Characterisation and Application of Sphagnum to Indoor Agriculture Food Production Systems

Abstract

In response to the impacts of climate change and global population growth on traditional food production activities, agricultural industries and government agencies are now investing significant time and funding into researching alternative novel, sustainable and carbon friendly processes by which global food demand can be met. Application of disruptive, high yield-low cost technologies such as indoor (vertical) agriculture, shift the focus of food production away from traditional intensification of land use and pesticide-based crop yield promotion, which is attributed to destruction of surrounding habitats. Development of organic based growth media for use in indoor agricultural are now a key priority to replace single use materials such as extruded plastics and rockwool. Sphagnum moss, an aquatic plant found in peatlands, is investigated as such an alternative growth medium.

Three sphagnum moss species were investigated as potential living growth media alternatives for application to a recirculating nutrient film technique (NFT) hydroponics crop production system within an enclosed 4.45m2 growth chamber. Wild sourced Sphagnum cuspidatum, S. fallax and S. magellanicum were chosen based on the attributed nutrient availability of their natural habitats, of nutrient poor, nutrient rich and moderate respectively. Each species was utilised as a growth medium in the production of Lactuca sativa cultivars Flandria and Lollo rossa, to determine growth rates, nutrient uptake, microbial community profile and antioxidant production. Horticultural rockwool was used as a control medium. An adapted Hoagland’s nutrient solution was developed based on sphagnum moss compositional analysis and nitrogen loading (max of 6g N.m-2.y-1 of NH4+) and utilised at 0.5x concentration, pH 5.8 and EC of 1.2 S.m-1 for three crop trials, lasting 28 to 36 days. Nutrient solution quality of sphagnum based trays were determined via TOC (avg ~2 µg C.lt-1) and COD (avg of 40 mg.lt-1)over the growth period with no significant difference to that of the control. Algae befouling was inhibited by S. fallax and S. magellanicum. Lactuca sativa Flandria was also grown using a 0.1x urine simulate nutrient solution at pH5.8 and 1.6 S.m-1 and as a result, S. fallax was determined suitable for single use grey waste water remediation. Impacts of atmospheric CO2 concentrations of 1200 µmol.mol-1 were determined in one trial while ambient atmospheric CO2 was used in two based on the determination of photosynthetic rate (Pnet) for S. fallax as 0.0148 µmol.g FW-1.min-1 at a PAR of 302 µmol.m-2.s-1.

Results demonstrated that two of the three sphagnum species successfully supported the production of a lettuce crop under both nutrient solution recipes and atmospheric CO2. S. fallax grown Flandria % dry matter content at final harvest ranged from 5.2 to 5.5% with adapted Hoagland’s solution and 5.54 to 6.19% with urine simulate solution. S. magellanicum grown Lollo rossa % dry matter at final harvest ranged from 4.0 to 5.14% with adapted Hoagland’s solution. Sphagnum cuspidatum proved to be a poor growth medium due to its physical structure not coping with the NFT set-up and failed to produce a full crop, while S. magellanicum proved very robust and reusable.

Microbial community profiling was undertaken using 3rd generation MinION DNA sequencing. It demonstrated transfer of S. magellanicum plant growth promoting endophytes directly to the root zone of Lactuca sativa Lollo rossa. ~17,000 bacterial species were also isolated from S. cuspidatum and S. magellanicum sampled from 6 Irish bogs. These have potential for application as plant growth promoting bacteria or for nutraceutical development.

Antioxidant production was assessed using FRAP assay. The highest antioxidant concentration within Lactuca sativa ‘Flandria’ was 245.49mg Fe2+ eqv./100g DW at final harvest (28DAP) from plants grown in 0.1x urine simulate nutrient solution and 178.15 +/- 4.24 mg Fe2+ eqv./100g DW in Lactuca sativa ‘Lollo rossa’ plants grown in S. magellanicum at interval harvest (15DAP).

In summary, two species of sphagnum moss, S. fallax and S. magellanicum were found to successfully support two Lactuca sativa cultivars over a full plant growth cycle of ~28DAP. Molecular screening of microbial communities within S. cuspidatum and S. magellanicum also identified over 17,000 potential bacteria with phytoremediation, phyto-protection or phyto-growth promotional abilities, with commercial potential. The results of the thesis contribute significantly to the potential use of Sphagnum in indoor agricultural systems with transferability to ALS in space travel.