Soil porosity along a plant diversity gradient in the Jena Experiment (Main Experiment, 2013)

Soil porosity is the fraction of total volume occupied by pores or voids measured at matric potential 0. To measure soil porosity, soil samples were taken from each plot using sample rings with an internal diameter of 57 mm and height of 40.5 mm (inner volume of Vs=100 cm**3). The samples were placed on a sand bed box with water level set to allow saturation of the samples with water. After 48 h the samples were weighed (ms), oven dried at 105 °C and weighed again to determine the dry weight (md). We calculated soil porosity (n [%]) using the density of water (pw=1 g cm**-3), n=100 * (mw-md) / (pw*Vs). To account for the spatial variation of soil properties, three replicates were taken per plot, approximately 2, 3 and 4 weeks after the flood that occurred at the field site during June 2013. Data are the average soil porosity values per plot.
All data where measured in the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown in the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, or 4 functional groups). Plots were maintained by bi-annual weeding and mowing.

土壤孔隙度是指在基质势（matric potential）为0时，土壤孔隙或空腔所占总容积的比例。为测定土壤孔隙度，采用内径57 mm、高40.5 mm（内部容积Vs=100 cm³）的环刀（sample ring）采集各样地的土壤样品。将样品置于砂床盒中，调整水位使样品完全被水饱和。48小时后称量样品鲜重（ms），随后置于105 ℃烘箱中烘干，再次称量以获得干重（md）。我们以水的密度（pw=1 g·cm⁻³）为参数，通过公式n=100×(mw−md)/(pw×Vs)计算土壤孔隙度（n，单位为%）。为消除土壤属性的空间变异影响，每个样地设置3个重复样品，分别于2013年6月野外样地发生洪水后的约2周、3周和4周进行采样。本数据集为各单个样地的土壤孔隙度平均值。
所有数据均采集自一项大型草原生物多样性实验（耶拿实验，Jena Experiment；详见下文）的主实验样地。该主实验共设置82个20 m×20 m的草原样地，所用植物均来自包含60个物种的物种库，这些物种分属4个功能群：禾草类、豆科类、高大草本与低矮草本。2002年5月，研究人员从该物种库中选取不同数量的植物物种进行播种，以此构建植物物种丰富度（1、2、4、8、16和60种）与功能群丰富度（1、2、3或4个功能群）的梯度样地。所有样地通过每年两次的除草与刈割进行维护管理。