Root exudates. What are they, what are their functions and how can we collect them. Ellis Hoffland, Angela Straathof, Diederik Keuskamp

Transcription

1 Root exudates What are they, what are their functions and how can we collect them Ellis Hoffland, Angela Straathof, Diederik Keuskamp

2 What are they? Dennis etlal FEMS Microbiol Ecol 72: Jones et al Plant Soil 321: 5

3 Rhizodeposits vs root exudates 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 3

4 Rhizodeposits vs root exudates 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 4

5 5 Dennis et al FEMS Microbiol. Ecol. 72: 313

6 Types of compounds Soluble, insoluble, volatile Sugars, amino acids, organic acids, fatty acids, sterols, enzymes, etc. 6 Dennis et al FEMS Microbiol. Ecol. 72: 313

7 How much? Kuzyakov & Domanski 2000 J Plant Nutr. Soil Sci. 163: 421 Rhizodeposits: 11% of total C fixed Jones et al Plant Soil 321: kg C ha -1 7

8 Why are root deposits relevant? They (probably) shape the rhizobiome 8 Berendsen et al Trends Plant Sci. 17: 478

9 Shaping the rhizobiome Bacteria: all phylla Proteobacteria: families Distribution (%) Family: Phyllum: Soil Rhizosphere Soil Rhizosphere Lundberg et al Nature 488: 86 9

10 Shaping the rhizobiome Bacterial phylla Composition (%) Plant Philippot et al Nature Rev. Microbiol. 11:789 10

11 Disclaimer: the environment matters! Cúcio et al Front. Microbiol.7:

12 Why are root deposits relevant? They affect cycles of C, N, P, Zn, Fe,... 12

13 C cycle Rhizodeposits:500 kg C ha -1 Kuzyakov & Domanski 2000 J Plant Nutr. Soil Sci. 163: 421 Half life h But: Half life bacterial cells: 224 d Miltner 2012 Biogeochemistry 111: 41 Labile litter forms stable SOM Cotrufo et al Global Change Biol. 19: 988 Bradford et al Biogeochemistry 113:

14 C cycle Plant species Phenylalanine Plant species rhizobiomes differentially support decomposition of labile compounds Agrostis capillaris Anthoxantum odoratum Festuca rubra Holcus lanatus Centaurea jacea Leucanthemum vulgare Plantago lanceolata Rumex acetosa µmol CO 2 g -1 soil h b 0.29 b 0.61 a 0.08 b 0.16 b 0.61 a 0.62 ab 0.84 a Brolsma et al In preparation 14

15 C cycle - Priming Keiluweitet al Nature Climate Change 5:

16 Plant Plant Interactions Mommeret al Trends Plant Sci. 21: 3 16

17 Facilitation a b Ca P Dissolved P Organic P 17 Plant Plant Interactions Complementarity Competition a b a b Ca P Dissolved P Organic P Ca P Dissolved P Organic P Hinsingeret al Plant Physiol. 156:1078

18 Root exudate: Citric acid Old ph 6-7 Citrate: 80 mmol/h/g fw Mature ph 4-5 Citrate:1400 Neumann 2010 Young ph 5-6 Citrate: 350 Neumann & Martinoia 2009

19 Root exudates Facilitation Content peanut shoot (mg kg -1 ) Zn Fe Zou & Zhang 2009 Agron. Sustain. Dev. 29: 63 19

20 Plant Plant Interactions - Signalling Semchenkoet al New Phytol. 204:

21 Root exudate collection methods Angela Straathof & Diederik Keuskamp Soil - Rhizoboxes (Sterile) hydroponic systems 21

22 Sterile vs. Non-Sterile Net exudation of a range of organic acids in sterile (white bars) and non-sterile (black bars) rhizosphere conditions of cultivar Moneymaker Kuijkenet al Plant Soil 387:

23 The Rhizobox 12.5 cm 12.5 cm Pros: Full grown plants Exact location Timing Soil(types) 50 o 40 cm Cons: Not Sterile Turnover Producing compounds Small volumes Adsorption 23

24 The Rhizobox - Mini Lysimeters Shen & Hoffland 2007 Plant Soil 292:

25 Rhizobox 2.0 Pros: Soil! Test different soils More relevant?! Different methods in 1 Cons: Too Complex? Expensive? Still artificial? Oburgeret al Exp. Environm. Bot. 87:

26 Sorption materials Pros: Soil! Test different soils More relevant?! Cons: Effectiveness Adsorption by soil Specificity? More relevant?! Neumann et al Front. Microbiol. 5:

27 Decades ago... Hoffland et al Plant Soil 113:

28 Hydroponic system Pros: Relatively simple Plants of any size/age Cons: Non sterile Dilution effect Root morphology 28

29 Sterile Hydroponic systems Pros: Relatively Simple Plants of any size/age Sterile Cons: Morphology Anaerobic Dilution effect Sterile?! Kaiser et al Plant Physiol. 130:

30 Sterile Hydroponic systems PCR tubes 3 weeks 50 ml bottles Pros: Relatively Simple Plants of any size/age Sterile Cons: Anaerobic Dilution effect Sterile!!! Strehmelet al Pytochemistry 108: 35 30

31 Sterile Hydroponic systems Pros: Relatively Simple Plants of any size/age Sterile Cons: Kuijkenet al Plant Soil 387:

32 Thank you 32