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American Journal of Applied Sciences
Year: 2009  |  Volume: 6  |  Issue: 3  |  Page No.: 456 - 462

Effect of Ambient Gasess on Respiration of Soil Supporting Four Crops in Central Saudi Arabia

Akram Ali, Ahmad Alfarhan, Ibrahim Aldjain and Nagat Bokhari    

Abstract: This study was conducted at four localities (Maseef, Naseem, Oleya and Industrial City) in Riyadh city, KSA to determine the effect of increased tropospheric gases on responses of in situ soil respiration (Rs) of wheat (Triticum aestivum L. cv. Giza 68), broad bean (Vicia faba L. cv. Lara), kidney bean (Phaseolus vulgaris L. cv. Giza 3) and pea (Pisum sativum L. cv. Perfection) rhizosphere soil. These plants were grown to a full-season in pots to recieve four air quality localities treatments. Daily mean of O3, SO2, NO2 and CO2 concentrations were recorded by portable gas analyzers in the center of studied localities. The Rs values were measured monthly before seed germination, during all growth stages and after harvesting (October, December, February, April and June) at three times during the day (morning, noon and afternoon) for each stage. The maximum values recorded for O3 in mid June, 2007 were 39, 77, 95 and 166 nL L-1, in Maseef, Naseem, Olea and Industrial City localities, respectively. Significant decreases in Rs were observed for all polluted localities in compared Maseef site (less polluted). The greatest decreases in Rs were found at Industrial City followed by Naseem and Oleya. More reductions in Rs were observed for the Industrial City treatments during flowering and grainfill stages, while normal respiration at Maseef area was recorded. This study concluded that O3 injury can reduce the Rs by decreasing the activities and reactions in soil supporting plants.

Table 1. It showed low values during months of January, June, October, May and June, and October, November and June for air temperature, humidity, wind velocity and rain-fall, respectively. While an increase in June, January, November and January for air temperature, humidity, wind velocity and rain-fall, respectively. Gradual decrease in the air temperature occur, reaching to a minimum of 18°C in January followed by gradual increase reaching to a maximum of 42oC in June. On the other hand, the gradual decrease in humidity and rain-fall tend to be in summer months, while wind velocity vary throughout the year. Monthly and daily mean values of gases' (O3, SO2 and NO2) concentration (nL L-1) in Riyadh city, KSA during the growth period of studied crops (2006/2007) were listed in Table 2, 3. The results showed that O3 levels are higher in the urban (Industrial City and Olea) than in the suburban (Naseem) or surrounding rural sites (Maseef), because the presence of high concentrations of NO in the city centre is a major cause of destroying O3[12]. When the behavior of the localities is compared, it was observed that monthly values captured at Industrial City were significantly high in comparing to other localities (Table 2). The greatest values follow the highest solar radiation, which is the basis of the photochemical reactions, involving the components of vehicle emissions and other sources. This behavior is typical of the urban areas where O3 quickly increases during the day through the photochemical cycle and just as quickly decreases in the reversible reaction NO+O3 = NO2+ O2[11]. Industrial City showed the highest O3 values at the mid-day. In every examined day, it is recorded higher concentrations than the other localities, showing values ranging from 43-167 nL L-1. This site observed the greatest hourly average of 185 nL L-1, recorded on 8 June 2007. This is largely believed to be from horizontal air transport, high solar radiation (temperature and light), heavy traffic and a subsequent accumulation of photochemical products, which is common in all big cities[12].

Table 1: Mean values of meteorological parameters in Riyadh city, KSA (2006/2007)

Table 2: Monthly mean values of gases concentration in Riyadh city, KSA during the growth period of studied crops (2006/2007)

Table 3: Daily mean values of gases concentration in Riyadh city, KSA during the growth period of studied crops (2006/2007)

Fig. 1: In situ soil respiration rates (μ mol CO2 m-2 sec-1) for soils of wheat grown in pots under four air quality localities treatments at Riyadh city, KSA

Fig. 2: In situ soil respiration rates (μ mol CO2 m-2 sec-1) for soils of broad bean grown in pots under four air quality localities treatments at Riyadh city, KSA

This value is above the threshold for public warning (ca. 184 ppb). Saturday recorded the highest ozone levels in comparing to other days of the week due to the heavy traffic at the beginging of the work days (Table 3).

Effect of air quality on Rs rates: The effects of atmospheric O3 on Rs rates for soil supporting wheat at four growth stages of plant development (vegetative, flowering, grainfill and pre-harvesting) are shown in Fig. 1. Pre-seed germination produced non-significant effects for allprepared soils Air quality treatments in four localities caused significant differences during the 1st day of vegetaive growth in compared to pre-cultivation, while significant decreases in the Industrial City site in compared to Maseef site. Moreover, gradual increase in Rs rates during vegetative and flowering stages, then droped starting at grainfill (Fig. 1).

