Näsholm T, Kielland K, Ganeteg U
Uptake of organic nitrogen by plants
New Phytologist: 2009, published on line
Summary
Languishing for many years in the shadow of plant inorganic nitrogen
(N) nutrition research, studies of organic N uptake have attracted
increased attention during the last decade. The capacity of plants to
acquire organic N, demonstrated in laboratory and field settings, has
thereby been well established. Even so, the ecological significance of
organic N uptake for plant N nutrition is still a matter of discussion.
Several lines of evidence suggest that plants growing in various
ecosystems may access organic N species. Many soils display amino acid
concentrations similar to, or higher than, those of inorganic N, mainly
as a result of rapid hydrolysis of soil proteins. Transporters
mediating amino acid uptake have been identified both in mycorrhizal
fungi and in plant roots. Studies of endogenous metabolism of absorbed
amino acids suggest that L- but not D-enantiomers are efficiently
utilized. Dual labelled amino acids supplied to soil have provided
strong evidence for plant uptake of organic N in the field but have
failed to provide information on the quantitative importance of this
process. Thus, direct evidence that organic N contributes significantly
to plant N nutrition is still lacking. Recent progress in our
understanding of the mechanisms underlying plant organic N uptake may
open new avenues for the exploration of this subject.
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