Interaction Between Ageratina Adenophora Sprengel And Soil Microorganism In Invaded Habitat

The successful invasion of particular species is neither mechanistically uniform nor predictable. Positive feedback of soil biota may facilitate exotic plant invasion which attracts increasing attention recently. Ageratina adenophora Sprengel is a notorious worldwide invasive weed and one of the most unwanted in China. Ageratina adenophora Sprengel may alter underground microbial communities, and the feedback of modified soil biota in invaded ranges may promote its invasivibility. To examine this possible underground invasion mechanism, effects of Ageratina adenophora Sprengel invasion on soil microbial communities were analyzed, and plant-soil biota feedback experiments were designed to measure the effect of invasion-induced changes of soil biota on A. adenophora growth and competition. The main results are as follows:1. The effect of the invasion of the Ageratina adenophora Sprengel on soil process.The micro-habitat of the invaded-soil was changed greatly. The fungi and the actinomycetes are increased because of the invasion of the Ageratina adenophora Sprengel, but the bacterial decreased,. The DGGE result indicate that the bacterial decreased because of the invasion too. The content of absorbable NO3--N, NH4+-N, available P and K, organic matter in soil were increased sharply. The highest amount of NH4+-N in heavily invaded soil reached 53.00mg/kg, which was almost 14.1, 9.9 and 5.9 times each as high as bare soil, multi-native-plants soil and single-native-plant soil, respectively. The content of NO3--N in soil had a tendency to increasing with the intensification of invasion and was different significantly (P<0.001) among soils with various invasion degree. The amount of NO3--N in heavily invaded soil, with the content of 91.98mg/kg, was as nearly 7.3 times as that in bare soil.2. The difference of the soil functional bacterial, the activity of soil enzyme and the soil nutrient level between the rhizosphere and nonrhizosphere of the soil because of the invasion of the Ageratina adenophora Sprengel.It was found that the number of the soil functional bacteria, the activity of the soil enzyme(except for the phosphatase), the NH4+-N, the NO3--N and the soil available K in the rhizosphere soi1 was extreme higher than the nonrhizosphere soil, the phosphobacteria vary the most in the bacteria group , the R/S vary from 4 to 6; the sucrase vary the most in the soil enzyme, the R/S vary from 1 to 2,the NH4+-N vary the most in the heavily invaded area and the middling invaded area, the R/S are 1.32 and 1.41 respectively, the NO3--N vary the most in the newly invaded area and the native soil with native plants, the R/S are 1.4 and 1.3 respectively. In the heavily invaded area, The number of the soil functional bacteria, the activity of the soil enzyme and the soil nutrient level (except for the soil N and the soil K ) are higher than the other area. In the nonrhizosphere soi1, the available P vary the most, its content is 0.8 times more than the content in the newly invaded area, is 2.12 times more than the content in the native plants area, is 7.1 times more than the content in the bare soil area; in the rhizosphere soi1, the phosphobacteria vary the most, its number in severe area is 2.0 times more than the number in the mildly invaded area, is 0.8 times more than the number in the native plants area, is 21.2 times more than the number in the bare soil.At the same time, after analysing the correlations coefficient among soil microbe groups, soil enzyme and soil nutrient we found that there were significant positive correlations between soil enzymatic activities and soil nutrient level (except that the soil N and soil K) . also there were significant positive correlations between soil functional bacterial and soil nutrient level (except that the soil N and soil K) . In the nonrhizosphere soil, the correlations coefficient between the sucrase and the available P is the most significant one, in the rhizosphere soil, the correlations coefficient between the nitrogen-fixing bacterial and the soil N is the most significant one. The effects of invasive plants on the soil is an important part of the invasive mechanism, the invasive of the Ageratina adenophora increase the number of the soil functional bacterial and the activity of the soil enzyme, which made the soil nutrient level changed at the same time, these changes may raise its competent ability compared to the native plants. This study provided a basal theory for further exploring the microorganism mechanism of its invasion.PSB may an important role in the invasion of Ageratina adenophora Sprengel compared to the other functional bacterial.3. Feedback of invasion-induced changes of soil biota to A. adenophora and native plants.Plant-soil biota feedback experiments tested that: 1)The soil microorganism play an important role in the growth of plant, no matter Ageratina adenophora Sprengel or native plant, the plant grown much better in nonsterilized soil than sterilized soil (p<0.0001). The Ageratina adenophora Sprengel vary the most between nonsterilized soil and sterilized soil, the biomass of the Ageratina adenophora Sprengel in nonsterilized soil was 8 to 9.times than in sterilized soil.2) The change of the soil induced by Ageratina adenophora Sprengel is benefie to the growth of Ageratina adenophora Sprengel, the native soil is benefit to the growth fo the native plants. 3) In the nonsterilized soil, the Ageratina adenophora Sprengel grow much better in invaded soil than the plant in the native or bare soil(p<0.0001),the Avena fatua L grow much better in the native soil than in the invaded soil, at the same time, the Avena fatua L grow much better than in competitent with Ageratina adenophora Sprengel(p<0.0001). The Galinsoga parviflora Cav grow better in inbaded soil. 4) In sterilized soil, the Ageratina adenophora Sprengel in competent with native plant in middling and newly invaded soil grow better than the biomass of single plant, there is no obvious variance between single plant and grown in competent with Ageratina adenophora Sprengel(p>0.05), at the same time, the biomass of single Galinsoga parviflora Cav was higher than thr biomass in competent with Ageratina adenophora Sprengel except in the native soil. 4. SummaryAgeratina adenophora Sprengel is more positively affected by the soil biota in invaded sites than resident natives, and earns its competition superiority directly or indirectly through the beneficial soil biota and antagonistic rhizosphere microbes. Once it establishes in new ranges it further alters the soil community in a way that favors itself and inhibits natives helping promote invasion. Soil biota alteration following A. adenophora establishment may be an important part of its invasion process, which is used as an underground self-reinforcing invasion mechanism to strengthen its invasiveness.