Fueling the Underground

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1 Fueling the Underground Jill Clapperton Ph.D. Principal Scientist Rhizoterra Inc Copyright Rhizoterra Inc

2 Photosynthesis Plants converts CO 2 from the atmosphere to simple sugars (photosynthate). These sugars are translocated within the plant and used to make amino acids, organic acids, lipids and other carbon based molecules. Plants export sugars to the roots so they don t build up in the leaves and halt photosynthesis.

4 Symbiosis Growth promoting substances Rhizodeposition Nutrients Water Growth inhibiting substances

5 Plants, Soil and Soil Organisms Each plant species or crop species modifies the soil and soil organisms in ways that can benefit, inhibit or have no affect on the establishment and growth of the subsequent crop. We can use these processes to manage crops, weeds, diseases to increase soil and plant health and productivity, and animal and human wellness. The Rhizosphere Effect

6 Oxidized SOM from roots that have penetrated deep into the soil profile. Channels that move water, air, solutes, and more roots Earthworms channels are the chief soil engineer.

7 Rhizosphere Plants Organisms chemical Soil physical

8 Root Exudates and the Rhizosphere

9 Soil Food Webs Soil food webs are mainly based on three primary carbon (C) sources: root exudates, litter or residues, and soil organic matter (SOM). These C sources vary in their availability and accessibility to soil organisms, and can thus, increase the C flow and biodiversity within the food web.

10 Soil Food Webs Soil Carbon from roots is retained and forms more stable soil aggregates than shoot derived C (Gale et al. 2000) Roots normally account form only 10-20% of the total plant weight Contribute 12% of soil organic C, 31% soluble organic C, and 52% of the microbial biomass C (Liang et al. 2002)

11 Soil Food Webs The amount of carbon from corn roots and corn root exudates can be as much at times higher than the organic C contribution from corn stover (Allmaras et al. 2004; Wilts et al. 2004)

12 The percentage of N in the roots as nitrate (blue), amino acids (green), amides (yellow) and ureides (red). These compounds leak from the roots as exudates and are part of the plant s signature to create a unique rhizosphere. oat barley corn sunflower beans peas radish lupine white clover

13 Plants colonised by mycorrhizal fungi have higher rates of photosynthesis and export more amino acids, organic acids and neutral sugars to the roots compared with non mycorrhizal plants (Clapperton and Reid, 1992).

14 The quality and quantity of root exudates determines the function and population density of the microbial community associated with the roots

15 Amoebae can engulf bacteria in the tiniest soil pore, fungal spores and protozoa. There can be as many as 40,000 in a gram of healthy soil.

16 Soil Organic Matter (SOM) SOM is the primary food source for most soil organisms The quantity and quality of SOM is what drives nutrient cycling C:N between 30 and 50:1 is ideal for optimised N cycling.

17 Photo by V Behan-Pelletier AAFC

20 Further study is required to realize the potential for targeted cropimprovement strategies based on root traits that favor carbon sequestration in soil while also efficiently producing food. Richard D Bardgett (2011), The Scientist, August 1, 2011.

21 In a model grassland system it was recently shown that increasing plant diversity enhances CO 2 assimilation by surrounding plants. This in turn increased the amount of C allocated to the roots and mycorrhizal fungi, which is a key mechanism driving carbon sequestration in soil. These effects, however, were due to the presence of legumes in high-diversity mixtures, rather than to diversity per se (Gerlinde De Deyn et al. 2009, Journal of Ecology 97: ).

22 Weeds vs Natives Cheat grass or Downy Brome (Bromus tectorum), Japanese Brome (Bromus japonicus), and dandelion (Taraxacum officinale) all produce root exudates that inhibit bacterial nitrification (stop the conversion of NH 4 to NO 3 ). Native grasses such as Stipa comata (Needle and thread grass) have exudates that promote nitrification. John Neal, Can J Bot. 1976

23 Increasing the amount of carbon exuded from the roots drove the microbes to release more extracellular enzymes to breakdown the organic N accelerating the turn over of organic N in the soil- a cascading (Phillips et al. 2011, Ecol. Lett. 14: ).

24 Rhizosphere interactions and processes Beneficial Symbiosis Growth promotion Soil stability Water uptake Nutrient availability Nutrient uptake Enzyme release Biocontrol Antibiosis Competition Allelopathy Deleterious Growth inhibition Infection Phytoxicity

25 Aboveground diversity is a mirror for belowground diversity, and carbon from photosynthesis is fueling the system.

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