Resource partitioning between shrubs and grasses in the Patagonian steppe

Abstract

Experiments were conducted in the Patagonian steppe in southern South America to test the following hypotheses: (a) grasses take up most of the water from the upper layers of the soil and utilize frequent and short-duration pulses of water availability; (b) shrubs, on the contrary, take up most of the water from the lower layers of the soil and utilize infrequent and long-duration pulses of water availability. Grasses and shrubs were removed selectively and the performance of plants and the availability of soil resources were monitored. Results supported the overall hypothesis that grasses and shrubs in the Patagonian steppe use mainly different resources. Removal of shrubs did not alter grass production but removal of grasses resulted in a small increase in shrub production which was mediated by an increase in deep soil water and in shrub leaf water potential. The efficiency of utilization of resources freed by grass removal was approximately 25%. Shrubs used water exclusively from lower soil layers. Grasses took up most of the water from upper layers but they were also capable of absorbing water from deep layers. This pattern of water partitioning along with the lack of response in leaf nitrogen to the removal treatments suggested that shrubs may be at a disadvantage to grasses with respect to nutrient capture and led to questions about the role of nutrient recirculation, leaching, and nitrogen fixation in the steppe.

Higher effect of plant species diversity on productivity in natural than artificial ecosystems

“…Resources used by plants supported the idea of niche complementarity. We found that plots with grasses, which in the Patagonian steppe are shallow-rooted in comparison with shrubs (22), decreased soil water content on the upper 20 cm of the soil profile in spring and at the end of the growing season (ANOVA: Oct 02, F 1,82 ϭ 4.095, P Ͻ 0.05; May 03, F 1,82 ϭ 3.620, P Ͻ 0.061) (SI Fig. 6).…”

“…In the Patagonian experiment, niche partitioning and positive interactions reflected long-term species coexistence. Grasses and shrubs in the steppe showed extensive niche partitioning for soil water use with depth (22,24). Other differences are also very likely to occur, such as soil water use in time by species with different phenology, and differences in nutrient use in space and time (25).…”

Controls on nitrification in a water-limited ecosystem: experimental inhibition of ammonia-oxidising bacteria in the Patagonian steppe

“…The vegetation is classified as semiarid steppe, with the dominant life forms of perennial tussock grasses and shrubs, which account for . 95% of the aboveground biomass of this community (Sala et al, 1989;Golluscio and Sala, 1993). Vegetative cover is discontinuous, with cover of 25% by grass species and 12% by shrub species (Fernández et al, 1991).…”

“…Ecosystem processes in semi-arid ecosystems such as those located in the Patagonian region of Argentina, are primarily limited by water availability (Sala et al, 1989;Jobbágy and Sala, 2000). The Patagonian steppe is codominated by shrubs and grasses on a matrix of bare soil.…”

Tree–grass co-existence in savanna: Interactions of rain and fire

“…Models based on the 'Walter hypothesis' -4-have been widely applied in literature (Walker et al, 1981, Walker and Noy-Meir, 1982, Eagleson and Segarra, 1985, van Langevelde et al, 2003. Some experiments and observations have supported 'Walter hypothesis' (Knoop and Walker, 1985, Sala et al, 1989, Pelaez et al, 1994 but many others have cast doubts on the existence of vertical rooting niche separation (Scholes and Walker, 1993, Belsky, 1990, Le Roux et al, 1995, Mordelet et al, 1997, Smit and Rethman, 2000, Hipondoka et al, 2003.…”