Allelopathic Effects Of Invasive Plant Solidago Canadensis L. On Soil-borne Pathogens

Allelopathy is a common phenomenon in nature, and is an important ecological mechanism for plants. It is an part of the evolution of plant defense, but also a chemical means for some plants to improve their competitive ability. Strong allelopathy often accompanied by the invasion progress of exotic plants. Canada goldenrod (Solidago canadensis L.) is a typical invasive plant in southeastern coastal areas of China. Currently a large number of studies have shown that Solidago canadensis could'enhance the competitive advantage by allelopathy. However, at present there is no study about allelopathy of invasive S. canadensis on soil-borne pathogens. In this paper, I design Petri dish experiment, in situ simulation experiments and field studies to study the effects of different concentrations of root extracts of S. canadensis, also the effects of allelochemicals secreted into the soil on the Pythium ultimum and Rhizoctonia solani. At last, I studied whether the accumulation of allelochemicals in the soil affected by soil microbes. Main results obtained from these experiments are as follows:1 Effects on growth of colonies of two species of Soil-borne pathogensRhizome and root extracts of S. canadensis at different concentrations could inhibit the colony growth on agar medium. The higher concentrations of the extracts, the stronger the inhibitory effects.2 Effects on damping-off rates of seedlingsBoth two species of pathogens could cause diseases on M. sativa and tomato seedlings. Extracts or roots exudates of S. canadensis can inhibit activity of these pathogens. The inhibitory effects increase with the increasing of allelochemicals concentrations. Roots exudates of K. striata has no effects on pathogenic activity. Rhizospheric soil of S. canadensis could decrease damping-off rates of tomato seedlings contast to rhizosphere soil of K. striata. 3 Effects on mortality rates of seedlingsBoth extracts and soil-borne pathogens could increase the mortality rate of tomato seedlings. The mortality caused by allelopathy increases with the concentration of extracts. Contrast to only-pathogens treatment, the rhizome and root extract of S. canadensis at different concentrations could decrease the mortality rates of tomato seedlings, that is it could inhibit activity of soil-borne pathogens. The inhibitory effects increase with the higher concentrations of rhizome and root extract. The allelochemicals of S. canadensis secreted into sands can also inhibit the activity of soil-borne pathogens. They can decrease the mortality rate of tomato seedlings. But the roots exudates of Kummerowia striata have no allelopathic effects on these two species of soil-bome pathogens. Concentrations of three kinds of allelochemicals (total saponins, total flavonoids and total polyphenols) in sands culture become higher with increasing of the density of S. canadensis. When the sands inoculated with soil-borne pathogens, the mortality rate of native plant Medicago sativa L. decreases, because of the increasing concentrations of allelochemicals. Rhizosphere soil of S. canadensis has allelopathic effects, but rhizosphere soil of K. striata has no allelopathic effects on tomato seedlings.4 Effects of soil microbes on accumulation of allelochemicalsIn field experiment, during the invasion progress of S. canadensis, concentrations of allelochemicals in soil increase, and the allelochemicals can inhibit the activity of Pythium ultimum. The accumulation of allelochemicals are affected by soil microbes. The allelochemicals degrade slowly in sterilized soil, but degrade quickly in unsterileized soil. After 8 days of addition extracts of S. canadensis into soil that never planting this invasive species, total saponin retained only about 55%, total flavonoid retained only about 26%, total polyphenols retained only about 17%.