Hydraulic architecture, leaf functional traits and environmental adaptation strategies of three understory shrubs in Beijing mountainous areas

doi:10.17521/cjpe.2024.0165

Abstract

Abstract:

Aims In-depth research on the hydraulic traits of plant xylem and leaf functional traits would be helpful to reveal their adaptation strategies to the environment, providing a theoretical basis for vegetation management and restoration.
Methods This study focuses on three typical shrub species in the mixed Pinus-Quercus forests of Beijing mountains areas: Vitex negundo, Grewia biloba, and Morus mongolica. Leaf functional traits (e.g., leaf area, net photosynthetic rate, leaf water potential, etc.) are determined through outdoor measurements and indoor experiments, while the xylem anatomical structure of the roots, stems, and branches of the three shrub species (e.g., vessel diameter, vessel density, etc.) is observed through sectioning, and hydraulic traits (e.g., specific hydraulic conductivity, hydraulic vulnerability index) are calculated, so as to understand the plant hydraulic structure and leaf functions and to reveal the adaptation strategies of these three shrub species to the shaded understory environment.
Important findings (1) Significant differences in leaf morphology, hydraulics, and functional traits were observed among the three shrubs; Vitex negundo had smaller leaf area but greater specific leaf mass, with the highest specific leaf mass and net photosynthetic rate; Grewia biloba had the largest vein volume but the lowest net photosynthesis and transpiration rates; Morus mongolica had the largest leaf area and midday leaf water potential. (2) Notable differences were found in the xylem vessel characteristics and hydraulic traits of the roots, stems, and branches of the three shrubs; Vitex negundo’s aboveground water transport efficiency exceeded that of its underground part; Grewia biloba maintained a balanced water transport efficiency across all xylem parts, with the strongest resistance to embolism; Morus mongolica maintained high water transport efficiency in all parts, with the weakest resistance to embolism. (3) Correlation analysis indicated that the xylem hydraulic traits of the three shrubs influence most of the variations in leaf structural traits and hydraulic traits. (4) Principal component analysis reveals that Grewia biloba tends towards a conservative slow strategy, Morus mongolica leans towards a water-consuming fast strategy, and Vitex negundo’s adaptation strategy lies between the former two.

Key words: shrub, hydraulic structure, xylem, water transport, vessel, leaf functional traits, adaptation strategies

ZHANG Xiao-Di, WANG Xiao-Xia, ZHANG Yu-Wen, HOU Jing-Yu, SHI Xiao-Peng, HE Lu-Lu, LIU Ya-Dong, XUE Liu, HE Bao-Hua, DUAN Jie. Hydraulic architecture, leaf functional traits and environmental adaptation strategies of three understory shrubs in Beijing mountainous areas[J]. Chin J Plant Ecol, 2025, 49(7): 1128-1143.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2024.0165

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Figures/Tables 12

Table 1 Characteristics of understory plant communities of three plots in West Mountain of Beijing

样方 Plot	灌木及幼树 Shrubs and young trees				草本 Herb
样方 Plot	盖度 Coverage (%)	平均高度 Mean height (m)	香农-威纳指数 Shannon-Winer index	辛普森指数 Simpson index	盖度 Coverage (%)	平均高度 Mean height (m)	香农-威纳指数 Shannon-Winer index	辛普森指数 Simpson index
P1	60.568	0.560	1.508	0.777	17.706	0.122	0.505	0.437
P2	72.113	0.578	1.593	0.767	8.687	0.121	0.336	0.400
P3	32.537	0.360	1.202	0.750	6.667	0.008	0.339	0.252

Table 2 Order of importance values and sampling frequency of three shrub species in three plots in West Mountain of Beijing (mean ± SE)

样方 Plot	黄荆 Vitex negundo			扁担杆 Grewia biloba			蒙桑 Morus mongolica
样方 Plot	重要值及序次 Importance value & order		取样数 Sampling frequency	重要值及序次 Importance value & order		取样数 Sampling frequency	重要值及序次 Importance value & order		取样数 Sampling frequency
P1	0.219 ± 0.041^a	I	7	0.146 ± 0.037^b	II	7	0.106 ± 0.039^b	III	4
P2	0.134 ± 0.037^b	II	6	0.238 ± 0.052^a	I	6	0.134 ± 0.013^b	III	3
P3	0.095 ± 0.006^b	II	4	0.362 ± 0.073^a	I	6	0.109 ± 0.013^b	III	6
总计 Total	0.149 ± 0.025^b	II	17	0.269 ± 0.042^a	I	19	0.114 ± 0.014^b	III	13

