Allelopathic Study Of Switchgrass (Ppanicum Virgatum L.)

Switchgrass (Panicum virgatum L.) is a perennial warm season high yield forage grass, which is originated from North American. It has a wide adaptability to barren soil, flood and drought conditions. Some cultivar is also very well adapted to acidic soil. In addition, switchgrass is recognized as the excellent bioenergy plant. And it is a best material for development of bioethanol. During the 40’s of last century foreign Countries had started to conducted research on morphology, ecophysiology, genetics as well as bioenergy.Professor Nobumasa Ichizen had conducted research on rehabilitation of the loess plateau from 1988. He had introduced 20000 plant species from all over the world. The results turns out that only switchgrass could be able to adopt to the loess plateau climate conditions. In the meanwhile it also has the ability for protect soil erosion. However, there is no research on different cultivars and different chromosome ploidy switchgrass adaptability and its competition as well as allelopathy effect on the local plant species in the loess plateau.Allelopathy is refers to chemical interaction among plants including microorganism by a donor plant release secondary compound into the environment, which have simulative or inhibitive effect on surrounding plants (receptor plant) growth and development. Allelopathic phenomenon is widely existed in agricultural and forestry systems.In this study the research on nine different chromosome ploidy and different ecotypes switchgrass with different grow stage’s allelopathic effect on the local plant species in the loess plateau were conducted by using bioassay and comprehensive analysis.Main contents and results were as follows: 1. Allelopathic differences among cultivarsThe allelopathic effect of different cultivars and different chromosome ploidy switchgrass on perennial ryegrass (Lolium multiflorum ) and alfalfa (Medicago sativa L.) were significantly different. Among 9 switchgrass cultivars the high ploidy cultivar performances high allelopathic affects than that of lower ploidy cultivar during the seedling stage to receptors plants. In addition, up land switchgrass cultivars showed a high allelopathic affect than that the lower land cultivars. Ploidy is the main factor to determine the affect, but ecotype also has effect on allelopathy.Cluster analysis for allelopathic potential of switchgrass could divided the nine cultivars into three groups: Dakota, Forestberg, Sunburst, Nebraska 28 and Pathfinder belongs strong allelopathic group. Black Well and Cave_in_Rock belong to middle allelopathic group and third group has weak allelopathic effect, which are Alamo and Kanlow.2. The changes of allelopathic effect during the growing seasonsThe different tissues of switchgrass extracts have different allelopathic effect on receptors plant growth and development. The same tissue in different growth period has different affects on receptors growth. With the growth of the switchgrass in different seasons, the distribution of allelopathic substances also changes. In case of perennial ryegrass the comprehensive allelopathic index were as follows: emergence>maturity>flowering. Switchgrass stem and leave extracts displayed a stronger allelopathic affect than that of the root during the seedling stage. However, during flowering and after maturity the root had shown a stronger allelopathic affect.3. Allelopathic affect change by drought stressSwitchgrass allelopathic affect were enhanced by drought stress. Four ploidy lower land cultivars Alamo and Kanlow expressed high allelopathic affect under the drought conditions in Guyuan whereas under sufficiently water supply they displayed weak allelopathic affect in Yangling. This indicatesd that secondary metabolites (allelochemicals) concentrations in the organization of switchgrass increased under drought stress.4. The allelopathic effect of different allelochemicalsDeferent allelochemicals have indicated different allelopathic affect on alfalfa and perennial ryegrass. For receiver plant perennial ryegrass, among isolated four groups of the chemicals, the allelopathic affects are as follows: alkaloids>phenolics>organic acids>neutral substances, whereas there was a little difference among organic matters in allelopathic affects on alfalfa. To any kind of organic matter, its allelopathic affect on perennial ryegrass was greater than on alfalfa, that is to say the performance of allelochemical in switchgrass on different receptor plants is different. Different receptor plant showed different sensitivity to same allelochemical, so we should choose more receptor plants to study plant allelopathy comprehensively and give more accurate evaluation.