Effect of potassium phosphate fertilization on production and emission of methane and its ^1^3C-stable isotope composition in rice microcosms [An article from: Soil Biology and Biochemistry]

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Description:
Rice fields are an important source for atmospheric CH"4, but the effects of fertilization are not well known. We studied the turnover of CH"4 in rice soil microcosms without and with addition of potassium phosphate. Height and tiller number of rice plants were higher in the fertilized than in the unfertilized microcosms. Emission rates of CH"4 were also higher, but porewater concentrations of CH"4 were lower. The @d^1^3C values of the emitted CH"4 and of the CH"4 in the porewater were both 2-6% higher in the fertilized microcosms than in the control. Potassium phosphate did not affect rate and isotopic signature of CH"4 production in anoxic soil slurries. On the other hand, roots retrieved from fertilized microcosms at the end of incubation exhibited slightly higher CH"4 production rates and slightly higher CH"4-@d^1^3C values compared to roots from unfertilized plants. Addition of potassium phosphate to excised rice roots generally inhibited CH"4 production and resulted in increasingly lower @d^1^3C values of the produced CH"4. Fractionation of ^1^3C during plant ventilation (i.e. @d^1^3C in pore water CH"4 versus CH"4 emitted) was larger in the fertilized microcosms than in the control. Besides plant ventilation, this difference may also have been caused by CH"4 oxidation in the rhizosphere. However, calculation from the isotopic data showed that less than 27% of the produced CH"4 was oxidized. Collectively, our results indicate that potassium phosphate fertilization stimulated CH"4 emission by enhancing root methanogenesis, plant ventilation and/or CH"4 oxidation, resulting in residence times of CH"4 in the porewater in the order of hours.