Table 3 Morphological characteristics of leaves of the three shrubs in West Mountain of Beijing (mean ± SE)

物种 Species	叶厚度 Leaf thickness (mm)	叶干物质量 Leaf dry matter content (g)	叶面积 Leaf area (cm²)	比叶质量 Leaf mass per area (g·cm^-2)
黄荆 Vitex negundo	0.085 ± 0.004^b	0.573 ± 0.089^a	23.533 ± 2.964^c	268.895 ± 42.217^a
扁担杆 Grewia biloba	0.147 ± 0.009^a	0.511 ± 0.089^a	43.770 ± 4.668^b	128.332 ± 23.951^b
蒙桑 Morus mongolica	0.159 ± 0.007^a	0.604 ± 0.140^a	76.033 ± 5.307^a	80.979 ± 18.977^b

Fig. 1 Differences in leaf vein structure of three shrubs in West Mountain of Beijing. Different lowercase letters indicate significant differences among three shrubs (p < 0.05).

Fig. 2 Differences in photosynthetic physiological parameters of leaves of three shrubs in West Mountain of Beijing (mean ± SE). Different lowercase letters indicate significant differences among three shrubs (p < 0.05).

Fig. 3 Characteristics of xylem vessels in roots, stems, and branches of three shrubs in West Mountain of Beijing (mean ± SE). Different uppercase letters indicate significant differences among different species, and different lowercase letters indicate significant differences among different water delivery sites (p < 0.05).

Fig. 4 Cross-sectional microstructure of root-stem-branch xylem of three shrubs in West Mountain of Beijing. From left to right (A-C) are xylem cross-sectional microscopic images of annual branches of Vitex negundo, Grewia biloba, Morus mongolica. Red sections were dyed by safranin, while blue-green sections were dyed by fast green.

Fig. 5 Xylem vessel diameter distributions in roots, stems, and branches of three shrubs in West Mountain of Beijing (mean ± SE). A-C, Size distribution of the xylem vessel diameters in the roots, stems, and branches of Vitex negundo. D-F, Size distribution of the xylem vessel diameters in the roots, stems, and branches of Grewia biloba. G-I, Size distribution of the xylem vessel diameters in the roots, stems, and branches of Morus mongolica. I, distribution of vessel diameter frequency; II, contribution of a certain size class of conduits to hydraulic conductivity (Kh).

Fig. 6 Correlation between xylem hydraulic traits of three shrubs in West Mountain of Beijing. Dm, mean vessel diameter; Dh, hydraulic diameter; Dv, vessel density; Aves/Axy, vessel area/xylem area; Ks, specific hydraulic conductivity; VI, hydraulic vulnerability Index. Ks and VI were averaged from the three organs in each species.

Fig. 7 Correlation network between functional traits of three understory shrubs in West Mountain of Beijing. Only significant correlations (p < 0.05) were shown, the red border represents the trait with the highest degree centrality values, excluding the xylem anatomical structural traits mentioned in 2.4. ψmid, mid-day leaf water potential; Gs, stomatal conductance; Ks, xylem specific hydraulic conductivity (root-stem- shoot mean); Pn, net photosynthetic rate; Tr, transpiration rate; WUEi, leaf instantaneous water use efficiency; VD, secondary vein diameter; VI, hydraulic vulnerability index (root-stem- shoot mean); VLA, secondary leaf vein density; VV, leaf vein volume.

Fig. 8 Linear regression analysis between different functional traits of three understory shrubs in West Mountain of Beijing (mean ± SE). Shading represents a 95% confidence interval. VV, VI, Ks see Fig. 7.

Fig. 9 Principal component (PC) analysis of hydraulic structure and functional traits of three shrubs in West Mountains of Beijing. Aves/Axyl, vessel area/xylem area; Dh, hydraulic diameter; Dm, mean vessel diameter; Dv, vessel density; Gs, stomatal conductance; Ks, xylem specific hydraulic conductivity (root, stem, shoot mean); LA, leaf area; LDMC, leaf dry matter content; LMA, leaf mass per area; LT, leaf thickness; Pn, net photosynthetic rate; Tr, transpiration rate; VD, secondary vein diameter; VI, hydraulic vulnerability index (root, stem, shoot mean); VLA, secondary leaf vein density; VV, leaf vein volume; WUEi, leaf instantaneous water use efficiency; ψmid, mid-day leaf water potential.

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