| Ageratina adenophora (Sprengel) is a worldwide noxious weed and has caused tremendous detrimental effects on agriculture, forestry, rangeland and natural ecosystem since it invaded in Southwesten China in last century. It is replacing native species and leading to alteration of ecosystem structure and function and causing enormous economic losses. Management actions that control the spread and impacts of the weed become very stringent, and controlling the weed by other competitive and economic grasses or by restoring native species biodiversity was thought to be most hopeful ways. In this study, the morphological characteristics, resource use physiological strategies, competition effect and competition response of A. adenophora and non-invasives were studied comparatively and the resistance of different plant functional type communities on A. adenophora invasion were explored. The main contents and results were as follows:1. Three comparative competition experiments between A. adenophora and non-invasives (i.e. Setaria viridis, Digitaria sanguinalis, and Galinsoga parviflora) with a replacement series design were studied in greenhouses at seedling stage with N supply or without N supply. The results showed that the plant shoot height, tiller number and biomass of A. adenophora were significant lower than those of non-invasives and there was no consistent relations in leaf number between A. adenophora and non-invasives. Comparad to in no N supply treatment, the plant shoot height, tiller and biomass of two species increased significantly in N supply treatments, and the non-invasives showed greater increasing response to N supply than A. adenophora. With the relative density decreasing, the plant shoot height, tiller and leaf numbers and biomass of A. adenophora decreased significantly or had a trend of decreasing, but those of non-invasives showed significant increasing or no obvious changes. Those indicated that the competitive ability of A. adenophora was less than that of non-invasives at seedling stage. N supply had greater effect on facilitating growth and competition of non-invasives seedling compared to A. adenophora, and the negative effects of non-invasive on growth of A. adenophora were heavier with the decreasing of A. adenophora density.2. The effects of N and P supply on root biomass, total biomass, relative growth rate (RGR), net assimilation rate (NAR), relative biomass ratio (RBR), photosynthetic nitrogen-use efficiency (PNUE), photosynthetic phosphorus-use efficiency (PPUE) and photosynthetic water-use efficiency (PWUE) of A. adenophora and S. sphacelata were studied in the greenhouse using a pair comparative design. The results showed that the root biomass and total biomass of S. sphacelata were higher than those of A. adenophora, RBR of S. sphacelata increased significantly when nutrient provided and this become more obvious with the increasing of N supply. The PNUE, PPUE and PWUE of A. adenophora were higher than those of 5. sphacelata when no nutrient supplied, but nutrient supply increased the PNUE, PPUE, PWUE, RGR and NAR of S. sphacelata significantly, and those of A. adenophora decreased or no obvious changes were observed. N supply had greater effect on these changes than P supply. Those indicated that the relative competitive ability of S. sphacelata was greater than that of A. adenophora, N supply had greater effect on improving the relative competitive ability of S.sphacelata compared to the effect of P supply.3. The monoculture and mixture communities of A. adenophora and S. sphacelata were established for 2 yr on three experimental densities in the field, the above- and blow-ground biomass of the two species were measured, and the growth response and relative competitive ability were evaluated. The results showed that the total biomass, relative yield and competitive balance index of 5. sphacelata were significant higher than those of A. adenophora, the relative yield total was significant lower than 1. The relationships mentioned above become more obvious with the increasing of density. The total biomass of A. adenophora at the densities of 20, 45 and 175 plants.m-2 in mixture decreased by 33.0%,38.5% and 70.1% compared to those in monoculture, respectively. However, the total biomass of S. sphacelata at the same density between monoculture and mixture showed no significant difference. The ratios of root mass vs shoot mass of S. sphacelata in mixture were significant lower than those in monoculture. However, the ratios of root mass vs shoot mass of A. adenophora in the mixture were significant higher than those in monoculture. Those indicated that the relative competitive ability of S. sphacelata was higher than that of A. adenophora, which decreased the growth of A. adenophora mainly by aboveground competition. It will be a good strategy for replacement control of A. adenophora by using S. sphacelata