Effect of Beneficial Microorganisms against the Impact of Global Climate Change
Authors: A. Kandan, J. Akhtar, Pardeep Kumar and Z. Khan
Division of Plant Quarantine, ICAR-National Bureau of Plant Genetic Resources (NBPGR), Pusa Campus, New Delhi-110 012.

Climate change is usually caused by factors like oceanic circulation, variations in solar radiation, volcanic eruptions, plate tectonics and man-made alterations. Extensive loss of sea ice, high level of accelerated rise in sea level, longer periods of drought, more intense heat waves, and an increase in the number, duration and intensity of tropical storms are due to this global climate change. According to the International Panel on Climate Change (IPCC) report (2007), warming of the climate system is occurring at unprecedented rates and an increase in anthropogenic greenhouse gas concentrations is responsible for most of this warming. Global surface temperatures are predicted to increase in between 1.8 and 3.6°C by the year 2100 due to this climate changing phenomenon. Soil microorganisms contribute significantly to the production and consumption of greenhouse gases, including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and nitric oxide (NO), and human activities such as waste disposal and agriculture have stimulated the production of greenhouse gases by microbes. As concentrations of these gases continue to rise, soil microbes may have various feedback responses that accelerate or slow down global warming, but the extent of these effects are unknown. Understanding the role soil microbes have as both contributors to and reactive components of climate change can help us determine whether they can be used to curb emissions or if they will push us even faster towards climatic disaster.

Last few decades, scientists across the continents are digging to generate evidence of the beneficial associations among microbes and crops such as rice, wheat, corn, cotton, tomato, peppers etc. All plants normally exude a carbon-rich liquid that feeds the microbes. Plants also exude various chemicals in response to a range of biotic and abiotic stressors, including insect attacks and water stress. Soil bacteria sense these chemical based messages, and secrete chemicals of their own that can activate complex plant defenses in the plant.

The plant-microbe interaction in soil is either beneficial or harmful. The beneficial plant-microbe interactions are caused by symbiotic or non-symbiotic bacteria and a highly specialized group of fungi (mycorrhizal fungi). Beneficial plant-associated microbes are known to stimulate the plant growth and enhance their resistance to degenerative diseases and abiotic stresses. Bacterial genera such as Azospirillum, Bacillus, Pseudomonas, Rhizobium, Serratia and Streptomyces come under this category. As understanding of plantâ€"microbe interactions in the soil has improved, it has become possible to exploit specific beneficial organisms in order to induce faster plant growth, higher crop and timber yields, and improved disease resistance.

Enhancement in nutrient acquisition pathway, extensive production of plant growth regulators, subsequent alterations in physiological and biochemical properties of the host plant and defending the plant roots against soil-borne pathogens are the possible mechanisms usually involved during this beneficial bacteria association with the host. For farmers struggling to adapt to climate change, especially small-scale farmers with limited land and water resources, an increase in yield can open fresh opportunities for the simple reason that crop sales generate cash, including money that can be invested in a range of climate-smart farming techniques that further conserve water and soil fertility and sustainably increase production on small plots of land.

Microbial processes are often dependent on environmental factors such as temperature, moisture, enzyme activity, and nutrient availability, all of which are likely to be affected by climate change. Few microbes reported to be acted against the change in the effect of climate. In the carbon cycle methanogens convert carbon dioxide to methane in a process called methanogenesis. Microbial methanogenesis is responsible for both natural and human-induced CH4 emissions since methanogenic archaea reduces carbon into methane in anaerobic, carbon-rich environments such as ruminant livestock, rice paddies and wetlands. Methanotrophs are important regulators of methane fluxes in the atmosphere, but due to their slow growth rate and firm attachment to soil particles it is difficult to isolate. Further exploration of these methanotrophs nature could effectively help to reduce methane emissions.

In the nitrogen cycle nitrogen-fixing bacteria such as Rhizobium fix nitrogen, which means they convert nitrogen in the atmosphere into biological nitrogen that can be used by plants to build plant proteins. Prochlorococcus and Synechococcus are single celled cyanobacteria. These bacteria are the smallest and yet most abundant photosynthetic microbes in the ocean. They are so small and there are around 100 million Prochlorococcus cells per litre of seawater. Scientists estimated that Prochlorococcus and Synechococcus remove about 10 billion tons of carbon from the air each year; this is about two-thirds of the total carbon fixation that occurs in the oceans. Scientists also understand that these bacteria being able to harness such microbial power could slow down increases in levels of carbon dioxide and other greenhouse gases and eventually reduce global climate change.

All microorganisms interact inside the soil at different levels and in some case interactions among microorganisms cause no effect. However under mutualistic interactions microorganisms share reciprocal beneficial effects. In disparity, there are competitive interactions where microorganisms can produce antibiotic substances or compete for nutrients and space; in some cases the parts involved in this interaction are a beneficial microorganism, which is called as biocontrol agent (BCA), which act against various plant pathogens. These different interactions influence the soil microbial dynamics and their study could allow the identification of new biocontrol agents, which could be helpful in preserving soil quality and/or fertility.

The physicochemical pattern of soil is also strongly affecting and explaining some differences in the microbial communities’ structure. Soils differing in microelements (Al, Fe, Si, Mn, B), macroelements (N, P, K, Na, Ca, Mg, S) and heavy metals (Cu, Zn, Ni, Pb) contents are characterized by different bacterial and fungal communities. However the impact of biocontrol agents may be modified by various interaction factors, such as plant species, soil type, soil temperature, moisture and nutrient availability.

In this general article, authors want to give some important integrated approaches for crop production and protection to overcome the climate change. Extensive educational outreach efforts and other tools, such as appropriate pests and pathogen diagnostics, will need to be further intensified and updated to keep pace with the changing pests and disease situation which enhance the yield of the crops. Disease-forecasting models are needed for more pests and pathogens and with further improved quality to be used to guide farmers. Such a precise prediction tools may allow farmers to respond in a timely and efficient manner with plant protection products applications. On quarantine point of view, use of climate matching tools and geographical information systems (GIS) may assist several quarantine agencies in determining the future threat posed by a given pathogen in different regions under current and future climate shifts. Potential use of superior cultivars resistant and / or tolerant to abiotic and biotic stress and reliable tools for forecasting pathogen occurrence in order to respond in a timely manner to plants pests and pathogens.

However, this has resulted in constant adjustments to conditions differing from region to region, year to year, and within a season. In addition, the ongoing, yet accelerating progress in agricultural technologies, mainly new cultivars, agrotechnical innovations and novel plant protection products which has constantly required for significant adaptations of the production systems by farmers, with increased yields and higher revenues to the growers. Consequently, very diverse, highly flexible and proper resilient crop production systems will be urgently needed, even more than today that can cope more readily with conditions in a changing environment.

About Author / Additional Info:
Senior Scientist (Plant Pathology), Division of Plant Quarantine, Indian Council of Agricultural Research (ICAR)-National Bureau of Plant Genetic Resources (NBPGR), Pusa Campus, New Delhi-111012