Functional Differences in Water‐Use Patterns of Contrasting Life Forms in Great Basin Steppelands

Abstract

The temporal pa erns of evapotranspira on were monitored for 2 yr for four species of differing life form that currently form near monoculture communi es in the Great Basin, USA, a region with a growing season spanning early spring to autumn and predictable overwinter water accumula on in the vadose zone. Species included an annual grass (Bromus tectorum L.), a perennial grass [Agropyron desertorum (Fisch. ex Link) Schult.], a shrub (Artemisia tridentata Nu . ssp. wyomingensis Beetle and Young), and a tree [Juniperus osteosperma (Torr.) Li le]. The two grasses and shrub were growing on the same soil type with uniform texture and subject to near surface percola on of the vadose zone only, while J. osteosperma was growing on soils with a petrocalcic layer below which water was near fi eld capacity. These monotypic stands were found to diff er in quan ty and ming of vadose zone water use, in use pa ern of shallow and deeper water resource pools, and in depth and quan ty of rainwater hydraulically redistributed. All species rapidly u lized shallow vadose zone water in the spring when growth was observed, but use of deep vadose zone water varied by life form and was not linked with the period of growth for any species. Water in the vadose zone of the grass species increased between years, with evapotranspira on less than precipita on inputs and contrasted to water use in A. tridentata where water use approximately equaled precipita on inputs. Juniperus osteosperma used water below the petrocalcic zone, par cularly in late summer. Water use by all species was consistent with the concept of a shallow vadose zone "growth pool" of water and a deeper vadose zone "maintenance pool" used during the summer drought period. The pa erns of water use suggest that water per se is not a limited resource for survival, but infl uences the availability of nutrients necessary for plant growth that are associated with shallow vadose zone water. We postulate that cold-adapted plants in the Great Basin have converged on a general pa ern of rapidly u lizing soil moisture in shallow depths, in part, to infl uence nutrient availability. Our results strongly suggest describing the pool dynamics of vadose zone water will be necessary to further our understanding of plant fi tness, interac ons among species for resources, and species coexistence in arid and semiarid ecosystems.Abbrevia ons: ET, evapotranspira on; LAI, leaf area index.The emerging science of ecohydrology explicitly recognizes the fundamental role that vegetation plays in vadose zone hydrology at scales from the community to the watershed. Th ese eff ects modify, and in part control, water inputs, movement, and losses from the vadose zone. For example, plants modify water input to soils and ultimately watersheds through processes including precipitation interception (Bosch and Hewlett, 1982;Brown et al., 2005;LaMalfa and Ryel, 2008), fog condensation (Azevedo, 1974;Ewing et al., 2009), alteration of surface movement by slowing fl ow paths (Schlesinger et al., 1990; Wilcox et al....

The role of resource limitation in restoration of sagebrush ecosystems dominated by cheatgrass (Bromus tectorum)

“…Other annual plant biomass was negatively correlated with cheatgrass biomass per plot, and this relationship was likely due to direct competition for soil resources. Nutrients, particularly NH 4 þ , in cold desert shrublands are most available to plant roots in shallow soil depths when soil water is high enough to facilitate diffusion to root surfaces (Ryel et al 2010). Cold-adapted annuals in these systems generally utilize soil water and nutrients from this same resource pool (Ryel et al 2010).…”

“…Nutrients, particularly NH 4 þ , in cold desert shrublands are most available to plant roots in shallow soil depths when soil water is high enough to facilitate diffusion to root surfaces (Ryel et al 2010). Cold-adapted annuals in these systems generally utilize soil water and nutrients from this same resource pool (Ryel et al 2010). Disturbances like fire that reduce litter and cheatgrass seed density and increase available soil nutrients and water can shift the competitive balance in favor of invasive annual forbs (Ducas et al 2011, Chambers et al 2014b.…”

A Process-Based Application of State-and-Transition Models: A Case Study of Western Juniper (Juniperus occidentalis) Encroachment

“…Plant community composition, structure, and productivity are all strongly coupled with the timing and amount of ecosystem water availability (Flerchinger et al, 1998(Flerchinger et al, , 2010Rodriguez-Iturbe, 2000;Ryel et al, 2010;Chauvin et al, 2011;Roundy et al, 2014b). Sagebrush and herbaceous productivity is strongly tied to soil water recharge deep in the soil profile (Cline et al, 1977;Sturges, 1977;Richards and Caldwell, 1987;Caldwell and Richards, 1989;Ryel et al, 2004;Schlaepfer et al, 2012).…”

Importance of soil and plant community disturbance for establishment of Bromus tectorum in the Intermountain West, USA

“…This raises the possibility that B. tectorum may facilitate its own persistence on the landscape if its early senescence in summer increases N availability (due to lack of N uptake by other species) in autumn when it germinates (Leffler et al 2011, Jones et al 2015. A similar enhancement of soil water was observed in B. tectorum compared to perennial communities in western Utah (Ryel et al 2010).…”