Desert shrub responses to experimental modification of precipitation seasonality and soil depth: relationship to the two‐layer hypothesis and ecohydrological niche

Abstract

Summary1. Ecohydrological niches are important for understanding plant community responses to climate shifts, particularly in dry lands. According to the two-layer hypothesis, selective use of deep-soil water increases growth or persistence of woody species during warm and dry summer periods and thereby contributes to their coexistence with shallow-rooted herbs in dry ecosystems. The resourcepool hypothesis further suggests that shallow-soil water benefits growth of all plants while deep-soil water primarily enhances physiological maintenance and survival of woody species. Few studies have directly tested these by manipulating deep-soil water availability and observing the long-term outcomes. 2. We predicted that factors promoting infiltration and storage of water in deep soils, specifically greater winter precipitation and soil depth, would enhance Artemisia tridentata (big sagebrush) in cold, winter-wet/summer-dry desert. Sagebrush responses to 20 years of winter irrigation were compared to summer-or no irrigation, on plots having relatively deep or shallow soils (2 m vs. 1 m depths). 3. Winter irrigation increased sagebrush cover, and crown and canopy volumes, but not density (individuals/plot) compared to summer or no irrigation, on deep-soil plots. On shallow-soil plots, winter irrigation surprisingly decreased shrub cover and size, and summer irrigation had no effect. Furthermore, multiple regression suggested that the variations in growth were related (i) firstly to water in shallow soils (0-0.2 m) and secondly to deeper soils (> 1 m deep) and (ii) more by springtime than by midsummer soil water. Water-use efficiency increased considerably on shallow soils without irrigation and was lowest with winter irrigation. 4. Synthesis. Sagebrush was more responsive to the seasonal timing of precipitation than to total annual precipitation. Factors that enhanced deep-water storage (deeper soils plus more winter precipitation) led to increases in Artemisia tridentata that were consistent with the two-layer hypothesis, and the contribution of shallow water to growth on these plots was consistent with the resource-pool hypothesis. However, shallow-soil water also had negative effects on sagebrush, suggesting an ecohydrological trade-off not considered in these or related theories. The interaction between precipitation timing and soil depth indicates that increased winter precipitation could lead to a mosaic of increases and decreases in A. tridentata across landscapes having variable soil depth.

Soil properties and climate mediate the effects of biotic interactions on the performance of a woody range expander

“…Given the increasing frequency of climatic variability predicted by climate-change scenarios (Adler et al 2012, Cleland et al 2013, plant communities may be exposed to increasing instability at both local and regional scales (Bates et al 2006, Bai et al 2008, Heisler-White et al 2008, Bachman et al 2010, Cleland et al 2013, Germino and Reinhardt 2014. Although we cannot tease apart the role of climate from that of soil abiotic properties, our results indicate these factors combined may have contributed to different levels foliar damage, which in turn affected growth rate and survival.…”

Soil characteristics are associated with gradients of big sagebrush canopy structure after disturbance

“…For example, rougher soil surfaces and coarser soil textures can promote seed accumulation, germination, and the development of a tap root to access deeper soil moisture, with the latter being important for seedling survival (Chambers 2000, Germino and Reinhardt 2014, Brabec et al 2017. For example, rougher soil surfaces and coarser soil textures can promote seed accumulation, germination, and the development of a tap root to access deeper soil moisture, with the latter being important for seedling survival (Chambers 2000, Germino and Reinhardt 2014, Brabec et al 2017.…”

Mid‐latitude shrub steppe plant communities: climate change consequences for soil water resources

“…). Germino and Reinhardt () found that increases in winter precipitation increased big sagebrush canopy cover, due to higher soil water content in both upper and lower soil layers, but only on deep soils. Evidence from recent observations in western Wyoming indicate that extremely dry years may result in large big sagebrush die‐offs (Clause and Randall ) and smaller big sagebrush individuals may be particularly susceptible to drought‐related mortality due to small roots systems for water uptake (Campbell and Harris ).…”