Sequence and preference in the use of electron acceptors in flooded agricultural soils

*Corresponding author e-mail: t.wlodarczyk@ipan.lublin.pl **The paper was partly financed by project No. NN310115338 sponsored by Ministry of Science in Poland (2010-2013). Ab s t r a c t. Specifically, it was tested whether the presence of O2 in the headspace modified the sequence and preference of electron acceptor use under hypoxic conditions after prolonged drought in arable soils. This laboratory study was conducted in order to examine the use of electron acceptors: oxygen (O2), nitrate (NO3 ̄) and nitrous oxide (N2O), during aerobic and anaerobic respiration (denitrification). Agricultural soils (Typic Dystrudepts) classified as sandy, silty and loamy soils from arable top soils (0-30 cm) were used in the study. The change of oxidation states of different chemical species in the soil affected the use of electron acceptors during denitrification. The use of O2, NO3 ̄ and net N2O use was gradual and differed greatly among the soils. Furthermore, microorganisms were shown to be able to use all three investigated electron acceptors simultaneously, but with clearly visible preferences. The rate of electron acceptor use per day differentiated the investigated soils into a few different groups. Overall, the results of this study indicated that N2O was a more preferable electron acceptor than NO3 ̄ when O2 was present in the headspace for the most investigated soils. Moreover, a correlation existed between the final electron acceptor use and particle-size distribution and the native organic C content (Corg). The rate of electron acceptor use per day calculated for O2, NO3 ̄ and N2O may provide very important information for distinguishing the preference of electron acceptor use during aerobic and nitrate respiration in agroecosystems under hypoxic conditions after prolonged drought for different kinds of electron acceptor. K e y w o r d s: electron acceptor use, N2O net use, O2 consumption, NO3 ̄ reduction, flooded soils after drought INTRODUCTION