L. Landi et al., CHANGES IN INORGANIC-N AND CO2 EVOLUTION IN SOIL INDUCED BY L-METHIONINE-SULFOXIMINE, Soil biology & biochemistry, 27(10), 1995, pp. 1345-1351
Short-term (up to 48 h) incubation assays were conducted in the presen
ce of L-methionine-DL-sulphoximine (MSX), an inhibitor of glutamine sy
nthetase, to assess its effect on exchangeable NH4+-N, NO3--N producti
on, and CO2 evolution. A sandy-clay-loam (Pistoia) and a sandy (Romola
) soil were moistened and either amended with glucose (200 mu mol gluc
ose-C g(-1) soil), glucose + (NH4)(2)SO4 [50 mu mol N g(-1) soil as (N
H4)(2)SO4] or left unamended. In the two unamended soils, NH4+-N conce
ntration was increased by the highest MSX level (1 mu mol g(-1) soil),
while the lowest inhibitor concentration (0.5 mu mol g(-1) soil) had
less influence. NH4+-N concentrations were higher with 1 mu mol MSX th
an without the inhibitor in the glucose-only-treated Pistoia soil in t
he 0-12 h period; thereafter the opposite situation was observed. Prob
ably the CO2 evolution increased as a result of inhibitor mineralizati
on after 12 h. In the glucose-treated Romola soil both MSX concentrati
ons were generally effective in increasing NH4+-N concentrations with
respect to the same amendment without the inhibitor. These increases w
ere probably due to glutamine synthetase inhibition by MSX and not to
the presence of mineralization of the inhibitor because CO2 evolution
was only slightly increased at 48 h by MSX. Probably, as a result of t
his inhibition, NO3--N was used as an alternative N source in the gluc
ose-amended Romola soil. The inhibitor had no significant effect on NH
4+-N concentration when both soils were amended with glucose + (NH4)(2
)SO4 probably because, in the presence of high NH4+-N concentrations,
NH3 assimilation occurred more through glutamate dehydrogenase than th
rough glutamine synthetase-glutamate synthase enzymes. NO3--N concentr
ations were decreased by MSX in the glucose-amended Romola but not in
the glucose-amended Pistoia soil.