Effects of Tropospheric Ozone (O3) on Yield and Nutritional Quality of Mung Bean (Vigna radiata Cv. MN 98): Evidence from Pakistan
Received Date: Mar 12, 2018 / Accepted Date: Mar 18, 2018 / Published Date: Mar 22, 2018
The effects of ambient ozone concentrations on the yield and nutritional quality of Mung bean (MN-98) grown in Northern Pakistan was assessed using EDU. Passive samplers results revealed that ozone was significantly lower (24.2 ppb) in April compared to May, June (49 ppb). The mean pods number/plants, length/plant, and biomass of both fresh and dry weight of EDU and NEDU treated plants were all significantly not different. The mean biomass for EDU leaves was (4.0 g) and significantly reduced compared to NEDU (2.8 g). The mean root length and shoot biomass of EDU plants compared to NEDU treated plants remained unchanged. However, the total biomass of EDU plants were significantly higher (10.0 g) compared to NEDU (7.3 g). The overall plant biomass was 30% significantly higher than N-EDU plants. The nutritional quality parameters (Ash, Moisture, Fats, Fiber and Protein) reduced significantly in NEDU seeds compared to EDU. The %moisture contents of seeds was (F=0.017; p<0.05), %Ash (F=3.987; p<0.05), %Protein (F=3.467; p<0.05) %Fats (F=2.574; p<0.05), %Fiber content was positively affected by EDU treatment. It was concluded that ozone is directly affecting the growth and quality of summer crops grown in Pakistan that can affect the future food security of the region.
Keywords: Ozone; Air pollution; Food security; Mung bean; Pakistan
Large parts of Asia have experienced a rapid increase in urbanization and industrialization during the last three decades, which has led to enhanced emissions from household (burning of fossil fuels or wood), transport and industry. As a result, significant increases in atmospheric concentrations of primary and secondary air pollutants have been reported [1-3]. Due to its high phytotoxicity and occurrence not only in urban but in particular in peri-urban and rural, agricultural areas, the secondary air pollutant ozone (O3) has been identified as a main threat to crop production. Effects of elevated O3 concentrations include a decrease in plant growth by affecting the plant metabolism, which ultimately reduces crop yield . O3 acts as a strong oxidant which alters the basic metabolic processes in plants, destroying the structure and function of biological membranes leading to electrolyte leakage causing accelerated leaf senescence and reduced photosynthesis .
In fact, various surveys from different parts of the world have shown that increased O3 concentrations can cause foliar injury and biomass reduction of sensitive crop species, such as wheat, rice, beans, spinach and potatoes [6-9]. Moreover, studies conducted in North America and Europe have clearly shown significant yield losses for a range of major crop species due to ambient O3 concentration levels in rural areas [10,11]. Elevated concentrations of tropospheric O3 at peri-urban and urban sites of major Asian cities of developing countries, including Pakistan [9,12], Indonesia [13,14] and India have been widely reported. There are indications of major yield reductions due to ambient air pollution in Pakistan, too. For example, Wahid et al. demonstrated a grain yield reduction of 46 and 38% for two cultivars of winter wheat in an open top chamber study in the vicinity of Lahore, Pakistan, using ambient and charcoal filtered air . Mage et al. have further shown significant reductions in various yield parameters of both wheat and rice near Lahore at annual mean nitrogen dioxide (NO2) concentrations of 20-25 ppb and 6 h mean O3 concentrations reaching 60 ppb in certain months. In both cases the effect was attributed primarily to O3 .
Mung bean (Vigna radiate L.) is a well-known and widely grown pulse crop in Asia and is now becoming popular in other continents because of its excellent source of easily digestible proteins content that compliments the cereal based diet of Asian people. In Pakistan, mung bean is grown from April (Northern region) to August (Southern region). Mung bean area of production in Pakistan from 1998 to 2009 has increased from 67,000 ha producing 31,500 t to 195,000 ha with production of 90,500 t. Mung bean is also grown in and around Peshawar, NW Pakistan, by local farmers for whom ozone-induced yield losses would have economic consequences. Mung bean was selected for this experiment because it is considered sensitive to ozone and shows dark brown pepper like spots on interval spaces when exposed to ozone. However, little is known about the response of this plant to increasing ambient O3 levels under field conditions in this region. Some studies in South Asia have revealed Mung bean’s sensitivity to ozone , which highlights the importance of an ozone impact study with this crop in Peshawar. To assess the impact of O3 on the growth and nutritional status of mung bean, ethylenediurea (EDU), an anti-ozonant, has successfully been used in a number of experimental campaigns in South Asia to assess the damage caused by ambient ozone concentrations on a range of crop growth and physiological parameters (including quantity (e.g., yield) and quality (e.g., nutritional content) [17-19].
