Data from: Soil aggregate stability and grassland productivity associations in a northern mixed-grass prairie

Soil aggregate stability data are often predicted to be positively associated with measures of plant productivity, rangeland health, and ecosystem functioning. Here we revisit the hypothesis that soil aggregate stability is positively associated with plant productivity. We measured local (plot-to-plot) variation in grassland community composition, plant (aboveground) biomass, root biomass, % water-stable soil aggregates, and topography. After accounting for spatial autocorrelation, we observed a negative association between % water-stable soil aggregates (0.25-1 and 1-2 mm size classes of macroaggregates) and dominant graminoid biomass, and negative associations between the % water-stable aggregates and the root biomass of a dominant sedge (Carex filifolia). However, variation in total root biomass (0-10 or 0-30 cm depths) was either negatively or not appreciably associated with soil aggregate stabilities. Overall, regression slope coefficients were consistently negative thereby indicating the general absence of a positive association between measures of plant productivity and soil aggregate stability for the study area. The predicted positive association between factors was likely confounded by variation in plant species composition. Specifically, sampling spanned a local gradient in plant community composition which was likely driven by niche partitioning along a subtle gradient in elevation. Our results suggest an apparent trade-off between some measures of plant biomass production and soil aggregate stability, both known to affect the land's capacity to resist erosion. These findings further highlight the uncertainty of plant biomass-soil stability associations.土壤团聚体稳定性（soil aggregate stability）通常被认为与植物生产力、牧场健康及生态系统功能的各项指标呈正相关。本研究重新探讨了土壤团聚体稳定性与植物生产力呈正相关这一假说。我们测定了草原群落组成、植物（地上）生物量、根系生物量、水稳性土壤团聚体占比以及地形因子的样地间局域变异。在控制空间自相关效应后，我们发现：水稳性土壤团聚体占比（0.25~1 mm及1~2 mm粒级大团聚体）与优势禾草生物量呈负相关，同时该团聚体占比与优势莎草——细叶苔草（Carex filifolia）的根系生物量亦呈负相关。但0~10 cm与0~30 cm土层的总根系生物量变异，与土壤团聚体稳定性要么呈负相关，要么无显著关联。整体而言，回归斜率系数均为负值，这表明本研究区域内，植物生产力各项指标与土壤团聚体稳定性之间普遍不存在正相关关系。此前预测的因子间正相关关系，很可能因植物物种组成的变异而受到混淆。具体而言，本研究的采样覆盖了植物群落组成的局域梯度，该梯度很可能由沿微弱海拔梯度的生态位分化所驱动。本研究结果表明，部分植物生物量生产指标与土壤团聚体稳定性之间存在明显的权衡关系——二者均被证实会影响土地的抗侵蚀能力。这些发现进一步凸显了植物生物量与土壤稳定性之间关联的不确定性。