The soil organic carbon sequestration potential of the perennial Arundo donax (also known as giant reed) has been confirmed on several occasions. Carbon sequestration – the intake and storage of the element carbon – plays a major role in keeping the balance of the global carbon cycle – and if this balance breaks global warming will accelerate. It is now crucial to consider investing in energy crops with outstanding photosynthetic capacities – like the giant reed.
Why soil organic carbon loss is an issue
According to Amundson, soil is the second largest carbon reservoir after the oceans and plays an important role in global carbon recycling, with positive effects on soil quality. Soil has a great carbon sink potential, but intensive land management and land-use change from (semi-) natural ecosystems to arable farming can lead to soil organic carbon (SOC) loss at a faster rate than it is stored. Smith et. al. estimated that at a world level
these anthropic disturbances have added about 124 petagrams (1 petegram= one billion metric tonnes!) of carbon to the atmosphere, derived from SOC losses.
When a land-use change occurs from an arable crop system, some options are advisable to enhance SOC stocks, for example a shift to perennial biomass crops, such as Arundo donax. Beside the enhancing ability of SOC, giant reed can produce low input, low cost biomass for the renewable industry, like biomass power stations, biogas plants, 2G (cellulose-based) ethanol production, furthermore it can replace wood in furniture and paper industries as well.
Arundo donax and its photosynthetic abilities
Rossa et al. observed the outstanding photosynthetic abilities of Arundo donax in South Africa, comparing it to other co-occurring plants. In the region of the study, the maximal height of the plants were about 3.8 m in the vegetative state and over 4.5 m when flowering.
In the 28-day experiment, measurements of CO2 exchange and transpiration were carried out with a gas exchange device, and daily gas exchange was measured continuously in a chamber where the conditions were set so that they tracked the outside climate, that is 27 Celsius degrees.
Maximum photosynthetic CO2 uptake ranged between 19.8 and 36.7 micromoles depending on leaf age, and the amount of sun-ray the plant got (thus, the weather). Based on this data, it was concluded that CO2 exchange rates in Arundo donax were unusually high compared to other locally co-occurring species. Rossa et al. summarized the results in the following table:
High CO2 exchange possibly contributes to high growth performance of this species. High yield of the giant reed is also associated with other factors that influence whole plant carbon gain, such as foliage arrangement.
How much soil organic carbon can Arundo donax store?
Gioacchini et al. devoted a study to the comparison of Miscanthus and Arundo donax versus maize/wheat in the Mediterranean area, namely in Italy. By storing soil organic carbon, these plants are able to contribute to a healthy global carbon cycle.
In the experiment the plants were placed on a farm where soil was divided into three different layers of depth, since it contains the majority of the root apparatus of perennial and annual species, like this:
- l0–0.15 m
- 15–0.30 m
- 30–0.60 m.
It was observed that Miscanthus and Arundo donax stored 44 and 35 metric tons of carbon/hectare in the lowest layer, whereas the values for the upper layers were 30 metric tons of carbon/hectare and 22 metric tons of carbon/hectare for Miscanthus and 21 metric tons of carbon/hectare and 20 metric tons of carbon/hectare for giant reed. The data is summarized in the tables below:
Gioacchini et. al concluded that the carbon derived from Arundo donax in the three layers was much more evenly distributed, thanks to the dense root system of the plant, making it a fundamental source of energy for the microbial biomass. It could stimulate the microbial activity and the rate of carbon turnover.
Based on this study, it can be calculated that Arundo donax is able to store ca. 2, 4-4 metric tons of soil organic carbon/hectare/year under Southern European climate, below-ground.
Giant reed has a remarkable potential for soil organic carbon sequestration under Mediterranean conditions, thus supporting the growing bioenergy sector ie. biomass power stations, pellets/briquettes and biochar production, biogas and 2G (cellulose-based) ethanol refineries with biomass supply.
Find out more about Arundo’s remediation capabilities on our website at www.arundobioenergy.com/bioremediation/
