Dynamic niche partitioning in root water uptake of Populus tomentosa and Robinia pseudoacacia in mixed forest

doi:10.17521/cjpe.2022.0197

Abstract

Abstract:

Aims The research on dynamic niche partitioning of soil resource uptake is crucial for the understanding of plant coexistence mechanisms. However, there are still knowledge gaps in the interpretation of this field.

Methods In the growing season of 2019, a mature mixed forest of Populus tomentosa and Robinia pseudoacacia on the North China Plain was repeatedly sampled for water isotopes and soil water content, and fine root sampling was performed at the end of the growing season. Seasonal water uptake patterns of trees were determined by the hydrogen-oxygen stable isotope method and Bayesian mixture model (MixSIAR). The degree of niche overlap between P. tomentosaand R. pseudoacaciawas assessed by Pianka’s normalized overlap value.

Important findings Both tree species have deep root systems. Nevertheless, P. tomentosa tended to develop horizontal lateral roots and a higher proportion of fine roots were distributed in the shallow soil layers (0-30 cm). In contrast, R. pseudoacacia inclined to develop vertical taproots and a high proportion of fine roots were distributed in the deep soil layers (100-600 cm). In terms of the mean values of the whole growing season, the primary water sources for P. tomentosa and R. pseudoacacia were water from the middle (30-100 cm) and deep soil horizons. However, the contribution of water from shallow and middle soil horizons to the water uptake of P. tomentosa was higher than that of R. pseudoacacia, while the opposite was true for deep soil water and groundwater for the two species. Populus tomentosa and R. pseudoacacia showed completely opposite water uptake strategies in response to drought and heavy summer rainfall. During the dry season, P. tomentosa enhanced the water uptake contribution of the middle soil layer, while R. pseudoacacia promoted the relative water uptake from the groundwater. When heavy rainfall events occurred, P. tomentosa increased the water uptake contribution of the shallow soil layer, while R. pseudoacacia increased the water uptake contribution of the deep soil layer. In conclusion, there was niche complementarity in the fine root and water uptake between P. tomentosa and R. pseudoacacia. Furthermore, the degree of niche complementation in water uptake varied with seasons, and the water-uptake niche complementation degree in the dry season was relatively higher than that in other seasons. In addition, the study also showed that the root niche partitioning was not representative of the water uptake partitioning of trees. This study provides support for further understanding of plant coexistence mechanisms, and will provide an important reference for the formulation of future mixed forest management strategies to cope with climate change.

Key words: dynamic water uptake niche, fine root niche, Populus tomentosa, Robinia pseudoacacia, mixed forest, the North China Plain

ZHU Wei, ZHOU Ou, SUN Yi-Ming, Gulimire YILIHAMU, WANG Ya-Fei, YANG Hong-Qing, JIA Li-Ming, XI Ben-Ye. Dynamic niche partitioning in root water uptake of Populus tomentosa and Robinia pseudoacacia in mixed forest[J]. Chin J Plant Ecol, 2023, 47(3): 389-403.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2022.0197

https://www.plant-ecology.com/EN/Y2023/V47/I3/389

Figures/Tables 10

Fig. 1 Schematic diagram of fine root, isotope, and soil water content (SWC) sampling design and stand structure in a mixed forest of Populus tomentosa and Robinia pseudoacacia on the North China Plain.

Fig. 2 Daily precipitation and reference evapotranspiration at the experimental site in a mixed forest of Populus tomentosa and Robinia pseudoacacia on the North China Plain in 2019.

Fig. 3 Fine root morphology of Robinia pseudoacacia (A) and Populus tomentosa (B).

Fig. 4 Monthly variations in hydrogen and oxygen stable isotopes ratio (δD, δ18O) of different water sources, tree xylem water of Populus tomentosa and Robinia pseudoacacia in a mixed forest of P. tomentosa and R. pseudoacacia on the North China Plain. Horizontal bands depict confidence interval.

