Variation and correlation of plant functional traits in the riparian zone of the Lijiang River, Guilin, Southwest China

doi:10.17521/cjpe.2018.0119

Abstract

Abstract:

Aims Patterns of variation in plant functional traits and the correlation among them are important for understanding species coexistence and the maintenance of biodiversity. Our objectives in this study were to understand how variation and correlation of plant functional traits, at both the species and community levels, influence 1) plants adaptation to changing environments, and 2) the mechanisms of community assembly.
Methods We investigated species composition of riparian plant communities in 36 plots along the longitudinal gradient (represented by upstream, midstream, downstream) of the Lijiang River, Guilin, Southwest China. We measured three functional traits for 42 woody plant species: leaf area (LA), specific leaf area (SLA), and wood density (WD). For each plant community, we calculated 1) species abundance-weighted mean community trait values, and 2) species-level mean trait values. For each of these calculations, we used trait-gradient analysis to partition the three traits into alpha and beta components. We then conducted Pearson correlations to analyze the relationships among the three traits along the longitudinal gradient. Finally we tested the strength of environmental filtering using a null model that generates randomly assembled communities with species richness given by observed values.
Important findings The species abundance-weighted mean community value of LA was lowest in the midstream communities, which was significantly different from that in the downstream communities. The mean community value of WD for midstream and upstream communities was significantly higher than that for downstream communities. Mean community value of SLA was significantly different among the three reaches. The beta components of the three functional traits significantly differed among the three reaches and had observed values that are, on average, lower than simulated values. However, alpha components for all three traits were not significantly different among the three reaches and had consistently lower variation than beta components. This implies that the variation in the mean community trait value across plots was greater than trait variation between species within plots. The observed and simulated values of the alpha components for both LA and SLA were weakly correlated with each other within and among communities, which suggests that there are independent axes of differentiation among coexisting species. On the other hand, comparisons between observed and simulated values indicated that significantly negative correlations between SLA and WD were largely the result of strong environmental filters. Finally, these results imply that variation of plant functional traits is greater among communities than within communities.

http://jtp.cnki.net/bilingual/detail/html/ZWSB201901002

Key words: Lijiang River, riparian zone, functional traits, scale variation, trait-gradient analysis, RDA ordination, correlation, null model

LIANG Shi-Chu, LIU Run-Hong, RONG Chun-Yan, CHANG Bin, JIANG Yong. Variation and correlation of plant functional traits in the riparian zone of the Lijiang River, Guilin, Southwest China[J]. Chin J Plant Ecol, 2019, 43(1): 16-26.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2018.0119

https://www.plant-ecology.com/EN/Y2019/V43/I1/16

Figures/Tables 8

Table 1 Basic information of the sampled plots in the riparian zone along the longitudinal gradient of the Lijiang River

河段 Reach	样方数 Plot number	海拔 Elevation (m)	温度 Temperature (℃)	降水量 Precipitation (mm)	干扰强度 Disturbance intensity	群落类型 Community type
上游 Upstream	3	154	24.7	1 941	轻度 Light	枫杨-石榕树群落 Pterocarya stenoptera-Ficus abelii communities
	3	148	23.0	1 941	轻度 Light	枫杨+朴树-萝芙木群落 Pterocarya stenoptera + Celtis sinensis-?Rauvolfia verticillata communities
	6	144	23.7	1 941	轻度 Light	枫杨+阴香-石榕树群落 Pterocarya stenoptera + Cinnamomum burmannii-Ficus abelii communities
中游 Midstream	4	138	26.0	1 900	重度 High	枫杨+乌桕-细叶水团花群落 Pterocarya stenoptera + Sapium sebiferum-Adina rubella communities
	5	134	25.0	1 900	重度 High	阴香群落 Cinnamomum burmannii communities
	3	104	24.0	1 900	重度 High	枫杨-萝芙木群落Pterocarya stenoptera-?Rauvolfia verticillata communities
下游 Downstream	8	111	30.1	1 900	中度 Middle	乌桕+朴树-牡荆群落Sapium sebiferum + Celtis sinensis-Vitex negundo var. cannabifolia communities
下游 Downstream	4	105	26.8	1 900	中度 Middle	乌桕-木槿群落 Sapium sebiferum + Hibiscus syriacus communities

Fig. 1 The scatterplot between species mean specific leaf area (i.e. lgSLAs, cm2·g-1) vs. plot mean specific leaf area (i.e. lgSLAp, cm2·g-1) between Cinnamomum burmannii and Vitex negundo in the riparian zone of the Lijiang River. Each grey point represents a species in a specific plot; the green solid points and the orange solid triangles represent Cinnamomum burmannii and Vitex negundo respectively, and a column of grey points in a black rectangle represent all the species within community. For each species, the abscissa values of the large open point show the mean position of occupied plots (i.e., the beta component of the species trait value, βi), while the ordinate values of the solid symbols are their mean species trait value (ti). The difference between βi and ti, or the distance from the y = x line is αi (because αi = ti - βi ). Regression line shows abundance-weighted least squares regression of species trait values relative to plot mean trait values, with slope bi. bi is the slope of each species’ s regression line of species mean trait values (ti) relative to plot mean trait values (pj), it reflects the intraspecific variation of the species mean specific leaf area along a gradient defined by community-level mean trait values.

