Variations of morphology, anatomical structure and nitrogen content among first-order roots in different positions along branch orders in tree species

doi:10.3773/j.issn.1005-264x.2010.11.011

Abstract

Abstract:

Aims First-order roots play a key role in water and nutrient uptake from soil, and their positions along the branch orders may display differences in functions. However, few studies focused on the structure and functions of first-order roots with different positions in trees. Our objective was to explore the differences in morphological, anatomical and chemical properties among first-order roots with different branching positions and to understand the correlation between root structure and functions.
Methods First-order root samples from plantations were separated into three categories, Ar (from 2nd-order roots), Br (from 2nd-4th-order root tips) and Cr (from 3rd-5th-order roots). We made paraffin slices stained by safranin and fast green to observe anatomical traits, including cortex proportion, development of stele and protoxylem type. We also examined morphology and tissue nitrogen concentrations among these roots.
Important findings The first order roots in different branch positions showed differences in morphology and anatomy in three hardwood trees. Compared with root Br and root Cr, root Ar have larger root numbers, shorter length, lower stele/root diameter ratio, higher cortex proportion and N concentration, and more diarch roots. Root Br and Cr have smaller root numbers, longer length, higher stele/root diameter ratio, lower cortex proportion and N concentration, and more triarch-pentarch roots. These results suggest that the differences of the first-order roots in morphology, anatomy and tissue chemistry are related to root positions along branch orders, and are important in understanding root structures and functions in trees, particularly in revealing the roles of fine root longevity and turnover in forest ecosystems.

Key words: anatomical structure, branch order, Fraxinus mandshurica, Juglans mandshurica, Phellodendron amurense

LIU Ying, GU Jia-Cun, WEI Xing, XU Yang, WANG Zheng-Quan. Variations of morphology, anatomical structure and nitrogen content among first-order roots in different positions along branch orders in tree species[J]. Chin J Plant Ecol, 2010, 34(11): 1336-1343.

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URL: https://www.plant-ecology.com/EN/10.3773/j.issn.1005-264x.2010.11.011

https://www.plant-ecology.com/EN/Y2010/V34/I11/1336

Figures/Tables 5

Table 1 Root numbers and proportion of 1st-order roots in different positions in Juglans mandshurica, Phellodendron amurense and Fraxinus mandshurica trees

树种 Species	Ar		Br		Cr		Total
树种 Species	数量 Number	百分比 (%) Percentage	数量 Number	百分比 (%) Percentage	数量 Number	百分比 (%) Percentage	数量 Number
胡桃楸 Juglans mandshurica	224 ± 17	72	59 ± 5	19	31 ± 3	9	314 ± 21
黄波罗 Phellodendron amurense	22 ± 2	39	14 ± 1	25	21 ± 2	36	57 ± 5
水曲柳 Fraxinus mandshurica	188 ± 15	56	62 ± 6	19	83 ± 7	25	333 ± 24

Fig. 1 Mean root diameter (A) and mean root length (B) of 1st-order roots in different positions in Juglans mandshurica (Juma), Phellodendron amurense (Pham) and Fraxinus mandshurica (Frma) trees (mean ± SE). Ar, Br, Cr, see Table 1. Within each panel, mean values sharing different letters (a, b, c) indicate significantly differences within species at p < 0.05 level.

Fig. 2 Anatomical traits of 1st-order roots in different positions in Juglans mandshurica (Juma), Phellodendron amurense (Pham) and Fraxinus mandshurica (Frma) trees. A, Stele diameter. B, Ratio of stele diameter to root diameter. C, Cortical thickness. D, Cortical proportion. E, Mycorrhizal colonization. Ar, Br, Cr, see Table 1. Within each panel, mean values sharing different letters (a, b) indicate significantly differences within species at p < 0.05 level.

Fig. 3 Protoxylem type and proportion of 1st-order roots in different positions in Juglans mandshurica (A), Phellodendron amurense (B) and Fraxinus mandshurica (C) trees. Ar, Br, Cr, see Table 1.

Fig. 4 Root N content of 1st-order roots in different positions in Juglans mandshurica (Juma), Phellodendron amurense (Pham) and Fraxinus mandshurica (Frma) trees. Ar, Br, Cr, see Table 1. Within each panel, mean values sharing different letters (a, b) indicate significantly differences within species at p < 0.05 level.

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