Competition for amino acids between wheat roots and rhizosphere microorganisms and the role of amino acids in plant N acquisition

• Published in: Soil biology & biochemistry 2001-04, Vol.33 (4), p.651-657
• Main Authors: Owen, A.G, Jones, D.L
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Amino acids; Biological and medical sciences; Dissolved organic nitrogen; Economic plant physiology; Fundamental and applied biological sciences. Psychology; Mineral nutrition; Nutrition. Photosynthesis. Respiration. Metabolism; Plant-microbial competition; Rhizosphere
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/S0038-0717(00)00209-1

The direct uptake of organic nitrogen compounds from the soil solution by plant roots has been hypothesised to constitute a significant source of N to the plant particularly in N limiting ecosystems. The experiments undertaken here were designed to test whether wheat roots could out-compete the rhizosphere microflora for a pulse addition of organic N in the form of three contrasting amino acids, namely lysine, glycine and glutamate. Amino acids were added at a concentration reflecting reported soil solution concentrations (100 μM) and the uptake into either plant biomass or respiration or microbial biomass and respiration determined over a 24 h chase period. The results showed that the plant roots could only capture on average 6% of the added amino acid with the remainder captured by the microbial biomass. We therefore present direct in vivo evidence to support earlier work which has hypothesised that organic N may be of only limited consequence in high input agricultural systems. We suggest that this is a result of the higher concentrations of NO 3 − in agricultural soil solutions, the slow movement of amino acids in soil relative to NO 3 −, the rapid turnover of amino acids by soil microorganisms, and the poor competitive ability of plant roots to capture amino acids from the soil solution.