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Plant-Microbe Interactions SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt INTERAKSI TANAMAN-MIKROBA Plant-microbe interactions diverse – from the plant perspective: • Negatif – e.g. Parasitis/ Pathogenik • Neutral • Positif – Simbiotik bahasan important positive interactions with respect to plant abundance and distribution – related to plant nutrient and water supply: Pokok Dekomposisi BOT Mycorrhizae Fiksasi N2 Rhizosphere Peranan interaksi ini dalam siklus N SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt I. Dekomposi Bahan Organik Pemasok utama hara tanaman – terutama N & P A. Bahan mentah Soil organic matter derived primarily from plants – • Mainly leaves and fine roots • Wood can be important component in old growth forests Input rates – • Generally follow rates of production • Deciduous = evergreen SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt B. Proses-Proses 1. Fragmentasi Bahan Organik • Breakdown of organic matter (OM) into smaller bits = humus • By soil ‘critters’ – including nematodes, earthworms, springtails, termites • consume and excrete OM incomplete digestion nematode springtail (Isotoma viridis) termites SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt 2. Mineralisasi Bahan Organik • Breakdown OM senyawa an-organik • Microbial process: accomplished by enzymes excreted into the soil For Nitrogen energy for heterotrophic bacteria Mineralization proteins (insoluble) amino acids Ammonium NH4+ proteases Nitrification Nitrite NO2- Microbial uptake Plant uptake SUMBER: energy for nitrifying bacteria* Nitrate NO3- * In 2 steps by 2 different kinds of bacteria – (1) culter.colorado.edu/~kittel/Slides18_13Nv07.ppt Nitrosomonas oxidize NH3 to nitrites + (2) C. Serapan N oleh Tanaman – Chemical form taken up can vary 1) Nitrate (NO3-) • Lebih disenangi oleh tanaman, lebih mudah diserap • Even though requires conversion to NH4+ before be used lots of energy • vs. taking up & storing NH4+ problematic • More strongly bound to soil particles • Acidifies the soil • Not easily stored Protein mineralization NH4+ NO3Serapan Tanaman 2) Ammonium (NH4+ ) – Digunakan langsung oleh tanaman dalam tanah yang nitrifikasinya lambat (mis. Tanah basah) SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt 3) Beberapa jenis tanaman menyerap sedikit asam amino (mis. glycine) • Circumvents the need for N mineralization • Difasilitasi oleh adanya mycorrhiza mineralization proteins NH4+ amino acids immobilization nitrification microbial uptake NO3- Penyerapan langsung Serapan Tanaman SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt D. Kontrol thd Kecepatan Dekomposisi BO 1) Temperature – • Warmer is better • <45°C Respirasi Mikroba Tanah 2) Moisture – intermediate is best • Too little desiccation • Too much limits O2 diffusion T Soil Moisture % SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt 3) Faktor Tanaman – Kualitas biomasa seresah a) Rasio C:N biomasa seresah ( = Konsentrasi N) • If C relative to N high N limits microbial growth • Immobilization favored • N to plants Decomposition rate as fn(lignin, N) Deciduous forest spp b) Material struktural tanaman • Lignin – complex polymer, cell walls • Confers strength with flexibility – e.g. oak leaves • Relatively recalcitrant • High conc. lowers decomposition SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt c) Senyawa sekunder tanaman • Anti-herbivore/microbial • Common are phenolics – e.g. tannins – Aromatic ring + hydroxyl group, other compounds OH R • Kontrol dekomposisi Bahan organik oleh: Bind to enzymes, blocking active sites lower mineralization N compounds bind to phenolics greater immobilization by soil Phenolics C source for microbes greater immobilization by microbes SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt II. Mycorrhiza = Jamur Akar A. Hubungan Simbiotik antara tanaman (akar) & fungi tanah • Plant provides fungus with energy (C) • Fungus enhances soil resource uptake Penyebarannya: • Occurs ~80% angiosperm spp • All gymnosperms • Sometimes an obligate relationship. SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt B. Kelompok utama Mycorrhiza: 1) Ectomycorrhiza – • Fungus forms “sheath” around the root (mantle) • Grows in between cortical cells = Hartig net – apoplastic connection • Occur most often in woody spp SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt 2) Endomycorrhiza – Fungi menembus sel-sel akar • Common example is arbuscular mycorrhizae (AM) • Found in both herbaceous & woody plants • Arbuscule = exchange site Arbuscule in plant cell SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt C. Fungsi Mycorrhiza: 1) Peranan penghubung tanaman-tanah: a) Increase surface area & reach for absorption of soil water & nutrients b) Increase mobility and uptake of soil P c) Provides plant with access to organic N d) Protect roots from toxic heavy metals e) Protect roots from pathogens 2) Efek hara tanah thd mycorrhiza • Intermediate soil P concentrations favorable • Extremely low P – poor fungal infection • Hi P – plants suppress fungal growth – taking up P directly • Kejenuhan N SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt III. Fikisasi N2 N2 abundant – chemically inert N2 must be fixed = converted into chemically usable form • Lightning • High temperature or pressure (humans) • Biologically fixed Nitrogenase – Ensim Katalisis N2 NH3 Expensive process – ATP, Molybdenum