Big sagebrush (Artemisia tridentata) is a widespread and locally dominant shrub that is a key driver of water fluxes and storage in western North America. There are several recognized subspecies of big sagebrush that occupy different microsites across the landscape according to moisture availability, yet little is known about how these subspecies vary in drought tolerance or water management strategies. We measured diurnal and seasonal (i.e., early-, mid-, and late summer) variation in water status and transport efficiency, transpiration, and stomatal regulations in two subspecies of big sagebrush (A.t. wyomingensis and A.t. vaseyana) at the Reynolds Creek Critical Zone Observatory in southwestern Idaho. We hypothesized that water status, transport efficiency, and stomatal regulations would be greater in A.t. vaseyana compared to A.t. wyomingensis, because the first subspecies occupies wetter microsites. Predawn and midday water potentials were up to 2× more negative in A.t. wyomingensis compared to A.t. vaseyana, and transpiration was up to ~ 4× greater in A.t. vaseyana compared to A.t. wyomingensis. A.t. vaseyana was more isohydric with ~ 1.5× greater stomatal sensitivity to atmospheric vapor pressure deficit and a smaller hydroscape, compared to A.t. wyomingensis. Our data demonstrate that there are fundamental differences in plant–water relations among these subspecies that constitute the vast, but not homogeneous sagebrush landscapes. These important differences can have implications for modeling water fluxes in big sagebrush-dominated communities at shrub to ecosystem scales.

大鼠尾草（Artemisia tridentata）是一种分布广泛且局部占主导地位的灌木，是北美西部水通量和储水量的主要驱动力。根据含水量的可用性，有几种公认的大鼠尾草亚种在整个景观中占据着不同的微地点，但对于这些亚种在耐旱性或水管理策略上的变化知之甚少。我们测量了两个大亚枝树亚种（怀俄明州和凡塞那州）的水分和运输效率，蒸腾作用和气孔调节的昼夜和季节性（即夏初，夏中和夏末）变化）在爱达荷州西南部的雷诺兹克里克临界区天文台。我们假设水状态，运输效率和气孔规定将在更大在vaseyana相比，在wyomingensis，因为第一个亚种占据多雨微型网站。相比于Atyyana，黎明前和中午的水势在At怀俄明州高达2倍以上，而在At yayayana的蒸腾能力比在Atyomingana高达〜4倍。在vaseyana用〜1.5×更大气孔敏感性大气水汽压亏和较小hydroscape更isohydric相比，在wyomingensis。我们的数据表明，这些亚种之间植物与水的关系存在根本差异，这些亚种构成了广阔但并非均一的鼠尾草景观。这些重要差异可能会对在灌木丛至生态系统规模的大型以鼠尾草为主的社区中的水通量建模产生影响。