在一些实验中已经证明了氮沉积导致陆地生态系统物种流失的现象。氮(N)和磷(P),作为植物生长所需的主要营养素,在许多生态系统中表现出生态化学计量耦合。氮的有效性增加会加剧磷的生态效应。为揭示氮限制和非限制条件下磷的生态效应,我们在呼伦贝尔草甸草原进行了5年的受控N-P相互作用实验,其中实施了两种氮添加水平:0gN·m-2·a-1(氮限制条件)和10gN·m-2·a-1(氮非限制条件),以及六个水平的磷添加(0、2、4、6、8和10gP·m-2·a-1)。结果表明,氮的添加(在氮的非限制条件下)显著降低了草原群落的物种多样性,在磷添加下加剧了这种情况。在氮限制条件下,与对照相比,磷的添加对物种多样性没有显着影响;但是,不同的磷添加水平之间有很大的差异,表现出单峰变化。在两种实验氮气条件下,添加6gP·m-2·a-1是影响群落物种多样性的阈值。氮的添加降低了豆科植物的相对生物量,束草,和forbs,但大大提高了根茎草的相对生物量。相比之下,磷的添加仅显着影响花草和根茎草的相对生物量,前者表现出随着磷添加水平的增加先增加后减少的单峰模式,而后者则表现出相反的模式。观察到根茎草和其他功能群对氮和磷添加的不同响应对草地群落结构的变化具有调节作用。添加磷可能会增加氮沉积引起的物种损失的风险。氮和磷的添加都导致土壤酸化,并增加了已经占主导地位的物种的优势,随之而来的forb官能团中的物种损失代表了群落物种多样性减少的主要机制。
The phenomenon of nitrogen deposition resulting in species loss in terrestrial ecosystems has been demonstrated in several experiments. Nitrogen (N) and phosphorus (P), as major nutrients required for plant growth, exhibit ecological stoichiometric coupling in many ecosystems. The increased availability of nitrogen can exacerbate the ecological effects of phosphorus. To reveal the ecological effects of phosphorus under nitrogen-limiting and non-limiting conditions, we conducted a controlled N-P interaction experiment over 5 years in the Hulunbuir meadow steppe, where two nitrogen addition levels were implemented: 0 g N·m-2·a-1 (nitrogen-limiting condition) and 10 g N·m-2·a-1 (nitrogen-non-limiting condition), together with six levels of phosphorus addition (0, 2, 4, 6, 8, and 10 g P·m-2·a-1). The results showed that nitrogen addition (under nitrogen-non-limiting conditions) significantly decreased species diversity in the steppe community, which was exacerbated under phosphorus addition. Under nitrogen-limiting conditions, phosphorus addition had no marked impact on species diversity compared to the control; however, there were substantial differences between different levels of phosphorus addition, exhibiting a unimodal change. Under both experimental nitrogen conditions, the addition of 6 g P·m-2·a-1 was the threshold for affecting the community species diversity. Nitrogen addition reduced the relative biomass of legumes, bunch grasses, and forbs, but substantially increased the relative biomass of rhizomatous grasses. In contrast, phosphorus addition only markedly affected the relative biomass of forbs and rhizomatous grasses, with the former showing a unimodal pattern of first increasing and then decreasing with increasing phosphorus addition level, and the latter exhibiting the opposite pattern. The different responses of rhizomatous grasses and other functional groups to nitrogen and phosphorus addition were observed to have a regulatory effect on the changes in grassland community structure. Phosphorus addition may increase the risk of nitrogen deposition-induced species loss. Both nitrogen and phosphorus addition lead to soil acidification and an increase in the dominance of the already-dominant species, and the consequent species loss in the forb functional group represents the main mechanism for the reduction in community species diversity.