| Reducing the interference of human activities and promoting the natural succession of vegetation is one of the main measures for the ecological restoration of the Loess Plateau. Since 1999, when the state practices the system of returning farmland to forest(grass), the area has carried out many studies on vegetation succession, and achieved rich results from the plants, soil and so on. However, the available information about the effect of allelopathy on the natural vegetation community is scarce and the chemical ecological relationship between plants is not clear. Therefore, to explore the relationship between the vegetative community structure and allelopathic effects during natural succession, we investigated the effects of water and methanol extracts from the root, the aboveground part and the rhizosphere soil of A. capillaris and A. sacrorum, the dominant populations of different successional stages on the hilly-gully region of Loess Plateau, on the seed germination and seedling growth for themselves and accompanying species. We aimed to identify an explanation for the vegetative community structure during the natural succession from the view of chemical ecology and provide scientific basis for understanding the internal mechanism of vegetation recovery. The main results are as follows:1. Allelopathy of extracts from the dominant species during the vegetation successionThe allelopathy of extracts from the dominant populations of different successional stages on receptor plants was significant. The water extracts from A. capillaris, the dominant species of the early vegetation succession, promoted the growth of S. Beauv. and with the succession, the promotion gradually increased, while the aqueous extracts of rhizosphere soil inhibited the growth of A. sacrorum, compared with 5a, the inhibitory effect of extracts of 10 a and 15 a in succession decreased. High concentrations of the root and the aboveground caused strong inhibition of seed germination on itself, and this inhibition gradually increased with the succession. The water extracts from the rhizosphere soil of A. sacrorum promoted the growth of L. davurica, but with the succession, promotion gradually decreased and became inhibited. Additionally, with respect to the succession of 10 a, the inhibitory effect of extracts from the root and aboveground part of A. sacrorum of 10 a and 15 a on itself decreased.2. The difference between the concentration, parts and matrix of AllelopathyReceptor plants responded differently to the different extracts of concentration of A. capillaris and A. sacrorum. 0.002g/m L of water extract promoted or slightly inhibited seed germination of the receptor plants, while 0.1g/m L caused strong inhibition of seed germination, the growth of root and shoot had s similar phenomenon,Extracts of different parts of A. capillaris and A. sacrorum exerted different allelopathic effect on the plants. Compared to the rhizosphere soil extracts, extracts from the root had a stronger inhibition influence and the aboveground part was the strongest: each part of the water extracts promoted the seed germination and seedling growth of S. Beauv., but the aboveground part inhibited seed germination of the three other plants,especially at a concentration of 0.1g/m L, the response index of A. capillaris and A. sacrorum is-1.00, seeds can not germinate.Receptor plants responded differently to the different extracts. Compared with water extracts, methanol extracts from the roots of A. capillaris showed stronger inhibition on S. Beauv. and A. sacrorum, especially A. sacrorum, seeds can not germinate on methanol extracts. A. sacrorum had a similar phenomenon, in general, methanol extracts showed stronger inhibition than water extracts.3. Aellopathic effect of the dominant population extracts on main accompanying species and themselves.A. capillaris extracts had a significant allelopathic effect on L. davurica, S. Beauv. and A. sacrorum, overall promoted the seed germination of S. Beauv., while significantly inhibited L. davurica and A. sacrorum,especially A. sacrorum, the seeds could not germinate in methanol extract. A. sacrorum, the dominant species of middle and late succession, had a similar allelopathic effect on L. davurica, S. Beauv. and A. capillaris as A. capillaris. Additionally, a self-allelopathic effect was found in A. capillaris and A. sacrorum, resulting in inhibition of seed germination, especially when used at 0.1 g/m L of the aboveground part, their own seeds can not germinate, root and shoot growth were inhibited.In conclusion, in the process of plant community succession, the advantage of the dominant species of community not only displays in the quantity, biomass, coverage and resource competitiveness, but also a high concentration of the root and aboveground part extract can inhibit the growth of other plants, therefore, in the herbaceous community succession of the Hilly-gully Region of Loess Plateau, there have allelopathic interactions between plants, and this may be one of the reasons to promote the vegetation succession. |
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