Chin J Plant Ecol ›› 2019, Vol. 43 ›› Issue (2): 119-130.doi: 10.17521/cjpe.2018.0269

• Research Articles • Previous Articles     Next Articles

Architectural analysis of root systems of mature trees in sandy loam soils using the root development classification

ZHU Wei1,YU Li-Xuan1,ZHAO De-Hai2,JIA Li-Ming1,*()   

  1. 1 Ministry of Education Key Laboratory of Silviculture and Conservation, Beijing Forestry University, Beijing 100083, China
    2 Warnell School of Forestry and Natural Resources, The University of Georgia, Athens, GA 30602, USA
  • Received:2018-10-30 Accepted:2019-01-30 Online:2019-06-04 Published:2019-02-20
  • Contact: JIA Li-Ming
  • Supported by:
    Supported by the National Key R&D Program of China (2016YFD0600403)(2016YFD0600403)

Abstract: <i>Aims</i>

Understanding the differences in root architectural strategies among the species and the differences in morphological characteristics among different root orders will facilitate our understanding root growth and development strategies, and thus provide a basis for predicting and modeling the root systems for mature trees. In this study, we analyzed the morphological characteristics and topological relationships for the root systems of two Populus tomentosa trees and one Robinia pseudoacacia tree.


A method combining both excavation and analysis was applied to extract and quantify root architectural characteristics of the three root systems. The morphological characteristics such as root basal diameter, root length, link length, and root number of different root orders were described using the developmental analysis method of Rose (1983), and their topological relationships were analyzed.

<i>Important findings</i>

1) The modified topological indices qa and qb were close to 0, and the topological index TI was close to 0.5 for all three root systems, indicating their dichotomous structure. The depth and width of the systems ranged from 5.7 to 6.4 m and from 7.6 to 13.5 m, respectively. Root grafts occurred in the same species. 2) The root systems could have the seventh or eighth order roots. The basal root diameter and root length significantly decreased with increasing root order. The first order roots had 5.79-36.92 times the basal diameter and 1.45-9.11 times the length of higher order roots. With increasing root order, the root number increased, and reached a maximum value for the third order roots, and then decreased. 3) In roots of each of the first three orders, the link length varied little from the root base towards its tip, indicating that the child roots were distributed evenly on their parent roots and thus help trees absorb soil resources more efficiently. 4) The regression of basal diameters of child roots on basal diameters of their mother roots showed that the smallest slope for the first order roots (average slope 0.15) and no big difference in the slope between the second and third order roots (0.34 versus 0.35). This suggested that the first order roots developed their own diameter first for anchoring and supporting the tree, while the second and third order roots developed their child roots to facilitate nutrient uptake from the soil. 5) The regression of root length on root basal diameter suggested that the slope increased from 10.46 to 90.43 with increasing root order, which implies that the higher order roots tended to develop their length to explore resources and expand their space.

Key words: developmental classification standard, root system classification, root architecture, mature tree, sandy loam soil

Table 1

General information of sample plots in Populus tomentosa stand and mixtures with P. tomentosa and Robinia pseudoacacia"

Stand type
Tree species
DBH (cm)
Average tree
height (m)
Plant & row
spacing (m)
crown width (m)
Thinning treatment
Populus tomentosa stand
P. tomentosa
36.1 35.5 6 × 6 7.0 造林后第十年间伐除去刺槐, 以前的混交林成为现有纯林
All R. pseudoacacia trees were removed from mixed-species stand after 10 years of planting, resulting in P. tomentosa pure stand
Mixtures with P. tomentosa
and Robinia pseudoacacia
P. tomentosa
37.0 26.4 3 × 6 6.6 无 None
Mixtures with P. tomentosa
and R. pseudoacacia
R. pseudoacacia
25.1 21.1 3 × 6 8.6 无 None

Table 2

Description of end states of the tracked roots in three root systems"

