Water & Nutrient Stress Increase Root Exudation A. Henry, J. - - PowerPoint PPT Presentation

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Feb 04, 2023 359 likes •575 views

Water & Nutrient Stress Increase Root Exudation A. Henry, J. Chard, J. Norton M. Hamilton, C. Palmer, M. Petersen, B. Bugbee J.R. Hess Objectives Develop procedures to: Grow healthy plants under sterile conditions Manipulate

SLIDE 1

Water & Nutrient Stress Increase Root Exudation

M. Hamilton, C. Palmer,

J.R. Hess

A. Henry, J. Chard, J. Norton
M. Petersen, B. Bugbee

SLIDE 2

Develop procedures to:

Grow healthy plants under sterile conditions
Manipulate root exudation with stress
Quantify total organic carbon in exudates
Determine composition of exudates using GC-MS

Objectives

SLIDE 3

Co-metabolism Increased plant uptake Increased/decreased contaminant mobility

Implications for Phytoremediation

Our focus for the qualitative analysis: organic acids The chelating properties of these compounds can be useful for phytoremediation, and they are a class of compound most likely to be found in root exudate

SLIDE 4

System for sterile culture

Foam plug Ground- glass joint Air filter Silicone stoppers Amber vial Septum Ottawa sand

SLIDE 5

HPS lamps Laminar flow hood

SLIDE 6

Treatments

High NH4

K+ stress Drought Flooding

SLIDE 7

Days After Planting

5 10 15 20 25 30 35 40 45 50 55 60 65

% Sterile Plants

20 40 60 80 100 Trial 3 in growth chamber Trial 5 enclosed shoot Trial 4 in laminar flow hood Trial 6 improved planting technique

SLIDE 8

Assessing microbial contamination

SLIDE 9

Verifying Plate Counts: Acridine Orange Stain

f Leachate

Clean sample

Root debris 10 µm

SLIDE 10

Contaminated sample

Verifying Plate Counts: Acridine Orange Stain

f Leachate

bacteria 10 µm

SLIDE 11

Clean root

Phenolic Aniline Blue Stain of Root

10 µm

SLIDE 12

Contaminated root

bacteria

Phenolic Aniline Blue Stain of Root

10 µm

SLIDE 13

Treatments started

Treatment Averages

days after planting

20 30 40 50 60 70

µg C exuded per day

200 400 600 800 1000

K+ stress flood drought control NH4

+ treatment

The K+ stressed plants had the highest amount of carbon exuded at any point in time. We think this is because the plants were releasing a compound to sequester K+ from the soil.

SLIDE 14

Cumulative carbon exuded per gram dry plant

mg C exuded per g dry plant

Percent

control

Average

Std. dev.

control

2.6

0.4

NH4+

2.3

0.1

90 K+

3.7 0.6

144 flood 3.8

0.9 145 drought 4.4 0.5

170

SLIDE 15

Compounds released by roots Sloughed-off cells

Primary types of exudates

SLIDE 16

Distribution of Carbon

Rhizosphere sand Bulk sand Leachates

17 % 9 % 63 % 11 % 100 %

Soluble Insoluble

Based on the distribution of carbon released by the roots (mostly soluble with not much left on the sand), we conclude that the exudates we’re seeing are mostly compounds released directly from the root, not whole cells released from the root.

SLIDE 17

GC-MS Data: Exudates

Fumaric Acid

Days after planting

30 35 40 45 50 55 60 65 70

Concentration (mg/L)

2 4 6 8 10

drought flood NH4+ trtmt K+ stress control

Malonic Acid

Days after planting

30 35 40 45 50 55 60 65 70

Concentration (mg/L)

2 4 6 8 10

drought flood NH4+ trtmt K+ stress control

Oxalic Acid

Days after planting

30 35 40 45 50 55 60 65 70

Concentration (mg/L)

2 4 6 8 10

drought flood NH4+ trtmt K+ stress control

Succinic Acid

Days after planting

30 35 40 45 50 55 60 65 70

Concentration (mg/L)

2 4 6 8 10

drought flood NH4+ trtmt K+ stress control

Unlike the TOC graph, organic acids were exuded in the largest amounts from the drought and flooding treatments. This may be due to buildup of osmotic potential to deal with the low water potentials in the drought treatment, or just leakier root cells due to the stress treatments.

SLIDE 18

What’s in the root vs. what’s released by the root

Succinic Acid Root (mg/kg)

100 200 300 400 500

Exudate (mg/L)

2 4 6 8 10 12 14

r2 = 0.55

Fumaric Acid Root (mg/kg)

500 1000 1500 2000

Exudate (mg/L)

2 4 6 8 10 12

r2 = 0.54

Oxalic Acid Root (mg/kg)

50 100 150 200 250 300 350 400

Exudate (mg/L)

2 4 6 8 10 12 Malonic Acid Root (mg/kg)

20 40 60 80 100 120

Exudate (mg/L)

1 2 3 4 5 6

r2 = ns r2 = ns

SLIDE 19

Conclusions

Treatment Averages

days after planting

20 30 40 50 60 70

µg C exuded per day

200 400 600 800 1000

K+ stress flood drought control NH4

+ treatment

1. Stress increases root
exudation. Drought and

flooding treatments increased release of organic acids.

2. Concentrations of succinic and

fumaric acid in the root correlated with amounts released by the root.

Succinic Acid

Days after planting

30 35 40 45 50 55 60 65 70

Concentration (mg/L)

2 4 6 8 10

drought flood NH4+ trtmt K+ stress control

Succinic Acid Root (mg/kg)

100 200 300 400 500

Exudate (mg/L)

2 4 6 8 10 12 14

r2 = 0.55