土壤肥力和物种属性决定亚高寒草甸实验群落的生产力

生物多样性与生态系统功能之间的关系及其形成的内在机制还存在很多争议。为了揭示植物群落生产力形成的生态学机制, 采用盆栽方法探讨了物种多样性、物种属性以及施肥水平与植物群落生产力之间的关系。研究结果显示: 在不施肥和每盆施5.0 g磷酸二铵的条件下, 随着物种多样性的增加, 地上生物量增加不显著; 在每盆施10.0 g磷酸二铵的条件下, 随着物种多样性的增加, 地上生物量显著增加。相对于中华羊茅(Festuca sinensis)而言, 垂穗披碱草(Elymus nutans)和垂穗鹅观草(Roegneria nutans)对群落生产力的贡献较大, 但在不同施肥水平和播种密度下, 其影响不完全相同。这表明物种多样性对群落生产力的影响随着土壤肥力的变化而变化; 并且植物群落生产力受组成群落的物种属性影响较大, 而物种属性又与特定时间和特定生境下资源的利用方式相联系。在高肥力水平下, 物种多样性之所以对群落生产力具有正效应, 可能是因为高肥力水平增加了可利用的生态位空间, 最终仍体现在物种组合上。因此, 植物群落的生产力与物种多样性之间没有必然的联系, 而与土壤肥力和土壤肥力决定的物种属性有关。

SOIL FERTILITY AND SPECIES IDENTITY CONTROL COMMUNITY PRODUCTIVITY IN AN EXPERIMENTAL PLANT COMMUNITY IN AN AREA OF SUBALPINE MEADOW

Aims Our objective was to determine ecological mechanisms of plant community productivity performance based on study of effects of species diversity, species identity and fertility level on productivity. Methods We carried out an experiment with combinations of three plant species (Elymus nutans, Roegneria nutans and Festuca sinensis) under three different fertility levels in an area of subalpine meadow in Hezuo County, Gansu Province, China. Using seeds collected in the area, we sowed seeds in monoculture with sowing densities of 20, 40 and 60 seeds•pot−1, in mixtures with sowing densities of each pair of species of 20/20, 20/40 and 40/20 seeds•pot−1 and in mixtures of all three species at a sowing density of 20/20/20 seeds•pot−1. We fixed seedling density at half of the sowed density. The pots were fertilized with 0, 2.5 and 5.0 g of phosphorate ammonium at tillering and jointing stages. There were five replicates of each treatment. We regularly removed weeds by hand. Aboveground biomass in each pot was harvested, dried and measured by species by early October. Important findings Under conditions of no-fertility and fertilizing 5.0 g diammonium phosphate per pot, aboveground biomass did not increase significantly with increasing species diversity; however, under condition of fertilizing 10.0 g diammonium phosphate per pot, aboveground biomass increased significantly with increasing species diversity. Compared with Festuca sinensis, both Elymus nutans and Roegneria nutans made larger contributions to community productivity. But the effects of different fertility levels and sowing density were not the same. Results suggest that effects of species diversity on productivity varied because of variation of soil fertility. Productivity of plant communities may be mainly influenced by species identity, in correspondence with resource use under the conditions of the habitat. The high productivity in the high fertility level was caused by species or species assembly, which can better adapt to the high soil fertilization, rather than by species diversity. Therefore, plant community productivity does not necessarily relate to plant species diversity, but relates to soil fertility level and species identity determined by the soil fertility.