Ceulemans Tobias, Hulsmans Eva, Berwaers Sigi, Van Acker Kasper, Honnay Olivier
Plant Conservation and Population Biology, University of Leuven, Leuven, Belgium.
Plant and Vegetation Ecology, University of Antwerp, Antwerp, Belgium.
PLoS One. 2017 Mar 23;12(3):e0174380. doi: 10.1371/journal.pone.0174380. eCollection 2017.
Anthropogenic activities have severely altered fluxes of nitrogen and phosphorus in ecosystems worldwide. In grasslands, subsequent negative effects are commonly attributed to competitive exclusion of plant species following increased above-ground biomass production. However, some studies have shown that this does not fully account for nutrient enrichment effects, questioning whether lowering competition by reducing grassland productivity through mowing or herbivory can mitigate the environmental impact of nutrient pollution. Furthermore, few studies so far discriminate between nitrogen and phosphorus pollution. We performed a full factorial experiment in greenhouse mesocosms combining nitrogen and phosphorus addition with two clipping regimes designed to relax above-ground competition. Next, we studied the survival and growth of seedlings of eight common European grassland species and found that five out of eight species showed higher survival under the clipping regime with the lowest above-ground competition. Phosphorus addition negatively affected seven plant species and nitrogen addition negatively affected four plant species. Importantly, the negative effects of nutrient addition and higher above-ground competition were independent of each other for all but one species. Our results suggest that at any given level of soil nutrients, relaxation of above-ground competition allows for higher seedling survival in grasslands. At the same time, even at low levels of above-ground competition, nutrient enrichment negatively affects survival as compared to nutrient-poor conditions. Therefore, although maintaining low above-ground competition appears essential for species' recruitment, for instance through mowing or herbivory, these management efforts are likely to be insufficient and we conclude that environmental policies aimed to reduce both excess nitrogen and particularly phosphorus inputs are also necessary.
人为活动已严重改变了全球生态系统中氮和磷的通量。在草原地区，后续产生的负面影响通常归因于地上生物量增加后植物物种的竞争排斥。然而，一些研究表明，这并不能完全解释养分富集效应，质疑通过割草或放牧降低草原生产力来减少竞争是否能减轻养分污染对环境的影响。此外，到目前为止，很少有研究区分氮污染和磷污染。我们在温室中型生态系统中进行了一项全因子实验，将氮和磷添加与两种旨在缓解地上竞争的修剪方案相结合。接下来，我们研究了八种常见欧洲草原物种幼苗的存活和生长情况，发现八个物种中有五个在地上竞争最低的修剪方案下存活率更高。添加磷对七种植物物种产生负面影响，添加氮对四种植物物种产生负面影响。重要的是，除了一个物种外，养分添加和较高地上竞争的负面影响相互独立。我们的研究结果表明，在任何给定的土壤养分水平下，缓解地上竞争能使草原上的幼苗存活率更高。同时，即使在地上竞争水平较低的情况下，与养分贫瘠条件相比，养分富集也会对存活率产生负面影响。因此，尽管维持低地上竞争对于物种的招募似乎至关重要，例如通过割草或放牧，但这些管理措施可能并不充分，我们得出结论，旨在减少过量氮尤其是磷输入的环境政策也是必要的。