It was also important to assess the effect of ozone on roots growth as significant reductions in root biomass and length have been reported for several plant species under exposure to elevated O3-concentrations. Ozone is known to reduce leaf longevity, Rubisco activity and impairment of stomatal function, and an increase in demand for carbon in the shoots for the processes of repair and the synthesis of antioxidants. Since the growth of roots usually depends on the products of photosynthesis, a decrease in the allocation of carbon to roots can have very rapid and significant consequences on their growth.
An earlier study by Ahmad et al. showed that the early summer (April-May) is the time of the year when O3 concentrations are at their peak in Peshawar . This time period also coincides with the main growing season of Mung bean in the region and was hence chosen for this field trial for the first time for this experiment in this region. Besides reducing yields, O3 is also known to affect the nutritional quality of mung bean in India: Agrawal et al. reported significant reductions in chlorophyll a, b and total chlorophylls, reducing sugar, total sugar, starch and protein content due to elevated ozone concentrations. This interms, will affects the nutritional status of women and children. According to NNS (2011), 58.1 per cent of the population is facing food insecurity and only 3% of children have standard dietary intake. Pakistan is among one of the three countries in which have half of malnourished women and children globally. Poverty, high illiteracy rates among mothers and food insecurity are the major factors contributing to the malnutrition of the country.
The findings of the NNS, indicate a very little slight improvement in the nutritional indicators of maternal and childhood nutrition from 2001 that can affect women and child’s immunity, growth and mental development . The current study is therefore, imperative to investigate the effects of O3 on the nutritional quality that is important to both plant health and food security prospective in the region.
This is the first study on the effects of ozone on the yield root growth and nutritional quality of mung bean using EDU in the Peshawar region.
This study was designed with the following objectives:
1) To determine the atmospheric ozone concentrations via passive samplers at crop canopy level in Peshawar. 2) To assess the effect of O3 on the biomass of mung bean seeds and roots.
2) To determine the effects of ozone on the nutritional quality of mung bean.
Peshawar is located at 34_010N 71_350E in Pakistan at an elevation of 510 m above sea level. The mean annual rainfall and temperature are 404 mm and 22°C respectively, with the prevailing wind direction mostly from the south Ahmad et al. . The experimental site was situated in an open field at the Agricultural University, Peshawar (AUP), with a good distance from any pollution point sources such as smelters, factories and roads as well as from larger buildings. The plot was fenced to prevent birds and small mammals from eating the plants. The immediate surroundings of the pots was kept free from tall growing plants (trees, bushes, tall grasses) to prevent eddy formulation from disturbed wind fields and overshadowing.
Passive samplers were installed from April 2015 to June 2015. The passive samplers were exchanged every four weeks. Two replicate samples were kept under a metal plate at each location to avoid direct sunlight and rain. The plates were then attached to wooden poles at 2 m height from the ground. Air temperature and humidity were monitored by the local weather station at AUP.
A local mung bean variety (Vigna radiata cv. MN 98) was chosen for the experiment as it is grown widely in the Khyber Pakhtun Khwah (KPK) province. The seeds of the cultivar were purchased from the Nuclear Institute of Food and Agriculture (NIFA), Peshawar. The experiment duration was from April to June 2011.
15 litre volume plastic pots with a surface diameter of approx. 30 cm and a height of approx. 30 cm were chosen for the experiment. Each had access to a water reservoir underneath (bucket) via three fiberglass wicks.
Local soil, sand and vermiculite in the ratio 1:1:1 were mixed to get an appropriate planting substrate. No fertilizers were used during the entire experiment, which reflected the common practice of local farmers. Ethylenediurea (EDU) was supplied in sufficient quantities by the Stockholm Environment Institute, University of York, U.K.
• Three seeds of mung bean were sown directly into 15 litre pots already exposed to ambient air. The soil mixture in each pot was thoroughly moistened after the sowing procedure. One week after the emergence of seedlings, they were thinned to one plant per pot. The number of replicates was 20 per treatment (EDU/non-EDU), i.e., 40 plants altogether.
