Ecological Responses of Two Mojave Desert Shrubs to Soil Horizon Development and Soil Water Dynamics

Abstract

In the arid southwestern United States, subtle differences in soil horizon development affect seasonal soil hydrology and consequently influence plant performance and community structure. We measured canopy development, population structure, and seasonal ecophysiology (predawn water potential, pd , and midday net photosynthetic assimilation, A net ) of two co-dominant warm-desert shrubs, the evergreen Larrea tridentata and drought-deciduous Ambrosia dumosa, in five Mojave Desert soils varying in surface and sub-surface soil development, and we used process-based soil hydrology modeling output to determine longer-term soil water dynamics underlying soil/plant responses. We hypothesized that ecophysiological performance would covary with plant development, which would reflect soil hydrological characteristics.Among three sites on alluvial fan deposits of different geological ages (Young Alluvial, Ͻ4000 yr BP; Intermediate Alluvial, ϳ12 000 yr BP; Old Alluvial, ϳ40 000 yr BP), total canopy volume of Larrea (cubic meters per 100 m 2 ground area) was highest on the Young Alluvial site, in close agreement with soil modeling results showing that these coarsetextured, weakly developed soils permit deeper water infiltration. In older, stronger developed soils, infiltration and persistence of soil water was sharply reduced, which was reflected by lower individual Larrea plant volumes. However, during peak spring conditions, pd and A net were highest in Larrea at the Intermediate Alluvial site (Ϫ4.2 Ϯ 0.32 MPa and 3.2 Ϯ 0.91 mol·m Ϫ2 ·s Ϫ1 ), where soils had substantial surface and subsurface horizons, and at the Pavement site, where soils had strong surface layers but little subsurface development. Concurrent plant performance at the Young Alluvial site was unexpectedly low (Ϫ4.8 Ϯ 0.49 MPa and 1.7 Ϯ 0.56 mol·m Ϫ2 ·s Ϫ1 , respectively). During summer drought pd and A net remained high in Intermediate Alluvial plants, but were extremely low in Pavement site Larrea (Ϫ8.17 MPa and Ϫ0.04 mol·m Ϫ2 ·s Ϫ1 , respectively), due to curtailed infiltration of summer precipitation. These findings suggest that Larrea growing in older soils experience greater mortality and reduced growth but are not subject to strong intra-specific competition resulting from the persistence of large individuals apparent in younger, coarser textured soils.In contrast to Larrea, density of Ambrosia increased with soil horizon development, but smaller plant sizes resulted in similar canopy volume per area, and identical pd and A net across all soils where it occurred, suggesting greater plasticity to the transmittal of precipitation. These findings show that a strong geomorphology and soils context is essential for understanding the variation in plant responses and vegetation structure in desert environments.

Inter- and under-canopy soil water, leaf-level and whole-plant gas exchange dynamics of a semi-arid perennial C4 grass

“…4). This is similar to dynamics observed in desert shrubs growing in contrasting soils that differ in infiltration depth and persistence of seasonal rainfall (Hamerlynck et al 2002). Such changes may also explain the higher intercanopy R auto frequently observed across 2008; however, the large degree of within-location variation (Fig.…”

“…Canopy volume (V in m 3 ) estimations accounted for age-dependent differences in canopy height/diameter relationships. Young plants were modeled as prolate spheroids Hamerlynck et al 2002). One-way ANOVA (Statistix v 8.0; Analytical Software, Tallahassee, FL, USA) was used to test for differences in basal diameter, canopy height, area, e and volume; volume data were log 10 -transformed to meet ANOVA data distribution assumptions (Zar 1974).…”

“…The consistently greater cover and density of bush muhly under trees and shrubs (McClaran and Bartolome 1989;Livingstone et al 1997) have been attributed to enhanced understory soil moisture (Livingstone et al 1997). However, more recently, Tiedemann and Klemmedson (2004) showed bush muhly productivity can increase with canopy removal, and McClaran and Angell (2007) suggested smaller plants sizes and higher densities of bush muhly under mesquite indicated limited soil moisture, as observed in other arid systems (Hamerlynck et al 2002), and postulated that bush muhly's dominance in these locations reflected a high degree of drought tolerance. We specifically tested McClaran and Angel's hypothesis, and expected that if it were true:…”

Response of net ecosystem gas exchange to a simulated precipitation pulse in a semi-arid grassland: the role of native versus non-native grasses and soil texture

“…For example, the dominant North American shrub, Larrea tridentata, is heavily influenced by soil characteristics (Shreve and Mallery 1933;Smith et al 1995;Hamerlynck et al 2000), such that the presence of cemented subsurface Calcic horizons and surface pavement development affect soil water balance, plant water-relations and productivity (Cunningham and Burke 1973;Hamerlynck et al 2002). Thus, characteristics of soil surfaces can modify climate signals into differential biological activity, impacting the surrounding vegetation composition and performance (McAuliffe 1994(McAuliffe , 1999Parker 1995;Smith et al 1995;Hamerlynck et al 2002). The interaction between plants and soil characteristics are also of importance for hydrological processes, such as runoff, recharge and sediment transport (Wainwright et al 2002).…”

Runoff Generation, Overland Flow and Erosion on Hillslopes

“…The difficulty plant roots have in penetrating these horizons -most likely because of feedbacks with soil-water chemistry -is often a significant feedback on the ability of desert plants to maintain themselves (Cunningham and Burk, 1973;McAuliffe, 1994;Escoto-Rodríguez and Bullock, 2002;Gibbens and Lenz, 2001). Other developments of soil horizonisation, either at the surface (Abrahams and Parsons, 1991a;Young et al, 2004) or in the subsurface (Hamerlynck, McAuliffe and Smith, 2000;Hamerlynck et al, 2002), have been noted as having significant effects on reducing infiltration rates.…”