as a competitor at higher density condition.4. The contents of nutrients (N, P and K) in plant, plant nutrient use efficiency and its two components (nutrient productivity and means residence time) of A. adenophora and S. sphacelata were studied in the monoculture and mixture communities of A. adenophora and S. sphacelata in the field. The results showed as follows: (1) The N and K contents in plant of S. sphacelata were higher than those of A. adenophora, but the plant P content of S. sphacelata was lower than that of A. adenophora. With the increasing of density, the N and K contents in plants of two species decreased sharply, but the P content in plant of them increased greatly. (2) The plant N nutrient use efficiency of S. sphacelata was significant higher than that of A. adenophora, but the plant P and K nutrient use efficiencies of S. sphacelata were significant lower than those of A. adenophora. The plant N, P and K nutrient use efficiency of S. sphacelata increased significantly with the density increasing, but those of A. adenophora decreased significantly. Compared to in the monoculture, the plant nutrient use efficiency of S. sphacelata decreased significantly in the mixture, similar with that of A. adenophora at the densitiy of 175 plant·m-2 in the mixture, but contrary to that of A. adenophor at densities of 20 and 45 plant.m-2 in the mixture. (3) There were significant different nutrient use strategies for A. adenophora and S. sphacelata, and there appeared to be a trade-off between nutrient productivity and means residence time, since both components of nutrient use efficiency could not be maximised together.5. Four kinds of soil enzymatic activities and soil available nutrients in communities of A. adenophora monoculture (A), S. sphacelata monoculture (S) and two species mixture (A+S) at the rhizosphere zones were studied at different development stages, and the correlations of soil enzymatic activities and soil nutrients were analyzed. The results showed as follows: (1) The rhizosphere soil NH4+-N and soil NO3--N contents in S. sphacelata monoculture community were higher significantly than these in community A, but there weren't different compared to these in communities A+S. The contents of soil available P or available K in community A were highest followed in community S, and these in community A+S were least. (2) The soil protease and soil urease activities in three kinds of plant communities decreased as protease: S＞A+S＞A, urease: A+S＞S＞A. And the soil phosphate and invertase activities increased as phosphate: A+S＜S＜A, invertase: S＜A＜A+S. (3) There were consistent relationships between soil enzymatic activities and soil available nutrients contents in the three kinds of plant communities. Our results indicated that S. sphacelata has higher net ammonification and nitrification rates compared to those of A. adenophora and could decrease the available P and available K in mixture communities of A. adenophora and S. sphacelata, which may be potential reasons for S. sphacelata out-competed A. adenophora. The soil enzymatic activities should play an important action on the changes of the soil available nutrients at the rhizosphere zones.6. The effects of different plant functional type communities on seed germination livability and seedling growth of A. adenophora were studied. The results showed that the seed germination livability of A. adenophora in the community of Setaria faberii was lower than those in the communities of Galinsoga parviflora and Artemisia lavandulaefolia, and the seed germination liabilities of A. adenophora in mixture community of S. faberii and G. parviflora was lower than those in their monoculture communities, respectively. However, the seed germination liabilities of A. adenophora were zero in the community of Setaria sphacelata and in mixture community of S. sphacelata and G parviflor. The productivity of A. adenophora was the lowest in mixture communities of A. adenophora with S. sphacelata and A. lavandulaefolia, but it was the highest in the community of S. faberii. The productivity in mixture communities of two kinds of plant functional types was higher than that in one plant functional type community, but it was lower than that in the other plant functional types community. Compared to one plant functional type community, the relative yield and relative yield total of mixture community of A. adenophora and two plant functional types had a trend of decreasing, indicating that different plant functional types had different resistance ability to the invasion of A. adenophora. The communities with various plant functional types had greater resistance ability to A. adenophora invasion. Restoring and protecting the native plant biodiversity will play an important role for control and prevention of further invasion of A. adenophora.
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