assimilation twigs; LWC, assimilation twig water content; P50, xylem water potentials for 50% loss of maximum hydraulic conductivity; P88, xylem water potentials for 88% loss of maximum hydraulic conductivity; Pn, net photosynthetic rate; SLA, specific leaf area.

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