Root communication among desert shrubs.

Abstract

Descriptive and experimental studies of desert shrub distributions have revealed important questions about the mechanisms by which plants interact. For example, do roots interact by mechanisms other than simple competition for limiting resources? We investigated this question using the desert shrubs Ambrosia dumosa and Larrea tridentata grown in chambers that allowed observation of roots during intraplant and intra-and interspecific interplant encounters. Two types of root "communication" were revealed. Ambrosia root systems appear to be capable of detecting and avoiding other Ambrosia root systems, whereas Larrea roots inhibit Larrea andAmbrosia roots in their vicinity.Horizontal distributions of desert plants have intrigued ecologists for many years and have been commonly interpreted in terms of competition, allelopathy, or protection (e.g., refs. 1-12). In the first experimental evaluation of such patterns Fonteyn and Mahall (11,12) found no evidence for intraspecific interference for water among Ambrosia dumosa Payne (Asteraceae) shrubs, which have a clumped distribution, but Ambrosia shrubs in this same population routinely interfered with water availability to Larrea tridentata Cov. (Zygophyllaceae) shrubs, relative to which Ambrosia shrubs are distributed randomly. Why, then, do Ambrosia shrubs not interfere for water with each other? This question cannot be answered by simply invoking competition for limiting resources. We investigated other postulated mechanisms that could answer this question using specially designed root observation chambers in the laboratory. Our results suggest the existence of an unexplored complexity of root-root interaction mechanisms. MATERIALS AND METHODSAmbrosia plants grown from seed and small Larrea plants collected from the field were planted in flat, rectangular chambers filled with fine sand and oriented at a 450 angle so that positively geotropic roots would grow down along Plexiglas viewing windows covered with removable, opaque shutters (Fig. 1). The chambers were placed in a bright, warm greenhouse and the sand in them was kept continually moist and flushed with one-eighth strength Hoagland's solution every 8-10 days. After a period of establishment and growth, pairs of chambers were connected together, so that roots of a "test" plant would grow into the rhizosphere of a "target" plant. Elongation rates of all test plant roots visible through the viewing windows were calculated from measurements of length (to an accuracy of 0.1 mm) made at recorded times every 2 days. Elongation rates of target plant roots were not monitored, because at times of contact many were reorienting at 90°and/or touching the sides or ends of the chambers. We used Ambrosia and Larrea for test plants and live Ambrosia and Larrea roots for targets. Inert physical barriers of braided dacron line were used for control targets. RESULTSRates of elongation of Ambrosia roots in the inert physical barrier control (PBC) experiments averaged 0.39 ± 0.10 mm/hr (mean ± standard deviation based on ...

Growing with siblings: a common ground for cooperation or for fiercer competition among plants?

“…Individual root recognition has been predominantly identified in experiments showing that the root tip growth of a plant responds differently when the plant runs into the roots of another plant than when it runs into its own roots, i.e. self/non-self (S/NS) root discrimination (Mahall & Callaway 1991;de Kroon et al 2003). A plant's ability to distinguish its own roots should be an inherent skill, because root growth occurs in a remarkably heterogeneous space (Hodge 2004).…”

Physiologically-Mediated Self/Non-Self Root Discrimination inTrifolium repenshas Mixed Effects on Plant Performance

“…Mahall and Callaway [14][15][16] found that roots of the desert shrub Ambrosia dumosa responded to contacts with roots of different Ambrosia plants by decreasing their rate of elongation, but showed no such response when contacting other roots of the same individual plant. By contrast, Falik et al 17 have shown that roots of Pisum sativum decreased root growth in the presence and in the direction of their own roots compared to roots of other plants.…”

Genotypic recognition and spatial responses by rice roots

“…There is evidence that the outcome of belowground interactions between plants, of the kind illustrated in the previous set of examples, can be mediated by identity recognition, including species-specific responses (23)(24)(25)(26), kin/stranger responses (27)(28)(29)(30), and self/nonself responses (2, 3). Mahall and Callaway (23) found that root systems of the desert shrub Ambrosia dumosa appear to be capable of detecting and avoiding other Ambrosia root systems.…”

“…Mahall and Callaway (23) found that root systems of the desert shrub Ambrosia dumosa appear to be capable of detecting and avoiding other Ambrosia root systems. In contrast, roots of another desert shrub species, Larrea tridentata, inhibit both Larrea and Ambrosia roots in their vicinity.…”