Allelopathic suppression by Conyza canadensis depends on the interaction between latitude and the degree of the plant’s invasion
作者：王從彥
https://doi.org/0102-33062017abb0045
ABSTRACT
Allelopathic suppression of the growth of co-occurring plant species in invaded ecosystems is an important factor in some plant invasion. This study uses leaf extracts of the invasive plant species Conyza canadensis to determine its allelopathic effects along a latitudinal gradient, and under different cover classes and degrees of invasion, on seed germination and growth of Lactuca sativa, a sensitive bioindicator of allelochemicals. The allelopathic effects of C. canadensis on seedling height, root length, seedling biomass, germination percentage, germination potential, germination index, germination rate index, and vigor index of L. sativa increased significantly with increasing latitude. A possible explanation is that the leaves of plants growing in high latitudes secrete a higher concentration of allelochemicals than do leaves of plants growing in low latitudes. The allelopathic effects of C. canadensis on seedling height, seedling biomass, germination potential, germination index, germination rate index, and vigor index of L. sativa decreased with increasing degree of invasion. The more intense allelopathic effects of C. canadensis at lower degrees of invasion may enable it to establish populations in ecosystems by inhibiting the seed germination and growth of co-occurring species.
Table 1. Differences in the indices of L. sativa under the addition of C. canadensis leaf exacts with different latitudinal gradients. Data with different letters in a vertical row indicate a significant difference (P < 0.05). Abbreviations: H, seedling height (cm); RL, root length (cm); BM, seedling biomass (g); GPe, germination percentage (%); GPo, germination potential (%); GI, germination index; GRI, germination rate index; VI, vigor index.
H
RL
BM
GPe
GPo
GI
GRI
VI
Control
2.14±0.11b
3.10±0.49a
0.20±0.01a
90.00±2.79a
76.00±1.63a
52.58±1.40a
47.29±1.77a
10.71±0.58a
Low latitude
3.09±0.07a
1.97±0.08b
0.22±0.01a
86.67±1.22ab
76.67±2.16a
44.49±1.83ab
38.71±1.94ab
9.70±0.55ab
Middle latitude
2.64±0.04a
1.47±0.04c
0.20±0.00a
80.00±1.53bc
74.22±1.47a
39.41±0.77c
31.60±1.06b
7.84±0.28b
High latitude
2.08±0.25b
0.99±0.14d
0.13±0.02b
75.13±4.11c
34.36±8.75b
23.96±4.44d
19.80±4.31c
3.93±1.04c
Table 2. Differences in the indices of L. sativa under the addition of C. canadensis leaf exacts with different invasion degrees. Data with different letters in a vertical row indicate a significant difference (P < 0.05). 「ns」 means no significant difference (P > 0.05). Abbreviations: H, seedling height (cm); RL, root length (cm); BM, seedling biomass (g); GPe, germination percentage (%); GPo, germination potential (%); GI, germination index; GRI, germination rate index; VI, vigor index.
H
RL
BM
GPe
GPo
GI
GRI
VI
Control
2.14±0.11ns
3.10±0.49a
0.20±0.01ns
90.00±2.79ns
76.00±1.63ns
52.58±1.40a
47.29±1.77a
10.71±0.58a
Low degree
2.47±0.24ns
1.35±0.17b
0.17±0.02ns
78.22±3.33ns
55.78±9.03ns
33.49±4.32b
27.86±3.97b
6.65±1.11b
Moderate degree
2.52±0.16ns
1.71±0.15b
0.18±0.01ns
79.49±2.77ns
60.77±7.39ns
36.73±3.92b
30.11±3.79b
7.26±1.06ab
High degree
2.88±0.06ns
1.47±0.06b
0.20±0.01ns
84.67±1.55ns
72.22±2.15ns
39.34±1.47b
33.52±1.77b
8.00±0.44ab
Table 3. Two-way ANOVA on the effects of latitude gradient and invasion stage on the indices of L. sativa. P values equal to or lower than 0.05 are in bold face print. Abbreviations: H, seedling height (cm); RL, root length (cm); BM, seedling biomass (g); GPe, germination percentage (%); GPo, germination potential (%); GI, germination index; GRI, germination rate index; VI, vigor index
PH
RL
BM
GPe
GPo
GI
GRI
VI
Latitude gradient
F
26.97
38.13
33.04
6.06
96.82
51.46
29.38
44.08
P
<0.0001
<0.0001
<0.0001
0.0014
<0.0001
<0.0001
<0.0001
<0.0001
Invasion stage
F
4.09
1.52
4.05
1.60
12.84
1.29
1.17
0.89
P
0.0232
0.2298
0.0240
0.2121
<0.0001
0.2845
0.3196
0.4163
Latitude gradient * Invasion stage
F
12.81
7.28
9.26
2.90
30.34
24.52
15.28
16.15
P
<0.0001
<0.0001
<0.0001
0.0174
<0.0001
<0.0001
<0.0001
<0.0001
Figure 1. The geographic location of the three sampling sites. The triangles represent the geographic location of the three sampling sites.
Figure 2. The indices of L. sativa under the addition of C. canadensis leaf exacts with different invasion degrees (L, low; M, moderate; H, high) along a latitudinal gradient (SY, Shenyang; JN, Jinan; ZJ, Zhenjiang). Bars with different capital letters indicate a significant difference between the three sampling sites at the same invasion degree and bars with different lowercase letters indicate a significant difference between the three invasion degrees in the same sampling site (P < 0.05). Note: white bar, low invasion degree; grey bar, medium invasion degree; black bar, high invasion degree.