Phenotypic plasticity of the coarse root system of Prosopis flexuosa, a phreatophyte tree, in the Monte Desert (Argentina)

Abstract

Prosopis flexuosa trees in the Monte Desert grow in dune and inter-dune valleys, where the water table is located at 6-14 m depth. We asked whether trees in the dunes, which are less likely to access the water table, present a coarse surface root architecture that might favor the exploration / exploitation of dune resources, compensating for water table inaccessibility. We characterized the architecture of surface roots of valley and dune trees, together with the soil environment. The dune held 50 % less and deeper gravimetric soil water (along a 4 m profile), 3-times less organic matter, 2-times less available phosphorous, and a sharper contrast of ammonium and nitrate concentration between plant canopies and uncovered soil than the valley. Coarse surface roots of dune trees were highly branched and grew tortuously at 0.56±0.16 m depth before sinking downward near the tree crown, suggesting an intensive exploitation of the ephemeral, deep, and canopy-linked resources. In contrast, trees from the valley spread their profuse and less branched surface roots mainly horizontally at 0.26±0.08 m depth, several meters outside the crown probably exploring this resource-rich site. A model for the environmental control of root architecture together with potential ecological effects is discussed.

Water status, drought responses, and growth of Prosopis flexuosa trees with different access to the water table in a warm South American desert

“…This confirms that P. flexuosa behaves as a facultative phreatophyte at the mostly arid end of its distribution, with the capacity to access groundwater and to survive entirely on rainfall, as suggested by previous xylem water isotopic analyses (Jobbágy et al 2010). We have previously demonstrated that P. flexuosa trees extend their surface roots deeper into the ground in the dune than in the valley which, coupled with a higher frequency of primary branches, would allow them to access subsurface rainfall-derived water reservoirs in the dune and thus compensate for inaccessibility of the water table (Guevara et al 2010), as occurs in Banksia attenuata dune (b) Photographs of leaves taken from the northern side of the tree crown at different hours; note that the sun is tilted toward the north in the southern hemisphere communities in western Australia (Zencich et al 2002). However, lower leaf W wPD in dune trees than in valley trees in dry periods indicates that plasticity of the former trees' surface roots is insufficient to avoid drought.…”

“…The depth of the water table was 7.1 m below the valley surface (assessed by a hand-dug well) with 25% w/w water in the 1.5-m wide capillary fringe (Jobbágy et al 2010). The dune held *3% w/w rainwater in 1-4 m deep water reservoirs, and both landscape units had a homogeneous sandy soil profile in the root zone (Jobbágy et al 2010;Guevara et al 2010).We studied three populations of P. flexuosa trees that due to their topographical position (valley-dune) or size (adultsapling) could have variable access to the water table and thus, varying dependence on rainfall: adult trees in the valley and the dune, for which we had isotopic evidence indicating different access to the water table (Jobbágy et al 2010), and saplings in the valley [nonreproductive tree-type individuals, base diameter 1.5-4.5 cm (Table 1), 4-10 years old], for which we have no isotopic data with which to distinguish water sources. We selected five similar-sized adult individuals at each landscape unit, and four saplings in the valley (14 individuals in total; Table 1).…”

Pruning effects on ring width and wood hydrosystem of Prosopis flexuosa DC from arid woodlands

“…This fact suggests that the effect of pruning would be even more evident in years when water availability is higher. The response found in small trees, alternatively, might be related to the root architecture of P. flexuosa, which presents a structure modulated by the geomorphology, nutrient availability and water supply (Guevara et al, 2010). P. flexuosa has a deep root system that allows trees to access the water table, thereby regulating the water supply; this provides some relative independence from the sporadic precipitation pulses that are typical in these arid regions (Noy Meir, 1973;Jobbágy et al, 2011).…”

Assessing the Potential of Sentinel-2 and Pléiades Data for the Detection of Prosopis and Vachellia spp. in Kenya

“…All these factors create favorable conditions for Prosopis proliferation. [11,16,22,23], summarizing the competitive advantages of Prosopis in seed production, root system, leaf and pod palatability. Figure 1.…”