Data from: Interactions between cattle grazing, plant diversity, and soil nitrogen in a northeastern U.S. coastal grassland.

Data to accompany:Kinnebrew, E., Champlin, L., &amp; Neill., N. 2019. Interactions between cattle grazing, plant diversity, and soil nitrogen in a northeastern U.S. coastal grassland. <i>Applied Vegetation Science.</i> https://doi.org/10.1111/avsc.12422<br>Questions: Can cattle grazing help maintain plant diversity in coastal grasslands? What is the relationship between soil available nitrogen and plant diversity in sandy and infertile soils? How does cattle grazing affect soil available nitrogen and how might this indirectly impact plant diversity via the N–plant diversity relationship? <br>Location: Grazed coastal grasslands on Naushon Island, off of Cape Cod, MA, USA. <br>Methods: We surveyed summer vegetation from 2014 to 2017 and analyzed soils for extractable nitrogen (N) in two grazed grasslands on Naushon Island. We also set up cattle enclosures and exclosures to manipulate grazing pressure and test how cattle grazing influenced plant diversity (species richness and Shannon's diversity) and extractable NH4+ and NO3−. In the enclosure experiment, cattle were enclosed for up to a week in the mid- summer of 2014, 2015 and 2016. For the exclosure experiment, we excluded cattle from areas from 2014 to 2017. <br>Results: In both the enclosure and exclosure experiments, higher grazing pressure corresponded to less negative change of plant species richness and Shannon's diversity from 2014 to 2017. Total extractable N had a weak positive correlation with plant diversity, but increasing extractable NO3− correlated with decreasing species richness (p = 0.001) and Shannon's diversity (p = 0.009). Neither the cattle enclosures nor exclosures were related to soil extractable N. <br>Conclusions: Cattle grazing may help prevent or slow losses of plant diversity that are occurring in many coastal grasslands, including Naushon Island. This effect does not seem to be regulated by cattle deposition of N in the soil or the N–plant diversity relationship. Our results of the N–plant diversity relationship differ from the mainstream understanding, perhaps due to Naushon's sandy and infertile soils.<br>

配套数据集：Kinnebrew, E., Champlin, L. 及 Neill, N. 于2019年发表于《应用植被科学（Applied Vegetation Science）》的研究《美国东北部沿海草原中牛放牧、植物多样性与土壤氮素的相互作用》，DOI：10.1111/avsc.12422
研究问题：牛放牧是否有助于维持沿海草原的植物多样性？在沙质贫瘠土壤中，土壤有效氮与植物多样性之间存在何种关联？牛放牧如何影响土壤有效氮，又可能通过氮素-植物多样性的关联间接作用于植物多样性？
研究地点：美国马萨诸塞州科德角周边的诺申岛（Naushon Island）沿海放牧草原。
研究方法：本研究于2014至2017年开展夏季植被调查，并对诺申岛两处放牧草原的土壤可提取氮（extractable nitrogen）进行分析。同时设置牛放牧围栏与禁牧小区以调控放牧压力，探究牛放牧对植物物种丰富度（species richness）、香农多样性（Shannon's diversity）以及可提取铵态氮（NH4+）、硝态氮（NO3−）的影响。在围栏实验中，2014、2015及2016年的仲夏时段，将牛圈养于围栏内长达一周；禁牧实验则于2014至2017年对指定区域实施禁牧处理。
研究结果：围栏与禁牧实验均显示，2014至2017年间，更高的放牧压力对应植物物种丰富度与香农多样性的负向变化幅度更小。总可提取氮与植物多样性呈弱正相关，但可提取硝态氮的水平上升与物种丰富度（p=0.001）及香农多样性（p=0.009）的下降显著相关。牛放牧围栏与禁牧处理均与土壤可提取氮水平无显著关联。
研究结论：牛放牧或可减缓乃至阻止包括诺申岛在内的诸多沿海草原的植物多样性流失。该效应似乎并非通过牛向土壤输入氮素或氮素-植物多样性的关联途径实现调控。本研究中氮素与植物多样性的关联结果与主流认知存在差异，这或许与诺申岛的沙质贫瘠土壤特性有关。