Lakes in our communities, are no longer clear. They are instead a mix of dead white and bright green. We used to see the koi, goldfish and shrimps swimming beneath the clear water surface. But now, the fish heaven became a “slaughterhouse”, with no escape. Fish bodies are floating on the surface, in between the algae blooms. It was rare to see a lake covered with algae in the past. Now this phenomenon is everywhere. Sad yet angry, our team decides to find on the reasons behind this mass “slaughter”. Algae blooms are the “murderers” of aquatic animals, and they are there due to excess nutrient in water body that results from human activities. The excessive nutrient level in water is related to eutrophication, and phosphorus pollution is one main cause. Phosphorus pollution has aroused many concerns in recent years because it accounts for more than 50% of the reasons of eutrophication in lakes in China (China Controlled Chemicals Association, 2016). It has posed many severe problems to our society. For instance, waste of water resources and diseases caused by long-term consumption of polluted water. There had been attempts to solve the issue, such as water diversion, dredging and deep aeration. However, these methods aim at processing polluted water instead of eliminating the problem from its possible origins. We came up with an idea: we want to solve the problem from its origin, and minimize the harm of the problem as much as possible. It is not just a small disaster for the fish, but inseparable from our lives. We intended to save the animals, and moreover, our environment and ourselves.
Sustainable development of food production during pandemic
In January, the sudden outbreak of the coronavirus impacted each one of us. The pandemic spread so rapidly, the ones we cared about, the ones we loved and we ourselves, were all under great danger. Two of our teammates have their families in Wuhan, the city was severely affected by this pandemic. They knew clearly how it felt, hopeless, heartbroken and horrendous… During the lockdown, people’s lives couldn’t have been more harsh. They couldn’t walk a step outside. They knew that outside the door, their lives would be under tremendous amount of threat. In a crisis like this, basic needs of people had become luxuries. We had no where to buy food, so we had to choose online food delivery and minimize our food consumption to the greatest extent. Although it was harder than usual to get food in the beginning, it is still better compare to many places in the world. According to Arif Husain, the Chief Economist and Director of the Food Security Analysis and Trends Service at United Nations World Food Programme, there were already 135 million people worldwide facing severe food shortages, but now with the outbreak, there may be 130 million more. By the end of the year, it is estimated that a total of 265 million people will be forced to suffer from food shortages. The issue is closely linked to everyone’s lives. We found out that the production of crops we eat is strongly dependent on phosphorus contents in soil, yet 43% of the world's 131.9 billion hm2 of arable land is deficient in it. Surprisingly, we also found that even if the farmers utilize phosphorus fertilizers, there is no improvement in the situations. Instead, surplus of the fertilizers caused further harms to the environment. This seems queer to us at first, until we realized the trouble lays in the absorption of phosphorus from the crops’ roots. Plants can use only a small amount of this phosphorus since 75–90% of added phosphorus is precipitated by metal–cation complexes, and rapidly becomes fixed in soils. To satisfy the demand of food under the pandemic background, we must make greatest use of the phosphorus fertilizers to alleviate the shortage problems. Such concerns have led to our project on the search for sustainable and effective way to ensure phosphorus nutrition of crops.
Phosphorus is one of the key elements in the crops’ nutrition. It is very essential to the metabolic processes, such as photosynthesis, energy transfer, signal transduction, macromolecular biosynthesis and respiration in plants (Khan et al., 2010). Thus, an input of phosphorus is crucial for food production. In fact, between 80-90% of the total world demand of phosphorus is from agriculture. So, phosphorus fertilizer is artificially used in arable lands, to increase crop yield and ensure crop qualities. There are several problems in the usage of this kind of fertilizer.
1) Efficiency of phosphorus fertilizer
Phosphorus in soil can be categorized in two types, organic and inorganic. Inorganic phosphorus occurs mostly in insoluble mineral complexes, appearing after frequent application of chemical fertilizers. These insoluble, precipitated forms cannot be absorbed by plants (Rengel & Marschner, 2005). Organic matter is important storage of immobilized phosphorus that accounts for 20–80% of phosphorus in soils (Richardson & Barea, 2009). Unfortunately, only 0.1% of the total P exists in a soluble form available for plant uptake (Zhou et al., 1992). Phosphorus fixation is the reason behind those unavailable forms of phosphorus, defined as reactions that remove available phosphate from the soil solution into the soil solid phase (Kamprath, 1985). Thus, the supplement of phosphorus fertilizer is necessary for agricultural productions. Even when phosphorus fertilizer is used, it is a major limiting factor for plant growth as it is in an unavailable form for root uptake. The efficiency of applied phosphorus fertilizers in chemical form rarely exceeds 30% and it has many other adverse harms such as disturbing microbial diversity and lowering crop yield. (Sharma et al., 2013) Consequently, excess phosphorus will lead to other issues, which will be discussed in the next section.
