Vesicular‐arbuscular mycorrhizas and the soil‐disturbance‐induced reduction of nutrient absorption in maize.

Abstract

SUMM.4RYMaize seedlings have been show-n to absorb more phosphorus (P) from soil from long term zero-til! plots than from the same soil after disturbance, apparently because of greater vesicular-arbuscular (VA) mycorrhizal colonization m the undisturbed soil. A growth room experiment was conducted to determine the effect of soil P availability on this phenomenon. Maize was grown for three 3-week cycles in initially disturbed soil. Phosphorus was mixed with tbe soil to create five P-amendment rates: 0, 40, 80, 120, and 160/igPg-' soil. After each growth cycle, the soil in half the pots w-as disturbed and replanted, -ivhereas the other half were replanted without disturbing the soil.In the third growth cycle, shoot dry w-eights were greater m the undisturbed soil than in the disturbed soil at the low.^er P-amendment rates, but soil disturbance had no effect at the 120 and 160/igPg"' soil amendments. Mycorrhizal colonization was much greater in the undisturbed soil at all P amendment rates. Shoot N, P, Mg, and Zn concentrations were higher in the undisturbed than in the disturbed soil at all P amendments, but only the increased P and Zn could be directly related to increased mycorrhizal colonization. While the benefit to the plant from mycorrhizal colonization induced by lack of soil disturbance can be quite large even at high rates of P amendment to the soil, the benefit achieved depends on the balance between the carbon (C) cost and P benefit to the host and may or may not favour the host.

Soil and fertilizer phosphorus: Effects on plant P supply and mycorrhizal development

“…Phosphorus fertilization does not always reduce mycorrhizal association. In studies reviewed by Miller et al (1995), extensive mycorrhizal colonization was observed even at very high rates of fertilization (Fairchild and Miller 1988). Localized concentration of P in fertilized systems could also influence mycorrhizal activity.…”

Arbuscular mycorrhizae and the phosphorus nutrition of maize: A review of Guelph studies

“…In addition, elimination of AM by either irradiation or application of a fungicide minimized the effect of disturbance (Evans and Miller 1988). Fairchild and Miller (1988) found that the manifestation of the effect did not require an extended period without disturbance. They began with disturbed soil and grew maize in a growth room for four cycles of 3-wk each, disturbing half the pots after each cycle.…”

Unraveling the network

“…Thus, the sym pathway is known to involve the perception of putative Myc or Nod factors by a receptor kinase (SYMRK; MtDM2 in Medicago truncatula), 57 followed by the presumed release of a plastidic factor via a putative plastid-localized ion channel (MtDM1), the involvement of a nucleoporin protein sharing homology with a component of the nuclear pore complex, and, ultimately, a down-stream induction of nuclear calcium signal spiking thought to be detected by a calcium-and calmodulin-dependent protein kinase (CCaMK; MtDM3), which leads to the induction of the complex genetic and metabolic re-programming required for the symbiosis. 31 An growth 26,27 or when the symbiosis-specific phosphate uptake mechanism of the plant is disrupted to such an extent that it prevents nutrient acquisition. 28,29 Signaling in the AM Symbiosis: New Messages From the Underground A plethora of experimental findings by diverse groups has dispelled some of the aura of mystery that still surrounds the mechanisms that lead to the establishment of the AM symbiosis.…”