The advantages of algae: Journal Club with Emanga Alobwede

This week’s Journal Club was led by Grantham Scholar Emanga Alobwede. Her research project focuses on making agriculture more sustainable by recycling algae from polluted water, and the paper she chose to for Journal Club explores some of the environmental benefits these tiny organisms present. Here, she covers some of the issues raised by the paper and her fellow Grantham Scholars.

This week’s paper

Evaluating the potential of plant growth promoting cyanobacteria as inoculants for wheat’ by N. Karthikeyanb, R. Prasannaa, L. Nainb and B. D. Kaushikb

emanga-alobwedeThe article for last week’s Journal club was an experimental paper titled ‘Evaluating the potential of plant growth promoting cyanobacteria as inoculants for wheat’. Its focus was on the use of algae as biofertilisers in agriculture.

Biofertilisers are beneficial microorganisms added to the soil to provide nutrients and make them available through various mechanisms. The significance of algae as biofertilisers was first recognised and documented back in 1939, when De (1939) attributed the fertility of tropical rice field soils to the nitrogen fixing abilities of blue-green algae (BGA) in the soil. Algal biofertilisers have been used extensively across many countries such as Spain, France, Ireland, Japan and other parts of Asia that have recognised algae’s economic and environmental significance as an organic fertiliser.

Algae are a diverse group of organisms inhabiting a wide range of environments: freshwater, marine and terrestrial and even the most hostile of environments such as hot springs and Antarctic environments. They range from 0.2um in diameter (microalgae) up to beyond 50m in length (macroalgae or seaweeds). They are normally referred to as aquatic and photosynthetic organisms and only possess simple reproductive structures, such as that of microalgae which possess unicellular/simple multicellular structures. They are without any roots, stems, leaves or vascular tissue as found in terrestrial plants. Cyanobacteria however, although also called blue-green algae, are classified as bacteria.

One of the big challenges of the 21st century is improving the way we produce our crops – making sure the technologies used are environmentally sound and sustainable so we can feed the growing global population. Biofertilisers are promising in this respect and have been touted as an eco-friendly and sustainable way of replacing synthetic fertilisers whose production is heavily reliant on fossil fuels, which in turn contribute to greenhouse gas emissions. Algae in particular have emerged as a suitable option for restoring soil fertility as well as enhancing plant growth and productivity. Their use as a biofertiliser can substantially limit the use of synthetic fertilisers.

Algal fertilisers could not only help in improving soil fertility through the increase of soil carbon and nitrogen, and through the aggregation of soil particles to improve soil structure – they are also reported to secrete extracellular polymeric substances which help bind soil particles together as well as help soil overcome conditions of water stress. They are known to release plant hormones, which increase plant growth and therefore yield, and phytochemicals, which protect plants and allow them to develop resistance toward biotic and abiotic stress.

The paper we discussed last week presented an example of an experiment carried out using cyanobacteria (blue-green algae) isolated from the root area (rhizosphere) of wheat crops. The cyanobacterial inoculants which emerged were shown to have positive effects on plant height, dry weight and grain yield, and even increased the number of microorganisms in the soil (this is important as these organisms, such as bacteria, are responsible not only for transforming soil nutrients which are unavailable to plants into forms that are available to plants, but they also improve soil air circulation). However, in our discussion, several of the scholars suggested there limitations in the study, where the cyanobacterial fertilisers were added in combination with inorganic fertiliser: this makes it hard to determine whether the growth of plants was due to cyanobacteria alone or rather due to the impact of the inorganic fertiliser. Despite this, there is evidence that cyanobacteria alone are able to increase rice and wheat grain and yield, so the problem is limited to just this paper. That said, the mechanisms behind the actions of cyanobacteria are yet to be fully understood.

The effects of algal fertilisers on soil are usually residual rather than immediate: ie, nutrients are not immediately provided to the soil but instead, they gradually build up and are usually available for subsequent crops – this a great advantage when it comes to maintaining soil fertility for longer periods. However, despite the numerous benefits provided by algal biofertilisers, there is a pressing need to understand this technology better so that it can be improved to become more readily available and reliable. Nonetheless, its benefits mean it is worth promoting this area of research and perhaps broadening the focus to other types of algae that also show promise as biofertilisers.

References

De, P. K. (1939) The role of blue-green algae in nitrogen fixation in rice-fields. Proceedings of the Royal Society of London. Series B, Biological Sciences. 127(846).p.121-139.

Karthikeyanb, N. Prasanna, R. Nain, L. and Kaushikb, B.D. (2007) Evaluating the potential of plant growth promoting cyanobacteria as inoculants for wheat. European Journal of Soil Biology. 43.p.23-30.