2) Phosphorus pollution
As discussed before, the unused phosphorus result from large scale of agricultural practices will have many negative results. Phosphorus pollution is one of it. Phosphorus can enter water body by agricultural runoff. It then increases the biological productivity of surface waters by accelerating eutrophication, the natural aging of lakes or streams brought on by nutrient enrichment. Although eutrophication is a natural process, it can be sped up by increase the amount of nutrients added to an aquatic system by phosphorus pollution. Eutrophication has devastating consequences, both on animals and humans. The biodiversity of most aquatic systems decreases with eutrophication. Depletion of dissolved oxygen in deep water is associated with eutrophication and resulted algae blooms, this can lead to a loss of species intolerant of such conditions (Ludsin et al., 2001). Additionally, the results on human is that toxic cyanobacteria dominating the water body can degrade the water quality and promote diseases like span style="font-family:'Times New Roman'; font-size:14pt">west nile virus, coral diseases, and malaria (Schutkowski, 2009).
As a result, controlling phosphorus absorption in soil is vital in many aspects.
3) Resource availability and sustainability
Phosphorus fertilizer is mainly derived from mined phosphate rocks. It is a finite resource and based on its current rate of use, it has been estimated that the worlds known reserves of high quality rock phosphorus may be depleted within the current century (Cordell et al. 2009). Also, the mining process is neither eco-friendly, economically feasible nor sustainable. On a worldwide scale, population growth and changes towards meat-rich diets will require more phosphate fertilizers in the future. As a result, we must make use of the resource wisely and avoid the waste due to plants’ limited phosphorus absorption. Effective utilization and management of phosphorus must then involve manipulation of soil and rhizosphere processes, which our project is about.
Making wiser use of phosphorus in the 70% of the world’s agriculture land with phosphorus surpluses will save millions of tonnes of phosphorus that will not need to be mined and applied. This will obviously benefit the farmer’s finances, the sustainability of phosphorus reserves and the amount of clean water bodies worldwide. This requires actions in two main areas: reducing phosphorus losses, especially from agriculture lands, and increasing phosphorus recovery and reuse to agriculture lands.
4) Existing solutions and disadvantages
The best approach to solve the problem now is to use microbial fertilizer, which involves bacteria, algae, fungi or biological compound which may help to benefit the soil and plants. Phosphate solubilizing microbes, specifically, are used to enhance the absorption of phosphorus in soil. There are several species of phosphate solubilizing microbes that have the potential to be used in fertilizers, but many has pathogenicity. For example, Pantoea Ananatis, a specie under the genus Pantoea of the family Erwiniaceae, recently separated from the genus Enterobacter, is a possible phosphate solubilizing bacteria that can be used to develop fertilizer products. It has the suitable function, but it is infects both monocotyledonous and dicotyledonous plants (Coutinho, T. A. et al, 2009). If it is used in microbial fertilizer to an area that originally does not have the microbes originally, it will be considered as a pathogenic alien microorganism invasion. This can have negative impact on host plants, such as changes in host defences which might affect ecosystem processes such as decomposition of litter from that host plant, and this could link host responses to changes in ecosystem-level processes (Thakur, Cobben & Geisen, 2019).
3. Purpose of our project
Process of discovery
At the beginning of the project, we asked for support from experts in Chinese Academy of Sciences Shanghai branch, to guide us on our project. By studying and reading past essays on our own, we learnt about the existing problems in microbial fertilizers based on PSM. The uncertainties of phosphate solubilizing bacterias were disadvantageous, so we wanted to minimize the possible defects. Inspired by a previous research done on control of nitrogen fixation in bacteria, we found out and summarized that sensors which respond to biocontrol agents can be engineered to restrict the range where microbes can survive. This mechanism of controlling ammonium repression could be used on PSMs as well. We wanted to restrict the microbes and the experts told us that salicylic acid could be used as a bio-control agent because they are concentrated at plants’ rhizospheres. So we researched more and read a published research about a mechanism of controlling bacterias by salicylic acid content. When there is salicylic acid in the environment, protein NahR can bind to promoter Psal and translate to express protein Lacl, thus repressing gef (Wang, 2008). By replacing Lacl with a necessary gene for survival in PSM, we could ensure that PSM only survives when certain salicylic acid concentration is reached. The expert mentioned a type of bacteria called Tatumella citrea, a specie under PSM that has high potential to meet our standards. We found that it is pathogenic only to pineapple pink fruits and there had been one case of infection (Pujol & Kado, 2000). Despite its minor limitations, it is suitable for most of the plants. By restricting the phosphate solubilizing bacteria to the rhizosphere of plants, it is a manipulation on their surviving ability. Since they can only survive with salicylic acid secreted by plant roots, they will not have possibilities to go further and harm the ecological niche. Also, it will not cause runoff, thus decreasing pollution. The absorption of phosphorus in plants will also be more effective, and a higher crop yield can be achieved.