Table 1 Seasonal dynamics of soil water content in each soil layer in a mixed forest of Populus tomentosa and Robinia pseudoacacia on the North China Plain (mean ± SD)

土层 Soil layer (cm)	土壤含水率 Soil water content (%)
土层 Soil layer (cm)	4月 Apr.	5月 May	6月 June	7月 July	8月 Aug.	9月 Sept.	平均值 Mean
0-30	6.60 ± 0.61^bB	3.24 ± 0.37^cC	3.85 ± 0.37^cB	4.19 ± 0.32^cB	8.11 ± 1.23^abB	8.71 ± 1.76^aAB	5.78 ± 2.33^B
30-100	4.99 ± 0.58^cC	4.29 ± 0.20^cdB	3.99 ± 0.35^dB	4.13 ± 0.29^cdB	8.18 ± 0.47^aB	6.61 ± 0.95^bB	5.36 ± 1.64^B
100-600	10.30 ± 0.40^aA	10.20 ± 0.71^aA	7.21 ± 0.35^bA	6.82 ± 0.70^bA	11.60 ± 1.41^aA	11.10 ± 1.12^aA	9.59 ± 2.06^A
平均值 Mean	7.32 ± 2.44^ab	5.94 ± 3.31^bc	5.02 ± 1.67^c	5.05 ± 1.39^c	9.32 ± 2.01^a	8.82 ± 2.28^a

Fig. 5 Vertical fine root distributions of different species in a mixed forest of Populus tomentosa and Robinia pseudoacacia on the North China Plain (mean ± SD). A, Fine root length density (FRLD). B, Cumulative fine root fraction. C, Fine root fraction in each soil layer. *, significant differences (p < 0.05) in the fine root index between different species; β, the root extinction coefficient, larger values of β imply deeper rooting profiles.

Table 2 Analyses by linear mixed-effects models for the effects of water source and species on water uptake contributions of different species in a mixed forest of Populus tomentosa and Robinia pseudoacacia on the North China Plain

因子 Factor	月份 Month
	4		5		6		7		8		9		平均值 Mean
	F	p	F	p	F	p	F	p	F	p	F	p	F	p
水源 Water source	1.93	ns	74.47	*	17.78	*	2.50	*	86.42	*	104.66	*	2.35	*
物种 Species	0.01	ns	0.80	ns	0.70	ns	0.10	ns	0.32	ns	0.13	ns	0.01	ns
水源×物种 Water source × species	19.73	*	11.61	*	93.43	*	10.09	*	94.23	*	47.36	*	5.70	*

Fig. 6 Effects of species on water uptake contributions of different water sources (mean values of the growing season) in a mixed forest of Populus tomentosa and Robinia pseudoacacia on the North China Plain (mean ± SD). A, Shallow, middle, and deep soil water and groundwater (GW). B, Vertical water uptake patterns. *, significant differences (p < 0.05) in water uptake contributions between different species; ns, no significant differences between different species (p > 0.05). Different lowercase letters indicate significant differences (p < 0.05) in water uptake contributions among water sources, according to the least significance difference test.

Fig. 7 Seasonal dynamics of vertical water uptake patterns of different species in a mixed forest of Populus tomentosa and Robinia pseudoacacia on the North China Plain (mean ± SD). GW, groundwater.

Table 3 Niche overlap index calculated using root length density and water uptake contribution in a mixed forest of Populus tomentosa and Robinia pseudoacacia on the North China Plain (mean ± SD)

指标 Index	生态位重叠指数 Niche overlap index
指标 Index	4月 Apr.	5月 May	6月 June	7月 July	8月 Aug.	9月 Sept.	平均值 Mean
吸水贡献 Contribution to water uptake	0.79 ± 0.03^b	0.94 ± 0.06^a	0.83 ± 0.05^b	0.84 ± 0.05^b	0.90 ± 0.03^a	0.94 ± 0.03^a	0.87 ± 0.03^A
根长密度 Fine root length density	-	-	-	-	-	-	0.40 ± 0.06^B

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