Root Communication Mechanisms and Intracommunity Distributions of Two Mojave Desert Shrubs

Abstract

Experimental studies using root observation chambers to observe the effects of encounters between individual roots on root elongation rates have revealed that the interactions among roots of Ambrosia dumosa and Larrea tridentata are more complex than simple competition for a limiting resource. Larrea roots inhibited elongation of either Larrea or Ambrosia roots in their vicinity, and Ambrosia roots inhibited elongation of contacted roots on other Ambrosia plants only. The purpose of the study reported here was to test the hypothesized involvement of inhibitory substances released by roots in these interroot encounters by attempting to remove such substances by adsorption to activated carbon. The presence of activity carbon caused a significant decrease in the inhibition of elongation of neighboring roots by Larrea roots, but activated carbon had no effect on the intraspecific responses of Ambrosia roots. These results support the hypotheses that the interaction mechanism of Larrea roots involves the release of a readily diffusible, generally inhibitory substance by Larrea roots into the soil, rather than a simple depletion of water or nutrients from around Larrea roots, and that the intraspecific, self—nonselfish—recognizing interaction mechanism of Ambrosia roots is mediated by contact and is fundamentally different from that of Larrea. These findings may enhance our understanding of Mojave desert community structure. The root—mediated allelopathy of Larrea may play a role in producing and maintaining the commonly occurring, regular distributions of Larrea. The complex communication mechanism of Ambrosia roots appears to constitute a detection and avoidance system that may allow this shrub to grow in clumped intraspecific distributions with little or no intraspecific competition for water. The interspecific interference between Larrea and Ambrosia in the field may be mechanistically asymmetrical due to their different root communication mechanisms.

Phytotoxicity, not nitrogen immobilization, explains plant litter inhibitory effects: evidence from solid‐state 13C NMR spectroscopy

“…The second bioassay, referred to as the 'root proliferation' experiment, was conducted in root observation chambers (Mahall & Callaway, 1992) with the aim of determining the capability of L. sativum seedling roots to colonize the different litter types independently from the germination process. A further aim was to assess the cause of growth inhibition.…”

Tragedy of the commons in plant water use

“…Is there any empirical evidence supporting these ideas? A study of desert shrubs in the Mojave desert revealed that Larrea tridentata (creosote bush) produces root allelochemicals that inhibit the root elongation of neighboring plants, both con specifics and of other species [Mahall and Callaway, 1992]. By virtue of this mechanism, Larrea individuals are able to have near exclusive access to the soil resources directly beneath their root system.…”

“…Studies of the water and carbon relations of Larrea do indicate that it is a species that has a strategy of very slow growth and remarkable drought resistance. The lifespan of a Larrea shrub can be longer than 100 years despite their very low stature, indicating extremely slow growth [Mahall and Callaway, 1992].…”

Microtopographic variation in soil respiration and its controlling factors vary with plant phenophases in a desert–shrub ecosystem

“…The C cycle in desert ecosystems cannot be ignored in the global C cycle (Austin, 2011;Poulter et al, 2014). R s represents the second largest C flux between ecosystems and the atmosphere (Raich and Schlesinger, 1992;Raich et al, 2002), and exhibits high spatial variation in desert ecosystems (Mahall et al, 1992;Gold et al, 1995;Xie et al, 2001). In addition, active, semi-active aeolian, and fixed sand dunes are the primary features of desert landscapes.…”