Fig. 2 Redundancy analysis (RDA) ordination diagram showing the relationships between the three abundance weighted functional traits and 10 selected environmental factors of the riparian plant of the Lijiang River. AN, soil available nitrogen; DI, disturbance intensity; Dis, distance; Ele, elevation; LA, leaf area; pH, soil pH value; Pre, precipitation; Rea, reach; SLA, specific leaf area; SOM, soil organic matter content; Tem, temperature; TN, soil total nitrogen content; WD, wood density. plot 1-12, upstream; plot 12-24, midstream; plot 25-36, downstream.

Table 2 The explained variance of environmental factors and their significant analysis in the first two axes in redundancy analysis (RDA) ordination

环境因子 Environmental factor	RDA₁	RDA₂	R²	p
有机质 Soil organic matter (g·kg^-1)	0.40	0.91	0.34	0.002^**
全氮 Soil total nitrogen (g·kg^-1)	-0.45	0.88	0.19	0.032^*
有效氮 Soil available nitrogen (mg·kg^-1)	-0.74	-0.66	0.57	0.001^***
pH	-0.26	0.96	0.21	0.015^*
干扰强度Disturbance intensity	-0.16	0.98	0.63	0.001^***
距离河岸距离 Distance (m)	-0.85	0.51	0.29	0.004^**
降水量 Precipitation (mm)	-0.66	0.74	0.79	0.001^***
温度 Temperature (℃)	-0.97	0.22	0.50	0.001^***
海拔 Elevation (m)	0.92	-0.38	0.57	0.001^***
河段 Reach	-0.90	0.41	0.88	0.001^***

Table 3 Statistics of the three plant functional traits across the three reaches of Lijiang River (mean ± SD)

河段 Reach	功能性状 Functional trait	性状参数 Functional trait parameter
河段 Reach	功能性状 Functional trait	物种性状值 t_i	β 组分 β_i	α 组分 α_i	群落性状值 p_j
上游 Upstream	叶面积 LA (cm²)	1.30 ± 0.35^a	1.36 ± 0.08^a	-0.06 ± 0.34^a	1.34 ± 0.14^ab
	比叶面积 SLA (cm²·g^-1)	2.40 ± 0.13^a	2.40 ± 0.02^a	-0.00 ± 0.13^a	2.39 ± 0.03^a
	木材密度 WD (g·cm^-3)	0.47 ± 0.10^a	0.44 ± 0.02^a	0.03 ± 0.10^a	0.44 ± 0.04^a
中游 Midstream	叶面积 LA (cm²)	1.16 ± 0.32^a	1.24 ± 0.08^b	-0.08 ± 0.27^a	1.26 ± 0.10^a
	比叶面积 SLA (cm²·g^-1)	2.47 ± 0.21^a	2.47 ± 0.06^b	0.01 ± 0.21^a	2.46 ± 0.07^b
	木材密度 WD (g·cm^-3)	0.42 ± 0.12^ab	0.47 ± 0.01^b	-0.04 ± 0.12^a	0.47 ± 0.02^a
下游 Downstream	叶面积 LA (cm²)	1.24 ± 0.32^a	1.45 ± 0.05^c	-0.20 ± 0.30^a	1.46 ± 0.07^b
	比叶面积 SLA (cm²·g^-1)	2.48 ± 0.13^a	2.53 ± 0.02^c	-0.06 ± 0.12^a	2.55 ± 0.03^c
	木材密度 WD (g·cm^-3)	0.36 ± 0.10^b	0.34 ± 0.01^c	0.02 ± 0.10^a	0.34 ± 0.02^b

Fig. 3 Scatterplots showing relationships between leaf area (LA), specific leaf area (SLA) and wood density (WD) for species trait values (A), beta components (B), alpha components (C), and plot mean trait values (D) of the riparian plant of the Lijiang River. The Pearson correlation coefficient (r) of these relationships are shown in each figure. Black solid dots and rm respectively represent observed values and observed correlation coefficient; black open circles and rs respectively represent random simulation values and simulation coefficient. *, p < 0.05; **, p < 0.01.

Fig. 4 Difference on beta components ranges in the observed and simulated values of the three functional traits at the three reaches in Lijiang River. Circles and squares represent simulated and observed values respectively. Filled squares indicate that the observed values differ significantly from the simulated values.

Fig. 5 Partitioning of the variance in plant functional traits explained by four scales (i.e. within-specie, among-species, communities and reaches) (A) and by two scales (i.e. within and among reaches) (B) of the riparian plant of the Lijiang River. LA, leaf area; SLA, specific leaf area; WD, wood density.

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