Nitrogen addition frequency and propagule pressure influence Solidago canadensis invasion into native plant community

Figures & data

Figure 1. Experimental design.

Table 1. Summary of ANOVAs for the effects of nitrogen addition frequency (N) and propagule pressure (P) on Solidago canadensis and native communities.

	N		P		N × P
	F5,30	P	F5,30	P	F5,30	P
(A)S. canadensis
Leaf area	0.37	0.693	16.76	<0.001	0.00	0.999
Number of leaves	1.03	0.370	45.84	<0.001	0.05	0.950
Stem length	0.13	0.875	50.76	<0.001	0.03	0.970
Leaf biomass	0.71	0.499	16.52	<0.001	0.08	0.927
Root biomass^a	1.53	0.233	17.39	<0.001	0.01	0.987
Stem biomass	0.77	0.471	14.15	0.001	0.34	0.712
Aboveground biomass	0.74	0.486	16.06	<0.001	0.15	0.864
Total biomass	0.89	0.423	16.52	<0.001	0.08	0.921
(B)Native communities
Total biomass	3.44	0.041	0.32	0.730	0.48	0.750
Aboveground biomass	3.11	0.054	0.34	0.715	0.36	0.835
Belowground biomass	4.05	0.024	0.14	0.873	1.91	0.125
(C)Legumes
Total biomass ^a	1.95	0.154	4.22	0.021	1.77	0.152
Aboveground biomass	1.30	0.283	5.05	0.011	1.77	0.152
Belowground biomass	2.34	0.108	3.18	0.051	2.78	0.038
(D)Grass
Total biomass ^a	1.23	0.302	1.72	0.190	0.80	0.531
Aboveground biomass	1.22	0.306	1.53	0.227	0.73	0.576
Belowground biomass	1.03	0.366	2.97	0.062	1.19	0.328
(E)Non-grass broadleaf herbs
Total biomass	1.92	0.158	1.15	0.327	0.03	0.999
Aboveground biomass	1.73	0.189	1.19	0.315	0.04	0.997
Belowground biomass	2.55	0.089	0.66	0.521	0.57	0.688

^aindicates square root-transformed data. Significant values of F and P are shown in bold. ANOVA, analysis of variance.

Figure 2. Effects of the frequency of nitrogen addition and propagule pressure on the growth measures (mean ± SE, n = 6) of Solidago canadensis. Means that share the same letter are not different at P < 0.05 within different frequencies of nitrogen addition.

Figure 3. Effects of the frequency of nitrogen addition and propagule pressure on biomass (mean ± SE, n = 6) of native plant communities. Means that share the same letter are not different at P < 0.05 within different frequencies of nitrogen addition.

Figure 4. Effects of the frequency of nitrogen addition and propagule pressure on biomass (mean ± SE, n = 6) of each functional group: legumes (A, D, G); grasses (B, E, H); forbs (C, F, I). Different capital letters indicate significant differences among propagule pressure, and lowercase letters indicate significant differences among the frequency of nitrogen addition.

Table 2. Summary of ANOVAs for the effects of nitrogen addition frequency (N) and propagule pressure (P) on the competitive effect (CE) and relative dominance index (RDI) of Solidago canadensis.

	N		P		N × P
	F5,30	P	F5,30	P	F5,30	P
CE	1.48	0.243	0.52	0.477	0.09	0.918
RDI ^a	2.22	0.126	14.46	0.001	0.03	0.973

^aindicates square root-transformed data. Significant values of F and P are shown in bold. ANOVA, analysis of variance.

Figure 5. Effects of the frequency of nitrogen addition and propagule pressure on the competitive (A) and relative dominance index (B) (mean ± SE) of Solidago canadensis. Different capital letters indicate significant differences among propagule pressure, and lowercase letters indicate significant differences among the frequency of nitrogen addition.

Data availability statement

The data that support the findings of this study are available from the corresponding author, Hong-Li Li, upon reasonable request.