Photosynthesisis the key-role to play in the fixation of inorganic carbon (CO2) from the atmosphereinto the organic carbon (glucose) in the biological system that is in plant.The rate of this process is determine by many physical and biological factorslike O3, CO2, temperature, humidity, light, soil, moisture and Rubisco,PEP-carboxylase respectively. Any change in the above mention factors leads tothe alteration in process which affect the overall growth and partitioning ofphotosynthates between the source and sink. O3 is one of the potent factoremerging among others which will discuss in details.O3 has the potential toalter the carbon- fixing process thereby reducing the carbon storage and plantperformance by many ways which disturb the natural process of carbon-cycling(Figure).
O3 limiting the stomatal pore movement , reduce CO2 uptake and alterphotosynthetic machinery .O3 negatively affect the photosynthetic enzymes andchlorophyll content caused reduction in photosynthates thereby decreasingoverall plant growth.O3caused reduction of total green part of the plant due to leaf injury, earlysenescence and abscission (Wittig et al., 2009).
Defence system against O3damages cost more available carbon in the plant system which again interfare inC-allocation, thereby reduction in both below and above ground plant biomass.ElevatedO3 causes increases the plant respiration which is again the factor loweringthe carbon fixation. The long term alteration in C- sequestration in soil isalter by O3 pollution as there is significant decreases in the root to shootratio which depicts that root biomass are more sensitive to O3 than shootbiomass.
On the other hand, O3 cause ethylene formation which directly affectroot formation (Wilkinson and Davis, 2010). Overall affect the C-allocationtowards soil is likely to decreased. O3 affects the litter quality and quantitywhich causes changes in soil C-cycle (Chapman et al., 2005). The reduction ofroot biomass due to O3 pollution was detected in single growing season (Wagg etal.
, 2012) which affects the soil C-pools. This effects leads to long termaffect of O3 on ecosystem. O3 has the capabilities to alter the timing and C-flux to soil which affect the root stock and root exudates consequent changesin soil community.
Other three important processes are potentially altered byO3 are changes in rhizodeposition, soil microbial structure and soilproperties. Soil biological community is directly depend on C-stock of soil,therefore changes in soil C bring bad impact on chemical and physicalproperties of the soil such as porosity, water holding capacity and aggregatestructure etc.