氮素添加和功能群去除对糙隐子草和大针茅根系特征的影响

由于草地不合理利用,中国北方草原严重退化,导致生态系统结构性破坏甚至功能性紊乱。随着草原退化,中能值功能群植物糙隐子草会取代高能值功能群植物大针茅成为群落中优势度最大的植物。为了解大针茅和糙隐子草在氮素添加以及去除功能群的情况下根系特征的变化趋势,选取锡林郭勒盟典型草原中的退化草原群落,分别开展两项实验,实验1:氮素添加梯度实验(0、10.5、17.5、28 gN/m~2),实验2:同时进行功能群的去除和氮素的添加,功能群去除实验(将植物分为高能值植物功能群、中能值植物功能群、低能值植物功能群3个功能群;每个处理分别剪除另外两个功能群,留取单一功能群),并同时进行氮素添加实验(0、17.5 gN/m~2)。在进行两年的实验处理后,通过Delta-T SCAN根系分析仪测量大针茅和糙隐子草根系的长度、直径、面积、体积指标。分析植物根系对氮素添加的响应,以及功能群去除是否改变这两种植物对氮素添加的响应格局。实验1研究结果表明:在受到其他功能群的竞争压力下,大针茅根系长度、面积、体积均在高氮素添加(28 gN/m~2)情况下显著增加,糙隐子草根系直径和体积在中氮素添加(17.5 gN/m~2)的情况下显著高于其他3个处理,退化样地中土壤氮素的增加,促使大针茅根系主要通过增加根系长度扩大在土壤中的空间分布,而促使糙隐子草主要通过增粗生长来扩大土壤分布空间。实验2研究结果表明:功能群的去除,中氮素添加对根系的影响,只有糙隐子草的根系直径显著增加。综合来看,功能群去除实验对大针茅的根系长度和面积有影响,对糙隐子草的根系长度、直径和面积有影响。功能群去除处理与氮素添加的交互作用对大针茅根系没有影响,对糙隐子草的根系直径和体积有影响。

The response of Cleistogenes squarrosa and Stipa grandis root characteristics to nitrogen adding gradient and removal of function groups

Overgrazing has severely degraded the grassland of Northern China causing serious loss of soil nitrogen (N). Along with the degraded steppe, Cleistogenes squarrosa will replace Stipa grandis, which was the original dominant species, to become the dominant plant in the community. In order to understand this transition, a study was made to examine the effect of N and selected functional plant groups on the rooting characterisitics of S. grandis and C. squarrosa. Two experiments were conducted in degraded grassland communities that were dominated by C. squarrosa.on the Xilingol steppe.on a degraded community. In Experiment 1 involved N addition along an increasing gradient (0, 10.5, 17.5, 28g N/m²) while in Experiment 2, two of three functional groups (high-energy, middle-energy and low-energy functional groups) were removed (1, 0, 0; 0, 2, 0; and 0, 0, 3) and adding N fertilizer(0, 17.5 g N/m²) in a factorial arrangement. After two years, the root length, diameter, area, and volume of S. grandis and C. squarrosa were measured using a Delta-T SCAN analyzer. Root response to N fertilizer as well as to the removal of functional groups, with two N levels, were analyzed. Under pressure from competition by other functional groups, the root length, area, and volume of S. grandis significantly increased under high N fertilizer (28 gN/m²) while root diameter and volume of C. squarrosa with 17.5 gN/m² were significantly higher than the other three N application rates. In Experiment 2, we did not detect a response in S. grandis to nitrogen addition(17.5 gN/m²)while removing functional groups but the root diameter of C. squarrosa increased significantly. In general removal of plant functional groups affects the root length and area of S. grandis and the root length, diameter and area of C. squarrosa. While the interaction between nitrogen addition and removal of plant functional groups affects the root diameter and volume of C. squarrosa, and it did not affect S. grandis.