Data from: Soil conditioning affects interactions between native and invasive exotic perennials of semi-natural grasslands

1. Semi–natural perennial grasslands are of increasing importance as components of multifunctional agroecosystems, combining biomass production with provision of other ecosystem services. Soil legacies from previous land use or exotic species can hinder their establishment, but might be overcome through a multi–stage successional strategy, whereby certain species are used to facilitate native grassland species establishment. We tested this strategy via a feedback experiment examining soil conditioning effects on interference interactions between native and exotic species. 2. Soils in a former maize–soybean production field in Minnesota, USA, were conditioned for three years with native or invasive exotic perennials or a maize–soybean crop rotation. Nitrogen (N) fertilisation was an additional treatment in field plots. In a greenhouse, native and invasive exotic perennial grassland seedlings were grown on these soils, in monoculture and in native–exotic species pairs, with and without N fertilisation. The impact of soil conditioning and field and greenhouse N fertilisation on interactions between native and exotic seedlings in mixture was determined. 3. Neighbouring plants suppressed biomass production in all native and exotic species. The maize–soybean rotation left a soil legacy that enhanced suppression of native species when grown with exotic species, while exotic species suffered no such disadvantage. 4. The strong and specific disadvantage to native species of maize–soybean soils decreased with greenhouse N fertilisation, but remained significant, while field N addition did not alter this effect. 5. Synthesis and applications. We find that the negative soil legacy of the maize–soybean rotation for native plant performance in interaction with exotics was greatly diminished in soils conditioned by native or exotic perennial species, irrespective of nitrogen addition. This highlights the potential value of perennial species in conversion from row–crop agriculture to grasslands, because all perennial species alleviated the enhanced suppression of natives observed on maize–soybean soils. We did not find strong evidence that these perennial species were capable of specifically facilitating native species over exotics, but a broader range of species should be evaluated.1. 半自然多年生草地作为多功能农业生态系统的组成部分，其重要性与日俱增——这类生态系统可兼顾生物量生产与其他生态系统服务的提供。既往土地利用或外来物种所形成的土壤遗留效应（soil legacy），可能会阻碍半自然多年生草地的建植，但可通过多阶段演替策略加以克服：即利用特定物种来促进本土草地物种的建植。本研究通过一项反馈实验（feedback experiment）验证了该策略，旨在探究土壤预处理效应（soil conditioning effects）对本土与外来物种间干扰互作（interference interactions）的影响。 2. 我们在美国明尼苏达州的一处前玉米-大豆种植田中，利用本土、入侵性外来多年生植物，或玉米-大豆轮作（maize–soybean crop rotation）体系对土壤进行了为期三年的预处理。田间小区（field plots）额外设置了氮肥施用（N fertilisation）处理。在温室（greenhouse）中，我们将本土与入侵性外来多年生草地幼苗分别以单作（monoculture）形式，以及本土-外来物种种对（native–exotic species pairs）形式，在施加与未施加氮肥的上述预处理土壤中进行栽培。本研究明确了土壤预处理、田间与温室氮肥施用，对混种（mixture）下本土与外来幼苗间互作的影响。 3. 邻株会抑制所有本土与外来物种的生物量生产。玉米-大豆轮作体系遗留的土壤效应，会在本土物种与外来物种混种时增强对本土物种的抑制，而外来物种则未受到此类不利影响。 4. 玉米-大豆轮作土壤对本土物种造成的强烈且特异性的不利影响，会随温室氮肥施用量增加而减弱，但仍具有统计学显著性；而田间氮肥添加并未改变这一效应。 5. 总结与应用。本研究发现，无论是否施加氮肥，由本土或外来多年生植物预处理的土壤，均可大幅削弱玉米-大豆轮作体系对本土植物与外来物种混种时生长表现的负面土壤遗留效应。这凸显了多年生植物在从大田作物农业向草地转型过程中的潜在价值——所有多年生植物均可缓解玉米-大豆轮作土壤中观测到的对本土物种的增强抑制效应。本研究未发现强有力的证据表明，这些多年生植物能够特异性地促进本土物种而非外来物种的生长，但仍需对更广泛的物种范围开展评估。