Research On The Ecological Adaptation Of Introduced Switchgrass (Panicum Virgatum.L) In The Loess Plateau

In the study, ten cultivars of switchgrass (Panicum virgatum L.) (Alamo,Blackwell,Cave-in-Rock,Dakota,Forestberg,Illinois USA,Kanlow,Nebraska 28,Pathfinder and Sunburst) were selected as the test materials. The field test and laboratory analysis of cultivation methods were conducted, and the growth traits, survival rate and ecological characters were observed to indentify their ecological adaptation. Exceptionally, photosynthesis and morphology characteristics of several cultivars of switchgrass have been assessed the yield potential and adaptability in diverse environments on the Loess Plateau of China (Yangling, Dingbian of Shaanxi Province, and Guyuan of Ningxia).The survival rate was observed in the second spring and identified which were the optimal cultivars to undergo the cold stress successfully. The height and biomass yield had been measured in the later growth period, then dried and measured the dry mater. The fully open leaves were selected, while switchgrass was in bloom, to survey photosynthesis rate (Pn) and transpiration rate (Tr) at 9:00, 10:00, 12:00, 14:00, 16:00, 18:00 and 20:00 respectively, using a Licor LI-6400 instrument. The internal mechanism of the biomass accumulation and drought tolerance were analyzed through the indicators mentioned above. Silica particles, vacuole size and other traits in switchgrass tissues (stem, leaf and root), as well as trichomes (leaf) were observed by the Scanning Electron Microscope (SEM), which should provide the proofs of the further researches of switchgrass on the physiological ecology.The results indicated that Alamo and Kanlow were the best adapted switchgrass cultivar for biomass production in Yangling with aerial parts dry matter (DM) yields of 44.22 t/ha per year due to it easily established and well grown; the lowland cultivars Alamo and Kanlow had not survived, probably owning to their sensitivity to the cold stress in Guyuan and Dingbian. Illinois USA and Cave-in-Rock grown at Guyuan had aerial parts DM yield of 10.59 t/ha and 9.36 t/ha, respectively. Similarly, Cave-in-Rock in Dingbian performed better than others except the lowland cultivars (Alamo and Kanlow), which could not overcome cold stress at Guyuan and Dingbian. Moreover, Cave-in-Rock and Nebraska 28 has the highest photosynthesis rate which reflects its high productivity. At 14:00, was the time-point of most significant difference among different cultivars in the photosynthesis rate, which displayed the pattern of Cave-in-Rock > Blackwell > Sunburst > Forestberg > Pathfinder > Nebraska 28 > Dakota. Maximum transpiration peak appeared in Cave-in-Rock and Blackwell, while the minimum was observed in Nebraska 28 and Dakota. The rate exhibited the most significant difference at 14:00, following Cave-in-Rock > Blackwell > Sunburst > Forestberg > Pathfinder > Dakota > Nebraska 28. In addition, Nebraska 28 and Pathfinder had shown stronger drought tolerance due to their higher WUE. Dakota showed it's most weak adaptability in the Loess Plateau areas; its productivity was the lowest among the cultivars. Optimal mown management seems to enhance the growth and productivity of switchgrass, the aerial parts biomass yield of Illinois USA mown had increased 61.7% than the control (not mown), and there was no significant difference between the two treatments (mown and not mown) the cv. Sunburst, Forestberg and Pathfinder. Morphological characteristics were further studied using light-and scanning electron microscopy (SEM). Silica particles, vacuole size and other traits in switchgrass tissues (stem, leaf and root), as well as trichomes (leaf) were observed and showed that Cave-in-Rock and Pathfinder had larger stoma area, up to 824.4μm2 and 770.1μm2, respectively. Silica particle length was the longest in Pathfinder and shortest in Cave-in-Rock. There was a highest density of silica particles in cv. Forestberg, and lowest in Cave-in-Rock and Pathfinder. Silica particle in plant stems and leaves was associated with degree of tenacity; vacuole size and water capacity of the plant is an effective way to overcome drought stress; switchgrass leaf trichomes were visible clearly through SEM (especially in the leaves of Blackwell and Cave-in-Rock, and Dakota in Guyuan), the trichomes formed in the process of adapting the environment and had play an important role on transpiration process.The four varieties of switchgrass Pathfinder, Forestberg, Nebraska 28 and Dakota were investigated in the experiment. The results indicated that Nebraska 28 had the strongest allelopathy while Pathfinder shown the weakest allelopathy. The allelopathy of Pathfinder root was higher than that of aerial part which was different from others. The allelopathic effects of methanol extracts were higher than that of aqueous extract in diluted treatments. The radicle length of Lettuce was shown significant influence at high concentration while the coleoptile length was displayed a significant influence at lower concentration.The morphological characters seemed to be associated with their ploidy levels and the arid habitat from which they were selected. Therefore, if switchgrass is to be introduced and extended on the Loess Plateau of China, Lowland cultivars Alamo and Kanlow, intermediate cultivar Illinois USA,Cave-in-Rock would be the optimal choices in cultivating in Yangling, and Cave-in-Rock,Illinois USA maybe the good cultivars grown in Guyuan; Cave-in-Rock,Illinois USA,Forestberg and Pathfinder exhibited better than others, and the optimal choice seem to be them.