Metabolomic analysis of night-released soybean root exudates under high- and low-K conditions

Aims Root exudates of soybean grown under low-, normal-,
and high-K+ conditions were evaluated using
metabolomics.
Methods Two soybean cultivars, ‘Satonohohoemi’
(low-K-tolerant) and ‘Tachinagaha’ (low-K sensitive),
were hydroponically grown with 6 (K6), 60 (K60), and
120 (K120) mg K L−1 for 7 and 14 days after
transplanting (DAT). Root exudates were collected,
and metabolites were evaluated using capillary electrophoresis
time-of-flight mass spectrometry.
Results Rroot K concentration was lower in K6 and
higher in K120 compared to K60. Number of metabolites detected in ‘Satonohohoemi’ and
‘Tachinagaha’ was 43 and 39, respectively. Score plot
of the principal component analysis (PCA) showed a
clear grouping of the root exudate metabolites based one
three K concentrations and two sampling times, with the
first PCA accounting for 65.7% and 71.5% of the variance
for the ‘Satonohohoemi’ and ‘Tachinagaha’, respectively.
High-K conditions enhanced release of root
exudate metabolites to rhizosphere in both soybean
cultivars from 18% to 42%. However, low-K conditions
resulted in a 1.2-fold increase and a 2.5-fold decrease in
the release of root exudate metabolites in ‘Tachinagaha’
and ‘Satonohohoemi’, respectively, at 7 and 14 DAT.
Conclusions These results reveal that soybean roots
exude many metabolites in response to high- and low-
K conditions. The number of increased metabolites was
higher after long-term (14 DAT) compared to that of the
short-term (7 DAT) of exposure of high- and low-K
conditions. Soybean cultivars differ in the capacity to
release metabolites by altering the exudation of specific
metabolites for a better adaptation to the high- and low-
K conditions.