Study On Niches Of Oil Flax Field Weed Community In Lanzhou Area And The Allelopathic Effect Of Dominant Weeds

Oil flax (Linum usitatissimum L.) is one of an important economic and oil crops in arid or alpine region of northwest and north China. Average planting area per year is about 133,000 hm~2 and total output is about 150,000 tons in Gansu Privince, which accounting for more than 30% of the sown area and more than 40% of the total output of the whole country, respectively. Oil flax production in Gansu Privince plays an important role in our country.There are many associated weed species in oil oil flax field, the weed's community density is large, and they had a long period of coexistence with oil flax. So weeds in oil flax field are quite serious, it is one of the major factors resulting in the decline of crop yield and quality. However, the research of weed species, community growth of dynamics and niches in oil flax field in Lanzhou area has been few reported. And the allelopathic effect of associated weeds to oil flax had not been reported at home and abroad. Therefore, this paper using niche theory, study the community growth of dynamics and niches in oil flax field in Lanzhou area, in order to reveal the weed community structure and the relationship between species, and the competition between dominant weeds and oil flax; and study the allelopathic effect of different concentrations of dominant weeds to oil flax, determine the main parts and the main features; then using the biggest relative abundance dominant weed's the main parts which release of allelochemicals, study it's stem and leaf volatiles, shoot litter and decomposing on oil flax allelopathic effect, and the allelopathic mechanism of the aqueous extracts of stem and leaf to oil flax. The main results obtained are as follows:1. There are 23 weed species, belonging to 11 families in the oil flax field weed community in Lanzhou area. Among them, the most important are Gramineae, Compositae, Chenopodiaceae, Amaranthaceae and Convolvulaceae. Weed community growth of dynamics change is: weeds beginning to happen in the middle of April, in mid-may and mid-June are two out of grass rush. From the objects of Herbicides, broad-leaved weeds and (or) annual weeds is the focus of prevention and treatment.2. The dominant weed species in oil flax field were: Kochia scoparia, Setaria viridis, Chenopodium album, Sonchus brachyotus, Echinochloa crusgalli and Calystegia hederacea. From the niche breadth, Kochia scoparia, Chenopodium album, Sonchus brachyotus, Echinochloa crusgalli, Setaria viridis, Calystegia hederacea and oil flax has descending order of time niche breadth; Kochia scoparia, Chenopodium album, Setaria viridis, Echinochloa crusgalli, Sonchus brachyotus, Calystegia hederacea and oil flax had descending order of horizontal niche breadth; Kochia scoparia, Setaria viridis, Echinochloa crusgalli, Chenopodium album,Calystegia hederace, Sonchus brachyotus had descending order of vertical niche breadth; integrated niche breadth descending order is Kochia scoparia, Setaria viridis and Chenopodium album, these three kinds of weeds occupy a dominant position in the community, and has long period of coexistence with oil flax, and do greater harm to oil flax. From the niche overlap, Kochia scoparia, and Setaria viridi had the largest time niche overlap, Kochia scoparia, and Sonchus brachyotus had the maximum horizontal niche overlap; Sonchus brachyotus and Chenopodium album had the maximum vertical niche overlap. All of these showed that the above weeds had the similarity using of resources with each other.3. The aqueous extracts of root, stem and leaf and their whole plant of 2 dominant weeds - Kochia scoparia and Chenopodium album had different degree's inhibition (promoting) on oil flax seed germination energy, germination rate, germination index, vigor index and seedling root length, shoot height, Root fresh weight and shoot fresh weight. However, the inhibition rate increased with the increasing concentration of aqueous extracts of stem and leaf and whole plant. Using the same concentrations of aqueous extracts of 3 weeds, except for 0.100g/mL stem and leaf and their whole plant of aqueous extracts having 100% inhibition rate to the synthesis effect, the other different concentrations had the largest synthesis effect of stems and leaves, then whole plant, and followed by the root. 2 kinds of weed aqueous extract inhibited the seed germination of oil flax were mainly because they inhibited the vigor index of seed; and they inhibited the growth of oil flax seedlings were mainly because they inhibited root growth.4. Different concentrations of Kochia scoparia aqueous extracts of stem and leaf, stem and leaf volatiles, shoot litter and decomposing, had different degrees of inhibition (or promotion) effect, this showed that the Kochia scoparia can affect oil flax growth through the release of allelochemicals by the leaching, volatilization, litter, and residues rot.5. At the different concentration of the stress of Kochia scoparia's stem and leaf aqueous extract, SOD and POD activity of oil flax were increased firstly, then decreased with the stress time prolong, and MDA content in oil flax was steadily increased; At the same time period, the promotion (or inhibition) rate of SOD and POD activity was increased with the increasing of concentration, MDA content increased. These showed that the allelochemicals that releasing from the Kochia scoparia's stem and leaf aqueous extract had importance to the activity of protective enzyme and the Membrane Liquid Peroxidation.