星星草(Puccinellia tenuiflora)人工草地氮素积累对松嫩盐碱草地植被演替的影响

通过对星星草(Puccinellia tenuiflora)生长不同年数盐碱土壤氮素营养状况的比较,研究氮素积累作用的机理,并探讨其在植被演替中的可能作用.结果表明:在一维生态位空间(土壤氮含量)星星草和羊草(Leymus chinense)之间具有较小的生态位分离值和较大的生态位重叠值,表明羊草对土壤高含氮量具有较强的竞争能力.这些也许是羊草以及其他植物在星星草生长一定年数后能够侵入碱斑土壤的机制.星星草作为盐碱土壤改良和植被恢复的先锋植物,它的生长增强了盐碱草地土壤氮素的矿质化作用和生物固氮强度,并减弱了氮素随地表径流的损失.最终促进了盐碱草地的氮素沉积,达到了适合于其它物种(如羊草)生长的水平,从而使碱斑植被得以恢复.

Effect of nitrogen accumulation in Puccinellia tenuiflora grassland on the succession of vegetation in Songnen alkaline grassland

With the exploitation and utilization of land resources, especially the non-sustainable utilization like overgrazing, the extent of alkalization of Song-Nen grassland has been enlarged and the vegetation has been degraded seriously. The area of preponderant grass Leymus chinense (L. chinense) also reduced, the height of grass and the extent of closed canopy of grassland decreased, and the alkali spot with very little grass occurred in the grassland. Puccinellia tenuiflora (P. tenuiflora) could grow in alkalized soil after artificial planting, and ameliorate the alkalized soil. Then L. chinense and other plants intruded into the alkalized spot where P. tenuiflora had been grown for certain years, making the plant population no longer the singularity population of P. tenuiflora. The mechanism about the vegetation of L. chinense succeeding in recovery was not only due to the improvement of physical or chemical property of the soil, but also due to the anthropogenic nitrogen deposition, which could cause vegetation-type conversion. But the mechanisms of vegetation succession were not very clear. As to the cause of vegetation succession, there were many hypotheses, such as frequent fire and grazing, but nitrogen deposition had only recently been considered.
There were two aims of this study on the growth of P. tenuiflora. The first was to reveal that how the P. tenuiflora could meliorate the salt-alkali soil, the second was to quantify the changes of niche after the vegetation succession from P. tenuiflora to other kinds of plants. Niches of various plants in Song-Nen alkaline grassland were calculated. Comparing with the controlled alkali spot soil, all the evidences from the experiment indicated that P. tenuiflora improved the nitrogen nutrition status of salt-alkali soil. There were smaller value of niche separation and bigger value of niche overlap between P. tenuiflora and L. chinense in one dimension niche space (N content of soil) than those among other species, which indicated that L. chinense had stronger competition ability on soil with high nitrogen content. These appear to be the mechanism of L. chinense and other plants intruding into the alkalized spot in which P. tenuiflora has grown for certain years. As the pioneer plant of meliorating alkalized soil and vegetation restoration, the growth of P. tenuiflora could improve the nitrogen mineralization and nitrogen fixation in salt-alkali grassland, and decrease the nitrogen loss with water run-off. Finally, the nitrogen deposition in salt-alkali grassland was improved to the level that other plants (such as L. chinense) could grow normally, and the vegetation in alkali spot was restored.