We then interviewed the expert to integrate our ideas and make it viable.
Since salicylic acid is a common root secretion, it exists only in range of plants’ rhizospheres. Gene nahR, a member of LysR regulators, controls translation of protein NahR (Wang, 2008). By binding to Psal promotor, it can initiate translation of GAPDH. GAPDH is crucial for survival of PSM because it catalyzes the sixth step of glycolysis and thus serves to break down glucose for energy and carbon molecules. So, PSMs can be genetically engineered to survive only within the range. We will first use green fluorescent protein (GFP) to examine our logics and use GAPDH to achieve our goals.
In short, the benefit from our innovation is that it can reduce pollution, reduce harmful effects on ecosystem and increase efficiency and pertinence.
We envision a smart and accurate way of agriculture practices to reduce excessive use of fertilizer. Our particularity lies in the generalization and expansion of product application. The design of expression mechanism is not limited to phosphorus, it can be applied to other elements like potassium as well. This can be obtained by altering genes and bacteria, the core mechanism is very similar. We named his form of agricultural practice “Accuriculture.”
5. Concern and ethics
We will only conduct experiment in the lab because there will be ecological contaminations if we do the experiments in open areas. It is vital to prevent contamination of gene-edited microorganisms because of the uncertainty it might cause. If in the future, there is a need for the experiment that involves planting, we will only conduct them in a controlled experimental environment. We will not use it in real agriculture practice unless the risks are properly evaluated.
Coutinho, T. A., & Venter, S. (2009). Pantoea ananatis: an unconventional plant pathogen. Molecular Plant Pathology, 10(3), 325-335. doi: 10.1111/j.1364-3703.2009.00542.x
Scavia, D., David Allan, J., Arend, K., Bartell, S., Beletsky, D., & Bosch, N. et al. (2014). Assessing and addressing the re-eutrophication of Lake Erie: Central basin hypoxia. Journal Of Great Lakes Research, 40(2), 226-246. doi: 10.1016/j.jglr.2014.02.004
China Controlled Chemicals Association. (2016).The harm of phosphorus pollution to the natural environment. Retrieved 10 August 2020, from http://www.zjhx.org/view.asp?id=2775
Wang, H. (2008). Bacterial Containment System Regulated by the Concentration of Salicylate. Chinese Journal Of Biotechnology, 25(24(2), 324. doi: 10.13345/j.cjb.2008.02.015
Cordell, D., Drangert, JO., & White, S. (2009). The story of phosphorus: global sfood security and food for thought. Glob Environ Chang, 19:292–305
Khan, M. S., Zaidi, A., Ahemad, M., Oves, M., & Wani, P. A. (2010). Plant growth promotion by phosphate solubilizing fungi – current perspective. Arch Agron Soil Sci 56:73–98
Schutkowski, H. (2009). Infectious Disease Ecology, Effects of Ecosystems in Disease and of Disease on Ecosystems. Journal Of Archaeological Science, 36(12), 2882-2883. doi: 10.1016/j.jas.2009.09.017
Richardson, A. E., Barea, J. M., McNeill, A. M., & Prigent-Combaret, C. (2009). Acquisition of phosphorus and nitrogen in the rhizosphere and plant growth promotion by microorganisms. Plant and soil, 321(1-2), 305-339.
Rengel, Z., Marschner, P. (2005). Nutrient availability and management in the rhizosphere: exploiting genotypic differences. New Phytology 168:305–312
Zhou, K., Binkley, D., Doxtader, KG. (1992). A new method for estimating gross phosphorus mineralization and immobilization rates in soils. Plant Soil 147:243–250
Kamprath, E. (1985). Soil Nutrient Bioavailability—A Mechanistic Approach. Soil Science, 140(2), 158. doi: 10.1097/00010694-198508000-00012
Sharma, S., Sayyed, R., Trivedi, M., & Gobi, T. (2013). Phosphate solubilizing microbes: sustainable approach for managing phosphorus deficiency in agricultural soils. Springerplus, 2(1). doi: 10.1186/2193-1801-2-587
Thakur, M., van der Putten, W., Cobben, M., van Kleunen, M., & Geisen, S. (2019). Microbial invasions in terrestrial ecosystems. Nature Reviews Microbiology, 17(10), 621-631. doi: 10.1038/s41579-019-0236-z
Pujol, C., & Kado, C. (2000). Genetic and Biochemical Characterization of the Pathway in Pantoea citrea Leading to Pink Disease of Pineapple. Journal Of Bacteriology, 182(8), 2230-2237. doi: 10.1128/jb.182.8.2230-2237.2000
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