Department of Biology, College of William and Mary, Williamsburg, Virginia, 23185, USA.
Am J Bot. 2018 Dec;105(12):2008-2017. doi: 10.1002/ajb2.1197. Epub 2018 Nov 28.
The tallgrass prairie ecosystem has experienced a dramatic reduction over the past 150 yr. This reduction has impacted the abundance of native grassland species, including milkweeds (Asclepias).
We used two long-term (27 yr) data sets to examine how fire, grazing, and nutrient addition shape milkweed abundance in tallgrass prairie. We compared these results to those of a greenhouse experiment that varied nutrient levels in the absence of competition, herbivory, and mutualistic relationships.
Asclepias species exhibited broad patterns in response to burning regimes that did not include grazing, but experienced more species-specific patterns in other combinations. Asclepias syriaca was the only species to increase in abundance in plots that included burning and nutrient addition. In the greenhouse we found that nitrogen significantly increased biomass, while no effect of phosphorus was detected.
These results indicate that A. syriaca will do best in settings with high nutrient loads, low competition, and no grazers. These characteristics define a small portion of the tallgrass prairie but exemplify modern agricultural settings, which have replaced prairies. However, other milkweeds examined did not share this pattern, which indicates that milkweed species will respond differently when exposed to agricultural settings, with some less able to cope with land conversion to pasture or row-crop agriculture.
在过去的 150 年中，高草草原生态系统经历了巨大的减少。这种减少影响了本地草原物种的丰度，包括乳草（Asclepias）。
我们使用了两个长期（27 年）的数据集来研究火、放牧和养分添加如何塑造高草草原中乳草的丰度。我们将这些结果与一个温室实验进行了比较，该实验在没有竞争、草食和互利关系的情况下改变了养分水平。
乳草物种对不包括放牧的燃烧制度表现出广泛的反应模式，但在其他组合中表现出更具特异性的模式。Asclepias syriaca 是唯一在包括燃烧和养分添加的斑块中丰度增加的物种。在温室中，我们发现氮显著增加了生物量，而没有检测到磷的影响。
这些结果表明，A. syriaca 在养分负荷高、竞争低且没有食草动物的环境中表现最好。这些特征定义了一小部分高草草原，但代表了现代农业环境，这些环境已经取代了草原。然而，其他检查过的乳草并没有表现出这种模式，这表明乳草物种在暴露于农业环境时会有不同的反应，有些物种不太能够应对土地转化为牧场或条播农业。
