Vol. 13, No. 2, November 2011: 197 - 208 Bionatura-Jurnal Ilmu-ilmu Hayati dan Fisik ISSN 1411 - 0903 DENITRIFICATION BY AZOSPIRILLUM BRASILENSE AND SINORHIZOBIUM SP IN THE PRESENCE OF THE NITRIFICATION INHIBITOR Tindaon, F., 1 Simarmata, T., 2 Benckiser, G., 3 and Ottow, J.C.G. 3 1 . Agroecotechnology Department, Faculty of Agriculture, Nommensen University, Medan 2 Department of Soil Sciences, Faculty of Agriculture, Padjadjaran University Bandung 3 . Institute for Applied Microbiology, Justus Leibig University, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany Tel. +49-641/99-37351,37352. Fax +49-641/99-37359 E-mail: Ferisman_Tindaon@yahoo.com ABSTRACT Investigation the effects of nitrifcation inhibitor viz, 3,4dimethylpyrazolephosphate (DMPP on denitrifcation and N 2 O/N 2 productions by N-fxers bacteria (Azospirillum brasilense Az204 and Sinorhizobium sp TNAU14 a model experiment was carried out in laboratory conditions. As a model experiments consisted of 3 treatments, control, 1% v/v C 2 H 2 and 1 µgDMPP mL -1 in combination with the inoculation of Azospirillum brasilense or Sinorhizobium sp. The concentration of N 2 O and CO 2 , the population density, and the level of nitrate, nitrite, and ammonium in the medium solution were analyzed. The results showed that the kinetic of N 2 O production by Azospirillum brasilense in the presence and absence of 1 % acetylene ranged about 2–18 µg N 2 O mL -1 day -1 , and 2–17 µgN 2 O mL -1 day -1 . The rate of N 2 O production by Sinorhizobium sp was about 4–15 µgN 2 OmL -1 day -1 and 4–12 µgN 2 OmL -1 day -1 in the presence and absence of 1% v/v acetylene.The N 2 O portion of total-denitrifcation los by Azosprillum brasilense or Sinorhizobium sp was about 70–98% and 80–95% and decreased until about 50–51% due to the decreasing of nitrate supply. The application of 1 µg DMPP mL -1 decreased both N-fxers population.The CO 2 -production by Azospirilum brasilense decreased signifcantly. DMPP may infuence the population of non-target-microorganism in soils. Key words : Azosprillium brasilense, Sinorhizobium sp, nitrifcation inhibitor PENGARUH INHIBITOR NITRIFIKASI TERHADAP AKTIVITAS DENITRIFIKASI OLEH AZOSPIRILLUM BRASILENSE DAN SINORHIZOBIUM SP ABSTRAK Kajian pengaruh inhibitor nitrifkasi 3,4 -dimethylpyrazolephosphat (DMPP) terhadap denitrifkasi dan produksi N 2 O/N 2 oleh bakteri pemfksasi nitrogen (Azospirillum brasilense Az 2 0 4 and Sinorhizobium sp TNAU14) telah dilakukan dalam bentuk percobaan model pada kondisi laboratorium. Percobaan terdiri dari 3 perlakuan yaitu kontrol: pemberian 1% v/v C 2 H 2 dan pemberian 1 µg DMPP mL -1 yang dikombinasikan dengan inokulasi Azospirillum brasilense atau Sinorhizobium sp. Pengukuran dilakukan terhadap konsentrasi gas yang dihasilkan yaitu N 2 O dan CO 2 , kerapatan populasi, kandungan nitrat, nitrit, dan ammonium dalam larutan media. Hasil penelitian menunjukkan bahwa produksi N 2 O oleh Azospirillum brasilense dengan perlakuan dan tanpa perlakuan 1% asetylen masing-masing sekitar 2–18 µg N 2 O mL -1 hari -1 , dan 2–17 µg N 2 O mL -1 hari -1 . Produksi N 2 O oleh Sinorhizobium sp berkisar 4–15 µg N 2 O mL -1 hari -1 dan 4–12 µg N 2 O mL -1 hari -1 yaitu dengan pemberian dan tanpa pemberian 1% asetylen. Kehilangan nitrat dalam bentuk emisi N 2 O melalui denitrifkasi oleh Azosprillum brasilense atau Sinorhizobium sp berkisar 70–98% dan 80–95% dan menurun hingga sekitar 50–51% akibat penurunan suplai nitrat. Perlakuan 1 µg DMPP mL -1 pada media pertumbuhan dapat menurunkan jumlah populasi kedua bakteri pemfksasi nitrogen. Produksi CO 2 oleh Azospirilum brasilense menurun secara signifkan. DMPP dapat mempengaruhi populasi mikroorganisma non target di dalam tanah. Kata kunci: Azosprillium brasilense, Sinorhizobium sp, inhibitor nitrifkasi