Abstract
Despite considerable attention over the last 25yr, the importance of early protein breakdown products to plant nitrogen (N) nutrition remains uncertain. We used rhizosphere injection of 15 N-, 13 C- and 14 C-labelled inorganic N and amino acid (l-alanine), with chase periods from 1min to 24h, to investigate the duration of competition for amino acid between roots (Triticum aestivum) and soil microorganisms. We further investigated how microbial modification of l-alanine influenced plant carbon (C) and N recovery. From recovery of C isotopes, intact alanine uptake was 0.2-1.3% of added. Soil microbes appeared to remove alanine from soil solution within 1min and release enough NH4+ to account for all plant 15 N recovery (over 24h) within 5min. Microbially generated inorganic or keto acid C accounted for <25% of the lowest estimate of intact alanine uptake. Co-location of C and N labels appears a reasonable measure of intact uptake. Potential interference from microbially modified C is probably modest, but may increase with chase period. Similarly, competition for l-alanine is complete within a few minutes in soil, whereas NO3- added at the same rate is available for >24h, indicating that long chase periods bias outcomes and fail to accurately simulate soil processes.
Highlights
A wide range of plants are known to have the capacity to take up and utilise a variety of sources of N through their roots
Evidence from plants growing in ecosystems where N mineralisation is slow tends to support this hypothesis with reports of equal or more rapid acquisition of amino acid or peptide N than inorganic N, especially NO3
We further aimed to evaluate the degree to which potential uptake of microbially-modified amino acid C and N may influence results of pulse-chase experiments
Summary
A wide range of plants are known to have the capacity to take up and utilise a variety of sources of N through their roots These include L- and D-enantiomers of amino acids, short peptides, tertiary ammonium compounds and even intact proteins and soil microbes (Paungfoo-Lonhienne et al, 2008, 2010, 2012; Hill et al, 2011ac, 2013; Warren, 2013, 2014). Microbes in soil from a wide range of ecosystems are able to acquire and utilise amino acids and short peptides with half-times in soil solution as short as 20 seconds, suggesting intense plant-microbe competition (Jones et al, 2009; Hill et al, 2011b, 2012; Farrell et al, 2011b, 2013; Warren, 2018; Wilkinson et al, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