• Day 1 of the experiment was when the seedlings emerged (germination). At day 7 (one week after seedling emergence/ germination), 50% of the plants were treated with 100 ml EDU solution with a concentration of 400 ppm EDU, freshly prepared in deionized water An EDU concentration of up to 400 ppm is commonly believed to protect most annual crops from O3 injury . The EDU application was repeated every 10 days up to the maturity of reproductive parts with an increasing amount of solution after every second treatment: day 7-100 ml, day 17-100 ml, day 27-150 ml, day 37-150 ml, day 47-200 ml, day 57-200 ml. The EDU solution was applied as a soil drench in the early morning (8 a.m.). Control plants (20 pots) were treated with the similar amount of deionized water only.
• Weeds were removed from the pots and around the pots as necessary throughout the experimental period. Careful observations for insect pests were carried out on a daily basis. Any viral, bacterial and fungal activity was monitored regularly during the entire experiment. Watering was done through the fiberglass wicks that reached into the water reservoir (water bucket).
• Foliar injury surveys were carried out on weekly basis until harvest. The mature leaves were examined during the entire experiment. The damage by ozone pollution was assessed on the basis of % injury of the projected leaf area of mature fully expanded leaves, as follows: no damage, 0% injury; little damage, <30% injury; significant damage, 30-70% injury; severe damage, >70% injury, in accordance with the ICPNWPC (1999) experimental protocol.
• The harvest was carried out when more than half of the pods had turned brown, i.e., on June 4th, 2015. The biomass (dry weight) of pods and leaves and the total biomass was recorded. The seeds were further analyzed for their nutritional quality (proximate composition). The proximate composition of crud fats, fibre and protein content of mung bean seeds i.e., EDU treated and NON-EDU treated were carried by standard methods of AOAC . Fat was determined by Soxhlet, s method, Crude fiber determination included alkali and acid digestion to saponify fatty acids and Analysis of protein was done by Kjeldahl method. The detailed method is given in AOAC .
The statistical analysis was carried out using SPSS 18.0. The dataset for all parameters was explored for skew, kurtosis and normality. The independent sample t-test was used for each of the parameters to determine whether or not the effect of ozone was significant at P=0.05.
The monthly atmospheric temperature varied significantly from April to June 2015. The mean temperature was around 21(°C) during April and raised to 32 (°C) in May/June (Figure 1). The relative humidity decreased from April (56%) to June (38%) (Figure 1). The lower relative humidity may be due to the lack of precipitation (12 mm rain fall) during the entire experimental period as early summer is usually dry in Peshawar.
The passive sampler results showed that ozone concentrations increased significantly from April (25 ppb) to May (40 ppb) and then further in June (48 ppb) as shown in Figure 1.
No O3-induced foliar injury was recorded during the entire experimental period. In contrast, leaf margin necrosis appeared on mature leaves in the 5th week of the experimental period on both EDU and N-EDU treated plants. Similar injuries also appeared on the same species in the nearby fields.
The biomasses of seeds and leaves were significantly higher in EDU plants as compared to N-EDU plants (Figure 2). However, there was no significant difference between the shoot biomass of both treatments (Figure 2). The overall above ground biomass in N-EDU was reduced significantly by 30% compared to EDU treated plants (Figure 2).
Effect on pods
There was no significant effect on the number of pods per plant between EDU and N-EDU treatments (Figure 3). However, the pod length increased significantly by 33% in EDU treated plants (Figure 3).
There was a significant effect of O3 on all nutritional quality parameters. Fats, fibre and protein contents of N-EDU treated plants were significantly reduced as compared to EDU treated plants. Fiber and protein content of EDU seeds were significantly higher from N-EDU treated seeds, i.e., by 33% and 25%, respectively.
In the current study, ambient O3 concentrations increased with increase in air temperature from April to June possibly due to the increase in primary pollutants (VOC’s, SO2 and NOx), which act as precursors for the formation of O3, and solar radiation. Similar results were also obtained by Ahmad et al.  who reported that ozone concentrations were highest in early summer in the Peshawar Region, which is in accordance with a study carried out in Lahore by Wahid et al. The relative humidity did not have any effects on the ozone concentration in the air due to lower rain fall during the experimental period. Similar result were also obtained by Ahmad et al. .