In situ soil respiration rates for soil supporting broad bean plants grown in pots under the effect of four air quality localities are showed in Fig. 2. Naseem, Oleya and Industril City localities exhibited slightly higher rates of respiration, while Maseef area recorde high Rs rates at vegetative growth in compared to soils before seeding. The effect of air quality in Oleya and Industril City localities on CO2 flux rates in soil supporting broad bean showed little significant decreases in compred to Naseem site.

Fig. 3: In situ soil respiration rates (μ mol CO2 m-2 sec-1) for soils of kidney bean grown in pots under four air quality localities treatments at Riyadh city, KSA

Fig. 4: In situ soil respiration rates (μ mol CO2 m-2 sec-1) for soils of pea grown in pots under four air quality localities treatments at Riyadh city, KSA

Generally, air quality treatments increased the rates of flux in Maseef in compared to other sites (Fig. 2).

Respiration rates levels in soils of kidney bean plants before seed germination were exactly similar (Fig. 3). In all growth stages, no significant differences between Rs rates of Naseem and Oleya localities. The Rs rates were lowered to low levels at the time of harvesting under air quality treatments of Industril City locality. Exposure of kidney bean plants to low O3 significantly deceases the levels of respiration. The highest respiration rates for all growth stages were observed during grainfill development (Fig. 3).

With respect to the combination of elevated NO2, SO2 and O3, respiration levels of pea soils were not only higher before the mid of the day, but also afternoon (Fig. 4). In term of air quality treatment effects, the results were typically significantly different between all studied localities except the times of grainfill and pre-harvesting. During grainfill and pre-harvesting times, only significant decreases were recorded between all sites and Maseef site (Fig. 4).

Typically, Rs rates found in soils with a recent input of easily degradable substrate. Such substrates would induce a microflora that usually respired more CO2 per unit degradable C[13]. Close relationship were found between the effects of air quality treatments and CO2 fluxes, however, Rs rates as reflecting the activity of whole microbial activity[14]. The relationships between Rs rates were found to be linked to climatic conditions. Part of the climatic effect may be explained by an altered quantity of metabolizable substrates due to an influence on primary production or substrate allocation to the roots and decomposition as such in response to climatic conditions[15]. The translocation of photosynthetic compounds below-ground made high linking between CO2-fluxes and the stimulation of microbial activity[16].

The flux of CO2 from soil can be a significant component of the carbon budget in an ecosystem. In a prairie environment, soil surface CO2 fluxes were comparable to daily gross photosynthetic rates when averaged over 24 hours[17]. Yim et al. [18] found that up to 20% of net CO2 uptake by a crop could originate in soil. There were strong positive responses to increased soil respiration under atmospheric CO2 concentrations [Fig. 30, 31, 32 and 33 (from 15-17)]. Elevated tropospheric gases decreased the CO2 fluxes for all studied crops. These results agree with that obtained by Stott et al. [19]. The respiration of roots, decay of organic matter, and activity of microbes primarily produce soil CO2[20]. Soil respiration is very dependent on soil temperature, organic content, moisture content and precipitation [21]. High in situ soil respiration rates due to more C mineralized as CO2 and transferred to the atmosphere; therefore, such soils acted as net sources of CO2[22]. However, the negative effects resulting from tropospheric O3 treatments on organic C fractions and respiration appear to have been balanced by the positive effects of higher inputs of decomposable C below-ground. A relatively low Rs in soils under localities treatments is an indication of environmental stress that to repair damages under stress requires soil microbes to divert an increasing amount of energy from growth and reproduction for maintenance and survival[23].

CONCLUSION

Increases in global climate will not only directly affect the growth of plants, but might also alter the living conditions for soil biota. Part of the climatic effect may be explained by an altered quantity of metabolizable substrates due to an influence on primary production or substrate allocation to the roots and decomposition as such in response to climatic conditions. Significant relationships between CO2-fluxes and the stimulation of microbial activity may be attributed to the translocation of photosynthetic compounds under ground. The suitable time for detecting Rs is the period after 12pm because higher temperatures correlate with soil surface CO2 fluxes and accelerate the development of a soil

ACKNOWLEDGEMENT

This study is part of the research activities of the Initial Center of Excellence of Biodiversity Research program, developed and funded by the Ministry of Higher Education, KSA. Thanks are expressed to Center of Excellence and anonymous referees for their constructive comments on the first draft of this study.

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