root exudates - wordpress.com · 2016. 12. 5. · kuijken et al.2015 plant soil 387: 131 22 net...
TRANSCRIPT
Root exudates
What are they, what are their functions and how can we collect them
Ellis Hoffland, Angela Straathof, Diederik Keuskamp
What are they?
2
Jones et al. 2009 Plant Soil 321: 5Dennis etl al. 2010 FEMS Microbiol Ecol 72: 313
Rhizodeposits vs root exudates
3
� Root exudation
● Active process, specific (ABC) transporters, controlled
● Organic acids, amino acids
● Quantitatively of limited importance
� Basal root exudation
● Meristematic regions behind root cap
● Vast majority of exudates
Rhizodeposits vs root exudates
4
� Rhizodeposits
● Mucilage produced by border cells
● Lysis of sloughed-off root cap and border cells
● Mucilage, glycoproteins, etc. produced by root hairs
● Rhizodermal lysis of older cells
� Both
● High turn-over rates
5
Dennis et al. 2010 FEMS Microbiol. Ecol. 72: 313
Types of compounds
� Soluble, insoluble, volatile
� Sugars, amino acids, organic acids, fatty acids, sterols, enzymes, etc.
6
Dennis et al. 2010 FEMS Microbiol. Ecol. 72: 313
How much?
7
� Kuzyakov & Domanski 2000 J Plant Nutr. Soil Sci. 163: 421
Rhizodeposits: 11% of total C fixed
500 kg C ha-1
� Jones et al. 2009 Plant Soil 321: 5
Why are root deposits relevant?
� They (probably) shape the rhizobiome
8
Berendsen et al. 2012 Trends Plant Sci. 17: 478
Shaping the rhizobiome
9
Dis
trib
ution (
%)
Proteobacteria: families
Soil
Rhiz
osphere
Soil
Rhiz
osphere
Family:
Phyllum:
Bacteria: all phylla
Lundberg et al. 2012 Nature 488: 86
Shaping the rhizobiome
10
Philippot et al. 2013 Nature Rev. Microbiol. 11:789
Com
positio
n (
%)
Bacterial phylla
Plant
Disclaimer: the environment matters!
11
Cúcio et al. 2016 Front. Microbiol.7: 440
Why are root deposits relevant?
� They affect cycles of C, N, P, Zn, Fe, ........
12
C cycle
� Rhizodeposits:500 kg C ha-1
Kuzyakov & Domanski 2000 J Plant Nutr. Soil Sci. 163: 421
� Half life 30 – 120 h
� But: Half life bacterial cells: 224 d
Miltner 2012 Biogeochemistry 111:
41
� Labile litter forms stable SOM
Cotrufo et al. 2013 Global Change Biol. 19: 988
13
Bradford et al. 2013 Biogeochemistry 113: 271
C cycle
14
Brolsma et al. 2017 In preparation
� Plant species’ rhizobiomesdifferentially support decomposition of labile compounds
Plant species Phenylalanine
µmol CO2 g-1
soil h-1
Agrostis capillaris 0.21 b
Anthoxantum odoratum 0.29 b
Festuca rubra 0.61 a
Holcus lanatus 0.08 b
Centaurea jacea 0.16 b
Leucanthemum vulgare 0.61 a
Plantago lanceolata 0.62 ab
Rumex acetosa 0.84 a
C cycle - Priming
15Keiluweit et al. 2015 Nature Climate Change 5: 588
Plant – Plant Interactions
16Mommer et al. 2016 Trends Plant Sci. 21: 3
Plant – Plant Interactions
17
Disso
lved P
Ca
P
Org
anic
P
a b
Competition
Org
anic
P
Disso
lved P
Ca
P
a b
Complementarity
Disso
lved P
Org
anic
P
Ca
P
a b
Facilitation
Hinsinger et al. 2011 Plant Physiol. 156:1078
Neumann 2010
Neumann & Martinoia 2009
YoungpH 5-6Citrate: 350
OldpH 6-7Citrate: 80mmol/h/g fw
MaturepH 4-5Citrate:1400
Root exudate: Citric acidRoot exudate: Citric acid
Root exudates – Facilitation
19
55 52 51
290 280 203
Content peanut shoot (mg kg-1)
Zn 44 44 44
Fe 206 206 206
Zou & Zhang 2009 Agron. Sustain. Dev. 29: 63
20Semchenko et al. 2014 New Phytol. 204: 631
Plant – Plant Interactions - Signalling
Root exudate collection methods
� Angela Straathof & Diederik Keuskamp
� Soil - Rhizoboxes
� (Sterile) hydroponic systems
21
Sterile vs. Non-Sterile
22Kuijken et al. 2015 Plant Soil 387: 131
Net exudation of a range of organic acids in sterile (white bars) and non-sterile (black bars) rhizosphere conditions of cultivarMoneymaker
The Rhizobox
23
40 cm
12.5 cm
12.5 cm
50o
Pros:• Full grown
plants• Exact location• Timing• Soil(types)
Cons:• Not Sterile
• Turnover• Producing
compounds• Small volumes• Adsorption
The Rhizobox - Mini Lysimeters
24Shen & Hoffland 2007 Plant Soil 292: 161
Rhizobox 2.0
25Oburger et al. 2013 Exp. Environm. Bot. 87: 235
Pros:• Soil!• Test different soils• More relevant?!• Different methods
in 1
Cons:• Too Complex?• Expensive?• Still artificial?
Sorption materials
26Neumann et al. 2014 Front. Microbiol. 5: 131
Pros:• Soil!• Test different soils• More relevant?!
Cons:• Effectiveness• Adsorption by
soil• Specificity?• More relevant?!
Decades ago......
27Hoffland et al. 1989 Plant Soil 113: 161
Hydroponic system
28
Pros:• Relatively
simple• Plants of any
size/age
Cons:• Non sterile• Dilution effect• Root
morphology
Sterile Hydroponic systems
29
Pros:• Relatively
Simple• Plants of any
size/age• Sterile
Cons:• Morphology• Anaerobic• Dilution
effect• Sterile?!
Kaiser et al. 2002 Plant Physiol. 130: 1263
Sterile Hydroponic systems
30
Pros:• Relatively
Simple• Plants of any
size/age• Sterile
Cons:
• Anaerobic• Dilution
effect• Sterile!!!
Strehmel et al. 2014 Pytochemistry 108: 35
PCR tubes
3 weeks
50 ml bottles
Sterile Hydroponic systems
31
Pros:• Relatively
Simple• Plants of any
size/age• Sterile
Cons:
Kuijken et al. 2015 Plant Soil 387: 131
Thank you
32