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Plant-Microbe Interactions SUMBER:‎

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1 Plant-Microbe Interactions SUMBER:‎

2 INTERAKSI TANAMAN-MIKROBA  Plant-microbe interactions diverse – from the plant perspective: Negatif – e.g. Parasitis/ Pathogenik Neutral Positif – Simbiotik  Pokok bahasan  important positive interactions with respect to plant abundance and distribution – related to plant nutrient and water supply: Dekomposisi BOT Mycorrhizae Fiksasi N 2 Rhizosphere  Peranan interaksi ini dalam siklus N SUMBER:‎

3 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:‎

4 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:‎

5 2. Mineralisasi Bahan Organik Breakdown OM  senyawa an-organik Microbial process: accomplished by enzymes excreted into the soil Microbial uptake Immobilization Plant uptake Nitrite NO 2 - Nitrate NO 3 - energy for nitrifying bacteria* Nitrification For Nitrogen proteins (insoluble) amino acids energy for heterotrophic bacteria proteases Ammonium NH 4 + Mineralization * In 2 steps by 2 different kinds of bacteria – (1) Nitrosomonas oxidize NH3 to nitrites + (2) Nitrobacter oxidize nitrites to nitrates SUMBER:‎

6 NH 4 + Protein mineralization NO 3 - Serapan Tanaman 1) Nitrate (NO 3 - ) Lebih disenangi oleh tanaman, lebih mudah diserap Even though requires conversion to NH 4 + before be used  lots of energy vs. taking up & storing NH 4 + problematic More strongly bound to soil particles Acidifies the soil Not easily stored C. Serapan N oleh Tanaman – Chemical form taken up can vary 2) Ammonium (NH 4 + ) – Digunakan langsung oleh tanaman dalam tanah yang nitrifikasinya lambat (mis. Tanah basah) SUMBER:‎

7 proteins NH 4 + mineralization microbial uptake immobilization NO 3 - nitrification Serapan Tanaman amino acids 3) Beberapa jenis tanaman menyerap sedikit asam amino (mis. glycine) Circumvents the need for N mineralization Difasilitasi oleh adanya mycorrhiza Penyerapan langsung SUMBER:‎

8 D. Kontrol thd Kecepatan Dekomposisi BO 1) Temperature – Warmer is better <45°C 2) Moisture – intermediate is best Too little  desiccation Too much  limits O 2 diffusion T Soil Moisture % Respirasi Mikroba Tanah SUMBER:‎

9 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:‎

10 c) Senyawa sekunder tanaman 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 Anti-herbivore/microbial Common are phenolics – e.g. tannins – Aromatic ring + hydroxyl group, other compounds OH R SUMBER:‎

11 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. II. Mycorrhiza = Jamur Akar SUMBER:‎

12 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:‎

13 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:‎

14 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:‎

15 III. Fikisasi N 2 N 2 abundant – chemically inert N 2 must be fixed = converted into chemically usable form Lightning High temperature or pressure (humans) Biologically fixed  Nitrogenase – Ensim Katalisis N 2  NH 3  Expensive process – ATP, Molybdenum  Anaerobik : Memerlukan struktur khusus SUMBER:‎

16 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 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 SUMBER:‎

17 Those with N 2 -fixing symbionts form root “nodules” – anaerobic sites that “house” bacteria soybean root Contoh sistem simbiotik fiksasi N 2 oleh tumbuhan 1) Legumes (Fabaceae) Widespread bacteria = e.g., Rhizobium spp. SUMBER:‎

18 Problem Toksisitas O 2 Symbionts regulate O 2 in the nodule with leghemoglobin Different part synthesized by the bacteria and legume Cross-section of nodules of soybean nodules SUMBER:‎ Symbionts mengendalikan O 2 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)

19 2) Simbiosis tumbuhan Non-legume: “Actinorhizal”= associated with actinomycetes (N 2 -fixing bacteria) genus Frankia Usually woody species – e.g. Alders, Ceanothus Ceanothus velutinus - snowbrush Ceanothus roots, with Frankia vesicles Bacteria in root or small vesicles SUMBER:‎

20 Buffaloberry (Shepherdia argentea) - actinorhizal shrub (Arizona) Bacteria in root or small vesicles SUMBER:‎ (2) Simbiosis tumbuhan Non-legume 1.“Actinorhizal”= associated with actinomycetes (N 2 -fixing bacteria) 2.genus Frankia 3.Usually woody species – e.g. Alders, Ceanothus 4.Bacteria occur in root or small vesicles

21 B. Makna Ekologis Fiksasi N 2 (1). Important in “young” ecosystems – Young soils low in organic matter, N SUMBER:‎ Ecological importance of N 2 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

22 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 SUMBER:‎ 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

23 3) Kompetisi: Interaksi tumbuhan fiksasi N N 2 -fixing plants higher P, light, Mo, and Fe requirements  Poor competitors Competitive exclusion less earlier in succession Though - N 2 fixers in “mature” ecosystems SUMBER:‎ Competition – N-fixers and plant community interactions because N 2 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 N 2 fixers in “mature” ecosystems) e.g. of plants important in early stages of succession: lupines, alders, clovers, Dryas

24 IV. Kehilangan N dari ekosistem Leaching  to aquatic systems Kebakaran  Penguapan Denitrifikasi  N 2, N 2 O to atmosfir – Closes the N cycle! Bacteria mediated Anaerobik. Natural N cycle PLANT REMAINS N2ON2O SUMBER:‎

25 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. ANTHROPOGENIC SOURCES Annual release (10 12 g N/yr) Fertilizer80 Legumes, other plants40 Fossil fuels20 Biomass burning40 Wetland draining10 Land clearing20 Total from human sources210 Altered N cycle NATURAL SOURCES Soil bacteria, algae, lightning, etc.140 Annual release (10 12 g N/yr) Annual release of fixed N2 (10 12 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.

26 V. Interaksi Rhizosphere Jaring-jaring makanan bawah tanah 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” N 2 -fixers thrive in the rhizosphere of some grass species Fine root SUMBER:‎

27 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:‎

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