PRP02 Plant diversity, richness, and plant species cover in konza prairie restoration heterogeneity plots, since 1998

The experiment is a randomized complete block design with four whole plot hetereogeneity treatments replicated within each of four blocks (n=16 whole plots). The whole plot treatments were created using different combinations of soil depth and nutrient manipulations. The control plots contained no depth or nutrient manipulations. The maximum hetereogeneity plots contained three 2 m x 8 m vertical strips assigned to ambient, enriched and reduced N treatments and four 2 m x 6 m horizontal strips assigned to deep and shallow soil to result in six treatment combinations. The maximum heterogeneity plots are a split-block design. Every plot contained 12 subplots (2 m x 2 m) for sampling. Prior to sowing, all of the plots were excavatedto a depth of approximately 25 cm. Natural limestone slabs were laid in strips assigned to the shallow soil treatment. The soil from all plots was then replaced, leveled, and disked (2-3 cm deep). In February 1998, we incorporated sawdust (49% C; C:N ratio=122) into the strips assigned to the reduced-N treatment. The average C concentration and bulk density in the surface 15 cm following long-term cultivation was 1.5% and 1.2 g cm-3, respectively. Sawdust was tilled into the soil at a rate of 5.5 kg dry wt./m2 to achieve a C concentration representative of native prairie soil (approx. 3% C). Surface applications of granular sugar were initiated in 2004 at a rate of 200 g sucrose m-2 (84.22 g C/m2) 3-4 times each growing season. Strips assigned to the enriched-N treatment were fertilized with 5 g N m2/y (applied as ammonium-nitrate) in July of the first growing season and early June of each subsequent years.本实验采用随机完全区组设计（randomized complete block design），共设置4个区组，每个区组内重复4个整区异质性处理，总计16个整区样地（n=16）。整区处理由土层深度与养分调控的不同组合构成，对照样地不施加任何土层深度或养分调控措施。 最大异质性样地采用裂区设计（split-block design）：设置3条2 m × 8 m的垂直样带，分别对应自然氮素、氮素富集与氮素消减处理；同时设置4条2 m × 6 m的水平样带以区分深、浅土层，最终形成6种处理组合。 所有样地均包含12个2 m × 2 m的副样地用于采样。播种前，所有样地均被翻挖至约25 cm深度；随后在浅土层处理对应的样带中铺设天然石灰岩板，再将所有样地的土壤回填、整平并耙耕（深度2-3 cm）。 1998年2月，向氮素消减处理的样带中施加锯末（碳含量49%，碳氮比=122）。经长期耕作后，地表15 cm土层的平均碳浓度与容重分别为1.5%和1.2 g·cm⁻³。为使土壤碳浓度接近天然草原土壤（约3%碳含量），以5.5 kg干重/㎡的用量将锯末翻耕入土。 2004年起，每个生长季向对应样带地表施加粒状蔗糖3-4次，施用量为200 g蔗糖/㎡（即84.22 g碳/㎡）。氮素富集处理样带在首个生长季的7月，以及后续每年的6月初，以硝酸铵形式施加氮肥，施用量为5 g N·m⁻²·y⁻¹。