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）通常被预测与植物生产力、牧场健康及生态系统功能等指标呈正相关关系。本研究重新检验了“土壤团聚体稳定性与植物生产力呈正相关”这一假说。我们实测了草地群落组成、植物地上生物量（aboveground biomass）、地下生物量（root biomass）、水稳性土壤团聚体（water-stable soil aggregates）占比以及地形的局域（样地间）变异。在控制空间自相关（spatial autocorrelation）效应后，我们发现：对应0.25~1 mm与1~2 mm粒级大团聚体（macroaggregates）的水稳性土壤团聚体占比，与优势禾本科植物（graminoid）生物量呈负相关；同时该水稳性团聚体占比也与优势莎草（丝叶薹草，Carex filifolia）的地下生物量呈负相关。不过，总地下生物量（0~10 cm或0~30 cm土层深度）与土壤团聚体稳定性之间，要么呈负相关，要么无显著关联。整体而言，回归斜率系数始终为负值，这表明本研究区域内，植物生产力指标与土壤团聚体稳定性之间普遍不存在正相关关系。二者间的预测正相关关系，很可能因植物物种组成的变异而受到混淆。具体而言，本次采样覆盖了一条植物群落组成的局域梯度，该梯度大概率由沿海拔细微梯度的生态位分化（niche partitioning）所驱动。我们的研究结果显示，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——二者均已知会影响陆地生态系统的抗侵蚀（erosion）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。