No visible ozone injury was found on either NEDU or EDU plants which indicates that the subjected mung bean variety is either resistant to ozone foliar injury or the ozone visible injuries are masked by the marginal necrosis that was due to sunburn and high temperatures. The reduced foliar injury might also be due to the stomata closure because of low relative humidity. This is in contrast to previous studies that reported a high sensitivity of mung bean to ozone foliar injury [15,24,25]. These varying effects may be due to differences in the physiological activity-such as stomatal functioning, photosynthesis, respiration and translocation of photosynthates and its susceptibility to ozone impacts of the different crop species and cultivars used in these studies. The variety used here (MN98) was for the first time subjected to an EDU experiment in NW Pakistan; no information about the sensitivity of its foliage to O3 was available. However, it is clear that ambient ozone has affected the growth and quality of NEDU treated mung bean plants. Ozone significantly reduced the seed, leaf and total biomass as well as pod and root length of the Mung bean cultivar used in this experiment, indicating the phytotoxicity of ambient levels of this air pollutant in Peshawar.
In addition to physiological parameters, the nutritional quality of mung bean seeds was also higher in EDU treated plant as compared to non-treated plants.
The crude protein content of mung bean seeds of NEDU were significantly reduced by 30% compared to EDU treated seeds. Mung bean is an important source of proteins for the poor mass population of South Asia . Due to low power purchase, most of the people fulfill their proteins needs from plant proteins (mainly pulses) instead of expensive animal proteins. On the basis of data reported by different workers the protein in Mung has been observed to range between 23.0 to 29.0 g/100 g [26-28]. Location and variety affects the protein content of Mung . The desirable content of protein should be 23.5 g/100 g, according to the Food Composition Table of Pakistan . Habibullah et al. reported the total protein content at 22.8 g/100 g in MN 92 variety of mung bean in Peshawar . However, in the current study the crude protein content of EDU was higher (32 g/100 g) and NEDU mung bean MN 98 variety was equal to 25 g/100 g reported by Food Composition Table of Pakistan . The suggested crude fat content is around 1.5 g/100 g reported by Food Composition Table of Pakistan . The current values of both parameters were lower than the recommended level for mung bean. The fat content of mung seed of EDU treated plants (0.3 g/100 g) were significantly higher than that of NEDU treated plants (0.1 g/100 g).
The crude fibre content of mung bean is around 2.2 according to the Food composition Table of Pakistan . The crude fibre content of the NEDU treated seeds were significantly lower compared to EDU treated seeds. However, both parameters recorded high values (5 g/100 g for NEDU and 8 g/100 g for EDU) than values suggested by Food composition Table of Pakistan . Protein, fats and dietary fibre were significantly lower in NEDU treated plants. Singh et al.  and Agrawal et al.  findings were in line with the current study in that they reported reduced protein content in mung bean seeds too.
The significant reduction in fats, fibre and protein content of Non- EDU treated mung bean due to ozone toxicity is of great concern especially to the developing South Asian Region, where food security is still a major concern. The reduced nutritional quality of crops as induced by exposure to O3 will result in malnourishment and related diseases, especially in women, infants and young children.
Therefore, the impacts of ozone on future food security should be considered in addition to other stress factors factor causing the global change, particularly for the countries with developing economies. The introduction of O3 resistant mung bean varieties would be one way to overcome O3 impacts on its yield. The air pollution control policies should be revised to control emission thereby tackling the high ozone concentrations. The recently developed crop varieties should be subjected to air pollution screening thereby identifying the resistance varieties before introducing it to the market to avid yield reductions. It is worth mentioning that the Food Composition Table for Pakistan is very old and therefore, it is suggested that table should be revised given the introduction of new varieties and environmental stress like climate change and increased air pollution and other abiotic stress.
Therefore, to enhance the food security, more detailed studies should be done to completely determine the effects of ozone on crops/vegetation with respect to the climate, and nutrient and water availability. It is therefore, recommended to develop flux models to assess the amount of ozone that has actually been taken up by the plants through their stomata. In the current study only the crude form of protein fats and fibre were analyzed. It is therefore, suggested to subject these cereals to amino acids and fatty acid fraction in order to determine the effect of O3 on the complete profile of protein and fatty acids that will be very valuable from nutritional aspects for women and children. Screening experiment with various Mung bean cultivars should be carried out. Taking initiative to breed ozone resistance into newly developed cultivars. The EDU experimental study should be expand thorough out the country/region for ozone as it is a regional pollutant there by assessing it economic and nutritional effect on a regional level.
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Citation: Jan I (2018) Effects of Tropospheric Ozone (O3) on Yield and Nutritional Quality of Mung Bean (Vigna radiata Cv. MN 98): Evidence from Pakistan. J Environ Anal Toxicol 8: 567. DOI: 10.4172/2161-0525.1000567
Copyright: © 2018 Jan I. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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