不同水分条件下混种密度对芦苇和反枝苋种间竞争的影响

与本地植物的种间竞争是影响外来植物能否成功入侵的关键因素之一,该研究通过受控模拟试验研究了本地植物芦苇(Phragmites australis)和外来入侵植物反枝苋(Amaranthus retroflexus)在淹水和干旱两种水分条件下混种密度(6∶2、4∶4和2∶6)对其种间竞争的影响。结果表明:(1)芦苇和反枝苋的相对产量与相对产量总和均小于1,即两种植物存在种间竞争。(2)种间竞争使芦苇和反枝苋的生长均受到了不同程度的抑制,表现在两者的株高和生物量均随着竞争者密度的增加而降低。(3)植株地上部分和地下部分的氮浓度表现出与株高和生物量相同的趋势,且在不同水分条件下存在差异。(4)芦苇和反枝苋分别在淹水和干旱环境下具有较强竞争力,但在各自较高混种密度下亦具有较强竞争力。可见,芦苇和反枝苋的种间竞争受到了水分和混种密度的影响。因此,在有反枝苋分布的湿地中,植物生长初期可通过增加土壤水分和/或增加芦苇等本地植物的种群密度以降低反枝苋的种群密度来限制其竞争能力,防止反枝苋在湿地中生长建群和扩散入侵。

Effects of planting density on interspecific competition between Phragmites australis and Amaranthus retroflexus under different water conditions

Interspecific competition between alien plants and native plants is one of the key factors determining whether alien plants can invade successfully or not. Controlled experiments were conducted to explore the effects of planting density(6:2, 4:4 and 2:6)on interspecific competition between native plant Phragmites australis and alien invasive plant Amaranthus retroflexus under two kinds of water conditions(dry and wet). The results were as follows:(1)Relative yield and total relative yield of Phragmites australis and Amaranthus retroflexus were all less than one, indicating that there was interspecific competition between the two plant species.(2)Growth of the two plant species was inhibited by interspecific competition leading to lower plant height and biomass with the increasing density of the competitor.(3)Aboveground and belowground nitrogen concentration of the two plants had the same trend as plant height and biomass, and there were differences under different water conditions.(4)Phragmites australis and Amaranthus retroflexus had higher competitiveness under wet and dry condition, respectively, while they also had higher competitiveness in higher planting density. In conclusion, both water condition and planting density have important effects on interspecific competition beween Phragmites communis and Amaranthus retroflexus. Therefore, in wetland with Amaranthus retroflexus distribution, its competitiveness can be restricted in plant initial growth by increasing water content of soil and/or increasing planting density of Phragmites australis and other native plants, so as to prevent the growth, population building, and furthermore diffusion and invasion of Amaranthus retroflexus in wetland.