Transcript DASAR ILMU TANAH INTERAKSI MIKROBA DAN TANAMAN

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