The functional role of carbonate-cemented soil horizons in desert ecosystems: Spatial and temporal dynamics of plant water availability

In water limited ecosystems, soil profile characteristics can control plant community composition and production through their effects on spatial and temporal patterns of plant available water. Little is known, however, about water availability in soil horizons cemented with carbonates (petrocalcic horizons), which occur extensively in arid ecosystems. To investigate petrocalcic water retention and dynamics, a series of replicated experiments at multiple spatial scales was conducted in a mixed shrub-grass community in southern New Mexico, USA. A laboratory study was conducted evaluating the water holding capacity of a variety of petrocalcic material. Petrocalcic temporal water availability and dynamics were monitored in two multiyear field studies: a pasture scale study comparing water availability across soils with differing degrees of petrocalcic development and a companion patch-interspace scale study investigating soil-water dynamics associated with woody shrub encroachment in a petrocalcic soil. Petrocalcic available water holding capacities were up to four times those of the sandy loam parent material. Calcic and petrocalcic horizons retained much greater amounts of available soil water for several months following above-normal winter and summer precipitation than similar depths in a non-carbonate sand. The companion study in the petrocalcic soil showed that unvegetated interspaces absorbed significantly more soil water during a wet winter and retained more available soil water into the spring than soils under shrubs. Wetting and drying dynamics indicate petrocalcic horizons release stored water into the grass rooting zone. Furthermore, patterns of water availability suggest soils with shallow petrocalcic horizons are beneficial to the establishment and persistence of grasses.