Relationships among xylem transport, anatomical structure and mechanical strength in stems and roots of three Podocarpaceae species

doi:10.17521/cjpe.2020.0402

Abstract

Abstract:

Aims Hydraulic failure is one of the primary cause of plant mortality during drought. Thus, quantitative analysis on inter-specific and inter-organ variance in hydraulic traits can help us to predict the response and even survivability of species under climate change.

Methods Here, three Podocarpaceae species (Podocarpus macrophyllus, P. macrophyllusvar. maki and Nageia nagi) grown in a mesic common garden were studied, with xylem hydraulic function (specific hydraulic conductivity (K_s); embolism resistance (P₅₀)), anatomical structure (tracheid diameter (D_t); hydraulic diameter (D_h); tracheid wall thickness (T_w); tracheid density (N_t); pit membrane diameter (D_p); pit density (N_p)) and mechanical strength (wood density (WD); tracheid thickness to span ratio ((t/b)²)) measured. Then, we analyzed hydraulic traits variance at the organ level (stem and root) in three Podocarpaceae species, and investigated the relationships among xylem hydraulic traits, anatomical structure and mechanical strength in stems and roots.

Important findings We found that: 1) The stem xylem in three Podocarpaceae species exhibited no safety- efficiency trade-off. In contrast, the root xylem exhibited safety-efficiency trade-off. 2) For stems, K_s was positively correlated with D_p, but decoupled with stem WD and (t/b)²; Stem P₅₀ was negatively correlated with D_p, but not correlated with WD and (t/b)². 3) For roots, K_s was positively correlated with hydraulic diameter, but negatively correlated with root T_w and (t/b)²; Root P₅₀ was positively correlated with T_w, (t/b)² and WD. Root xylem traits exhibited strong relationships with both K_s and P₅₀, demonstrating its cause-and-effect basis for the safety-efficiency tradeoff. On the other hand, the absence of safety-efficiency tradeoff in stems may be attributed to the overbuilt xylem of Podocarpaceae. More experimental evidence on the overbuilding of xylem is desired in the future study.

Key words: embolism, hydraulic conductivity, vulnerability curve, tracheid, Podocarpaceae

LU Shi-Tong, CHEN Sen, LI Yan, WANG Zhong-Yuan, PAN Tian-Tian, YE Lin-Feng, XIE Jiang-Bo. Relationships among xylem transport, anatomical structure and mechanical strength in stems and roots of three Podocarpaceae species[J]. Chin J Plant Ecol, 2021, 45(6): 659-669.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2020.0402

https://www.plant-ecology.com/EN/Y2021/V45/I6/659

Figures/Tables 7

Table 1 Basic characteristics of the sampling plots and trees of three Podocarpaceae species (mean ± SE)

树种 Species	海拔 Altitude (m)	坡向 Slope direction	坡度 Slope (°)	土壤类型 Soil type	土壤含水量 Soil water content (%)	土壤容重 Soil bulk density (g·cm^-3)	树高 Tree height (m)	胸径 DBH (cm)
罗汉松 Podocarpus macrophyllus	42.47 ± 0.23	西南 SW	3	黄红壤亚类 Yellow red soil subclass	36.87 ± 1.81	1.22 ± 0.15	5.93 ± 0.42	13.50 ± 1.55
短叶罗汉松 P. macrophyllus var. maki	39.40 ± 0.44	西南 SW	8	黄红壤亚类 Yellow red soil subclass	35.24 ± 1.75	1.20 ± 0.10	2.89 ± 0.32	11.99 ± 1.54
竹柏 Nageia nagi	41.48 ± 0.20	西南 SW	1	黄红壤亚类 Yellow red soil subclass	36.34 ± 1.74	1.23 ± 0.08	3.66 ± 0.18	8.52 ± 0.64

Fig. 1 Examples of light microscopy images of transverse and vertical sections of wood anatomy of three Podocarpaceae species. A-D, Transverse sections and vertical sections of stem, transverse sections and vertical sections of root in Podocarpus macrophyllus. E-H, Transverse sections and vertical sections of stem, transverse sections and vertical sections of root in P. macrophyllus var. maki. I-L, Transverse sections and vertical sections of stem, transverse sections and vertical sections of root in Nageia nagi.

Fig. 2 Hydraulic functional traits of three Podocarpaceae species (mean ± SE, n = 7). Different lowercase letters indicate significant differences at p ≤ 0.05 level.

Fig. 3 Xylem anatomical structure of three Podocarpaceae species (mean ± SE, n = 7). Different lowercase letters indicate significant differences at p ≤ 0.05 level.

Fig. 4 Xylem mechanical traits of three Podocarpaceae species (mean ± SE, n = 7). Different lowercase letters indicate significant differences at p ≤ 0.05 level.

Fig. 5 Relationship between hydraulic conductivity and embolism resistance in the three Podocarpaceae species. A, The stems of three Podocarpaceae species in this paper. B, The roots of three Podocarpaceae species in this paper. C, The stems of twelve Podocarpaceae species (Data from Brodribb & Hill (1999), van der Willigen et al. (2000), Pittermann & Sperry (2006)). D, The roots of five Podocarpaceae species (Data from Pittermann & Sperry (2006)). ns, non-significant relationships.

Fig. 6 Correlation analysis of ten xylem traits in Podocarpaceae species. A, Xylem traits of stem. B, Xylem traits of root. *, p ≤ 0.05; **, p ≤ 0.01. Dh, hydraulic diameter (μm); Dp, pit membrane diameter (μm); Dt, tracheid diameter (μm); Ks, specific hydraulic conductivity (kg·m-1·MPa-1·s-1); Np, pit density (mm-2); Nt, tracheid density (mm2); P50, the xylem water potential causing 50% loss of hydraulic conductivity (-MPa); Tw, tracheid wall thickness (μm); WD, wood density (g·cm-2); (t/b)2, tracheid thickness to span ratio.

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