Judul: Keragaman Streptomyces sp. Rizosfer Jagung Penambat Nitrogen
Abstrak: PGPR merupakan mikroorganisme yang mampu memacu pertumbuhan tanaman melalui beberapa mekanisme, antara lain melalui aktivitas senyawa pelarutan fosfat dan penambatan nitrogen. Salah satu kelompok PGPR yang memiliki kemampuan penambatan nitrogen adalah aktinobakteri. Penelitian bertujuan mengetahui keragaman aktinobakteri penambat nitrogen yang diisolasi dari rizosfer jagung. Sembilan isolat aktinobakteri yang diuji dapat tumbuh pada media bebas nitrogen. Pengukuran aktivitas penambatan nitrogen menggunakan metode acetylene reduction assays (ARA) menunjukkan laju penambatan nitrogen berkisar antara 0.046 μmol jam-1 sampai dengan 1.59 μmol jam-1. Identifikasi molekuler gen 16S rRNA menunjukkan kesembilan isolat aktinobakteri termasuk dalam genus Streptomyces tetapi berasal dari spesies dan strain yang berbeda. Hasil penelitian mengindikasikan bahwa isolat-isolat tersebut berpotensi sebagai agen pemacu tumbuh tanaman melalui fiksasi nitrogen.
Keyword: 16S rRNA, aktinobakteri rizosfer, acetylene reduction assays, fiksasi nitrogen

Judul: Aktivitas pemacuan pertumbuhan tanaman oleh aktinomiset yang diisolasi dari rizosfer tamanan jagung
Abstrak: Aktinomiset merupakan salah satu rizobakteri yang berperan penting sebagai pemacu pertumbuhan pada tanaman atau Plant Growth Promoting Rhizobacteria (PGPR). Penelitian ini dilakukan untuk mengetahui potensi aktinomiset asal rizosfer jagung dalam memacu pertumbuhan tanaman menggunakan benih jagung, menguji kemampuan isolat aktinomiset dalam melarutkan fosfat menggunakan media Pikovskaya, dan menguji aktinomiset rizosfer dalam memfiksasi nitrogen menggunakan media bebas nitrogen. Hasil uji hipersensitivitas terhadap daun tembakau menunjukkan hasil negatif pada seluruh isolat yang diujikan. Berdasarkan uji kolorimetri, 30 isolat diketahui mampu menghasilkan IAA dengan konsentrasi tertinggi 26.89 ppm (ARJ 21) dan konsentrasi terendah 1.05 ppm (ARJ 12). Hasil uji pemacu tumbuh pada kecambah jagung diperoleh 9 isolat (ARJ 51, ARJ 81, ARJ 14, ARJ 38, ARJ 44, ARJ 32, ARJ 16, ARJ 28, ARJ 15) yang mampu meningkatkan panjang akar primer, panjang batang, jumlah akar lateral, bobot basah dan bobot kering. Hasil uji pelarutan fosfat diperoleh 21 isolat dari 30 isolat yang diuji diketahui mampu melarutkan fosfat dengan indeks pelarutan fosfat tertinggi adalah ARJ 81. Hasil uji penambatan nitrogen menunjukkan 30 isolat mampu memfiksasi nitrogen yang ditandai dengan tumbuhnya koloni aktinomiset pada media bebas nitrogen. Pengamatan morfologi lima isolat potensial memiliki keragaman warna miselia aerial dan menunjukkan tipe miselium yang sama yaitu spiral, berdasarkan pengamatan tersebut kelima isolat potensial termasuk kedalam genus Streptomyces.
Keyword: fiksasi nitrogen, indole-3-acetic acid, pelarutan fosfat

Judul: Thermal Characteristics and Dynamics of Tropical Cyclone over Western North Pacific Ocean: A Case Study of Typhoon Songda (Chedeng) 2011
Abstrak: The frequent occasion of Tropical Cyclone (TC) over Western North Pacific (WNP) Ocean lies from 10˚N to 26˚N and 121˚E to 170˚E. Sources of TC development come from warm ocean temperature where latent heat is released during condensation processes and subsequently concentrated in the boundary layer. Relative humidity at 850-700 hPa is responsible to produce the most intense storm. Meanwhile, weak vertical wind shear between 850-200 hPa is one of the dynamical factors that lead to the development of TC. Pressure level of 850-200 hPa is chosen to minimize the thermodynamic effect in the lower troposphere. Typhoon Songda (Chedeng in the Philippines) or TSC lasted from May 18th to 30th, 2011 and strengthened into powerful Super Typhoon stage between May 24th and 27th. Long curving track and the exhibition of all sequences of TC life cycle, TSC is then considered as an ideal case of TC. The objective of the study with case of TSC is to investigate the role of thermal characteristics and dynamics on TC intensity. The research is carried out by using Advanced Research of Weather Research and Forecasting model (WRF ARW model) version 3.3. Two domains are employed in the model. The first domain situate from 02˚N to 40˚N and 118˚E to 149˚E and cover spatial resolution () of 33.1 km. The second domain situate from 09˚N to 27˚N and 119˚E to 132˚E with of 11 km. Timestep of the model () is 120 seconds. The model is supported by the following physical parameterization, i.e., Yonsei University Scheme (YSU) in the boundary layer, Kain-Fritsch scheme (KF) in the cumulus, and WRF Single-Moment 3-class scheme in the microphysics. Initial meteorological condition prior to the formation of the cyclone is generated using WRF ARW standard-release model. Sensitivity of the model output is obtained from a selected single-parameter change scenarios, namely, 10 % to 20 % decrease and increase of wind shear initial data at 850-200 hPa, and by 10 % to 20 % decrease of relative humidity initial data at 850-700 hPa. The result showed that the negative correlations between wind shear and intensity are found in wind shear scenarios. Wind shears of 10 ms-1 which lead to strengthening of the wind intensity in the early period of Typhoon development are found in wind shear scenarios. The effect of wind shear changes on wind intensity is statistically significant in the 20 % wind shear scenarios. During mature stage, weak wind intensity occurred when wind shear increase as given in the WRF standard-release and the 20 % decreasing scenario. Different situation is found in the 20 % increasing scenario where wind shear tend to weak and lead to strong wind intensity at this stage. Meanwhile, the reduction of moisture supply at 850-700 hPa resulting from 20 % decreasing relative humidity play a major role in the weakening of wind intensity and reduces mechanical energy of the cycle process as much as 300 J kg-1.
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