Populus tomentosa in pure stand
P. tomentosa in mixed stand
Robinia pseudoacacia in mixed stand
Code of the
tracked roots
depth (m)
End state
depth (m)
End state
depth (m)
End state
1 3.3 萌生幼树
Sapling from root sprouting
8.6 与邻株连生
Root grafted with neighbor tree
6.5 垂直向下生长
Vertically downward growth
2 5.1 与邻株连生
Root grafted with neighbor tree
11.1 分叉 Branching 8.2 分叉 Branching
3 6.1 垂直向下生长
Vertically downward growth
13.5 垂直向下生长
Vertically downward growth
8.5 垂直向下生长
Vertically downward growth
4 6.4 垂直向下生长
Vertically downward growth
5 7.6 垂直向下生长
Vertically downward growth
1 3.1 到头, 末端直径0.3 mm
To the end, root tip
diameter 0.3 mm
4.0 到头, 末端长瘤
To the end, with tumor
2.7 竖直向上生长
Vertically upward growth
2 4.3 到头, 末端直径0.3 mm
To the end, root tip
diameter 0.3 mm
4.3 到头, 末端直径0.5 mm
To the end, root tip
diameter 0.5 mm
3.7 到头, 末端直径0.3 mm
To the end, root tip
diameter 0.3 mm
3 5.7 到头, 末端直径0.25 mm
To the end, root tip
diameter 0.25 mm
4.3 到头, 末端直径0.76 mm
To the end, root tip
diameter 0.76 mm
5.9 到头, 末端直径0.02 mm
To the end, root tip
diameter 0.02 mm
4 6.4 向西转弯 Bend to the west

Fig. 1

Photos of root systems of Populus tomentosa in pure stand (A), P. tomentosa and Robinia pseudoacacia in mixed stand (B) (Lens position to the east)."

Table 3

The values of the topological indices for three root systems"

根系系统 Root system a (A) Pe V0 (M) b qa qb TI
纯林毛白杨 Populus tomentosa in pure forest 29 8 367 793 10.551 0.02 -0.000 2 0.50
混交林毛白杨 P. tomentosa in mixed forest 61 21 322 1 456 14.644 0.03 0.004 0 0.56
混交林刺槐 Robinia pseudoacacia in mixed forest 21 3 990 465 8.581 0.02 -0.006 0 0.50

Fig. 2

Variations of basal diameter, length, and number of roots for different order roots in root systems of Populus tomentosa in pure forest (A, D, G), P. tomentosa in mixed forest (B, E, H), and Robinia pseudoacacia in mixed forest (C, F, I). The individual points on the box plots represent outliers, the squares on the box plots represent the average."

Table 4

Results of fitting regression models of Populus tomentosa and Robinia pseudoacacia—regressing root diameter, length, and numbers (y) on root orders (x), respectively"

Root morphological
根系系统 Root system 方程 Regression model 拟合优度
Basal diameter
纯林毛白杨 P. tomentosa in pure forest y = 0.86381 + 99.24471exp(-2.32112x) 0.484 0 940
混交林毛白杨 P. tomentosa in mixed forest y = 0.70036 + 157.41951exp(-2.77342x) 0.414 9 1 527
混交林刺槐 R. pseudoacacia in mixed forest y = 0.80671 + 91.76619exp(-2.63586x) 0.374 7 541
纯林毛白杨 P. tomentosa in pure forest y = 67.63168 + 1098.3759exp(-3.32236x) 0.014 6 940
混交林毛白杨 P. tomentosa in mixed forest y = 39.71891 + 1313.84526exp(-1.98679x) 0.117 2 1 527
混交林刺槐 R. pseudoacacia in mixed forest y = 92.10741 + 477664.65953exp(-8.10278x) 0.079 5 541
纯林毛白杨 P. tomentosa in pure forest y = 5.97738 + 396.37817exp(-0.5((x-2.93757)/0.90608)2) 0.989 5 7
混交林毛白杨 P. tomentosa in mixed forest y = 22.41349 + 474.80796exp(-0.5((x-3.28655)/1.13184)2) 0.912 7 8
混交林刺槐 R. pseudoacacia in mixed forest y = 5.83356 + 196.21954exp(-0.5((x-2.79311)/1.01443)2) 0.936 7 8

Fig. 3

Link length variations along link sequence from the root base to the root tip in root systems of Populus tomentosa in pure forest (A), P. tomentosa in mixed forest (B), and Robinia pseudoacacia in mixed forest (C). 1-3 refer to root categories from first order to third order. The individual points on the box plots represent outliers, the squares on the box plots represent the average, and the lines connected the box plots."

Fig. 4

Basal diameter relationships between the mother roots and the child roots. 1, refer to mother-root categories from first order. 2, refer to mother-root categories from second order. 3, refer to mother-root categories from third order. A, root system of Populus tomentosa in pure forest. B, root system of P. tomentosa in mixed forest. C, root system of Robinia pseudoacacia in mixed forest."

Fig. 5

Relationships between basal diameter and root length for different order roots. A-F refer to root categories from first order to sixth order."

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