Impact of elevated atmospheric CO2 and temperature on plant available phosphorus (A value) in soil - assessment using 32P tracer technique

Atmospheric CO2 concentration is projected to exceed 600 ppm during the latter half of this century, with the consequent increase in atmospheric temperature as well (IPCC 2007). As current CO2 concentration is suboptimal for the photosynthesis, growth and yield responses of C3 crops (such as rice and wheat), any further increase in CO2 can be expected to increase their growth and biomass production in future. Rising temperature is an important factor governing the crop growth and regulating the nutrient availability and uptake by plants, can also interact with increasing CO2, potentially influencing the demand and supply dynamics of P in a changing climate. In view of such an important role of P availability in soil for sustainability of crop production under climate change, it is rather tempting to know as to how the rising levels of atmospheric CO2 and temperature might affect plant-available P in soil. A few traceable reports in this line suggest the possibilities of both increase as well as decrease in plant-available P in soil under elevated CO2 and temperature. Increased microbial activity in crop rhizosphere under elevated CO2 and temperature, due mainly to increased rhizodeposition of organic substrates, may reduce the availability of P in soil owing to the possible increase in P immobilization by soil microorganisms. On the contrary, a possible increase in the activity of P solubilizing/mobilizing rhizo-chemicals may increase the plant-available P in soil. It is, however, still unclear as to how the plant-available P in soil will respond to a more realistic scenario in of concurrently elevated CO2 and temperature, particularly in the soil and climatic conditions of India. The present study was, therefore, undertaken to explore the likely impacts of India-specific projected elevation in atmospheric CO2, and temperature on plant-available P (A-value) in soil using 32P isotope dilution technique