Anaerobik : Memerlukan struktur khusus SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt A. Hanya terjadi pada organisme Prokaryote: • Bacteria (e.g. Rhizobium, Frankia) • Cyanobacteria (e.g. Nostoc, Anabaena) Free-living in soil/water – heterocysts Symbiotic with plants – root nodules Loose association with plants Anabaena with heterocysts Simbiosis dengan tumbuhan – Mutualism • Prokaryote receives carbohydrates • Plant may allocate up to 30% of its C to the symbiont • Tumbuhan menyediakan tapak anaerobik – Bintil akar • Tumbuhan menerima N SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt Contoh sistem simbiotik fiksasi N2 oleh tumbuhan 1) Legumes (Fabaceae) • Widespread • bacteria = e.g., Rhizobium spp. • Those with N2-fixing symbionts form root “nodules” – anaerobic sites that “house” bacteria soybean root SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt Problem Toksisitas O2 • Symbionts regulate O2 in the nodule with leghemoglobin • Different part synthesized by the bacteria and legume Cross-section of nodules of soybean nodules Symbionts mengendalikan O2 dalam bintil akar dengan membentuk leghemoglobin 1. An oxygen carrier (in legumes) to prevent oxygen toxicity for the bacterium 2. different pieces synthesized by the bacteria (heme) and in the plant (protein) SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt 2) Simbiosis tumbuhan Non-legume: • “Actinorhizal”= associated with actinomycetes (N2-fixing bacteria) • genus Frankia • Usually woody species – e.g. Alders, Ceanothus Bacteria in root or small vesicles Ceanothus velutinus - snowbrush Ceanothus roots, with Frankia vesicles SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt (2) Simbiosis tumbuhan Non-legume 1. “Actinorhizal”= associated with actinomycetes (N2-fixing bacteria) 2. genus Frankia 3. Usually woody species – e.g. Alders, Ceanothus • Bacteria in root or small vesicles 4. Bacteria occur in root or small vesicles Buffaloberry (Shepherdia argentea) - actinorhizal shrub (Arizona) SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt B. Makna Ekologis Fiksasi N2 (1). Important in “young” ecosystems – Young soils low in organic matter, N Ecological importance of N2 fixation (1) Most important in “young” ecosystems (early in primary succession) young soils are low in organic matter, and thus N, which is often a limiting nutrient for plant growth •e.g., newly exposed (glaciated) or newly laid down rock (volcanic), •recently denuded landscapes(human activities, directly or indirectly – bulldozing, erosion SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt 2) Plant-level responses to increased soil N conc: Some plants (facultative N-fixers) respond to soil N concentration • Plant shifts to direct N uptake • N fixation • Number of nodules decreases Plant-level: responses on N-fixing plants to high soil N conc: In some plants (facultative N-fixers) – •As N conc , N fixation decreases •Plant shifts to direct N uptake •#nodules decreases SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt 3) Kompetisi: Interaksi tumbuhan fiksasi N N2-fixing plants higher P, light, Mo, and Fe requirements Poor competitors • Competitive exclusion less earlier in succession • Though - N2 fixers in “mature” ecosystems Competition – N-fixers and plant community interactions because N2 fixing plants have higher P, light, Mo, and Fe requirements . They are believed to be poor competitors; •chances for competitive exclusion lower earlier in succession (although there are N2 fixers in “mature” ecosystems) e.g. of plants important in early stages of succession: •lupines, alders, clovers, Dryas SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt Natural N cycle IV. Kehilangan N dari ekosistem N 2O PLANT • Leaching to aquatic systems • Kebakaran Penguapan • Denitrifikasi N2, N2O to atmosfir – Closes the N cycle! • Bacteria mediated • Anaerobik. REMAINS PLANT SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt Annual release (1012 g N/yr) NATURAL SOURCES Soil bacteria, algae, lightning, etc. ANTHROPOGENIC SOURCES Annual release (1012 g N/yr) Fertilizer Legumes, other plants 80 40 Fossil fuels Biomass burning Wetland draining Land clearing 20 40 10 20 Total from human sources 140 Altered N cycle 210 Annual release of fixed N2 (1012 g = teragram, trillion gr) Source: Peter M. Vitousek et al., "Human Alteration of the Global Nitrogen Cycle: Causes and Consequences," Issues in Ecology, No. 1 (1997), pp. 4-6. From - Peter M. Vitousek et al., "Human Alteration of the Global Nitrogen Cycle - Causes and Consequences," Issues in Ecology, No. 1 (1997), pp. 4-6. V. Interaksi Rhizosphere Jaring-jaring makanan bawah tanah Fine root Zone within 2 mm of roots – hotspot of biological activity • Roots exude C & cells slough off = lots of goodies for soil microbes lots of microbes for their consumers (protozoans, arthropods) • “Free living” N2-fixers thrive in the rhizosphere of some grass species SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt RINGKASAN • Plant–microbial interactions play key roles in plant nutrient dynamics Decomposition – mineralization, nitrification … immobilization, denitrification … Rhizosphere – soil foodweb Mycorrhizae – plant-fungi symbiosis N fixation – plant-bacteria symbiosis • Highly adapted root morphology and physiology to accommodate these interactions • N cycle, for example, significantly altered by human activities SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt