Direct acquisition of organic N by white clover even in the presence of inorganic N

Abstract

This study was conducted to answer the question of whether clover can absorb asparagine in the presence and absence of inorganic nitrogen, as well as to determine the resulting concentration of post-uptake compounds closely involved in asparagine metabolism. Clover was grown at two asparagine concentrations (10 μM and 1 mM) supplied in both the absence and presence of ammonium nitrate. Using dual-labeled 13C15N-asparagine, the uptake rate was analyzed via bulk 15N and 13C excess and the detection of intact 13C15N-asparagine in white clover. The results from the two methods indicated greater utilization of 13C15N-asparagine in the 10 μM treatment than in the 1 mM treatment. The 13C15N-asparagine uptake rate was higher when 13C15N-asparagine was provided alone than when it was supplemented with inorganic nitrogen. Up to nine times lower uptake rates were obtained when intact 13C15N-asparagine was measured than when bulk 15N and 13C excess were analyzed. The labeled amino acids that are closely related to 13C15N-asparagine metabolism (aspartic acid, glutamic acid and glutamine) were detected in clover roots and shoots. Using two different methods, white clover’s potential to absorb intact asparagine, even in the presence of inorganic nitrogen, was confirmed. The dual-methodology approach employed in this study demonstrates how the post-uptake metabolism can affect quantification of amino acid uptake.