plant-microbe interactions

Plant-Microbe Interactions

SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt

INTERAKSI TANAMAN-MIKROBAPlant-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 N2

Rhizosphere

Peranan interaksi ini dalam siklus NSUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt

I. Dekomposi Bahan OrganikPemasok utama hara tanaman – terutama N & P

A. Bahan mentahSoil 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


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


2. Mineralisasi Bahan Organik• Breakdown OM senyawa an-organik• Microbial process: accomplished by enzymes excreted

into the soil

Microbial uptakeIm

mobiliz

ation

Plant uptake

NitriteNO2

-

NitrateNO3

-

energy fornitrifying bacteria*

Nitrification

For Nitrogen

proteins(insoluble)

aminoacids

energy for heterotrophic bacteria

proteases

AmmoniumNH4

+

Mineralization

* In 2 steps by 2 different kinds of bacteria – (1) Nitrosomonas oxidize NH3 to nitrites + (2)

Nitrobacter oxidize nitrites to nitrates SUMBER: culter.colorado.edu/~kittel/Slides18_13Nv07.ppt

NH4+Protein mineralization

NO3-

Serapan Tanaman

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

C. Serapan N oleh Tanaman – Chemical form taken up can vary

2) Ammonium (NH4+ ) –

Digunakan langsung oleh tanaman dalam tanah yang nitrifikasinya lambat (mis. Tanah basah)


proteins NH4+

mineralization

microbial uptake

immobilization

NO3-

nitrification

Serapan Tanaman

aminoacids

3) Beberapa jenis tanaman menyerap sedikit asam amino (mis. glycine)

• Circumvents the need for N mineralization• Difasilitasi oleh adanya mycorrhiza

Penyerapan langsung


D. Kontrol thd Kecepatan Dekomposisi BO1) Temperature –

• Warmer is better• <45°C

2) Moisture – intermediate is best • Too little desiccation • Too much limits O2 diffusion

T

Soil Moisture %

Respirasi Mikroba Tanah


3) Faktor Tanaman – Kualitas biomasa seresaha) Rasio C:N biomasa seresah ( = Konsentrasi N)• If C relative to N high N limits microbial growth

• Immobilization favored• N to plants

Decomposition rateas fn(lignin, N)

Deciduous forest sppb) Material struktural tanaman• Lignin – complex polymer, cell walls

• Confers strength with flexibility – e.g. oak leaves

• Relatively recalcitrant• High conc. lowers decomposition


c) Senyawa sekunder tanaman

• Kontrol dekomposisi Bahan organik oleh:

Bind to enzymes, blocking active sites lower mineralizationN compounds bind to phenolics greater immobilization by soilPhenolics 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


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


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


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


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


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


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


• Those with N2-fixing symbionts form root “nodules”– anaerobic sites that “house” bacteria

soybeanroot

Contoh sistem simbiotik fiksasi N2 oleh tumbuhan

1) Legumes (Fabaceae)• Widespread• bacteria = e.g., Rhizobium spp.


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)

2) Simbiosis tumbuhan Non-legume:• “Actinorhizal”= associated with actinomycetes (N2-fixing bacteria)

• genus Frankia• Usually woody species – e.g. Alders, Ceanothus

Ceanothus velutinus - snowbrush

Ceanothus roots, withFrankia vesicles

Bacteria in root or small vesicles


Buffaloberry (Shepherdia argentea)- actinorhizal shrub (Arizona)

• Bacteria in root or small vesicles


(2) Simbiosis tumbuhan Non-legume1. “Actinorhizal”= associated with actinomycetes (N2-fixing

bacteria)2. genus Frankia3. Usually woody species – e.g. Alders, Ceanothus4. Bacteria occur in root or small vesicles

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

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

3) Kompetisi: Interaksi tumbuhan fiksasi NN2-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 interactionsbecause 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

IV. Kehilangan N dari ekosistem

• Leaching to aquatic systems• Kebakaran Penguapan• Denitrifikasi N2, N2O to atmosfir– Closes the N cycle!

• Bacteria mediated• Anaerobik.

Natural N cycle

PLANT

PLANT

REMAINS

N2O


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.

ANTHROPOGENICSOURCES

Annual release(1012 g N/yr)

Fertilizer 80Legumes, other plants 40Fossil fuels 20Biomass burning 40Wetland draining 10Land clearing 20Total from human sources 210

Altered N cycle

NATURAL SOURCES

Soil bacteria, algae, lightning, etc. 140

Annual release(1012 g N/yr)

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.

V. Interaksi RhizosphereJaring-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” N2-fixers thrive in the rhizosphere of some grass species

Fine root


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


plant-microbe interactions

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