Biotechnical Faculty, Agronomy Department, Jamnikarjeva 101, 1000 Ljubljana, Slovenia
SUMMARY
In the past few years the introduction of white clover into the indigenous grass swards of karst pasture was of very low success. Reasons for this included unsuitable weather conditions, insufficient level of phosphorus and pH value of the soil and the competition of indigenous plants for light, space and nutrients. Therefore, allelopathic effects of some most frequent indigenous herbs on germination and growth of white clover was investigated. Different concentrations (100, 50, 25, 6.25 and 1.56 percent) of cold water extracts from the aerial tissues of Satureja montana (S), Inula hirta (I) and Filipendula vulgaris (F) were tested on potential allelopathic effects on white clover. The germination of white clover was inhibited by the 100, 50 and 25 percent concentrate for all three herbs and by the 6.25 percent concentrate of F extract. Radicle elongation was affected by all concentrate of F, I and S extracts except with 1.56 percent extract of F. Root elongation of young white clover seedlings was inhibited by the 50 percent extracts of F and I. In the experiment it was shown that radicle growth of white clover was more sensitive to the water extracts of F, I and S than was germination. It was strongly inhibited even with low concentrate while germination was mainly affected with higher concentrate of extracts. For final judgement about the role of allelopathy in white clover introduction into the grass sward, some field experiments should still be performed.
Keywords: allelopathy, germination, herbs, root growth, Trifolium repens
INTRODUCTION
The grass sward of the experimental pasture established in 1994 was very diverse. It mainly belonged to the dry grasslands (order Scorzoneretalia villosae H-ic 75, association Carici-Centauretum rupestris) of Slovenian karst (Kaligaric, 1994). As there was low efficiency of introduction of white clover into the sward and because one of the most distinctive features of Mediterranean plant communities is their abundance of aromatic plants (Tarayre et al., 1995), the potential role of allelopathic influences of several indigenous herbs on germination and growth of young clover plants was investigated. The role of allelopathy within grass swards has been reviewed by several authors (Smith, 1990; Smith, 1991; Leigh, 1995; Stephenson, 1988). The aim of this work was to identify the ecological significance of allelopathy in white clover introduction into the indigenous swards of karst pastures.
MATERIALS AND METHODS
Plant material was collected in the middle of July. Above ground tissues of Satureja montana (S), Inula hirta (I) and Filipendula vulgaris (F) were cut into 0.5 to 1 cm segments and 200 g of each herb was soaked in 500 ml of de-ionized water for 40 hours (100 percent dilution). The plant material was then filtered from the leachates. The dilutions of 100, 50, 25, 6.25 and 1.56 percent of plant extracts were then bio-assayed on filter paper in glass petri dishes (90 x 15 mm). White clover seeds (milka) were placed on filter paper treated with 5 ml of dilution. Seeds were incubated in the dark in a growth chamber at 21°C for 60 hours and then additionally for 60 hours under 12 hour day period, (21°C and 750 lx) and 12 hour night period (18°C). Due to the concern of oxygen depletion by seed respiration, petri dishes were opened to ambient air for approximately five seconds every 24 hours. Seed germination and root length were determined after the incubation. Seeds were considered to be germinated if the radicle protruded at least 1 mm.
For testing influences of 50 percent concentrate of F and I on root and hypocotyl growth, white clover seeds were sown under the same conditions as the control treatment. After five days seedlings were treated with 5 ml of dilutions and left for another five days. Afterwards root and hypocotyl lengths were measured.
RESULTS
The extracts from all three herbs caused abnormal and retarded germination, radicle and root growth of a high percentage of the white clover seeds. Germination of white clover seeds was less sensitive to water extracts of F, I and S than radicle elongation and root growth. The effects of F and I extracts were less severe than effects of S extracts at the same concentration although even they reduced germination by 70-80 percent at 50 percent dilution. Influences of F and I water extracts were more or less proportional to their concentrations while the effect of S was much decreased between 25 and 6.25 percent dilutions. It is interesting that although the 100 and 50 percent dilutions of S completely stopped the germination of white clover, its lower concentrations had similar effects as F and I extracts.
Radicle elongation was significantly reduced even with the lowest concentrations of all three herbs. On average, radicles of the control seedlings after five days were more than 1 mm longer than radicles treated with 1.56 percent dilution of F, more than 2 mm longer than radicles treated with 1.56 percent dilution of I and even more than 3 mm longer than radicles treated with 1.56 percent dilution of S. The effects of higher concentrations were much more detrimental so the measurements of radicle length were not relevant.
Table 1. Germination of white clover as affected by different dilutions of water extracts of Satureja montana, Inula hirta and Filipendula vulgaris.
|
|
Percent germination |
||
|
Concentrations (%) |
F. vulgaris |
S. montana |
I. hirta |
|
100 |
1 |
0 |
21 |
|
50 |
17 |
0 |
27 |
|
25 |
46 |
13 |
71 |
|
6.25 |
62 |
82 |
84 |
|
1.56 |
83 |
85 |
91 |
|
Control |
90 |
90 |
90 |
* Least significant range. Any two means in the columns not marked with the same letter are significantly different at P<0.05 level.
In the second experiment, five days old white clover seedlings were treated with the 50 percent dilutions of Filipendula and Inula. The root length was depressed in five days for approximately 25 percent of the control treatment and the depression was the same for both herbs. It was interesting that hypocotyl growth was not affected; probably because of the very short period of the experiment.
DISCUSSION
The results confirm the statement of Chung and Miller (1995) and Hoveland (1964) that radicle elongation and root growth are more sensitive than either germination or hypocotyl growth. The allelopathy has been found to be of greater importance when vegetation residues are on the soil surface (Smith, 1990; Halsall, 1995; Leigh, 1995). Also, the allelopathic effects are several times higher when the plant material is allowed to decompose on its own than when it is mixed with the soil (Kaczmarek, 1992). The studies of Halsall (1995) and Leigh (1995) suggested that heavy grazing to reduce dry herbage and/or litter is important for maximum clover germination and growth.
One of the most characteristic features of karst grasslands and pastures in Slovenia is a high proportion of dead plant material within the sward which often exceeds 40 percent (Kotnik, 1993). Therefore, the easiest and probably the most efficient tool for improving white clover introduction could be increased levels of land exploration. From the latest observations of our experimental pasture we can conclude that, although it is still very low, the efficiency of white clover establishment within the indigenous sward is slowly increasing. This could be due to lower proportions of dead plant material in the sward. Therefore, we can suggest that introduction of legumes, although they are of great importance for quality of karst sward, should not be the first step in improvement of karst pastures.
REFERENCES
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Hoveland, C.S. 1964. Germination and seedling vigor of clovers as affected by grass root extracts. Crop Science, 211-213.
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