Amino Acid Absorption by Arctic Plants: Implications for Plant Nutrition and Nitrogen Cycling

Abstract

Recent studies of nitrogen (N) cycling in arctic tundra have indicated that inorganic N supplied to plants by mineralization is not sufficient to meet the annual requirement of N by many tundra species. Whereas N mineralization is slow in tundra soils and concentrations of inorganic N are low, these soils have large stocks of both structural and soluble organic N. In light of these observations, kinetics of absorption of three amino acids (glycine, aspartic acid, and glutamic acid) were measured in dominant vascular plant species of the four major ecosystems types in arctic Alaska and compared with concentrations of free amino acids in soils. Absorption rates were measured on roots using 14C—labeled substrates. Concentrations of free amino acids in soil were measured on water—extracted samples by high pressure liquid chromatography. All species had higher capacity (Vmax) for ammonium uptake (measured using methylamine as an ammonium analogue) than for any amino acid. However, at concentrations observed in the field, uptake rates estimated for amino acids were similar to (glycine) or less than (aspartic and glutamic acids) that for ammonium. On the basis of these comparisons, uptake rates of the three amino acids together may account for between 10 and 82% of the total N uptake in the field, depending on species and community. Deciduous shrubs had higher uptake rates than the more slowly growing evergreen shrubs, suggesting that new growth created a sink that strongly influenced capacity for amino acid uptake. In general, ectomycorrhizal species had higher amino acid uptake than did non—mycorrhizal species. In species that were sampled from more than one community, amino acid uptake rates were highest in the community where a given amino acid was most abundant in the soil. The results indicate that, in arctic tundra, plants short—circuit the mineralization step of decomposition by directly absorbing amino acids. This implies that in the organic soils of these tundra systems (1) inorganic nitrogen is an inadequate measure of plant—available soil nitrogen, (2) mineralization rates underestimate nitrogen supply rates to plants, (3) the large differences among species in capacities to absorb different forms of N provide ample basis for niche differentiation of what was previously considered a single resource, and (4) by short—circuiting N mineralization, plants accelerate N turnover and effectively exert greater control over N cycling than has been previously recognized.

Dissolved Organic Carbon in Terrestrial Ecosystems: Synthesis and a Model

“…We also do not address the direct uptake of DOC by plants. Plant uptake of dissolved organic nitrogen (DON) may occur in northern latitude ecosystems (Nasholm and others 1998;Kielland 1994), but to date, only amino acid uptake has been observed. Although this may be an important source of nitrogen for plants (Chapin 1995), it is not likely to have a large impact on soil DOC fluxes because the amino acid fraction of soil organics is generally less than 2% (Qualls and others 1991).…”

Phosphate Solubilizing Bacillus megaterium mj1212 Regulates Endogenous Plant Carbohydrates and Amino Acids Contents to Promote Mustard Plant Growth

“…5). The uptake of nitrogen by plants in the form of amino acids has been determined as a widespread ecological phenomenon [20]. The microbial colonization in plants strongly influences amino acid uptake [21].…”

Uptake and recovery of soil nitrogen by bryophytes and vascular plants in an alpine meadow

“…Furthermore, amino acid as one kind of organic N forms has been found to represent another important N source for plants in 'cold biomes' (Kielland 1995;Raab et al 1996Raab et al , 1999Persson et al 2003;Krab et al 2008). It is proposed that differences between species to utilize particular N sources can be an important feature of plant community composition (Kielland 1994;Schimel and Bennett 2004;Cambui et al 2011). Therefore, further studies are required to test how N utilization of different plants vary, which would be another significant issue to explore the differentiation of N utilization, especially at functional groups level (Ayres et al 2006;Krab et al 2008).…”