Aspen Bibliography

Root ammonium transport efficiency as a determinant in forest colonization patterns: an hypothesis

Document Type

Article

Journal/Book Title/Conference

Physiologia Plantarum

Volume

117

Issue

2

First Page

167

Last Page

170

Publication Date

2003

Abstract

Ratios of ammonium (NH4+) to nitrate (NO3–) in soils are known to increase during forest succession. Using evidence from several previous studies, we hypothesize that a malfunction in NH4+ transport at the membrane level might limit the persistence of early successional tree species in later seral stages. In those studies, 13N radiotracing was used to determine unidirectional fluxes and pool sizes of NH4+ and NO3– in seedlings of the late-successional species white spruce (Picea glauca) and in the early successional species Douglas-fir (Pseudotsuga menziesii var. glauca) and trembling aspen (Populus tremuloides). At high external NH4+, the two early successional species accumulated excessive NH4+ in the root cytosol, and exhibited high-velocity, low-efficiency (15% to 22%), membrane fluxes of NH4+. In sharp contrast, white spruce had low cytosolic NH4+ accumulation, and lower-velocity but much higher-efficiency (65%), NH4+ fluxes. Because these divergent responses parallel known differences in tolerance and toxicity to NH4+ amongst these species, we propose that they constitute a significant driving force in forest succession, complementing the discrimination against NO3– documented in white spruce (Kronzucker et al. 1997).

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