at Hilly and Riverine zones. Deep roots of Prosopis juliflora
Figure 3. Relationship between fungal abundance (per g of soil) and soil respiration rate was determined by regression analysis.
Figure 4. Relationship between bacterial abundance (per g of soil) and soil respiration rate was determined by regression analysis.
and other tree species were probably abundant in deepsoil of HZ-I and RZ-I, that might have helped in conserving the moisture in the soil. Thus greater soil respiration was recorded in deep soils. Similarly, the shallow roots of Desmostachya bipinnate at RZ-I probably favoured holding moisture in top-soil and mid-soil of RZ-II that led to increased respiration rate.
Changes in the day and night affect the temperature and moisture content of soil. The effect was much more in the top-soil as it was directly exposed to sun and heat. The effects gradually decreased with depth. However, the effects of day and night changes on the moisture content of soil might be less where the ground was covered with vegetation as no direct sunlight reaches the soil surface. Higher night time respiration from the top-soil in the forest area of Hilly zone and the plantation area of Riverine zone probably occurred because of decrease in soil temperature during the night  which favoured the growth and activities of the organisms in the soil. In general, high temperature instigates the respiration rate  but high temperature combined with low soil moisture reduces the soil respiration rate . Respiration rate during the day and night did not change in the top-soil of grassland area RZ-II, because the profuse ground vegetation protected the soil from the temperature fluctuation in day and night.
Distribution of microorganism in soil varies due to several factors including soil temperature, moisture, pH, organic matter content and their interactions. The abundant vegetation at Riverine zone  improved the moisture and organic matter of the soil that influenced the microbial, combined bacterial and fungal, population [23,24]. Similarly, the microbial population also varied along the soil depth and most organisms were concentrated near the root systems in the soil. In Hilly zone, the deep root system of P. juliflora encouraged the microorganism abundance by conserving moisture and organic matter in the deep-soil when compared to top-soil and mid-soil. Similarly, the shallow root system of D. bipinnata allowed the abundant growth of microorganisms in mid-soil and top-soil. Roots of the grasses didn’t reach in deep-soil which could be the reason for the low population of these organisms at that depth. Soil moisture in mid-soil of RZ-II and deep-soil of HZ-I, facilitated microbial growth and soil respiration, respectively . Sometime low soil moisture could reduce the CO2 efflux by limiting microbial contact with available substrate in the soil .
When fungal and bacterial population was compared at different depths, bacterial population was higher in the top-soil at both the sites. High temperature of the top-soil probably discouraged the fungal compared to bacterial growth . Similarly, the high moisture content in the deep-soil of RZ-I due to very high ground water level discouraged the bacterial growth compared to fungal growth. Moreover, lack of root system in the deep-soil of RZ-II caused overall low microorganisms growth. Fungi and bacteria were most abundant in the deep-soil compared to soils at other depths at HZ. The high abundance probably occurred because of deep roots of P. juliflora. Similarly, shallow root system of D. bipinnata allowed the abundance growth of fungus in mid-soil of RZ. However, the bacterial population was highest in top-soil and least abundant in the deep-soil of RZ.
Soil respiration is a function of microbial abundance because microorganisms are the main group that produces CO2 from soil. However, the role of bacteria and fungus was not same in CO2 production form soil. Fungal population was highly correlated to the soil respiration rate. Fungi are more important in the forest soil and are more active at low temperatures than bacteria . The high fungal population was observed in grassland area is supported by findings of Bardgett et al.,  which might be the reason for high biological activity and respiration rate at that site.
The study suggests that vegetation coverage determines the physical and chemical properties of soil, which influence the microbial activity that controls the soil respiration rate. The microbial activity below the ground is not uniform and soil respiration process is a function of bacterial and fungal abundance in the soil . However, fungal population is more responsible to CO2 emission than bacterial population. Deeper soil is more active than the surface soil in the dry area dominated by trees which have deep root system. However, in the grassland, the mid-soil is most active due to the shallow root system.
The research was financially supported by Centre for Environmental Management of Degraded Ecosystems (CEM-DE), University of Delhi. We thank staffs of Yamuna and Aravali Biodiversity Parks, New Delhi, India for their help during the study.
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